THE ORIGIN OF INTERMEDIATE COMPOSITION MAGMAS: INSIGHTS FROM
THE SIERRA DE VALLE FERTIL: A GEOCHEMICAL AND GEOCHRONOLOGIC
STUDY LINKING MECHANICS OF CONTINENTAL MAGMATIC ARCS AT
DEPTH TO THE SURFACE
by
Kelley N. Stair
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
2008
Abstract
The Sierra de Valle Fertil (northwestern Argentina) is a basement block in the
Sierras Pampeanas representing a continuous tilted crustal section that exposes a portion
of a ~471 Ma magmatic arc from paleo-depths of over 25 km to shallow upper crustal
levels. New zircon U-Pb geochronology data on fourteen samples from the Sierra Valle
Fertil provide further insights into the magmatic history of the Famatinian arc and its
tectonic significance. The results bolster the argument that the Famatinian arc was built
on the western margin of Gondwana as a continental magmatic arc. New isotopic (Rb-Sr,
Sm-Nd, Pb-Pb) and elemental (major and trace elements) compositions on 24 samples
across a transect including four major units (Mafic, Migmatite, Tonalite and
Granodiorite) in the Sierra de Valle Fertil, provide further insights into the crustal section
as well as the magmatic history of the Famatinian arc and its tectonic significance. Many
of the evolved plutonic compositions are a result of crustal contamination in which the
crustal component and mafic unit are directly intermingling. The isotopic and trace
element signatures suggest large involvement of old continental crustal material. Rb/Sr
values on the most primitive mafic rocks suggest that the mafic unit is coming out of the
continental lithosphere and progressively become more contaminated up-section.
Because of the contamination of the mafic samples, mixing and hybridization are
dominant processes in Famatinian arc petrogenesis.
Introduction
The role of recycling at a continental magmatic arc dictates the amount of crustal
growth. Thus, to fully appreciate arc processes it is necessary to understand
hybridization, mingling and mixing. Although we have vast knowledge of these arcs
from upper crustal observations, little data exists from the lower crust where these
important processes occur. Our understanding of complex petrologic processes in the
lower crust of continental magmatic arcs is based upon data from seismic velocity and
petrologic models, xenoliths and few preserved lower crustal terranes.
It is well documented that intermediate composition magmas produced at
continental magmatic arcs reflect a combination of addition of new material and
recycling of continental crust (Hurley et al., 1965, Allegre and Ben Othman, 1980,
Hamilton et al., 1980, Pickett and Saleeby, 1994), however the extent and timing of these
processes is still unknown. This is due to complex geologic relationships in which
simple source end-members cannot be easily identified and/or sampled, discontinuity
within the section in which a limited number paleodepths can be sampled as well as a
lack of a complete lower arc to understand fundamental petrologic processes and
generally lack of exposure of the lower crust. In order to understand the extent to which
these processes occur it is necessary to study continuous lower crustal sections of
continental magmatic arcs that have relatively simple geologic relationships.
The Sierra de Valle Fértil – La Huerta (SVF-LA) represents an intact tilted crustal
section that exposes a portion of a magmatic arc from paleo-depths of over 25 km to
shallow upper crustal levels (Figure 1). During primary pluton emplacement, the arc shut
off by the accretion of the Precordilleran terrane to the western margin of Gondwana
~430-390 Ma (Casquet, 2001; Ramos, 1998; Rapela and al., 2001; Vujovich, 2004).
Field observations and previous geochemical analysis show that fractional crystallization
alone did not generate the intermediate composition magmas, but that hybridization
played an important role (Pankhurst, 2000; Otamendi, personal communication), however
no attempts have been made at quantifying the end members or the extent of recycling.
The Ordovician continental magmatic arc provides a window into a simple, but
continuous and complete mid-lower crustal section including two source rocks (mafic
unit [primitive source] and migmatite [crustal component]) and two intermediate
composition magmas (quartz monzodiorite and granodiorite). The SVF-LA provides a
unique opportunity to address complex petrologic processes from a simple, intact midlower crustal section.
Using major and trace elements as well as radiogenic isotopes as a fingerprint,
this study addresses the role of petrologic processes of the SVF-LA. U-Pb zircon
geochronology provides constraints on the timing of crystallization, arc metamorphism,
and tectonic history through inheritance. Through these investigations, the importance of
recycling and other petrologic processes at static continental magmatic arcs can be better
understood.
Geological Background
Since Paleozoic time, the western proto-Andean margin has experienced fairly
continuous subduction with relatively short interruptions during terrane accretions. The
Pampean Orogeny occurred along the western margin of Rio del La Plata craton in the
eastern Sierra Pampeanas when subduction began ca. 535 Ma (Rapela et al, 1998).
Subduction paused with the accretion of the Pampean terrane (530-520 Ma), but stepped
out to the west and resumed on the western margin during the Ordovician Famatinian
Orogeny (Rapela et al, 1998).
Famatinian Arc
The Famatinian arc was a subduction related magmatic arc in Early Ordovician
time that formed along the western margin of Gondwana (Rapela et al, 1998). Docking of
the Precordilleran terrane paused arc activity (Rapela et al, 1998). The plutonic
stratigraphy of the arc is currently exposed in basement uplifts of the Sierra Pampeanas,
Argentina where the Nazca plate is being subducted at a low angle (Barazangi and Isacks,
1976). The complementary eruptive igneous rocks interbedded with sedimentary rocks
are exposed within the Puna – Altiplano region (Coira, 1999) and in the Sierra de
Famatina (Pankhurst, 1998).
Sierra de Valle Fértil -La Huerta
Sierra de Valle Fértil – La Huerta, a portion of the Sierra Pampeanas, is a
continuous tilted crustal section of the Famatinian arc exposing rocks that formed at
paleodepths of 5 to greater than 25 km. Presently, the SVF-LA is a tectonically bounded
crystalline block approximately 140 km long and 30 km wide (Jordan, 1986). The
package of plutonic rocks includes mafics, quartz monzodiorites, granodiorites, and
migmatites (Figure 1).
Rock units, petrology and sampling
There are four major rock units that include two end-members, a mafic and
migmatite units. There are also two intermediate composition magmatic units, quartz
monzodiorite and granodiorite. The units have been named according to the most
abundant rock type and are not formally defined plutonic units. Two additional crucial
groups have been identified for this study including mafic enclaves and granitic melt
associated with the intermediate units.
Mafic Unit
This unit is dominated by pyroxene-amphibolite gabbro and orthopyroxeneamphibole-biotite diorite. The gabbro is fine-grained and dominated by plagioclase +
amphibole + orthopyroxene + oxides + apatite + zircon. It is very thick (as much as
~12km), often layered and includes lens-shaped bodies of ultramafic/mafic cumulates of
plagioclase-bearing dunite and gabbroic troctolite as well as intrusions of massive finegrained mafic sills/dikes (Figure 2a). The sills and dikes are typically a massive, finegrained amphibole gabbro. In addition there are orthopyroxene diorites that occur as
lens-shaped bodies among the gabbros. Zircons from the mafic unit have been dated
using U-Pb geochronology to be 478 ± 4 Ma (Pankhurst, 2000; this study).
