EFFECTS OF EXTERNAL PARENT NUCLIDES ON APATITE HELIUM DATES
By
Devon Anne Orme
A Prepublication Manuscript Submitted to the Faculty of the
DEPARTMENT OF GEOSCIENCES
In Partial Fulfillment of the Requirements
for the Degree of
MASTER OF SCIENCE
In the Graduate College
THE UNIVERSITY OF ARIZONA
2011
TABLE OF CONTENTS ABSTRACT………………………………………………………………………………………...5 1. INTRODUCTION……………………………………………………………………………….6 2. METHODS………………………………………………………………………………..…….7 2.1 Apatite (U-­Th)/He Dating ……………………………………………………...7 2.2 External Parent Nuclide Phases………………………………………………………8 2.2.1 SEM Imaging 2.2.2 Modeling 2.3 Chemical Washing Experiments……………………………………………………...8 2.4 Multi-­Element Analyses……………………………………………………………….….9 3. RESULTS……………………………………………………………………………………….9 3.1. Observations: External Parent Nuclide Phases……………………………...9 3.1.1 Scanning Electron Microscope 3.1.2 Qualitative Effects of External Phases 3.1.3 Quantitative Modeling 3.2 Chemical Washing Experiments……………………………………………………12 3.2.1 Laboratory Standard 3.2.2 Detrital Samples: Sierra Nevada and Pyrenees Mountains 3.2.3 Bedrock Samples: Bighorn and Beartooth Mountains 3.3. Multi-­Element Analyses………………………………………………………….…..13 3.3.1 REE Patterns 3.3.2 Single-­‐Element Patterns 4. DISCUSSION………………………………………………………………………………..14 4.1. External Parent Nuclide Phases…………………………………………………..14 4.2 Chemical Washing Experiments…………………………………………………..15 4.2.2 Detrital Samples: Sierra Nevada and Pyrenees Mountains 4.2.3 Bedrock Samples: Bighorn and Beartooth Mountains 4.3. Multi-­Element Analyses………………………………………………………………17 5. CONCLUSION……………………………………………………………………………….17 ACKNOWLEDGEMENTS……………………………………………………………………….18 REFERENCES……………………………………………………………………………………19 FIGURE CAPTIONS……………………………………………………………………………..22 FIGURES…………………………………………………………………………………………25 SUPPLEMENTARY DATA…………………………………………………………………….34 5
EFFECTS OF EXTERNAL PARENT NUCLIDES ON APATITE HELIUM DATES Devon A. Ormea†, Peter W. Reinersa, S. Lynn Peytona,b, Uttam Chowdhurya, Jeff Rahlc, Andreas Mulchc, Brett Tipplee a Department of Geosciences, The University of Arizona, Tucson, AZ b Coal Creek Resources, Inc., Lakewood, CO 80228 c Department of Geology, Washington and Lee University, Lexington, VA d Biodiversity and Climate Research Centre, Goethe-­‐University Frankfurt , Frankfurt, Germany e Ehleringer Lab, The University of Utah, Salt Lake City, UT † Corresponding Author: dorme@email.arizona.edu ABSTRACT (U-­‐Th)/He dates of apatite grains from some environments display significantly more dispersion than predicted by known sources such as varying grain size, radiation damage, or parent-­‐nuclide zoning. For example, some bedrock samples from the Laramide Ranges show poor reproducibility and mean ages often older than AFT ages. In contrast, detrital samples from unheated Cenozoic sediments in several locations yield ages significantly younger than the depositional age of their host rocks and display inverse correlations between age and U, Th, and Th/U. SEM images of these samples in thin section show the occasional presence of external phases along grain boundaries or lining cracks. These phases include Fe-­‐ and Mn-­‐oxides and oxhydroxides and Rare Earth Elements. In some cases, the oxides are enriched in U and Th relative to the apatite crystal. These U-­‐Th-­‐
bearing phases are a possible source for dispersed He dates, since their presence violates a fundamental assumption that there are no significant sources of 4He within ~10-­‐20 μm of dated apatite grains. The potential impact of external U-­‐Th-­‐bearing phases on apatite He ages depends primarily on three factors: (1) their age of formation relative to the He cooling age of apatite, (2) whether or not they are recovered and analyzed with the apatite, and (3) their U-­‐Th concentration relative to apatite. Modeling these effects shows that detrital and bedrock Apatite Helium ages can be ~80% younger than their host depositional rock and upwards of 50% older than corresponding AFT ages, respectively. Chemical washing of apatite grains prior to analysis, intended to remove any secondary U or Th on the rims of apatite grains, reduces age scatter, eliminates negative age versus [eU] correlation in detrital samples and yields apatite crystals with geologically acceptable ages. However, chemical washing does not eliminate all age scatter. In some cases, we attribute remaining age scatter to variations in the characteristics of the external phases as well the inability of chemical washing experiments to remove portions of the apatite crystal affected by 4He implantation. 6
1. INTRODUCTION The apatite (U-­‐Th)/He system possesses a number of attributes that make it useful for low-­‐
temperature thermochronology. Specifically, high diffusivity of He at low temperatures, gives the system a low closure temperature (~40-­‐70 °C; Dodson, 1973), making it suitable for analyzing thermal histories in the uppermost few kilometers of Earth’s crust. This allows for high sensitivity to surface and near-­‐surface processes such as relief development and river incision (Ehlers and Farley, 2003). Apatite helium (AHe) dating is often used to resolve the timing and rates of mountain building processes, episodes of denudation and the landscape evolution of a particular region. Although much studied, a major challenge in AHe dating remains, namely resolving the source of single-­‐grain age dispersion in rocks from a wide range of environments. Several studies have focused on identifying and resolving possible sources of age scatter (Fitzgerald et al., 2006 and references therein). Sources of age scatter may include the following: (1) U-­‐Th-­‐rich inclusions which locally contribute excess 4He (Farley, 2002); (2) variations in grain size (Reiners and Farley, 2001); (3) the influence of α-­‐ejection on He diffusion (Meesters and Dunai, 2002); (4) zonation of U and Th (Hourigan et al., 2005); (5) He-­‐implantation from external primary phases (i .e.“bad-­‐neighbours” such as zircon, apatite or monazite) (Spencer et al., 2004; Spiegel et al., 2009); and (6) radiation damage (Shuster et al., 2006; Flowers et al., 2009). Fitzgerald et al. (2006) also highlight the effects of cooling rate on rocks from different environments. Although one or more of the above processes may explain age scatter in some suites of apatite crystals, significant age dispersion remains a common problem in AHe dating. This study is motivated by new observations from many single-­‐grain replicate analyses from bedrock and detrital samples that show contrasting types of age dispersion and age anomalies that cannot be explained from analytical uncertainty or known sources of age scatter previously described. Bedrock samples from the Beartooth and Bighorn Mountains in Wyoming, show poor reproducibility and mean ages often older than AFT ages on the same rock (Fig. 1; Peyton et al., submitted). Age dispersion among single-­‐grain replicates exceeds that of analytical uncertainty and may display a range exceeding 200 Myr (e.g. maximum age is 300% greater than the mean) between apatite grains from the same rock. Detrital samples from shallowly buried (<~1 km) Cenozoic sediments in several locations yield ages significantly younger than the depositional age of their host rocks and display inverse correlations between age and U, Th, and Th/U. Figure 2 presents AHe ages from three sedimentary sequences which were not heated above ~ 30-­‐40 °C after burial, namely paleofluvial gravels from the Sierra Nevada, sediments from the Bighorn Basin in the Laramide province, and syn-­‐orogenic conglomerates from the Sis Conglomerate body in the Pyrenees Mountains. In some cases, multiple grains from a single clast exhibit large age scatter and distinct negative age versus effective uranium correlations. Detailed examination of these samples in thin section reveals the occasional presence of external phases along grain boundaries or lining cracks. These phases commonly comprise Fe-­‐ and Mn-­‐oxides and oxyhydroxides, and sometimes have concentrations of Rare Earth Elements (REE) detectable by SEM-­‐EDS methods. In at least some cases, these phases are 7
also enriched in Th and U relative to the apatite crystal. Under an optical microscope, many of these grains exhibit red or yellow staining on their surface. Figure 3 details two apatites examined during fission track analyses that show a yellow-­‐to-­‐red stained surface that is enriched in U. The presence external U-­‐Th-­‐rich external phases violates a fundamental assumption in (U-­‐Th)/He dating that there are no significant sources of 4He within ~10-­‐20 µm of a dated grain and that all measured nuclides are interior to the grain itself. In this paper, we hypothesize that the presence of secondary, U-­‐Th-­‐rich external phases may be a significant source of single-­‐grain age dispersion in bedrock and detrital apatite. We test this hypothesis by characterizing the frequency, origin, and effects of external U-­‐
Th-­‐bearing phases on AHe ages by using a combination of SEM analyses and ICP-­‐MS analyses of elements associated with secondary phases such as Mn and REEs. A series of qualitative and quantitative models depict the effect of these phases on AHe ages. In addition, problematic samples (i.e. those with identified U-­‐Th rich external phases) were subjected to a series of chemical washing experiments that attempt to reduce age dispersion and eliminate anomalous apatite cooling ages. Chemically washed grains show a reduction in age scatter and yield geologically acceptable ages. However, chemical washing does not eliminate all age scatter. 2. METHODOLOGY 2.1 Apatite (U-­Th)/He Dating The (U-­‐Th)/He dating method is based on the accumulation of 4He produced by the alpha decay of the parent isotopes 238U, 235U, 232Th, and 147Sm (Zeitler et al., 1987). When determining an AHe age on apatites of typical dimensions (~60-­‐200 µm), a correction must be made to account for α-­‐particle emission from U and Th nuclei within ~20 µm of the edge of the crystal. This correction (FT factor) generally assumes a homogenous distribution of parent nuclei and negligible implantation of 4He from outside the grain (Farley et al., 1996). All apatite grains presented here, with the exception of chemically washed grains (Section 2.3), were dated using the methods described in Reiners et al. (2004). Apatite grains range in width and length from 60 to 150 μm and from 100 to 250 μm, respectively. Apatite grains were selected on the basis of clarity and the lack of visible inclusions. In order to test for possible sources of age scatter, additional procedures were conducted on grains from samples that show large age dispersion between multiple replicates (Fig. 1 and 2). A Scanning Electron Microscope (SEM) was used to detect U-­‐Th-­‐rich inclusions and obvious intracrystalline zonation. U-­‐Th inclusions were eliminated as a possible source of age scatter by processing euhedral apatite crystals using zircon dissolution methods that recover all the U-­‐Th (Peyton et al., submitted). In addition, multiple replicates of different laboratory standards were run in correlation with these grains and all yield accurate and reproducible ages. Radiation damage, which can increase He retentivity in apatite, was also examined in these samples, but eliminated as a source of age scatter because the range of 8
thermal histories for any samples capable of producing AHe ages older than AFT ages is extremely narrow and therefore radiation damage alone cannot produce the observed age scatter (Shuster et al., 2006; Flowers et al., 2009). 2.2 External Parent Nuclide Phases 2.2.1 SEM Imaging In order to examine apatite crystals from bedrock and detrital samples with highly scattered and anomalous AHe ages, we analyzed a series of thin sections using an SEM. A series of back-­‐scattered images (BSE) and elemental maps were produced for detrital clasts from the Sierra Nevada and Pyrenees Mountains, as well as for bedrock samples from the Beartooth and Bighorn Mountains. In addition, single-­‐grain specimens from each of these samples were analyzed in order to assess whether or not elemental phases detected in thin-­‐section analyses are recovered after the mineral separation process, and therefore possibly analyzed with the apatite crystal during standard analytical procedures. 2.2.2 Modeling A series of qualitative and quantitative models depict the effects of a U-­‐Th-­‐rich external phase on AHe dates. Following previous approaches, we simplify the hexagonal shape of an apatite crystal as a sphere (Farely et al., 1996; Hourigan et al., 2005). We apply a U-­‐Th-­‐rich rim of uniform thickness around the circumference of an apatite crystal. Then, we vary (1) the age of the external phase, (2) the ratio of the [U] in the external phase to the [U] in the apatite grain (Cp/Cg; assuming an average stopping distance, S, for the 238U decay chain), (3) the thickness of the external phase and (4) whether or not the phase is retained or lost during analysis. Section 3.2 qualitatively presents this model, whereas Section 3.3 details the numerical results. 2.3 Chemical Washing Experiments We performed a series of chemical washing experiments intended to remove any secondary U or Th on the rims of apatite grains. A series of euhedral apatite crystals from the Sierra Nevada, Pyrenees Mountains and Bighorn and Beartooth Mountains, were selected for chemical washing. Prior to washing, at least five of these grains were screened for external phases using the SEM. Grains with identified external Fe-­‐ and Mn-­‐oxides and light REEs were subjected to chemical washing. In addition, a number of non-­‐washed apatite grains from the each sample were run in parallel with chemically washed grains. After washing, all apatite grains were analyzed following the procedures described in Reiners et al. (2004). All errors are 1 standard deviation (stdev). Three different solutions were used in chemical washing experiments: (1) 1% HNO3, (2) 5% HNO3 and (3) 2% HNO3 and HCl. Single apatite crystals were bathed in 25 µl of one of these solutions for 90 seconds, while observed under a stereozoom microscope. A minimum of five grains per sample were subjected to the same chemical solution and 9
washing procedures, along with five non-­‐washed grains. When possible, more grains were analyzed and all three solutions (each 25 µl for 90 seconds) were used on different sets of grains from the same sample. The surface area to volume ratio of each grain was measured pre-­‐ and post-­‐chemical washing. In addition, a series of experiments using the same procedures and all three chemical solutions were conducted on a laboratory standard with a known AHe age. 2.4 Multi-­Element Analyses The presence of REE and other elements aside from Th (and presumably U) during SEM analyses suggests that there may be a detectable difference in the chemical signature between apatite grains with external phases present and those without. In turn, one might expect a distinguishable difference between chemically washed and unwashed apatite grains. In order to test this, we performed a multi-­‐element analysis on dissolved apatite grains, both washed and unwashed. We measured elements such as Mn that were detected during SEM analyses, as well as other fluid mobile large-­‐ion lithophile elements such as Ba. In addition, we analyzed concentrations of REEs for each of the dissolved apatite grains. All measurements were done on an Element2 HR-­‐ICP-­‐MS at the Arizona Radiogenic Helium Dating Laboratory. 3. RESULTS 3.1 Observations: External Parent Nuclide Phases 3.1.1 Scanning Electron Microscope A series of back-­‐scattered images (BSE) and elemental maps show the presence of Fe-­‐
oxides, oxyhydroxides and Mn-­‐rich material on the surface of the grains, as well as lining fractures on several samples from the Beartooth and Pyrenees Mountains. In addition, these phases show high REE and Th concentrations relative to the apatite crystal (Fig. 4 and 5). In addition to these external phases, thin section analyses showed some apatites sited close to (<20 μm) primary minerals such as monazite and zircon. The external phases are only seen on a few apatites, but when observed, they have concentrations much higher than the apatite crystal, as seen by the intensity signal of specific elements. We documented several thin sections in which roughly 15-­‐20% of apatites examined in a single plane show the presence of these Fe-­‐, Mn-­‐, REE-­‐ and Th-­‐rich phases (i.e. Bedrock: Beartooth Mountains, Bighorn Mountains; Detrital: Sierra Nevada clasts). These percentages are a minimum value for these samples, as other phases may be present in a different plane. 10
SEM imaging of single apatite crystals from granitoid bedrock in the Bighorn Mountains and a granitoid detrital clast from the Sierra Nevada also reveal the presence of Fe-­‐ and Mn-­‐rich phases (Fig 6). In contrast to imaging of apatite in thin-­‐section (Fig 4 and 5), the phases appear to be coating large portions of the apatite crystal. 3.1.2 Qualitative Effects of External Phases The presence of external phases with significant concentrations of U-­‐Th relative to the apatite violates a fundamental assumption that there are no significant sources of 4He within ~10-­‐20 μm of dated apatite grains (Farley et al., 1996). The possibility for extracrystalline He implantation has been noted before (e.g., Spiegel et al., 2009; Kohn et al., 2008), but in the context of primary mineral phases such as monazite or zircon, which may contribute excess He to the system and cause AHe ages to be “too old”. Our new findings suggest that the precipitation of secondary external phases, enriched in U-­‐Th relative to the apatite crystal, may be a possible origin for dispersed AHe ages. The potential impact of external U-­‐Th-­‐bearing phases on apatite He ages depends primarily on three factors: (1) their age of formation relative to the He cooling age of apatite, (2) whether or not they are recovered and analyzed with the apatite, and (3) their U-­‐Th concentration relative to apatite. As shown in Figure 8, two different external phases are distinguished: (1) an Early-­
Formed Secondary external phase that is present along the grain-­‐boundary formed before or about the same time as the cooling age of the grain and (2) a Late-­Formed Secondary external phase formed significantly later than the grain’s cooling age found along grain boundaries. 3.1.3 Modeling The following model follows the same set-­‐up as Figure 8, while varying the ratio of the [U] in the external phase (Cp) to the [U] in the apatite grain (Cg) (Cp/Cg), the thickness of the external phase, and whether or not the phase is retained or lost during analysis. Fractional age bias is based on helium production and the FT factor (correction made to account for α-­‐
particle emission) for both the grain and the external phase. Thus, following Farley et al. (1996), we modify the FT equation to the following: where S is the stopping distance of 4He (assumed to be 19.28 µm) , R is the radius of the grain, and P is the radial thickness of the external phase. 11
Early-­Formed External Phase Figures 9 and 10 depict the effects of an early-­‐formed external phase on AHe ages. If a U-­‐
Th-­‐rich phase precipitates onto an apatite crystal before or at the time of cooling and is later analyzed with the crystal, then AHe ages would be slightly “too young” (i.e. younger than depositional age of host rock) due to a high U-­‐Th rim zonation effect on the alpha-­‐
ejection correction (Fig. 9; Farley et al., 1996, Hourigan et al., 2005); In contrast, if the external phase is not included in the analysis, then a potentially very large “too-­‐old” age effect is possible as much of the implanted 4He would be measured but none of the U-­‐Th value. The loss of a secondary external phase with 2-­‐10 times higher U-­‐Th than the host apatite and a radial rim thickness of 1-­‐4 µm would produce ages ~ 20-­‐60% too old (Fig. 10). In the case of apatites derived from the Bighorn and Beartooth Mountains (Fig. 1), we hypothesize that secondary external phases are old features that formed before or at the same time as the cooling age of the grain. This hypothesis is consistent with constraints on the timing of U mobilization in Wyoming granites that place U mobilization pre-­‐80 Ma (Rosholt et al., 1973; Stuckless et al, 1977; Zielinski et al., 1981). Therefore, we hypothesize that the loss of an early-­‐formed secondary U-­‐Th rich phase prior to analysis can explain AHe ages from the Beartooth and Bighorn Mountains that are older than their corresponding AFT ages due to the presence of parentless 4He. The presence of secondary U-­‐Th-­‐rich coatings would have no effect on AFT ages, but could potentially add 4He in marginal regions normally expected to be depleted in 4He because of alpha ejection. AFT dating can potentially avoid regions of grains or whole grains with anomalous FT densities, whereas bulk grain AHe dating cannot avoid clearly anomalous regions. Late-­Formed External Phase Figure 11 shows the effects of a late-­‐formed external phase on AHe ages. If a U-­‐Th-­‐rich phase precipitates onto an apatite crystal much later than the cooling age of the apatite and not enough time has elapsed for U and Th to produce 4He, then if all or at least some of the phase is analyzed with the grain, the AHe age will be “too young” due to the addition of daughterless U and Th. In contrast, if the external phase is lost prior to analysis, the AHe age will not be affected if no 4He has been injected into the grain (i.e. phase formed recently). For example, the presence of a secondary external phase with 4-­‐10 times higher U-­‐Th than the host apatite and a radial rim thickness of 4-­‐10 µm would produce ages ~ 20-­‐
80% too young (Fig. 11). Our observations of “too-­‐young” detrital apatite grains with inverse age-­‐U-­‐Th correlations (Fig. 2) are consistent with the above model in which secondary material, with U-­‐Th comparable to or greater than that of the host apatite, forms on the apatite crystals much later than the cooling ages of the apatites and are analyzed with the grain. Likewise, this scenario is consistent with abundant high Fe-­‐ and U-­‐Th secondary phases around many 12
apatite crystals in bedrock samples that show age scatter towards younger ages (Fig. 2, 4, 6A). Similar to early-­‐formed external phases, AFT ages should not be affected by the presence of late-­‐formed secondary phases. First, AFT ages rely only on 238U and would therefore not be affected by the late-­‐stage addition of Th. Second, etching procedures prior to irradiation may remove much of the U that generates induced tracks in the mica monitors. Most importantly, however, is that trackers can avoid zonation and spots with anomalous high-­‐
density tracks, an option not available during whole-­‐grain dissolution methods used in AHe dating. 3.2 Chemical Washing Experiments If late-­‐formed external U-­‐Th is responsible for dispersion and inaccurate cooling ages, grain abrasion may ameliorate or solve the problem (e.g., Spiegel et al., 2009). Removal of > 20 µm of a crystal could potentially remove any effects from these external phases, as well as eliminate the application of the standard FT correction. Physical abrasion experiments using a Krogh device (e.g., Krogh, 1982) and various abrasive grits have proved difficult. Individual apatite crystals were cracked, broken or entirely lost during abrasion procedures. The few apatite crystals that were recovered did not lose a significant portion of their radii. Although we do not rule out physical grain abrasion as a possible solution to 4He implantation, as other workers have achieved success with this technique (e.g., Kohn et al., 2008), we focus here on a series of chemical washing experiments that seek to remove the observed external phases seen in Figures 4-­‐