Quartz Monzodiorite/Tonalite
This is a fairly heterogeneous unit of biotite-hornblende diorites/tonalites that
contain mafic enclaves and dikes/sills (Photo 1b). These rocks are found as m to km-scale
lensoid bodies that are interlayered with mafics and migmatites, more notably deeper in
the section. Typical quartz monzodiorites are medium to coarse grained, dominated by
plagioclase and quartz, with minor amphibole and biotite. Accessory minerals include
opaques, oxides, zircon, apatite, epidote, allanite and sphene.
Granodiorite
Granodiorite is typically a medium grained biotite-hornblend granodiorite. It is
batholithic in scale and contains inclusions and dikes/sills of amphibole gabbros (Photo
1c). The inclusions are microdioritic and are a distinctive feature of the granodiorite;
these can be found as individual 10 m scale inclusions or as tabular-shaped swarms of
multiple inclusions. In addition there are late-magmatic felsic dikes that intrude the unit
as well as rare monzogranites. These dikes have been categorized as granitic melt
(granite) and have not been included with the granodiorite samples. A less abundant
granodiorite of the same composition with a porphoritic texture containing K-feldspar
megacrystals is also present (Sample 081106-7, Photo 1d). Accessory minerals include
epidote, apatite, sphene, oxide, and zircon. Granodiorites were intruded at ~2 to 4 kbar,
based on preliminary Al-in-hornblende barometry (Otamendi et al., in progress),
consistent with textural observations, and metamorphic framework barometry (Murra and
Baldo, 2006).
The migmatite/supercrustal unit
Both metatexites and diatexites form this unit dominated by a garnet-cordieritesillimanite migmatitic gneiss derived from a clastic protolith, however composition is
highly varied based on the sedimentary protolith (Figure 2e). It is found in km-long
strips as interlayered inclusions within the igneous mafic and intermediate rocks. Cross
cutting relationships show that supercrustal sedimentary rocks were heated up to
granulite facies temperatures and experienced partial melting at the same time as mafic
magmatism (Otamendi, personal communication). Mesosomes typically include quartz,
plagioclase, and biotite with accessory minerals of garnet, corderite, sillimanite and Kfeldspar. The leucosome is dominated by quartz and K-feldspar with plagioclase, garnet
and corderite. Metamorphic ages coincide with the main phase of arc production 463 ± 2
and 465 ± 4.4 Ma (Rapela, 2001; this study).
In addition there are also felsic anatetic melts found near the boundary between
the mafic, tonalite and migmatitic units (Mirré, 1976) that have been interpreted as
magma crystallizing after partial melting and melt segregation from the migmatite unit
(Otamendi, personal communication). Field relationships show mixing between these
melts and quartz monzodiorite (Figure 2f).
Sampling
Sampling was done on a nearly east-west transect across the range ending in the
city of San Agustin de Valle Fértil (Figure 3). Elemental and isotopic analysis samples
reflect each units most representative characteristics as well as the petrologic diversity
and does not necessarily represent the overall proportions of the distinct rock types. In
the intermediate rock units, mafic enclaves and dikes were sampled separately and have
been categorized accordingly. In addition to the geochemical and isotopic analyses, we
report fourteen new zircon U-Pb ages.
Methods
Samples chosen for U-Pb zircon geochronology were prepared and analyzed at
the University of Arizona LaserChron Center. Samples were crushed and pulverized
using a jaw crusher and roller mill. Density separation was done using a Wilfley table.
Additional density separation was done with Methylene Iodide and magnetic separation
using a Franz magnetic separator. The sample with >90% purity was mounted in epoxy
within 1” diameter rings and sanded down ~40 microns depth to expose zircon interiors.
Analysis followed procedures described in Gehrels et al (2008). Additional information
can be found in Appendix A.
Elemental and isotopic samples are from whole rock samples that were powdered
in a tungsten carbide shatterbox.
Major and trace elements were performed by
Washington State University in the WSU GeoAnalytical Lab using X-Ray fluorescence
(XRF) and inductively coupled plasma mass spectrometry (ICP-MS). Isotopic analyses
were performed at the University of Arizona.
143
The isotopic ratios of
87
Sr/86Sr,
Nd/144Nd, and the trace element concentrations of Rb, Sr, Sm, and Nd were measured
by thermal ionization mass spectrometry. Rock samples were crushed to about one third
of their grain size. Rock powders were put in large Savillex vials and dissolved in
mixtures of hot concentrated HF-HNO3. The dissolved samples were spiked with Caltech
Rb, Sr, and mixed Sm-Nd spikes (Wasserburg et al., 1981; Ducea and Saleeby, 1998)
after dissolution. Mass spectrometric analyses were carried out on an automated VG
Sector multicollector instrument fitted with adjustable 1011 Ω Faraday collectors and a
Daly photomultiplier (Ducea and Saleeby, 1998). Concentrations of Rb, Sr, Sm, Nd were
determined by isotope dilution, with isotopic compositions determined on the same
spiked runs. Lead isotope analysis was conducted on a GV Instruments (Hudson, NH)
multicollector inductively coupled plasma mass spectrometer (MC-ICP-MS) (Thibodeau
et al., 2007). Additional isotopic information can be found in Appendix B.
Results
Geochronology
Fourteen zircon samples were analyzed for U-Pb geochronology with ~20 zircons
from each sample (Appendix C, Table 1, Figures 4, 17, and 18). Zircons were studied
optically under a petrographic microscope and with SEM in backscatter electron mode
and cathodoluminscence. The zircons are typically euhedral, clear, transparent and vary
in size from 50-200 microns. Backscatter electron images show that zonation is
common. Anhedral to sub-euhedral cores vary in U content. There is outer thick rim,
presumably of magmatic origin. Sample locations are shown on Figure 3. The Zircon
Age Extractor of IsoPlot (Ludwig, 2003) was used to determine which samples define a
coherent group. This group was then used to calculate the weighted mean. The weighted
mean average ages vary from 468.7 ± 8.4 Ma to 489.9 ± 9.1 Ma (2σ) for coherent groups
in which we presume to be magmatic origin samples (in which U/Th ratios are <3
[Rubbatto, 2002]) which is generally consistent with previous studies (Pankhurst, 2000).
In addition, there is one sample with a coherent group with a significantly older age,
sample 080906-4, which has obvious inheritance. It is clear from the overall probability
density plot that the vast majority of ages reflect crystallization that clusters at 471 Ma
(Figure 5). Additionally, minor clusters of significantly older ages are divided between
500-600 Ma, 600-800 Ma and 1000-1200 Ma (Figure 6). These older ages have been
interpreted as inherited ages that correspond to the tectonic provinces of Late Braziliano
(500-600 Ma), mid-Early Braziliano (600-800 Ma) and Grenville ages (1000-1200 Ma).
Selected Samples (Additional Samples in Appendix C)
Sample 080906-1, Migmatite
Thirty-one zircon grains were analyzed by MC-ICP-MS. There is a coherent
group of twelve with apparent concordance with a weighted mean age of 585.5 ± 9.97
Ma (2σ). Ten grains yield best ages from late Braziliano, mid-early Braziliano,
Grenvillian, and one Archean grain, presumably due to inheritance. Nine additional
grains were excluded due to Pb loss, high error and deviation from the coherent group of
twelve. In addition to this coherent group an age of 476.9 ± 11.4 Ma was determined for
two of the grains excluded from the coherent group due to deviation from the group,
presumably due to metamorphism.