7. Figures 12-­‐16 show results from multiple chemical washing experiments. All AHe ages are presented in Age versus eU plots, with the exception of the Pyrenees suite, which is shown as Age versus Th/U. Chemically washed grains are shown in red. Blue diamonds represent a collection of grains analyzed by the authors using standard AHe procedures described in Reiners et al. (2004) and error are reported as 1 stdev. 3.2.1 Laboratory Standard All three chemical solutions were used on a series of single-­‐grain apatites from a laboratory standard with an established AHe age (Fig. 12). Shown in red are the ages of apatite grains that were washed with each of the three solutions. There is good agreement amongst the ages of chemically washed grains, yielding reproducible ages with a mean of 65.0 + 1.1 Ma for all three solutions. Grains washed in 2% HNO3 and HCl yield the least amount of age scatter and a reproducible mean age of 66.0 + 1.0 Ma. 13
3.2.2 Detrital Samples: Sierra Nevada and Pyrenees Mountains As seen in Figure 13, chemically washed grains from a Sierra Nevada paleofluvial gravel that initially showed age scatter exceeding 100 Myr, yield a mean of 57.3 + 2.9 Ma with an age range of 28.9 + 3.5 Myr. Prior to analysis many grains showed the presence of Fe-­‐oxides, including the grain seen in Fig.6B. This grain was chemically washed in the 1% HNO3 solution and yields an AHe age of 55.3 + 2.0 Ma. During chemical washing, flakes of red material were visible seen coming off the apatite grain. However, not all of the red staining disappeared after washing. Chemically washed grains no longer show any correlation with [eU], and the range of [eU] has been reduced. The results from experiments on Pyrenees conglomerates are not as straightforward (Fig. 14). Chemically washed apatite grains from each clast show a minor reduction in age scatter, do not yield an inverse correlation with Th/U, and yield ages all older than the depositional age of the host rock. 3.2.3 Bedrock Samples: Bighorn and Beartooth Mountains Chemically washed apatite grains from the Bighorn Mountains yield a mean age of 68.9 + 1.6 Ma (Fig. 15). The range of ages is reduced from ~196 Ma to ~22 Ma. In addition, there is a slight reduction in the range of [eU] values for chemically washed grains. Chemically washed apatite grains from the Beartooth Mountains yield a mean age of 91.5 + 2.7 Ma, 114 + 5.8 Ma and 81.9 + 3.7 Ma for the 1% HNO3, 5% HNO3 and 2% HNO3, HCl solution, respectively (Fig. 16). With all three solutions, the range of ages is significantly reduced. As a whole, the population of chemically washed grains shows a slight negative age versus [eU] trend, but individual sets of washed grains do not show this correlation. The range of [eU] values is also significantly reduced for chemically washed grains. 3.3 MULTI-­ELEMENT ANALYSES A series of multi-­‐element analyses were conducted on dissolved aliquots of apatites from the Sierra Nevada, Pyrenees and Bighorn and Beartooth Mountains. The presence of elements such as Fe, Mn, La and Ce, detected during our SEM analyses, suggest that there is a detectable difference in the chemical signature between apatite grains with external phases present and those without. Therefore, we hypothesize that chemically washed grains should show a reduction in the concentrations of these elements if chemically washing has removed these phases. 3.3.1 REE Patterns As seen in Figure 17, the REE patterns for washed and unwashed apatite grains are indistinguishable. In specific cases, grains with detectable La and Ce during SEM analyses 14
do appear to be enriched in their entire REE pattern relative to washed and subsequently clear apatite crystals, but the pattern is not reproducible amongst the entire population of washed and unwashed crystals. Sm is enriched in all REE patterns due to the addition of a 147Sm spike during isotope dilution. The REE patterns among all grains from detrital samples from the Sierra Nevada and Pyrenees Mountains are reproducible, but do not reveal any differences between chemically washed and unwashed grains (Fig. 17A, B). In contrast, REE patterns amongst bedrock grains from the Bighorn and Beartooth Mountains show larger differences in [REE] and yield patterns which are often unique to individual grains and not indicative of the whole population. 3.3.2 Single-­element patterns During SEM analyses Fe and Mn were commonly detected on many apatite crystals, in both detrital and bedrock samples. Unfortunately, Fe concentrations between washed and unwashed grains were not obtainable during multi-­‐element analyses, but [Mn] yielded accurate results. We hypothesize that [Mn] should be reduced in chemically washed grains. Figure 18 summarizes these results for each of the four samples previously discussed. Results from additional elements are available in Table 7 in the supplementary material. In Figure 18A, washed grains from the Sierra Nevada show a reduction in age scatter, but an increase in [Mn] relative to unwashed grains. In contrast, in Figure 18B, washed grains from the Pyrenees show a reduction in age scatter and [Mn] relative to unwashed grains—
a pattern that we expect according to our hypothesis. In Figures 18C and 18D, there is no significant difference between washed and unwashed grains from the Bighorn and Beartooth Mountains. However, in the case of unwashed grains from the Beartooth Mountains (Fig.18D), we see a positive correlation between young ages and Mn. In contrast, grains with older ages have lower [Mn]. This pattern agrees with our hypothesis that the presence of late-­‐formed external phases that show the presence of such elements as Mn corresponds with ages that are “too young”. 4. DISCUSSION 4.1. External Parent Nuclide Phases SEM imaging reveals the presence of Fe-­‐ and Mn-­‐oxides and oxyhydroxides, as well as REE-­‐
rich and Th-­‐rich phases along the grain boundaries or surfaces of apatite crystals from samples that display a large amount of age scatter. The phases are found on ~15% of all imaged grains, with many crystals from these samples showing a pure Ca-­‐P-­‐rich peak, with no additional elemental signals. However, as seen in Figures 4 and 5, when Fe-­‐, Mn-­‐, La-­‐ or Th-­‐signals are detected, they are much more intense than any region within the apatite 15
grain. This indicates that the concentrations of these elements are greater in mineral phases surrounding the apatite crystal, than the apatite crystal itself. Under a stereozoom microscope, regions with Fe-­‐ and Mn-­‐oxides and oxhyhydroxides found during SEM analyses correspond to yellow or red surface stains on apatite crystals. Figure 7 details this on the grain imaged in Fig. 6A. In addition, this correlation is also observed in Figure 3, where a region of U-­‐enrichment corresponds to visible yellow staining. The structure of the Fe-­‐oxide seen on the inset of from Fig. 6A suggests that this phase precipitated onto the grain and therefore is younger than the apatite crystal in age. As seen in Figure 4, the presence of Fe-­‐ and Mn-­‐rich phases appears to correlate with regions on enriched Th. In addition, Fe-­‐rich phases also appear to correlate with U-­‐rich regions (Fig. 3), but this relationship is not easily detected during SEM analyses as the signal from U is likely too low to be detected. In addition, we see many cases where we identify a Fe-­‐ or Mn-­‐rich phase, but see no evidence for enrichment of Th or U. This may be due to low sensitivity of the SEM to U and Th in these two minerals, or they may simply not be present. Nevertheless, correlations between the presence of Fe-­‐ and Mn-­‐oxide and oxyhyrdoxides with grains that have anomalous ages, leads us to hypothesize that these phases are enriched in U and Th and therefore contributing additional U-­‐Th and possible 4He to the apatite crystal. The origin of these external phases is not discussed in this paper but we hypothesize that precipitation from fluids is a likely possibility. Similar metasomatic processes can chemically alter the composition of other minerals such as garnet and therefore may be a viable source for the precipitation of these external phases (e.g., Hames and Menard, 1993). In addition, zircon may be a possible source of U or Th as zircon may release some of its U and Th during metamictization (e.g., Woodhead et al., 1991). The three parameters that determine the potential impact of an external U-­‐Th bearing phase on apatite He ages are crucial in understanding anomalous ages, namely (1) their age of formation relative to the He cooling age of apatite, (2) whether or not they are recovered and analyzed with the apatite, and (3) their U-­‐Th concentration relative to apatite. If we identify and analyze a U-­‐Th-­‐rich phase with the apatite and its [U] or [Th] is high relative to the apatite grain, the age of that phase becomes the most important parameter affecting the cooling age of the apatite crystal. Although our model only addresses two end member scenarios, an early-­‐formed phase and a late-­‐formed phase, we acknowledge that external phases formed in between these two extremes will affect an apatite grain differently and complicate the cooling history of an apatite crystal. 4.2 Chemical Washing Experiments Experiments on the WFS age standard show that AHe ages on chemically washed grains are indistinguishable from those on unwashed grains, and display about the same magnitude of dispersion. This suggests that washing does not cause leaching of U or Th (or He) from the grain. 16
4.2.2 Detrital Samples: Sierra Nevada and Pyrenees Mountains Chemically washed grains from the Sierra Nevada paleofluival deposit yield geologically acceptable ages that are, with the exception of one apatite, older than the depositional age of the host rock (Fig. 13). We interpret the significant reduction in [eU] for chemically abraded grains as evidence for the removal of additional U and Th from an external phase. However, the observed age range of ~29 Myr between the youngest and oldest grain suggests that the procedures described above do not entirely resolve the age scatter. The chemically washed grains statistically yield two distinct populations with average ages of ~64 Ma and ~49 Ma. There are two explanations of these populations. First, the ~49 Ma population may comprise grains that did not lose all of their U-­‐Th-­‐rich external phases during washing and therefore still had additional U and Th during analyses. Secondly, the ~64 Ma population may reflect a group of apatites that had the external phases entirely removed, but contain implanted 4He from these phases and therefore yield ages that older than the expected apatite He cooling age of the host rock. We interpret the former to be a more likely scenario due to the reproducibility of the ~64 Ma population. The chemically washed grains from Pyrenees conglomerates yield AHe ages older than the depositional age their host clast, but younger than their maximum age (i.e. age of pluton from which they are derived is 300 Ma) (Fig. 14). However, similar to the Sierra Nevada populations, there is still a significant age range between grains. Clast 1 has a range between the youngest and oldest grain of ~40 Ma; the removal of the oldest outlier (i.e the only grain with significantly older AHe age) reduces the age scatter to ~12 Ma resulting in a new mean age of 65.5 + 1.1 Ma. This outlier may represent a grain that contains implanted 4He from an external phase removed during washing. Clast two has a range of ~24 Ma. As a result of washing, these clasts entirely lose their inverse correlation with Th/U. The most striking feature of chemically washed grains is that they are all older than unwashed grains. In addition, all AHe ages are older than their corresponding AFT ages of 45-­‐47 Ma (Rahl et al., 2011). If we removed an early-­‐formed U-­‐Th-­‐rich external phase, we expect ages to be older than an unwashed grain with a U-­‐Th-­‐rich phase present. However, early-­‐formed phases have had time to produce, and therefore implant, 4He into the apatite crystal. Thus, if we remove an early-­‐formed U-­‐Th-­‐rich phase, but no portions of the crystal affected by 4He implantation, our ages will be drastically “too old”. Early-­‐formed external phases may explain the excessive AHe ages as well as the large variations in AHe ages between grains. 4.2.3 Bedrock Samples: Bighorn and Beartooth Mountains Chemically washed grains from the Bighorn (Fig. 15) and Beartooth Mountains (Fig. 16) yield geologically acceptable ages for the Laramide structural province (e.g., Peyton et al., submitted; Cerveny, 1990), but show an age range of ~22 Ma (33% of average) and ~90 Ma (94% of average), respectively. In addition, there are no anomalously old AHe ages in the chemically washed populations. Chemically washed grains from the Beartooth Mountains 17
show a significant reduction in the range of [eU], with no ages corresponding to [eU] valise exceeding ~5 Ma; all grains that show a reduction in [eU] yield ages older than those with high [eU] values (Fig. 16). For each of these samples, we interpret the significant reduction in the range of ages as evidence for the removal of additional U and Th from a late-­‐formed external phase. We hypothesize that apatite grains that yield “too-­‐old” ages, reflect the presence of early-­‐
formed external phases, which have implanted 4He into the grain. As such, the chemical washing experiments applied here would not fully “correct” regions affected by implanted 4He (up to ~ 20 µm) as there is no significant reduction in grain size post chemical washing. Therefore, it appears that the population of grains chemically washed may have contained late-­‐formed U-­‐Th rich external phases that were removed during washing, but still contain implanted 4He that causes a trend towards older ages with lower [eU]. 4.3. Multi-­Element Analyses Elements such as La, Ce, Fe, and Mn are common constituents of the external phases observed during SEM analyses. However, we detect no chemical difference between washed and unwashed grains. In one respect, this is another line of evidence, in addition to analyses of a laboratory standard, that the chemical washing procedures do not drastically alter the chemistry of the apatite grain. However, the lack of correlation between grains with observed external phases and those without suggests that the REE rich phases may not be a significant source of additional U or Th and therefore may have no effect on the cooling history of the grain. Nevertheless, without analysis of Fe concentration, the most commonly observed composition of these external phases, we cannot rule out correlation. 5. CONCLUSIONS The presence of U-­‐Th-­‐rich external phases along grain boundaries or lining the cracks of apatite crystals may drastically alter the AHe age of a crystal by either (1) adding U and Th to the system causing ages to be younger than their true cooling age or (2) implanting 4He that causes ages to be older than corresponding AFT or plutonic ages. The latter will only affect the cooling age of the apatite if the external U-­‐Th-­‐rich phase is lost prior to analysis resulting in a “parentless” daughter product. The effect of He-­‐implantation from external primary phases such as zircon, apatite or monazite has been recognized before (e.g. Spencer et al., 2004), but what we present here is a more intrinsic problem. The external phases are physically part of the apatite crystal and in turn affect the cooling history of the grain. Chemically washing problematic samples prior analysis significantly reduces age scatter, eliminates negative age versus [eU] correlations in detrital samples and yields apatite crystals with geologically acceptable ages. Chemically washed grains from Sierra Nevada paleofluvial gravels show a marked decrease in the range of ages and [eU] (Fig. 13). Under a stereozoom microscope, apatites from this clast exhibit yellow-­‐red surface stains more than any other sample investigated. During chemical washing, may of these red surfaces 18
were seen flaking off. Together, these are strong lines of evidence for the removal of a U-­‐
Th-­‐rich phase during chemical washing. Nevertheless, chemical washing does not eliminate all age scatter. In the case of detrital samples, we credit the remaining age scatter to variations in the age of the external phase, its concentration relative to the apatite and how much of it was removed during chemical washing. Similarly, remaining age scatter in bedrock samples will be from the same processes, but will remain higher as the chemical washing experiments do not remove portions of the apatite crystal affected by 4He implantation. We recommend that further experiments should be developed in order to eliminate, if possible, the remaining age scatter. In the case of apatites affected by 4He implantation chemical or physical abrasion would be more appropriate. But apatites that are simply affected by the addition of U or Th from these external phases should in theory be fully corrected with the removal of the phase alone through chemical washing. In apatite suites where age dispersion and age anomalies cannot be explained from analytical uncertainty or known sources of scatter, we recommend routine SEM imaging and chemical washing in order to reduce age dispersion, especially with detrital samples. ACKNOWLEDGEMENTS Thank you to Jay Quade and George Gehrels for insightful reviews and discussion of this manuscript. Stuart Thomson provided the AFT image in Figure 3A. Stefan Nicolescu provided additional assistance during laboratory procedures. 19
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Omar, G. I., Lutz, T. M., and Giegengack, R., 1994, Apatite fission-­‐track evidence for Laramide and post-­‐Laramide uplift and anomalous thermal regime at the Beartooth overthrust, Montana-­‐Wyoming: Geological Society of America Bulletin, v. 106, p. 74-­‐
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Geochimica et Cosmochimica Acta, v. 68, p. 1857-­‐1887. Rosholt, J.N., Zartman, R.E., and Nkomo, I.T., 1973, Lead isotope systematics and uranium depletion in the Granite Mountains, Wyoming: Geological Society of America Bulletin, v. 84, p. 989-­‐1002. Shuster, D. L., Flowers, R. M., and Farley, K. A., 2006, The influence of natural radiation damage on helium diffusion kinetics in apatite: Earth and Planetary Science Letters, v. 249, p. 148-­‐161.
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Zeitler, P.K., Herczeg, A., McDougall, I., and Honda, M., 1987, U-­‐Th-­‐He dating of Durango fluorapatite: a potential thermochronometer: Geochimica et Cosmochimica Acta. 51, 2865-­‐2868. Zielinski, R.A., Peterman, Z.E., Stuckless, J.S., Rosholt, J.N., Nkomo, I.T., 1981, The chemical and isotopic record of rock-­‐water interaction in the Sherman granite, Wyoming and Colorado: Contributions in Mineral Petrology 78:209-­‐219. 22
Figure Captions Fig. 1. A, B. Single-­‐grain apatite He ages and AFT ages of surface samples from this and previous studies in the (A) Beartooth and (B) Bighorn Mountains. The large AHe age ranges examined in this study are circled. Fig. 2. Single-­‐grain apatite He ages versus [Th], [U], and Th/U from Cenozoic sedimentary rocks in the Sierra Nevada (A), Pyrenees Mountains (B), and Bighorn Basin (C). Black horizontal line represents the depositional age of the host rock or sedimentary succession. Many grains are younger than the depositional age and show inverse correlations between age and parent nuclide content, including distinct correlations in individual clasts (A, B). Fig. 3. A. Optical microscope image of a yellow-­‐red stain on the edges of an apatite crystal. B. The stain is enriched in U relative to the rest of the crystal, as indicated by high-­‐induced track density. Spontaneous track density is very low in this crystal. A and B are mirror images of each other (Image: S. Thomson). C, D. Yellow-­‐red stain corresponds with a region of high U relative to other parts of the crystal. C and D are mirror images of each other. Fig. 4. BSE and elemental maps of apatite grains from granitoid bedrock in the Beartooth Mountains. Fe-­‐, REE-­‐ and Th-­‐rich phases appear as bright-­‐colored areas around the edges of the apatite, in addition to a Fe-­‐rich phase lining the cracks of the apatite crystal in 3B. Fig. 5. BSE and elemental maps of apatite from a granitoid detrital clast in the Pyrenees Mountains showing secondary Fe-­‐ and REE-­‐rich phases spottily coating the edges of the crystal. Fig. 6. A. BSE and elemental maps of a single apatite crystal from granitoid bedrock in the Bighorn Mountains. Only portion of the grain appears covered by Fe-­‐oxide, whereas the entire grain has a Mn-­‐oxide coating. The red inset depicts the precipitated secondary Fe-­‐rich phase. B. Single grain derived from a granitoid detrital clast from the Sierra Nevada. High Fe coincides with low Ca and P signals. The appearance of Ti is also seen on this apatite, along with an Al-­‐Si-­‐K phase, which may be clay, derived from altered feldspar (not shown). 23
Fig.7. Optical image taken on a stereozoom microscope of the apatite crystal seen in Figure 6A. Red staining correlates with a Fe-­‐oxide phase detected during SEM imaging (Fig. 6A). Fig. 8. A, B Conceptual model showing the effects of U-­‐Th-­‐rich early-­‐formed external phase (A) and late-­‐formed external phase (B) on an apatite He age. Each model assumes Ces > Cg (i.e. C = U and Th concentration; es = external phase; g=grain). “Too-­‐old” AHe ages seen in Fig. 1 may be explained by A; “Too-­‐young” AHe ages seen in Fig. 2 may be explained by B. Fig. 9. Early Formed External Phase: Fractional age bias as a function of the external phase thickness and Cp/Cg. The external phase is retained and analyzed with the apatite grain. Ages can be up to ~25% too young due to a zoning effect created when Cp > Cg (Hourigan et al., 2005). Ages are slightly too old when Cp < Cg; Cp = [U] of the phase; Cg = [U] of the grain. Fig. 10. Early Formed External Phase. The external phase is lost prior to analysis and ages can be significantly too old (e.g., 4 µm thick phase, with 4x [U] causes an age ~ 43 % too old). Fig. 11. Late Formed External Phase. Fractional age bias as a function of late-­‐formed external phase thickness and Ces/Cg. If Ces > Cg and the external phase is retained during analysis, ages can be substantially too young (e.g. 10 µm thick phase, with 10x [U] causes an age ~ 80% too young). Fig. 12. Age versus eU concentration for single-­‐grain apatite crystals from a laboratory standard with a reproducible average age of 64.1+ 3.7 Ma. Laboratory standards shown in blue show a slight positive correlation with [eu] suggesting some degree of radiation damage. Red squares, circles and triangles represent grains washed in 1% HNO3, 2% HNO3 and HCl, and 5% HNO3, respectively. Fig. 13. Age versus eU concentration for single-­‐grain apatite crystals from a granitoid clast from the Sierra Nevada (Sample OF-­‐7; Fig. 2A, green shade). All grains were washed in the 1% HNO3 solution. After chemical washing, age scatter is significantly reduced. Black line represents the depositional age of the host sedimentary rock. Fig. 14. Age versus Th/U for single-­‐grain apatite crystals from two conglomerates in the Pyrenees Mountains (samples Sis1.1A and Sis2Ag; Fig. 2B). All grains were washed in the 1% HNO3 solution. 24
Fig. 15. Age versus [eU] for single-­‐grain apatite crystals from granitoid bedrock in the Bighorn Mountains. All grains were washed in the 2% HNO3, HCl solution. Fig. 16. Age versus [eU] for single-­‐grain apatite crystals from granitoid bedrock in the Beartooth Mountains. Red squares, circles and triangles represent grains washed in 1% HNO3, 2% HNO3 and HCl, and 5% HNO3, respectively. Fig. 17. [REE] normalized to C1 chondrite Orgueil for all REE elements, excluding Er, which did not yield acceptable analyses. The peak in Sm is likely caused by the spike of 147Sm during isotope dilution. A, B are detrital samples; C, D, are bedrock samples. Each panel has the same scale. Red lines = chemically washed grains; Blue lines = unwashed grains. Fig. 18. Age (Ma) versus [Mn] (ppm) for washed and unwashed grains from the Sierra Nevada, Pyrenees Mountains, Bighorn Mountains and Beartooth Mountains. Red squares = chemically washed grains; Blue diamonds = unwashed grains. The vertical scale is the same in all panels, but the horizontal scale is unique to each sample. 25
Figure 1 Figure 2 26
Figure 3 27
Figure 4 Figure 5 Figure 6 28
Figure 7 Figure 8 29
Figure 9 Figure 10 30
Figure 11 Figure 12 31
Figure 13 Figure 14 32
Figure 15 Figure 16 33
Figure 17 Figure 18 34
Table 1: Bedrock Apatite (U-Th)/He Results
Sample Name
Depth sub-Pc
Mass
(µg)
U
(ppm)
Th
(ppm)
Sm
(ppm)
eU
(ppm)
4He
(nmol/g)
Raw Age
(Ma)
Ft
Corrected Age
(Ma)
1!