Sample 080906-4, Tonalite
Thirty-six zircon grains were analyzed by MC-ICP-MS. There are a coherent
group of twenty-two with apparent concordance and no inheritance with a weighted mean
age of 477.1 ± 8.41 Ma (2σ). Ten additional grains yield best ages from late Braziliano,
mid-early Braziliano and Grenvillian, presumably due to inheritance. A subset of four of
the Grenvillian age grains yielded a weighted mean age of 1054 ± 46.4 Ma. Four were
excluded due to Pb loss, high error and deviation from the coherent group.
Sample 081006-4, Tonalite
Thirty zircon grains were analyzed by MC-ICP-MS. There are a coherent group
of twenty-one with apparent concordance and no inheritance with a weighted mean age
of 489.9 ± 9.09 Ma (2σ). Four additional grains yield best ages from mid-early
Braziliano and one Grenvillian, presumably due to inheritance. Five were excluded due
to discordance, Pb loss, deviation from the coherent group and high error.
Sample 081106-2, Granodiorite
Thirty-five zircon grains were analyzed by MC-ICP-MS. There are a coherent
group of 22 with apparent concordance and no inheritance with a weighted mean age of
468.7 ± 8.42 Ma (2σ). Ten grains yield best ages from late Braziliano, mid-early
Braziliano, Grenvillian, and an Archean grain, presumably due to inheritance. Three
additional grains were excluded due to discordance, Pb loss and high error.
Major and Trace Element Geochemistry
Major element analyses are listed in Table 2. QAP diagrams from CIPW modal
concentrations show the divisions of gabbros, quartz monzodiorites, granodiorites and
granites (Figure 7). Mafic enclaves and migmatites fall in a range of QAP divisions as
well as the migmatite. Samples are both metaluminous and perlalumnious (Al2O3 /
(Na2O+K2O+CaO) molar). These rocks are classified as calc-alkaline with molar ratios
of Al2O3/(Na2O+K2O) > 1. MgO, FeOt, CaO, Al2O3, MnO and P2O5 all form fairly linear
trends showing a decrease with increasing SiO2 (Figure 8 and 9). Na2O and K2O
generally increase with increasing SiO2, but show slightly more complexity (Figure 9).
Na2O for mafic composition rocks have extreme variability. Sr ppm vs. SiO2 shows little
to no correlation (Figure 9f). Rb ppm is abnormally low for parental mafic magmas and
generally clusters with mafic enclaves showing slight increase in Rb ppm with increasing
SiO2 (Figure 9c). All other rock types appear to have generally constant Rb ppm
unaffected by SiO2 weight percentage.
Trace elements results can be found in Table 3 and Figures 10a-e and 11. The
most striking features of the spider diagrams are the large peak at Pb and the trough at Nb
throughout the suite as well as the convergence of all rock types at Sr between ~8-10
times primitive mantle with the exception of mafic enclaves. Mafic unit and enclaves
show high variability in LREE with converging scatter in HREE. The quartz
monzodiorite has lower HREE and LREE than the mafic samples and little variability
with the exception of Zr. The granodiorite has generally similar trends to the quartz
monzodiorite from the HREE and LREE values to the slight scatter, however sample
080906-3 is highly variable. For the granites, the LREE are highly variable and the
HREE < 10 times primitive mantle values. The migmatites show the highest LREE
values with the exception of 080606-4a, a leucosome melt.
All rocks show general major and trace element patterns that are typical of arc
rocks. Eu anomalies both positive and negative are present in some, but not all of the
samples and are not restricted to a distinctive rock type with the exception of the mafic
units (Figures 10a-e). For the mafic enclaves it appears that these only exhibit a negative
Eu anomaly or no anomaly and similarly this seems to be the case for the mafic unit, but
with the exception of sample 080406-2 which has been described as a plagioclase-richcumulate gabbro, which has a positive Eu anomaly. Generally, the intermediate and
felsic units have trace elemental values that fall between the mafic unit and the
migmatite.
Isotopic Geochemistry
Sr and Nd isotopic results can be found in Table 4 and Pb results in Table 5 and
Figure 12. Mafic samples show the most scatter for both Nd and Sr initial isotopes.
144
Nd/143Nd (i) for mafic samples range from .51235 to .51264 and have 87Sr/86Sr (i)
values from .70522 to .71086. In addition the smallest Nd and Sm ppm were recorded
for mafic sample 080406-2 at 1.47 and .37 respectively. Mafic enclaves show large
variations of .70670 to .71062 for 87Sr/86Sr (i) and the greatest scatter in Sr ppm from
19.94 to 305.30. In contrast, little variation is seen in the 144Nd/143Nd (i) from .51226 to
.51228. Quartz monzodiorites have little variation in 87Sr/86Sr (i) from .71379 to .71403
and have 144Nd/143Nd (i) between .51221 and .51232. Granodiorites have highly varied
144
87
Nd/143Nd (i) from .51210 to .51220 and extremely large scatter in initial Sr isotopes for
Sr/86Sr ranging from .70574 to .72173. Granites have little scatter with initial Sr from
.70927 to .71123 and 144Nd/143Nd (i) from .51210 to .51204. Migmatites show almost no
initial 144Nd/143Nd scatter, but slight scatter for little 87Sr/86Sr from .71635 to .72348.
Pb isotopic results can be found in Table 5 and trends do not appear as clear as the
Sr-Nd isotopes. This is primarily because the mafic unit and enclaves both show large
variations with the exception of 207Pb/204Pb from mafic enclaves. The mafic unit records
the lowest 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb at 18.214, 15.635 and 38.070
respectively. The quartz monzodiorite has little variation between Pb isotopes while
migmatites have large 208Pb/204Pb variations ranging from 38.170 to 40.039. At a larger
scale, the series generally falls within a small cluster that resembles previous Ordovician
granitoids of the region (Figure 13a). The sample suite shows an overall linear trend for
both 208Pb/204Pb vs. 206Pb/204Pb and 207Pb/204Pb and 206Pb/204Pb (Figure 13a and b).
Major and Trace Elements Constraints
Major and Trace elements are typical of a continental magmatic arc. Some plots
have outliers, however the scatter can be attributed to a combination of analytical errors
and the type of variation generally found in nature. Harker diagrams are consistent with
open-system processes such as mixing. Slight curvature of Harker diagrams in Figures
9a, b, d, and e may indicate that some fractionation may have taken place. The REE
patterns place important constraints on the petrogenesis. The Nb (Nb-Ta) trough is a
distinctive signature indicating this entire suite of rocks, including the most primitive
gabbros sampled, have been contaminated by crustal rocks. Similarly there is a Sr trough
for the entire suite that could supports low-pressure plagioclase fractionation, however
negative Eu anomalies are not present in all samples. High Cr and Ni in samples in
samples 080306-1B and 080406-2 indicate derivation of parental magmas from a
peridotite mantle source. The decrease in Ni and Cr throughout the suite suggests
fractionation of olivine ± spinel ± clinopyroxene.
Isotopic Constraints
Sr, Pb, and Nd isotopic signatures are critical for fingerprinting and constraining
petrogenetic processes. Sr isotopes suggest that a combination of mixing and
fractionation caused the variation of the samples (Figure 14). For example, initial
87
Sr/86Sr vs. 1/Sr ppm shows a slight positive correlation that may be attributed to AFC
processes, however some samples show little variation in initial 87Sr/86 Sr, which suggest
fractional crystallization could have occurred. Initial 87Sr/86Sr and εNd of the mafic unit
and the mafic enclaves cluster near the most evolved Ordovician granitoids previously
studied. One mafic sample (080606-5) is much more primitive isotopically than the
others. Initial 87Sr/86Sr and εNd of the migmatite are more highly evolved than previously
sampled sedimentary rocks of the region. The intermediate magmas and granitic melt
(granite) lie in between the mafic region and the migmatite (Figure 14). This indicates a
strong crustal component involved in their generation. It is likely that the crustal
component is more evolved than previously reported. The intermediate and felsic
magmas suggest a defined mixing trend. In addition, the Pb isotopes bolster these results.