(Ma)
6.32
197.8
4.05
2.97
10.0
1.58
1.22
5.42
2.33
2.80
7.74
2.27
2.32
4.44
3.83
7.70
4.42
3.40
4.56
2.89
4.26
0.95
1.59
2.90
1.38
2.23
2.37
2.61
2.46
1.18
71.6
25.0
20.7
22.3
26.3
16.9
25.37
16.46
42.83
19.35
8.74
2.49
2.69
5.12
4.16
8.22
4.98
4.01
5.14
3.17
2.66
1.00
2.61
0.59
1.23
0.99
0.01
0.01
0.03
0.00
55.6
73.3
175.6
21.3
54.4
22.2
59.7
73.9
239.0
67.7
0.77
0.92
0.73
0.71
0.79
0.66
0.60
0.75
0.69
0.70
72.7
79.3
239.6
30.1
68.9
33.7
99.0
97.9
348.5
96.7
1.40
1.35
9.36
1.02
1.33
1.29
3.16
2.35
7.87
2.97
2868
2868
2868
2868
2868
2868
2868
2868
2868
2868
9.12
9.04
6.91
10.26
12.45
5.29
1.01
5.89
0.85
122.8
112.8
39.5
10.49
13.84
5.49
4.75
4.06
1.85
1.6
0.9
1.4
0.02
0.01
0.02
104.8
68.2
79.4
2.02
1.17
1.75
2868
2868
2868
Mass
(µg)
U
(ppm)
Th
(ppm)
Sm
(ppm)
eU
(ppm)
4He
(nmol/g)
Raw Age
(Ma)
Ft
Corrected Age
(Ma)
1!
(Ma)
# grains
0.65
2.11
1.48
2.82
1.12
1.66
1.04
1.98
1.35
1.68
0.35
1.55
1.98
0.60
1.20
1.39
0.77
1.05
1.00
0.71
0.48
1.13
1.51
2.64
1.87
2.66
1.90
1.86
1.00
1.97
1.29
1.49
1.04
1.14
1.88
1.54
2.02
3.35
4.67
2.87
2.47
2.98
2.59
2.74
1.29
1.34
7.77
32.14
7.67
10.82
13.18
18.04
7.33
3.44
9.58
5.50
13.57
21.17
14.51
9.40
5.85
7.09
6.51
6.82
7.71
17.59
32.00
5.05
4.65
6.79
14.68
5.67
6.61
1.11
4.90
8.44
3.75
5.53
4.93
3.72
5.21
5.56
8.68
9.80
7.25
10.38
10.97
9.33
9.13
10.72
13.78
16.93
20.14
50.00
16.44
27.49
41.88
38.91
25.45
8.70
26.44
12.05
24.15
42.10
29.99
25.68
14.27
11.99
13.38
15.37
16.30
78.60
52.37
13.24
14.04
9.90
48.24
12.97
19.31
8.56
15.69
10.65
9.74
9.91
17.19
13.43
11.58
9.61
9.82
32.03
42.29
49.39
60.98
27.49
45.85
21.91
71.47
64.15
203.02
184.34
162.14
205.09
192.96
147.86
209.19
145.03
187.08
117.82
156.02
115.99
195.68
167.25
244.46
230.43
230.73
223.98
225.04
182.57
378.12
233.78
127.64
115.45
187.16
86.40
142.38
100.66
184.80
100.33
116.15
108.19
164.06
85.22
76.13
139.65
102.20
141.76
154.81
179.49
175.02
130.08
161.32
144.95
172.76
175.60
12.51
43.89
11.53
17.28
23.02
27.19
13.32
5.49
15.79
8.33
19.25
31.06
21.56
15.44
9.21
9.91
9.65
10.44
11.54
36.06
44.31
8.16
7.95
9.11
26.02
8.72
11.15
3.12
8.59
10.94
6.04
7.85
8.97
6.87
7.94
7.82
10.98
17.33
17.19
21.99
25.30
15.79
19.91
15.87
30.58
32.01
3.93
5.09
3.34
4.46
4.19
2.90
5.44
2.01
5.04
2.71
3.81
4.78
3.96
4.61
2.91
2.77
2.52
2.63
2.59
3.00
0.85
2.52
1.44
1.22
1.41
1.44
1.44
1.34
1.80
1.52
1.30
1.72
1.76
2.12
1.28
0.21
1.48
2.37
3.72
4.22
4.01
5.16
3.40
5.08
4.73
6.26
56.8
21.3
52.5
46.9
33.2
19.6
73.7
65.5
1.1
58.9
36.2
28.3
33.6
54.3
56.3
50.1
46.7
45.3
40.4
15.3
3.5
55.1
32.7
24.4
9.9
30.2
23.5
75.9
37.7
25.3
38.9
39.9
35.3
55.9
29.4
4.8
24.7
25.0
39.4
35.0
29.0
59.5
31.1
58.3
28.3
35.8
0.56
0.68
0.64
0.72
0.62
0.66
0.59
0.68
0.01
0.66
0.49
0.68
0.65
0.55
0.62
0.63
0.59
0.62
0.61
0.56
0.55
0.62
0.65
0.71
0.67
0.72
0.68
0.66
0.56
0.65
0.61
0.63
0.56
0.61
0.64
0.62
0.70
0.72
0.76
0.71
0.71
0.74
0.70
0.73
0.62
0.64
101.2
31.2
81.9
65.2
54.0
29.6
124.5
96.4
94.8
88.7
74.0
41.8
51.3
97.9
90.5
79.9
79.1
73.0
66.6
27.3
6.4
89.2
50.7
34.3
14.9
42.2
34.6
114.2
67.7
38.7
63.6
63.1
62.5
91.7
46.2
7.8
35.4
34.5
51.8
49.4
40.7
80.8
44.2
80.4
45.8
56.1
2.33
0.65
1.84
1.31
0.97
0.54
14.72
14.32
1.77
4.69
7.21
0.66
0.82
2.19
1.68
1.52
1.76
1.47
1.28
0.48
0.16
15.65
1.09
0.65
0.26
0.85
0.64
31.24
5.08
1.99
5.19
5.67
2.82
4.73
1.47
0.42
0.94
0.61
0.87
0.86
0.70
1.53
0.79
1.66
0.90
1.03
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Sample elev. unconformity
(m)
(Ma)
# grains
Beartooth Mountains
BT07-S
11AA200_BT072007AA
11AA201_BT2007_2ay
11AA203_BT2007_2ax
11AA204_BT2007_2aw
11AA207_DO_BT2007_2au
BT072007-AB
BT072007-AC
BT072007-AD
BT072007-AE
1
1
1
1
1
1
1
1
1
1
Bighorn Mountains
11AA212_DO_BH090606_1a
11AA213_DO_BH090606_1b
11AA216_DO_BH090606_1e
Table 2: Detrital (U-Th)/He Results
Sample Name
Sierra Nevada
OF-3a1
OF3an1
OF3an2
OF3an3
OF3an4
OF3an5
OF3a-6
OF3a-7
OF-3a_I
OF-3a
OF-3d2
OF-3AB
OF-3AC
OF-3AD
OF-5a1
OF-5a2
OF5an1
OF5an2
OF5an3
OF5an4
OF5an5
OF5a-7
OF7an1
OF7an2
OF7an3
OF7an4
OF7an5
OF7a-6
OF-7d
OF-7g
OF-7i
OF-7j
11AA188_OF-7aa
11AA189_OF-7ab
11AA190_OF-7ac
11AA197_OF-7ah
11AA199_OF-7aj
BL-P5aA
BL-P5aB
BL-P5aC
BL-P5aD
BL-P5aE
BL-P5aF
BL-P5aG
BL-P5aH
BL-P5aI
1359
1359
1359
1
1
1
35
Sample Name
BL-P5aJ
BL-P5an1
BL-P5an2
BL-P5an3
BL-P5an4
BL-P5an5
BL-P5an6
BL-P5an7
BL-P5an8
BL-P5b
BL-P5c
BL-P5d
BL-P5e
Mass
(µg)
U
(ppm)
Th
(ppm)
Sm
(ppm)
eU
(ppm)
4He
(nmol/g)
Raw Age
(Ma)
Ft
Corrected Age
(Ma)
1!
(Ma)
# grains
1.09
3.09
3.61
3.95
1.41
3.26
5.77
5.24
5.06
0.36
1.40
0.91
1.25
9.19
10.02
10.71
13.98
10.70
10.91
12.69
2.54
10.10
6.06
18.28
9.00
12.60
38.69
48.78
44.34
39.28
33.40
22.87
32.70
8.95
43.48
20.34
40.86
35.46
31.08
191.14
164.53
175.04
174.58
172.21
170.08
167.84
41.78
154.81
160.98
130.13
133.80
161.28
18.28
21.49
21.13
23.21
18.55
16.29
20.37
4.64
20.32
10.84
27.88
17.33
19.91
4.39
4.09
4.60
5.48
4.41
4.92
6.23
3.48
4.12
3.44
5.93
3.27
1.18
43.7
34.7
39.7
43.1
43.4
55.0
55.8
135.7
37.1
57.5
39.0
34.5
10.8
0.60
0.72
0.73
0.73
0.65
0.72
0.77
0.76
0.76
0.43
0.63
0.57
0.62
73.4
48.3
54.7
58.7
66.5
76.9
72.9
178.6
48.6
135.2
62.4
60.3
17.6
2.09
0.81
0.88
0.97
1.11
1.29
1.17
3.07
0.76
18.47
1.91
2.96
0.89
1
1
1
1
1
1
1
1
1
1
1
1
1
1.19
2.21
1.01
0.85
1.53
1.47
1.20
0.91
0.98
1.99
4.66
3.23
0.67
2.19
2.32
1.96
1.95
1.51
3.21
90.92
138.34
79.43
34.99
212.37
166.57
12.16
96.04
68.15
14.89
62.87
25.37
96.55
3.88
66.48
3.43
25.82
27.45
141.06
59.09
32.61
9.30
239.28
71.34
75.02
157.45
44.38
70.55
55.75
56.53
53.69
1545.68
32.14
61.34
38.67
21.60
48.16
154.69
335.80
340.76
313.39
56.40
613.58
416.41
86.52
161.23
205.93
101.41
43.40
62.50
300.67
92.49
87.03
103.01
103.47
133.51
63.02
104.80
146.00
81.61
91.22
229.14
184.20
49.16
106.47
84.73
28.00
76.15
37.99
459.79
11.43
80.89
12.51
30.90
38.77
177.42
13.32
24.18
11.26
4.66
37.23
33.74
0.76
13.53
10.50
2.43
14.34
5.17
2.86
0.68
11.66
0.44
4.39
4.89
27.21
23.4
30.6
25.4
9.4
30.0
33.8
2.8
23.5
22.9
15.9
34.8
25.1
1.1
10.8
26.6
6.5
26.2
23.2
28.3
0.58
0.67
0.58
0.57
0.67
0.66
0.62
0.61
0.62
0.68
0.78
0.74
0.54
0.67
0.71
0.70
0.70
0.66
0.74
40.4
45.6
43.5
16.5
45.0
51.2
4.6
38.4
36.6
23.6
44.7
34.1
2.1
16.2
37.3
9.3
37.6
35.0
38.4
0.74
0.80
0.90
0.33
0.99
1.12
0.11
0.89
0.82
0.50
0.99
0.72
0.05
0.36
0.83
0.25
0.87
0.76
0.84
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1.44
1.84
1.00
1.29
1.23
1.40
0.95
0.71
1.25
1.40
0.88
0.65
0.94
0.32
0.34
1.14
0.69
1.16
0.91
1.29
0.77
0.44
0.64
0.75
0.80
0.77
1.70
0.40
0.61
53.35
13.10
7.74
7.26
24.70
5.24
29.52
3.06
6.01
16.91
12.16
3.32
24.31
1.62
14.78
0.89
1.41
8.44
0.44
2.90
6.72
12.84
4.32
0.27
10.39
4.45
18.98
10.24
3.58
83.63
46.09
40.19
24.83
98.34
21.92
74.34
7.87
14.23
97.44
100.43
21.93
117.36
12.70
40.31
7.10
26.92
50.29
14.04
27.20
30.42
36.56
12.09
10.53
62.92
9.94
104.08
18.93
9.21
280.77
156.35
210.22
186.23
313.02
131.90
232.60
299.66
64.78
263.85
206.78
97.99
249.53
112.44
282.46
212.42
142.49
107.04
109.34
213.18
441.61
220.77
90.03
85.30
175.08
39.68
203.61
158.05
99.70
73.01
23.93
17.18
13.09
47.81
10.39
46.98
4.91
9.36
39.81
35.76
8.47
51.89
4.60
24.26
2.56
7.73
20.26
3.74
9.30
13.87
21.43
7.16
2.75
25.17
6.78
43.44
14.69
5.74
0.65
1.53
2.73
1.79
7.97
1.14
8.59
3.54
1.08
1.26
0.41
0.81
1.34
1.51
1.43
0.93
0.86
4.19
1.25
1.07
2.35
3.15
1.42
0.79
1.01
0.22
1.59
5.87
1.24
1.6
11.7
28.9
24.8
30.5
20.0
33.5
123.2
21.2
5.8
2.1
17.5
4.7
58.7
10.7
61.1
20.1
37.9
59.5
20.5
30.0
26.8
36.0
51.1
7.4
6.1
6.7
72.6
39.1
0.63
0.66
0.59
0.61
0.61
0.63
0.59
0.55
0.62
0.61
0.55
0.54
0.59
0.45
0.44
0.58
0.53
0.60
0.53
0.61
0.56
0.47
0.53
0.52
0.57
0.58
0.65
0.49
0.54
2.6
17.8
49.4
40.6
50.1
31.6
56.5
222.0
34.4
9.6
3.8
32.6
8.1
130.3
24.3
105.7
37.9
62.7
112.3
33.9
53.9
57.3
67.8
98.5
12.9
10.4
10.3
149.1
72.2
0.71
2.11
3.71
4.36
2.41
3.53
2.69
19.24
3.27
1.35
1.84
15.83
1.84
44.89
8.51
24.28
17.34
5.20
20.57
4.83
8.22
10.94
20.29
29.82
0.43
0.65
0.31
5.96
4.10
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Pyrenees Mountains
11AA236_DO_Sis11A_d
11AA239_DO_Sis11A_g
11AA240_DO_Sis11A_h
Sis11Aa1
Sis11Aa2
Sis11Aa3
Sis2Aa3
Sis2Ag1
Sis2Ag2
Sis2Ag3
Sis2Ag4
Sis2Ag5
Sis2Ag6
Sis2Ag7
Sis2Ag8
Sis2Ag9
Sis2Ag10
Sis2Ag11
Sis2Ag12
Bighorn Basin Sediments
693_3_2
693_3_3
693_3_4
693_3_5
693_3_6
693_3_7
693_3_8
693_3_9
693_3_10
693_3_11
693_3_12
693_3_13
693_3_14
693_3_15
693_3_16
693_3_17
693_3_18
693_3_19
693_3_20
693_3_21
693_3_22
693_3_23
693_3_24
693_3_25
693-3-26
693-3-27
693_3_28
693_3_29
693_3_30
36
Table 3a: Apatite (U-Th)/He Results, Laboratory Standard
Sample Name
U
(ppm)
Th
(ppm)
Sm
(ppm)
eU
(ppm)
4He
(nmol/g)
Raw Age
(Ma)
Ft
Corrected Age
(Ma)
1σ
(Ma)
# grains
175.22
157.16
178.64
221.20
145.66
176.47
137.52
158.86
116.69
161.82
106.70
154.92
205.68
118.50
126.06
249.39
126.24
165.98
173.14
116.07
191.22
144.14
143.84
185.54
103.21
179.91
197.72
122.75
197.24
202.21
141.09
156.49
146.11
162.43
139.14
11241.96
447.26
104.40
63.71
140.09
160.05
128.40
129.03
102.96
161.16
158.18
130.62
149.21
174.79
178.08
88.56
114.58
135.89
150.09
135.31
244.79
118.04
155.57
111.52
166.01
115.90
145.10
116.96
151.22
162.89
81.09
102.89
22.05
145.73
172.75
137.69
82.56
161.24
114.80
119.87
149.90
83.68
160.68
193.84
110.63
139.50
195.44
117.02
125.51
101.77
121.57
136.44
134.54
417.66
82.37
59.21
79.84
110.51
112.02
111.40
124.40
146.45
164.73
103.41
138.30
138.03
167.40
86.50
108.28
32.88
32.83
33.55
53.00
30.83
35.32
25.42
33.55
21.97
34.22
26.65
32.01
36.69
19.53
23.34
5.14
30.22
43.38
29.58
21.44
39.07
30.87
30.48
32.64
21.13
38.58
42.79
27.37
34.41
42.79
27.20
31.91
26.03
26.33
33.09
29.20
104.69
24.01
12.94
19.83
21.64
23.37
23.96
30.93
37.09
37.74
24.52
28.88
29.19
34.46
20.29
28.50
44.6
40.4
45.7
39.9
48.1
41.9
42.0
37.3
35.0
43.5
42.0
39.1
41.5
44.4
41.8
42.4
38.3
46.3
39.6
47.9
44.7
49.5
46.9
40.2
46.5
44.3
40.7
45.6
45.5
40.4
42.9
46.9
47.1
40.0
44.7
36.4
46.2
53.7
40.3
45.8
36.1
38.5
39.7
45.9
46.7
42.3
43.7
38.5
39.0
38.0
43.3
48.5
0.64
0.65
0.70
0.56
0.73
0.63
0.65
0.61
0.58
0.67
0.67
0.66
0.64
0.66
0.62
0.73
0.59
0.71
0.68
0.77
0.65
0.69
0.74
0.64
0.76
0.65
0.60
0.75
0.70
0.60
0.64
0.71
0.75
0.62
0.61
0.61
0.59
0.79
0.75
0.73
0.59
0.65
0.66
0.77
0.74
0.66
0.72
0.61
0.63
0.62
0.70
0.71
69.6
61.7
64.9
71.8
65.7
66.8
64.6
61.3
60.2
65.1
62.7
59.4
64.6
67.1
67.0
58.0
64.4
65.4
58.5
62.4
68.8
72.1
63.5
62.4
61.5
68.5
68.2
60.5
64.8
67.7
66.6
65.9
63.2
64.4
73.3
59.7
78.4
67.6
53.7
62.5
61.1
59.2
59.9
59.7
63.1
64.3
60.8
63.4
61.8
61.3
62.0
68.6
1.59
1.43
1.47
1.65
1.51
1.54
2.92
2.16
2.06
1.59
1.43
1.35
1.40
1.55
1.27
1.75
1.16
1.29
1.11
0.96
1.20
1.13
1.11
1.32
1.28
1.55
1.43
1.07
1.11
1.41
1.19
1.38
1.21
1.33
1.21
0.95
1.91
1.51
1.23
1.41
1.76
1.69
1.46
1.40
1.19
1.41
1.51
1.69
0.95
0.98
0.99
1.08
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Sierra Nevada Laboratory Standard (WFS)
Run Normally
05WFS5a1
05WFS5a2
05WFS5a3
05WFS5a4
05WFS5a5
05WFS5a6
AB05WFS5aA
AB05WFS5aB
05WFS5A
05WFS5C
05WFS5D
05WFS5E