One outlier suggests that the migmatite that was sampled is not evolved enough to have
produced sample 081206-8a, seen drastically in the Pb and additionally in Sr and Nd
isotopes. In spite of this, mixing appears to be supported by the Pb isotopic data.
Representative mixing models using the most primitive mafic sample and the
most evolved crustal component (the migmatite) are presented in Figure 16a and b. The
crustal component shows some variation in major and trace elements, however it has a
tightly constrained Nd isotopic signature. The primitive mafic unit also has quite a bit of
variation, both elemental and isotopic, however for the purposes of this study the most
primitive sample has been chosen for mixing models. It is clear from the models that
mixing was an important process in the petrogenesis of the intermediate composition
magmas. Generally the intermediate composition magmas and granitic melts fall in
between the primitive mafic unit and the evolved migmatite. The quartz monzodiorite is
less easily explained by this simple mixing model and tends to deviate from the
hypothetical mixing curve. In addition there is one granodiorite sample that does not
seem to be explained by any of the proposed mixing curves. These models are unable to
prove that mixing is the only process creating the intermediate and felsic magmas;
instead it is more likely that mixing and assimilation with some portion of fractionation
are occurring at the same time.
Discussion
Age of arc emplacement
The crystallization ages of 468.7 ± 8.42 Ma to 489.9 ± 9.09 Ma for magmatic
samples is identical to previously published regional geochonological results on
Famatinian arc plutonic rocks, and supports two major interpretations concerning the
evolution of the arc. The first is that the Famatinian arc experienced high flux mode
(known by the shear volume of the magmatic bodies) during a short period (< 20 Ma) of
time in which large amounts of intermediate composition magmas were formed, similar
to flare-ups documented elsewhere in Cordilleran arcs (Ducea, 2007 and references
therein). Second, the emplacement of mafic magmas in the section was coeval with the
felsic batholith flare-up. The migmatite sample has pre-Ordovician (detrital?) zircons and
a few metamorphic zircons that grew during the magmatic flare-up (468-490 Ma)
(Appendix A). Based on field evidence and these ages, we interpret that the parental
metasedimentary rock of the migmatite underwent high temperature metamorphism and
partial melting during Ordovician magmatism.
Significance of Inheritance
The inherited grains of Late Proterozoic age are consistent with a Gondwana
basement. The pattern of inheritance is indicative of continental crust and rules out a
juvenile island arc setting. This supports the idea that this arc was being built on the
western margin of Gondwana during the Early Ordovician. The metamorphic age from
the migmatite (080906-1) is similar to the magmatic ages and thought to be evidence of
metamorphism associated with Famatinian arc processes.
Generating Intermediate Units
Field relationships indicate extensive interaction between the mafic unit and the
migmatite. This interaction had significant effects thermally, mechanically, and
chemically. Closed system fractional crystallization has been ruled out by field
observations of the crustal component mixing with the mafic unit (Figure 2f), as well as
major and trace element and isotopic variations. Although mixing and hybridization
seem to have large effects on elemental and isotopic variation, major and trace element
compositions do not form entirely linear mixing arrays. Initial Sr vs. SiO2 shows that
quartz monzodiorite forms almost entirely by AFC processes whereas the granodiorite
and granitic melts involve some fractionation (Figure 15). In addition, this is supported
by field observations and mixing models from Sr-Nd isotopes (Figure 16). Mixing
models explain the isotopic variability fairly well, but considerably better for the
granodiorite and the granitic melt than for the quartz monzodiorite. This may indicate
that there was more fractionation of the quartz monzodiorite than the granodiorite. In
addition, the mafic units variability is most easily explained by crustal contamination. If
sample 080605-2 was the parental magma and simple mixing was the only process
causing isotopic variation, the mafic units would be contaminated from between 15-30%.
Although this area represents a simple two-end member system that can be
sampled, the end member variability presents some challenging problems. The extensive
variability in both the mafic and migmatite units make it extremely difficult to interpret
the exact amount of mixing occurred in the system. From our calculations, if simple two
component mixing occurred within this system, with our most primitive rock being the
primary magma and our most evolved migmatite as the crustal component, the
intermediate composition magmas are ~30-40% gabbro and ~60-70% crustal component.
This is highly unlikely since we know that fractional crystallization is also taking place,
but this provides a maximum amount of crustal component incorporation.
In addition we can infer the timing of recycling. Since it is likely that the magma
chamber is a homogeneous mixture at any given time, we conclude that they are rapidly
changing which is evident in the distribution of mafic unit samples and enclaves.
CONCLUSIONS
We find that the generation of intermediate and felsic magmas forms by a
combination of mixing, hybridization and some fractional crystallization. Because of the
contamination of the mafic samples, mixing and hybridization are dominant processes in
Famatinian arc petrogenesis. There are at minimum two major components, one a
primitive mafic magma and the other a supracrustal component, a migmatite.
This study concludes that the Famatinian arc was a continental magmatic arc built
on the western margin of Gondwana or at least built on a fragment that was originally
part of Gondwana supported by the inherited ages in the intermediate composition rocks
as well as the crustal isotopic signatures and trace elemental concentrations for the entire
suite. The inherited age populations could not have been from an exotic terrane or from
an island arc. The isotopic and trace element signatures suggest significant involvement
of old continental crustal material.
References
Allegre, C. J. and Othman, D. B., 1980. ND-SR ISOTOPIC RELATIONSHIP IN
GRANITOID ROCKS AND CONTINENTAL-CRUST DEVELOPMENT - A
CHEMICAL APPROACH TO OROGENESIS. Nature 286, 335-342.
Barazangi, M. and Isacks, B. L., 1976. SPATIAL-DISTRIBUTION OF
EARTHQUAKES AND SUBDUCTION OF NAZCA PLATE BENEATH SOUTHAMERICA. Geology 4, 686-692.
Carr, M.J., 2005, Igpet June 2005. Terra Softa Inc., Somerset, NJ, USA.
Casquet, C., Baldo, E., Pankhurst, R. J., Rapela, C. W., Galindo, C., Fanning, C. M., and
Saavedra, J., 2001. Involvement of the Argentine Precordillera terrane in the Famatinian
mobile belt: U-PbSHRIMP and metamorphic evidence from the Sierra de Pie de Palo.
Geology 29, 703-706.
Coira-Beatriz, Kay-Suzanne-Mahlburg, and Viramonte, J. R.-V.-A., 1998. Upper
Cenozoic magmatic evolution of the Argentine Puna; a model for changing subduction
geometry.; Cordillera de los Andes; geological and mining potential; the new tectonic
and metallogenic approach.
Ducea, M. N. and Barton, M. D., 2007. Igniting flare-up events in Cordilleran arcs.
Geology 35, 1047-1050.
Galer, S. J. G. and Abouchami, W., 2004. Mass bias correction laws suitable for MCICP-MS measurement.