05WFS5G
SN05WFS5aA
SN05WFS5aB
05WFS5F
05wfs-5alp1
05WFS5-AR-1
05WFS5a_AB1
DG05WFS5a1
DG05WFS5A-2
05WFS5G
05WFS5-5 (LP)
05wfs5-jm1
GA05wfs5a1
05WFS5H
05wfs5-613a
5WFS5a3
05wfs5-jm2
05wfs5-613a
05wfs5a-9-26a
std 5wfs5a1
Std_5WFS5a2
05WFS5-AR-4
05WFS5-AR-3
05wfs5a9-26b
AB05WFS5a1
MC_05WFS_A1
MC_05WFS_A2
MC_05WFS_A3
WSF51
WFS52
WFS53
07WFS1_AB
07WFS1aAB1
AB07WFS1a1
BA 07WFS1a4
BA_07WFS1a_3
11AA186_WSF5_DO1
11AA187_WSF5_DO2
11AA191_WSF5_DO3
11AA191_WSF5_DO4
105.23
121.35
100.23
188.59
93.90
122.22
87.70
135.24
92.02
113.48
95.27
124.27
126.80
68.03
82.32
15.95
116.80
134.35
110.31
64.30
126.95
88.34
94.94
114.66
67.25
125.47
152.28
87.96
109.21
153.56
96.64
99.29
79.27
97.51
104.28
106.81
327.49
63.98
48.67
62.80
85.93
87.51
87.33
99.04
120.70
132.07
82.18
110.52
107.18
134.53
69.27
88.81
130.50
122.27
149.30
239.12
102.70
141.89
101.36
130.92
101.60
134.55
92.34
114.69
153.59
55.57
87.53
25.92
123.10
163.43
116.50
77.71
145.89
112.61
106.09
149.94
69.91
149.82
176.86
96.47
128.89
178.22
86.76
111.61
95.73
102.39
136.84
117.98
383.71
78.26
44.84
72.49
104.60
104.29
102.44
107.91
109.61
139.01
90.33
118.21
131.25
139.87
73.35
82.84
Table 3b: Chemically Washed Apatite (U-Th)/He Results, Laboratory Standard
Sample Name
U
(ppm)
Th
(ppm)
Sm
(ppm)
eU
(ppm)
4He
(nmol/g)
Raw Age
(Ma)
Ft
Corrected Age
(Ma)
1σ
(Ma)
# grains
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Sierra Nevada Laboratory Standard (WFS)
Washed 1% HNO3
WSF5-9C
WSF5-9D
WSF5-9E
05WFS5a_J
05WFS5a_K
05WFS5a_L
11AA177_05WSF5_F
11AA178_05WSF5_G
11AA179_05WSF5_H
11AA180_05WSF5_I
Washed 2% HNO3, HCl
11AA181_05WSF5_J
11AA182_05WSF5_K
11AA183_05WSF5_L
11AA184_05WSF5_N
11AA185_05WSF5_O
Washed 5% HNO3
05WFS5a_M
05WFS5a_N
05WFS5a_O
05WFS5a_P
96.55
75.99
112.01
72.42
94.47
88.82
99.12
97.06
100.09
70.22
139.25
84.82
129.78
108.66
113.56
107.53
83.06
106.55
116.05
81.67
169.76
97.45
150.79
228.05
158.81
148.11
166.88
151.40
157.82
129.47
129.28
95.92
142.50
97.66
115.56
112.42
118.64
122.10
127.36
89.41
27.91
27.26
36.08
20.16
30.27
28.34
26.24
26.88
31.40
17.63
39.8
52.4
46.7
37.9
46.1
45.8
40.8
40.6
45.5
36.4
0.61
0.70
0.69
0.57
0.69
0.72
0.68
0.67
0.71
0.69
64.9
75.2
68.1
67.2
66.9
64.8
60.2
61.0
63.7
52.5
1.15
2.17
1.15
1.24
1.00
0.97
0.96
0.97
0.98
0.80
141.85
68.71
83.79
88.00
74.27
162.45
84.52
108.42
109.02
81.85
179.22
171.23
166.33
140.29
128.56
180.02
88.57
109.27
113.62
93.50
41.42
24.17
24.46
24.61
22.75
42.4
50.3
41.3
39.9
44.9
0.64
0.75
0.61
0.63
0.67
66.1
67.0
67.2
63.8
66.6
1.03
1.01
1.05
0.99
1.05
96.63
106.62
100.36
107.69
106.30
128.18
132.27
112.18
166.65
172.03
171.28
141.71
118.99
118.26
125.68
131.50
29.00
31.22
36.62
31.14
44.0
42.1
51.3
42.9
0.70
0.58
0.75
0.66
63.0
73.0
68.6
64.5
0.93
1.25
0.99
1.01
37
Table 4: Detrital (U-Th)/He Results, Chemically Washed Grains
Sample Name
Mass
(µg)
U
(ppm)
Th
(ppm)
Sm
(ppm)
eU
(ppm)
4He
(nmol/g)
Raw Age
(Ma)
Ft
Corrected Age
(Ma)
1σ
(Ma)
# grains
1
1
1
1
1
1
1
1
1
Sierra Nevada Laboratory Standard (WFS)
Solution: 1% HNO3
Clast OF-7
OF-7d
OF-7g
OF-7i
OF-7j
11AA192_OF-7ad
11AA193_OF-7ae
11AA194_OF-7af
11AA195_OF-7ag
11AA198_OF-7ai
1.00
1.97
1.29
1.49
2.34
1.97
1.70
2.30
1.41
4.90
8.44
3.75
5.53
6.35
5.72
5.55
3.71
7.38
15.69
10.65
9.74
9.91
21.61
17.14
8.45
10.48
15.17
184.80
100.33
116.15
108.19
101.09
103.51
88.87
123.73
155.74
8.59
10.94
6.04
7.85
11.43
9.75
7.54
6.17
10.98
1.80
1.52
1.30
1.72
1.98
2.18
1.49
1.47
2.11
2.8
1.3
3.2
3.6
31.6
40.7
36.1
42.8
34.9
0.56
0.65
0.61
0.63
0.67
0.66
0.65
0.67
0.64
67.7
38.7
63.6
63.1
47.4
61.5
55.3
64.3
54.5
5.08
1.99
5.19
5.67
1.03
1.58
2.03
2.42
1.64
1.729339621
2.308830162
2.299843128
8.905622489
49.16
61.72
113.75
72.29
34.34
27.33
44.45
87.14
169.31
296.20
387.35
207.74
57.23
68.14
124.19
92.77
14.44
14.91
44.97
27.78
46.4
40.2
66.5
55.1
0.67
0.70
0.69
0.79
69.2
57.2
97.0
70.0
1.24
1.06
1.65
1.05
1.367341949
2.360581616
2.488056407
5.06445394
1.796786672
206.76
187.79
106.95
95.10
203.21
36.87
68.41
24.70
34.58
22.55
351.45
353.68
264.62
396.53
396.27
215.42
203.87
112.76
103.23
208.51
34.23
52.69
23.29
24.44
47.10
29.4
47.7
38.1
43.6
41.7
0.63
0.67
0.68
0.76
0.66
46.5
70.7
56.3
57.0
63.6
0.82
1.23
1.00
0.98
1.22
Pyrenees Mountains
Solution: 1% HNO3
Clast 1
11AA224_DO_Sis2Ag_a
11AA225_DO_Sis2Ag_b
11AA227_DO_Sis2Ag_d
11AA229_DO_Sis2Ag_f
Clast 2
11AA232_DO_Sis11A_a
11AA233_DO_Sis11A_b
11AA235_DO_Sis11A_c
11AA237_DO_Sis11A_e
11AA238_DO_Sis11A_f
1
1
1
1
1
1
1
1
1
1
1
1
Table 5: Bedrock (U-Th)/He Results, Chemically Washed Grains
Sample Name
Mass
(µg)
U
(ppm)
Th
(ppm)
Sm
(ppm)
eU
(ppm)
4He
(nmol/g)
Raw Age
(Ma)
Ft
Corrected Age
(Ma)
1σ
(Ma)
# grains
10.11
15.72
12.92
7.04
2.56
2.19
2.39
4.43
137.50
72.74
93.48
197.12
10.71
16.23
13.48
8.08
3.49
4.54
4.48
1.72
59.2
51.4
60.8
38.2
0.81
0.77
0.77
0.68
73.5
67.2
78.8
56.5
1.34
1.25
1.47
2.43
1
1
1
1
9.97
1.22
5.42
2.80
6.48
3.73
1.81
4.42
3.40
2.89
3.47
4.05
0.39
2.37
2.61
1.18
1.03
2.17
11.30
25.37
16.46
19.35
18.09
27.79
1.90
4.98
4.01
3.17
3.71
4.56
0.63
0.01
0.01
0.00
1.85
1.10
61.3
59.7
73.9
67.7
91.1
44.2
0.80
0.60
0.75
0.70
0.77
0.73
76.3
99.0
97.9
96.7
118.5
60.7
3.28
3.16
2.35
2.97
2.90
1.74
1
1
1
1
1
1
2.40
2.09
3.16
3.50
3.38
3.28
2.65
1.64
1.45
25.75
28.24
26.99
4.12
3.76
3.62
1.57
1.19
0.76
69.5
58.1
38.7
0.67
0.66
0.71
103.2
88.2
54.5
4.65
4.55
2.09
1
1
1
15.10
2.74
10.93
1.75
0.71
1.42
0.75
2.78
0.33
15.31
8.95
13.83
1.93
1.36
1.50
1.26
0.47
0.70
119.3
63.1
85.7
0.83
0.68
0.80
143.7
92.9
106.6
3.38
10.58
3.35
1
1
1
Bighorn Mountains
Solution: 2% HNO3, HCl
11AA214_DO_BH090606_1c 11.50
11AA218_DO_BH090606_1f 6.39
11AA219_DO_BH090606_1h 6.88
11AA220_DO_BH090606_1i 2.05
Beartooth Mountains
Solution: 1% HNO3
BT072007-2H
BT072007-AB
BT072007-AC
BT072007-AE
11AA202_BT2007_2az
11AA206_DO_BT2007_2av
Solution: 2% HNO3, HCl
11AA208_DO_BT2007_2at
11AA209_DO_BT2007_2as
11AA210_DO_BT2007_2ar
Solution: 5% HNO3
BT072007-2C
BT072007-2D
BT072007-2E
38
Table 6: REE patterns, Unwashed and Chemically Washed Grains
Sample Name
La
(ppm)
All elements normalized to Orgueil
C1 chondrite Orgueil
0.236
Ce
(ppm)
Pr
(ppm)
Nd
(ppm)
Pm
(ppm)
Sm
(ppm)
Eu
(ppm)
Gd
(ppm)
Tb
(ppm)
Dy
(ppm)
Ho
(ppm)
Tm
(ppm)
Yb
(ppm)
Lu
(ppm)
0.619
0.090
0.463
-
0.144
0.055
0.199
0.035
0.246
0.055
0.022
0.166
0.025
1769.35
1314.76
1554.60
1275.57
1649.82
1162.16
1474.07
1179.80
1727.62
1119.47
1633.69
1204.07
1364.71
854.37
1298.98
930.49
-
1394.03
900.25
1219.10
907.51
426.92
161.38
274.96
213.90
877.90
481.42
778.69
580.17
968.74
487.18
837.70
587.28
809.97
423.99
687.71
509.43
653.10
327.88
627.02
420.45
488.01
269.67
469.18
336.17
404.49
244.45
366.11
259.89
17726.25
246.65
330.79
230.39
1208.17
1697.21
1063.81
1321.13
2183.13
1063.92
1447.80
969.29
1271.26
1916.22
1100.05
1446.66
974.72
1399.01
1883.39
879.50
1056.33
816.51
1172.48
1412.72
-
847.23
1060.10
779.62
1059.93
1365.60
240.31
219.35
168.22
263.22
352.58
557.66
618.44
463.13
684.49
836.85
625.82
650.14
491.12
743.17
925.71
526.22
477.89
405.48
593.57
774.29
474.48
429.40
341.57
513.22
646.88
384.67
348.20
297.90
393.50
510.45
301.31
274.21
210.04
331.43
398.43
277.82
262.33
240.49
293.67
387.36
778.93
1000.69
739.44
1101.53
1241.55
983.05
1490.08
1609.84
1342.22
1368.14
1471.00
1212.22
2796.93
2754.55
2943.59
252.53
648.98
456.24
1845.12
1578.16
1736.91
3008.73
2260.66
2527.07
2236.96
1739.29
1867.93
1536.27
1099.13
1184.28
1203.38
780.82
978.23
1044.76
640.91
820.73
886.12
497.93
666.86
935.39
927.03
756.60
1096.42
999.62
1236.38
1225.56
980.73
1417.20
1346.89
1690.00
1665.92
1311.62
1897.18
1837.29
1443.91
1484.18
1141.95
1666.95
1651.85
-
2969.61
2956.95
2211.96
3029.10
3142.64
261.46
242.55
240.45
305.01
225.55
2065.67
1973.89
1507.22
2153.33
2157.71
3442.61
3258.63
2392.77
3457.43
3710.47
2674.21
2568.20
1781.99
2764.31
2999.17
1858.78
1692.93
1223.62
1912.87
2073.18
1508.47
1361.86
904.41
1525.85
1776.00
1357.32
1205.66
788.44
1274.32
1421.13
1168.99
997.59
687.42
1023.24
1269.99
423.65
550.63
66.27
463.38
524.02
88.00
661.94
653.31
132.28
734.60
674.83
177.67
-
992.38
890.39
341.07
408.93
445.44
113.43
760.35
713.97
305.27
995.53
903.73
483.73
861.92
791.62
491.08
738.34
672.58
480.62
584.88
502.82
493.49
495.03
398.79
383.13
442.59
341.56
341.35
332.80
179.28
223.89
534.57
439.73
193.25
235.86
760.06
666.13
264.89
336.88
1085.74
798.24
301.78
421.12
1117.36
-
1068.68
590.17
758.60
1631.33
253.44
451.06
410.51
215.34
798.50
534.91
582.71
1078.55
978.19
837.28
759.20
1475.96
814.52
801.40
615.50
1206.94
667.48
718.11
496.58
1021.75
553.21
584.76
365.38
822.13
418.95
452.78
290.42
598.94
347.17
397.32
248.55
477.22
130.46
133.71
154.26
165.47
116.36
152.50
154.45
182.54
192.08
166.62
214.72
199.45
231.25
255.36
159.99
204.20
186.55
226.59
237.80
161.93
-
172.48
246.37
306.79
238.29
341.00
141.09
120.66
153.66
168.97
121.74
103.30
90.86
111.00
133.03
81.14
99.50
82.68
108.08
131.36
78.77
74.56
72.14
107.74
104.94
105.09
72.85
64.25
80.77
97.49
67.18
70.54
62.96
86.91
104.22
67.72
61.23
56.34
90.20
95.28
92.55
58.30
57.65
82.25
82.13
60.12
157.87
88.27
190.13
103.80
252.08
133.72
246.24
129.88
-
328.43
180.79
189.76
139.98
137.00
91.53
139.93
118.16
114.23
105.75
95.40
99.80
104.65
99.68
101.22
80.89
76.02
75.59
170.10
146.22
164.99
211.08
180.32
199.57
258.64
239.86
263.66
237.76
249.57
259.14
-
313.31
345.73
289.74
144.79
172.13
156.68
114.12
129.67
134.08
107.93
115.39
133.87
90.43
113.55
118.24
63.69
80.75
92.43
53.95
82.47
94.06
65.07
79.57
121.28
45.34
75.11
82.64
Detrital Samples
Sierra Nevada
Unwashed
11AA188_OF_7aa
11AA189_OF_7ab
11AA197_OF_7ah
11AA199_OF_7aj
Washed: 1 % HNO3
11AA192_OF_7ad
11AA193_OF_7ae
11AA194_OF_7af
11AA195_OF_7ag
11AA198_OF_7ai
Pyrenees Mountains
Unwashed
11AA239_DO_Sis11A_g
11AA240_DO_Sis11A_h
11AA236_DO_Sis11A_d
Washed: 1 % HNO3
11AA232_DO_Sis11A_a
11AA233_DO_Sis11A_b
11AA235_DO_Sis11A_c
11AA237_DO_Sis11A_e
11AA238_DO_Sis11A_f
Bedrock Samples
Bighorn Mountains
Unwashed
11AA212_DO_BH090606_1a
11AA213_DO_BH090606_1b
11AA216_DO_BH090606_1e
Washed: 2 % HNO3, HCl
11AA214_DO_BH090606_1c
11AA218_DO_BH090606_1f
11AA219_DO_BH090606_1h
11AA220_DO_BH090606_1i
Beartooth Mountains
Unwashed
11AA200_BT072007AA
11AA201_BT2007_2ay
11AA203_BT2007_2ax
11AA204_BT2007_2aw
11AA207_DO_BT2007_2au
Washed: 1 % HNO3
11AA206_DO_BT2007_2av
11AA202_BT2007_2az
Washed 2 % HNO3, HCl
11AA208_DO_BT2007_2at
11AA209_DO_BT2007_2as
11AA210_DO_BT2007_2ar
39
Table 7: Single-element concentrations, Unwashed and Chemically Washed Grains
Sample Name
Mn
(ppm)
Mg
(ppm)
Al
(ppm)
Ti
(ppm)
Cr
(ppm)
Ba
(ppm)
616.16
465.04
618.14
450.05
3735.09
2834.59
4291.03
2769.56
8965.12
7063.33
10208.22
4386.84
1662.65
1180.50
2055.20
1264.99
3115.25
1744.17
823.42
1089.88
219.37
166.64
116.94
125.03
543.73
664.01
2372.64
666.02
852.73
1623.62
2738.37
6410.13
2633.78
5396.53
4965.76
16640.48
21644.74
11725.10
17747.53
1182.57
1433.46
1215.08
1599.00
2428.85
658.39
1992.96
4336.50
1345.70
2606.56
73.37
127.35
112.75
88.27
271.48
3719.87
3010.87
3844.22
2946.41
9572.18
3611.32
19224.49
24866.18
14499.77
1366.33
1526.24
1791.70
2367.46
3149.51
3609.51
74.76
245.53
197.67
3745.86
4054.75
4201.03
4518.84
4616.05
2404.55
3413.81
5901.79
1629.28
2761.57
25415.73
29889.76
23432.09
4505.03
73366.49
2047.55
1320.94
1341.02
1436.82
1273.37
3671.29
1705.74
1306.02
2705.54
2995.48
106.87
72.71
209.91
86.92
99.21
450.49
664.16
328.65
572.71
634.90
559.96
1420.53
6053.73
4195.15
1275.60
1609.98
1080.69
415.44
671.06
697.02
33.58
55.60
108.03
393.83
409.47
483.50
668.70
434.03
1015.99
1351.52
5621.90
4113.95
12561.33
7875.04
25449.23
1217.19
1070.24
1056.61
1578.23
382.64
480.00
408.65
2077.28
19.16
50.48
57.28
172.76
787.84
796.17
944.95
796.82
880.58
215.36
852.51
2531.23
481.52
4404.90
1708.78
1752.98
32090.68
9110.92
12983.85
1695.05
1212.06
1383.87
1207.98
1436.57
20.78
855.24
2189.92
208.84
3364.31
3.41
36.36
85.14
20.91
149.97
820.05
857.65
1331.26
1228.16
12052.59
4039.09
1203.18
1221.76
547.81
882.67
59.15
43.88
793.89
755.21
794.45
2128.98
5933.99
810.15
11001.26
6524.19
5991.29
1346.41
1326.52
1212.55
688.46
1837.97
698.35
219.66
109.67
89.97
Detrital Samples
Sierra Nevada
Unwashed
11AA188_OF_7aa
11AA189_OF_7ab
11AA197_OF_7ah
11AA199_OF_7aj
Washed: 1 % HNO3
11AA192_OF_7ad
11AA193_OF_7ae
11AA194_OF_7af
11AA195_OF_7ag
11AA198_OF_7ai
Pyrenees Mountains
Unwashed
11AA239_DO_Sis11A_g
11AA240_DO_Sis11A_h
11AA236_DO_Sis11A_d
Washed: 1 % HNO3
11AA232_DO_Sis11A_a
11AA233_DO_Sis11A_b
11AA235_DO_Sis11A_c
11AA237_DO_Sis11A_e
11AA238_DO_Sis11A_f
Bedrock Samples
Bighorn Mountains
Unwashed
11AA212_DO_BH090606_1a
11AA213_DO_BH090606_1b
11AA216_DO_BH090606_1e
Washed: 2 % HNO3, HCl
11AA214_DO_BH090606_1c
11AA218_DO_BH090606_1f
11AA219_DO_BH090606_1h
11AA220_DO_BH090606_1i
Beartooth Mountains
Unwashed
11AA200_BT072007AA
11AA201_BT2007_2ay
11AA203_BT2007_2ax
11AA204_BT2007_2aw
11AA207_DO_BT2007_2au
Washed: 1 % HNO3
11AA206_DO_BT2007_2av
11AA202_BT2007_2az
Washed 2 % HNO3, HCl
11AA208_DO_BT2007_2at
11AA209_DO_BT2007_2as
11AA210_DO_BT2007_2ar