Gehrels, G. E., Valencia, V. A., and Ruiz, J., 2008. Enhanced precision, accuracy,
efficiency, and spatial resolution of U-Pb ages by laser ablation-multicollectorinductively coupled plasma-mass spectrometry. Geochemistry Geophysics Geosystems 9.
Hamilton, W., 1981. CRUSTAL EVOLUTION BY ARC MAGMATISM. Philosophical
Transactions of the Royal Society of London Series a-Mathematical Physical and
Engineering Sciences 301, 279-291.
Hurley, P. M., Bateman, P. C., Fairbair.Hw, and Pinson, W. H., 1965. INVESTIGATION
OF INITIAL SR87/SR86 RATIOS IN SIERRA NEVADA PLUTONIC PROVINCE.
Geological Society of America Bulletin 76, 165-&.
Jordan-Teresa, E. A.-R.-W., 1986. The Sierras Pampeanas of Argentina; a modern
analogue of Rocky Mountain foreland deformation.
Ludwig, K.R., 2003, Isoplot 3.00. Berkeley Geochronology Center, Special Publication
4, p. 70.
Mirre, C. and Stahl, A., 1976. ULTRASTRUCTURAL-STUDY OF NUCLEOLAR
ORGANIZERS IN QUAIL OOCYTE DURING MEIOTIC PROPHASE-1. Journal of
Ultrastructure Research 56, 186-201.
Murra, J. A. and Baldo, E. G., 2006. Tectonothermal ordovician evolution of the western
margin of the Famatinian magmatic arc: metamorphism of the mafic and ultramafic rocks
of Sierra de La Huerta-Las Imanas (Pampean Ranges, Argentina). Revista Geologica De
Chile 33, 277-298.
Otamendi, J., Ducea, M., Tibaldi, A., Bergantz, G., De La Rosa, J., Vujoich, G., in
review, Generation of Tonalitic and Dioritic Magmas by Coupled Partial Melting of
Gabbroic and Metasedimentary Rocks within the Deep Crust of the Famatinian
Magmatic Arc: Journal of Petrology.
Otamendi, J. August 2006. Personal Communication.
Pankhurst, R. J. R.-C. W. S.-J. B.-E. D.-J. P.-I. F.-C. M., 1998. The Famatinian magmatic
arc in the central Sierras Pampeanas; an Early to Mid-Ordovician continental arc on the
Gondwana margin.; The proto-Andean margin of Gondwana.
Petford, N., Atherton, M. P., and Halliday, A. N., 1996. Rapid magma production rates,
underplating and remelting in the Andes: Isotopic evidence from northern-central Peru
(9-11 degrees S). Journal of South American Earth Sciences 9, 69-78.
Pickett, D. A. and Saleeby, J. B., 1994. ND, SR, AND PB ISOTOPIC
CHARACTERISTICS OF CRETACEOUS INTRUSIVE ROCKS FROM DEEP
LEVELS OF THE SIERRA-NEVADA BATHOLITH, TEHACHAPI MOUNTAINS,
CALIFORNIA. Contributions to Mineralogy and Petrology 118, 198-215.
Rapela, C. W., Pankhurst, R. J., Casquet, C., Baldo, E., Saavedra, J., and Galindo, C.,
1998. Early evolution of the Proto-Andean margin of South America. Geology 26, 707710.
Rapela, C. W. P.-R. J. B.-E. C.-C. G.-C. F.-C. M. S.-J., 2001. Ordovician metamorphism
in the Sierras Pampeanas: new U-Pb SHRIMP ages in central-east Valle Fertil and the
Velasco Batholith.; III South American symposium on isotope geology.
Rubatto, D., 2002. Zircon trace element geochemistry: partitioning with garnet and the
link between U-Pb ages and metamorphism. Chemical Geology 184, 123-138.
Stacey, J. S. and Kramers, J. D., 1975. APPROXIMATION OF TERRESTRIAL LEAD
ISOTOPE EVOLUTION BY A 2-STAGE MODEL. Earth and Planetary Science Letters
26, 207-221.
Thibodeau, A. M., Killick, D. J., Ruiz, J., Chesley, J. T., Deagan, K., Cruxent, J. M., and
Lyman, W., 2007. The strange case of the earliest silver extraction by European colonists
in the New World. Proceedings of the National Academy of Sciences of the United States
of America 104, 3663-3666.
Vujovich, G. I., Fernandes, L. A. D., and Ramos, V. A., 2004. Cuyania: An exotic block
to Gondwana - Introduction. Gondwana Research 7, 1005-1007.
Wasserburg, G. J., Jacobsen, S. B., Depaolo, D. J., McCulloch, M. T., and Wen, T., 1981.
PRECISE DETERMINATION OF SM/ND RATIOS, SM AND ND ISOTOPIC
ABUNDANCES IN STANDARD SOLUTIONS. Geochimica Et Cosmochimica Acta 45,
2311-2323.
Appendix A
U-Th-Pb geochronologic methods for igneous zircon analysis
U-Pb geochronology of zircons was conducted by laser ablation multicollector
inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) at the Arizona
LaserChron Center. The analyses involve ablation of zircon with a New Wave/Lambda
Physik DUV193 Excimer laser (operating at a wavelength of 193 nm) using a spot
diameter of 25-35 microns. The ablated material is carried with helium gas into the
plasma source of a GV Instruments Isoprobe, which is equipped with a flight tube of
sufficient width that U, Th, and Pb isotopes are measured simultaneously. All
measurements are made in static mode, using Faraday detectors for 238U and 232Th, an
ion-counting channel for 204Pb, and either faraday collectors or ion counting channels
for 208-206Pb. Ion yields are ~1 mv per ppm. Each analysis consists of one 20-second
integration on peaks with the laser off (for backgrounds), 20 one-second integrations with
the laser firing, and a 30 second delay to purge the previous sample and prepare for the
next analysis. The ablation pit is ~15 microns in depth.
For each analysis, the errors in determining 206Pb/238U and 206Pb/204Pb result in a
measurement error of ~1% (at 2-sigma level) in the 206Pb/238U age. The errors in
measurement of 206Pb/207Pb and 206Pb/204Pb also result in ~1% (2-sigma) uncertainty
in age for grains that are >1.0 Ga, but are substantially larger for younger grains due to
low intensity of the 207Pb signal. For most analyses, the cross-over in precision of
206Pb/238U and 206Pb/207Pb ages occurs at ~1.0 Ga.
Common Pb correction is accomplished by using the measured 204Pb and assuming an
initial Pb composition from Stacey and Kramers (1975) (with uncertainties of 1.0 for
206Pb/204Pb and 0.3 for 207Pb/204Pb). Our measurement of 204Pb is unaffected by the
presence of 204Hg because backgrounds are measured on peaks (thereby subtracting any
background 204Hg and 204Pb), and because very little Hg is present in the argon gas.
Inter-element fractionation of Pb/U is generally ~20%, whereas fractionation of Pb
isotopes is generally <2%. In-run analysis of fragments of a large zircon crystal
(generally every fifth measurement) with known age of 564 ± 4 Ma (2-sigma error) is
used to correct for this fractionation. The uncertainty resulting from the calibration
correction is generally ~1% (2-sigma) for both 206Pb/207Pb and 206Pb/238U ages.
The analytical data are reported in Table 1. Uncertainties shown in these tables are at the
1-sigma level, and include only measurement errors.
The reported ages are determined from the weighted mean (Ludwig, 2003) of the
206Pb/238U or 206Pb/207Pb ages of the concordant and overlapping analyses (Figures
17 and 18, Appendix C). Analyses that are statistically excluded from the main cluster are
shown in blue on these figures. Two uncertainties are reported on these plots. The smaller
uncertainty (labeled “mean”) is based on the scatter and precision of the set of
206Pb/238U or 206PB/207Pb ages, weighted according to their measurement errors
(shown at 1-sigma). The larger uncertainty (labeled “age”), which is the reported
uncertainty of the age, is determined as the quadratic sum of the weighted mean error
plus the total systematic error for the set of analyses. The systematic error, which
includes contributions from the standard calibration, age of the calibration standard,
composition of common Pb, and U decay constants, is generally ~1-2% (2-sigma).
Appendix B
Analytical procedures for Sr, Nd and Pb isotopic measurements
April 2008
Mihai Ducea
The isotopic ratios of 87Sr/86Sr, 143Nd/144Nd, and the trace element concentrations
of Rb, Sr, Sm, and Nd were measured by thermal ionization mass spectrometry on whole
rock samples. Rock samples were crushed to about one third of their grain size. Rock
powders were put in large Savillex vials and dissolved in mixtures of hot concentrated
HF-HNO3 or alternatively, mixtures of cold concentrated HF-HClO4. The dissolved
samples were spiked with the Caltech Rb, Sr, and mixed Sm-Nd spikes (Wasserburg et
al., 1981; Ducea and Saleeby, 1998) after dissolution. Rb, Sr, and the bulk of the REEs
were separated in cation columns containing AG50W-X4 resin, using 1N to 4N HCl.
Separation of Sm and Nd was achieved in anion column containing LN Spec resin, using
0.1N to 2.5N HCl. Rb was loaded onto single Re filaments using silica gel and H3PO4. Sr
was loaded onto single Ta filaments with Ta2O5 powder. Sm and Nd were loaded onto
single Re filaments using platinized carbon, and resin beads, respectively.
Mass spectrometric analyses were carried out at the University of Arizona on an
automated VG Sector multicollector instrument fitted with adjustable 1011 Ω Faraday
collectors and a Daly photomultiplier (Ducea and Saleeby, 1998). Concentrations of Rb,
Sr, Sm, Nd were determined by isotope dilution, with isotopic compositions determined
on the same spiked runs. An off-line manipulation programs was used for isotope dilution
calculations. Typical runs consisted of acquisition of 100 isotopic ratios. The mean result
of ten analyses of the standard NRbAAA performed during the course of this study is:
85
Rb/87Rb = 2.61199±20. Fifteen analyses of standard Sr987 yielded mean ratios of:
87
Sr/86Sr = 0.710285±7 and 84Sr/86Sr = 0.056316±12. The mean results of five analyses of
the standard nSmβ performed during the course of this study are: 148Sm/147Sm =
0.74880±21, and 148Sm/152Sm = 0.42110±6. Fifteen measurements of the LaJolla Nd
standard were performed during the course of this study. The standard runs yielded the
142
144
143
144
145
144
following isotopic ratios: Nd/ Nd = 1.14184±2, Nd/ Nd = 511853±2, Nd/ Nd
150
144
= 0.348390±2, and Nd/ Nd = 0.23638±2. The Sr isotopic ratios of standards and
samples were normalized to 86Sr/88Sr = 0.1194, whereas the Nd isotopic ratios were
normalized to 146Nd/144Nd = 0.7219. The estimated analytical ±2σ uncertainties for
samples analyzed in this study are: 87Rb/86Sr = 0.35%, 87Sr/86Sr = 0.0014%, 147Sm/144Nd
143
144
= 0.4%, and Nd/ Nd = 0.0012%. Procedural blanks averaged from five
determinations were: Rb-10 pg, Sr-150 pg, Sm- 2.7 pg, and Nd - 5.5 pg.
Washes from the cation column separation were used for separating Pb in Sr–
Spec resin (Eichrom, Darien, IL) columns by using protocol developed at the University
of Arizona. Samples are being loaded in 8M HNO3 in the Sr spec columns. Pb elution is
achieved via 8M HCl. Lead isotope analysis was conducted on a GV Instruments
(Hudson, NH) multicollector inductively coupled plasma mass spectrometer (MC-ICP-
MS) at the University of Arizona (Thibodeau et al., 2007). Samples were introduced into
the instrument by free aspiration with a low-flow concentric nebulizer into a water-cooled
chamber. A blank, consisting of 2% HNO3, was run before each sample. Before analysis,
all samples were spiked with a Tl solution to achieve a Pb/Tl ratio of 10. Throughout
the experiment, the standard National Bureau of Standards (NBS)-981 was run to monitor
the stability of the instrument.
All results were Hg-corrected and empirically normalized to Tl by using an
exponential law correction. To correct for machine and interlaboratory bias, all results
were normalized to values reported by Galer and Abouchami (2004) for the National
Bureau of Standards (NBS)-981 standard (206Pb/204Pb = 16.9405, 207Pb/204Pb = 15.4963,
and 208Pb/204Pb = 36.7219). Internal error reflects the reproducibility of the measurements
on individual samples, whereas external errors are derived from long-term reproducibility
of NBS-981 Pb standard and result in part from the mass bias effects within the
instrument. In all cases, external error exceeds the internal errors and is reported below.
External errors associated with each Pb isotopic ratio are as follows: 206Pb/204Pb =
0.028%, 207Pb/204Pb = 0.028%, and 208Pb/204Pb = 0.031%.
Appendix C (Weighted Mean Plots on Figures 17 and 18)
Sample 080806-1, Tonalite
Thirty-nine zircon grains were analyzed by MC-ICP-MS. There are a coherent group of
32 with apparent concordance and no inheritance with a weighted mean age of 477.4 ±
7.09 Ma (2σ). Seven grains yield Grenvillian best ages, presumably due to inheritance.
Four additional grains were excluded due to discordance, Pb loss and high error.
Sample 080806-2, Tonalite
Twenty-six zircon grains were analyzed by MC-ICP-MS. There are a coherent group of
twenty with apparent concordance and no inheritance with a weighted mean age of 470.8
± 7.2 Ma (2σ). Three additional grains yield 206/207 ages of 1223, 1282 and 1852 Ma,
presumably due to inheritance. Three were excluded due to deviation from the coherent
group.
Sample 080906-3, Granite
Twenty-four zircon grains were analyzed by MC-ICP-MS. There are a coherent group of
fifteen with apparent concordance and no inheritance with a weighted mean age of 475.5
± 9.6 Ma (2σ). Two additional grains yield best ages one from the mid-early Braziliano
and Grenvillian time, presumably due to inheritance. Eight were excluded due to
discordance, Pb loss and high error.
Sample 081006-3a, Granite
Fourteen zircon grains were analyzed by MC-ICP-MS. There are a coherent group of
thirteen with apparent concordance and no inheritance with a weighted mean age of 472.7
± 10.4 Ma (2σ). One additional grain yielded a 206/238 age of 615 Ma, presumably due
to inheritance. Eight were excluded due to discordance, Pb loss, deviation from the
coherent group and high error.
Sample 081006-5, Diorite
Twenty-three zircon grains were analyzed by MC-ICP-MS. There are a coherent group
of eighteen with apparent concordance and no inheritance with a weighted mean age of
473.6 ± 7.28 Ma (2σ). Five grains were excluded due to high errors.
Sample 081106-4, Granodiorite
Forty-four zircon grains were analyzed by MC-ICP-MS. There are a coherent group of
13 with apparent concordance and no inheritance with a weighted mean age of 481.5 ±
7.90 Ma (2σ). Twenty-two additional grains yield best ages from late Braziliano, midearly Braziliano and Grenvillian, presumably due to inheritance. Seven were excluded
due to discordance, Pb loss and high error.
Sample 081106-5A, Granodiorite
Twenty-two zircon grains were analyzed by MC-ICP-MS. There are a coherent group of
thirteen with apparent concordance and no inheritance with a weighted mean age of 470.3
± 7.71 Ma (2σ). Three grains were excluded due to high errors.
Sample 081206-4, Granodiorite
Thirty-one zircon grains were analyzed by MC-ICP-MS. There are a coherent group of
twenty-five with apparent concordance and no inheritance with a weighted mean age of
476.4 ± 9.82 Ma (2σ). Three additional grains yield 206/238 ages in the late Braziliano,
presumably due to inheritance. Three were excluded due to Pb loss, deviation from the
coherent group and high error.
Sample 081206-6, Tonalite
Thirty-one zircon grains were analyzed by MC-ICP-MS. There are a coherent group of
twenty-eight with apparent concordance and no inheritance with a weighted mean age of
471.6 ± 8.18 Ma (2σ). Two additional grains yield best ages of 756 Ma and 2576 Ma,
presumably due to inheritance. One was excluded due to deviation from the coherent
group.
Sample 081206-8A, Granodiorite
Twenty-nine zircon grains were analyzed by MC-ICP-MS. There are a coherent group of
21 with apparent concordance and no inheritance with a weighted mean age of 473.4 ±
8.23 Ma (2σ). Five grains yield best ages from late Braziliano, mid-early Braziliano,
Grenvillian, and one Archean grain, presumably due to inheritance. Three additional
grains were excluded due to Pb loss, high error and deviation from the coherent group.
66˚W
GEN
IA
ATIN
FAM
N MA
San
Juan
ower
it o f L h is m
r n lim
rp
Weste n metamo
r ia
Camb
La Rioja
RO
PAMPEAN O
68˚W
64˚W
30˚S
Cordoba
TIC A
GMA
Valle
RC
ent
eam
il Lin
Fert
NIA /
CUYA DILLERA
OR
PREC ERRANE
T
32˚S
San Luis
Devonian - Carboniferous
post-orogenic granitoids
Ordovician
volcanic - volcaniclastic
Ordovician
plutonic rocks
Lower Paleozoic metasedimentary rocks
Lower Cambrian
granitoids
24o S
Middle Proterozoic
Crystalline Basement
Figure 1. Geological map showing the central segment of the Famatinian magmamtic arc.
Inset shows location on Figure 2. (From Otamendi, in review)
A
B
C
D
E
F
Figure 2. Photos from the SVF-LA. A) Foliated Gabbro. B)
Qtz Monzodiorite with enclave. C) Granodiorite with enclave.
D) Porphoritic Granodiorite. E) Close up of Migmatite. F) Mixing
of Mafic unit and Migmatite
W 67˚ 33’
W 67˚ 28’ 12”
San Agustín
de Valle Fértil
Corral Grande
60
c
83
64
a
a ja d it
La M
bo
78
o
n
bo
Ja
ll
ci
O rc o
70
80
30
bola
30˚ 40’ 12”
80
42
30˚ 42’ 36”
85
28
80
Pto.
Otarola
Qbra
86
. Sec
a
Las
Juntas
Los
Bretes
Salazar
0
1
2 km
Lithostratigraphic unit
Silicic unit
Granodiorite
Intermediate unit
Tonalite & granodiorite
Tonalite
Mafic unit
Gabbro & diorite
Supracrustal unit
Granite
Paragneissic migmatite
Marble
Geochronology Sample
Geochemistry Sample
Foliation (S2, mylonitic)
Foliation (S1, metamorphic)
Foliation (magmatic)
Fault (high angle reverse)
Creek
Road
Highway
Geochronology and
Geochemistry Sample
Figure 3. Geological map with sample locations from the central section of the Sierra de Valle Fertil (see
Figure 1 for location) based on field mapping and previously published maps (modified from Otamendi, in
review and Mirre, 1976).
A
080906-1 Weighted Mean
620
Mean = 585.5 ± 10.0 Ma
Systematic Error = 1.3%
MSWD = 1.07 (2σ)
box heights are 1σ
B
080906-1 Metamorphic Age
box heights are 1σ
488
484
Mean = 476.9 ± 11.4 Ma
Systematic Error = 1.3%
MSWD = 0.013 (2σ)
600
Best age
Best age
480
580
476
560
472
540
C
468
D
520
080906-4 Weighted Mean
464
080906-4 Inherited Ages Weighted Mean
box heights are 2σ
box heights are 1σ
510
1170
Mean = 477.1 ± 8.4 Ma
Systematic Error = 1.6%
MSWD = 0.82 (2σ)
1150
Mean = 1054 ± 46.4 Ma
Systematic Error 1.6%
MSWD = 2.7 (2σ)
1130
1110
Best age
Best age
490
470
1090
1070
1050
1030
450
1010
E
430
081006-4 Weighted Mean
box heights are 1σ
520
F
Mean = 489.9 ± 9.1 Ma
Systematic Error = 1.6%
MSWD = 1.14 (2σ)
box heights are 1σ
480
Best age
Best age
081106-2 Weighted Mean
500
500
480
990
460
460
440
440
420
Mean = 468.7 ± 8.4 Ma
Systematic Error = 1.5%
MSWD = 1.5 (2σ)
Figure 4. Weighted Mean Plots for Selected Samples. A) Weighted mean of coherent group of sample
080906-1, B) Weighted mean of metamorphic grains from sample 080906-1, C) Weighted mean of coherent group from sample 080906-4, D) Weighted mean of inherited Grenvillian age grains from sample
080906-4, E) Weighted mean of coherent group from sample 081006-2, F) Weighted mean of coherent
group from sample 081106-2. All uncertainties are reported at the 1-sigma level, and include only measurement
errors. Systematic errors would increase age uncertainties by 1-2%. U concentration and U/Th are calibrated
relative to NIST SRM 610 and are accurate to ~20%. Common Pb correction is from 204Pb, with composition
interpreted from Stacey and Kramers (1975) and uncertainties of 1.0 for 206Pb/ 204Pb, 0.3 for 207Pb/ 204Pb, and
2.0 for 208Pb/ 204Pb. U/Pb and 206Pb/ 207Pb fractionation is calibrated relative to fragments of a large Sri Lanka
zircon of 564 ± 4 Ma (2-sigma). U decay constants and composition as follows: 238U = 9.8485 x 10 -10, 235U =
1.55125 x 10 -10, 238U/ 235U = 137.88.
Relative probability
200
300
400
500
600
700
Ma
Figure 5. Probability density plot for all samples from the suite from
200-800 Ma.
800
Relative probability
Relative probability
500
700
900
1100
1300
1500
1700
1900
2100
2300
2500
2700
Ma
200
600
1000
1400
1800
2200
2600
3000
3400
Ma
Figure 6. Probability density plots of entire suite from 200-3400 Ma. The inset is selected data from 500 to 2800 Ma.
Figure 7. Rock Classification using a Quartz-Alkali Feldspar-Plagioclase ternary diagram. Samples are
labeled.
A
D
30
20
20
FeOt
10
MgO
10
0
40
50
60
70
0
40
80
50
60
SiO 2
70
80
50
60
SiO 2
70
80
SiO 2
B
E
20
30
20
CaO
Al2O 3
10
10
0
40
50
60
70
80
0
40
SiO 2
C
0.4
Legend
0.3
Mafic
Mafic Enclave
Granite
Migmatite
Granodiorite
Qtz Monzodiorite
MnO 0.2
0.1
0.0
40
50
60
70
80
SiO 2
Figure 8. Various major elements vs. SiO2. A) MgO, B) CaO, C) MnO, D) FeOt, E) Al2O3.
A
D 0.5
2
0.4
0.3
P 2O 5
TiO 2 1
0.2
0.1
0
40
B
0.0
50
60
SiO 2
70
40
50
0
40
50
80
E
3
60
SiO 2
70
80
60
70
80
70
80
7
6
5
2
4
Na 2O
K 2O
3
1
2
1
0
40
C
50
60
70
80
SiO 2
F
200
SiO 2
300
200
Sr
Rb 100
100
0
40
50
60
SiO 2
70
80
0
40
50
60
SiO 2
Figure 9. Various major elements vs. SiO2. A) TiO2, B) Na2O, C) Rb ppm, D) P2O5, E) K2O, F) Sr ppm.
1000
16
080206-1
B
17
1000
A
080306-6
080306-1b
080706-5b
080406-2
081006-3b
080406-7
081206-8b
100
080606-5
100
10
1.0
1
1
1.0
10
0.1
0.1
0.1
0.1
Rb
Ba
Th
U
Nb
K
La
Ce
Pb
Pr
Sr
P
Nd
Zr
Sm
Eu
Ti
Dy
Y
Yb
Lu
Cs
Rb
Ba
Th
U
Nb
K
La
Ce
Pb
Pr
D
1000
4
Sr
P
Nd
Zr
Sm
Eu
Ti
Dy
Y
Yb
Lu
3
1000
Cs
C
10
10
100
Sample/ Primitive Mantle
Sample/ Primitive Mantle
100
080706-5a
080706-2
080906-3
080806-4
081106-1
081106-7
10
Sample/ Primitive Mantle
1.0
1
1.0
0.1
0.1
0.1
0.1
Cs
E
1
10
Rb
Ba
Th
U
Nb
K
La
Ce
Pb
Pr
Sr
P
Nd
Zr
Sm
Eu
Ti
Dy
Y
Yb
Cs
Lu
1000
5
081006-3a
F
Rb
Ba
Th
U
Nb
K
La
Ce
Pb
Pr
Sr
P
Nd
Zr
Sm
Eu
Ti
Dy
Y
Yb
Lu
1
1000
Sample/ Primitive Mantle
100
10
100
100
100
10
081206-8a
080406-5
081106-6
080506-4
081206-3a
080606-4a
080606-4b
100
Sample/ Primitive Mantle
1.0
10
10
1
1.0
10
Sample/ Primitive Mantle
10
100
1
100
100
080906-1
0.1
0.1
0.1
0.1
Cs
Rb
Ba
Th
U
Nb
K
La
Ce
Pb
Pr
Sr
P
Nd
Zr
Sm
Eu
Ti
Dy
Y
Yb
Lu
Cs
Rb
Ba
Th
U
Nb
K
La
Ce
Pb
Pr
Sr
P
Nd
Zr
Sm
Eu
Ti
Dy
Y
Yb
Figure 10. Rare Earth Element Diagrams. Normalized to Primative Mantle (Sun and McDonald, 1989). A) Mafic unit, B) Mafic enclaves, C) Qtz Monzodiorite, D) Granodiorite, E) Granite, F)
Migmatite
Lu
1000
100
Sample/ Primitive Mantle
10
1
0.1
Cs
Rb
Ba
Th
U
Nb
K
La
Ce
Pb
Pr
Sr
P
Nd
Zr
Sm
Eu
Ti
Figure 11. Spider plot for all samples. Samples are normalized to primative mantle (Sun and McDonald,
1989).
Dy
Y
Yb
Lu
0.5127
0.5125
143 Nd/144 Nd(i)
0.5123
0.5121
0.5119
0.70
0.71
0.72
87Sr/86Sr
Figure 12. 143Nd/144Nd initial vs. 87Sr/86Sr initial compared to Sedimentary rocks and granitoids from the region. Grey region with vertical stripes
are Ordovican granitoids. Grey region with angular stripes are Sedimentay
rocks of Late Proterozoic to Ordovician. Data from Lucassen et al. (2005).
0.73
15.80
15.75
207Pb/204Pb
15.8
15.7
15.70
15.6
15.5
15.4
15.65
16.5
17.5
18.5
41
208 Pb/ 204 Pb
40
39
38
18
19
206 Pb/ 204 Pb
Figure 13. Various Pb isotopes vs. 206Pb/204Pb. A) 207Pb/204Pb vs.
206Pb/204Pb. From inset medium grey is Ordovician granitoids from
Lucassen et al. (2005). Light grey is field for non-cratonized crust from
Doe et al. (1979). B) 208Pb/204Pb vs. 206Pb/204Pb.
20
19.5
A
0.73
0.73
0.72
87Sr/86Sr
0.72
0.71
87Sr/86Sr
0.70
0.00
0.01
0.02
0.03
0.04
0.05
0.06
1/Sr ppm
0.71
0.70
0.00
0.01
0.02
1/Sr ppm
B
0.73
0.72
87Sr/86Sr
0.71
0.70
0
100
200
300
400
Sr ppm
Figure 14 87Sr/86Sr vs. A) 1/Sr ppm and B) Sr ppm. A) Inset is entire dataset. Sample 080306-1B was
excluded from larger figure.
0.73
0.72
87Sr/86Sr
0.71
0.70
40
50
60
SiO2
Figure 15. Initial 87Sr/86Sr vs. SiO2.
70
80
A
144Nd/143Nd (initial) vs. Nd ppm
0.5127
0.5126
6-5: 2 pxy gabbro
0.5125
144Nd/143Nd
0.5124
0.5123
0.5122
0.5121
0.512
0.5119
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
45.00
50.00
Nd ppm
B
143/144Nd vs. 87/86Sr
0.5127
6-5: 2 pxy Gabbro
0.5126
25% grey Represents a hypothetical mixing from
6-5 to 6-4B; 50% from 10-3b; 75% from 2-1
0.5125
143/144Nd
0.5124
0.5123
0.5122
0.5121
0.512
0.5119
0.704
0.706
0.708
0.71
0.712
0.714
0.716
0.718
0.72
0.722
0.724
87/86Sr
Figure 16. Mixing models for A) Nd isotopes vs. elemental concentrations and B) Models for Sr-Nd
Isotopes.
A
080806-1 Weighted Mean
520
Mean = 477.4 ± 7.1 Ma
Systematic Error = 1.3%
MSWD = 0.90 (2σ)
box heights are 1σ
B
Mean = 470.8 ± 7.2 Ma
Systematic Error = 0.8%
MSWD = 5.4 (2σ)
500
Best age
Best age
box heights are 2σ
520
500
480
460
C
080806-2 Weighted Mean
480
460
D
440
080906-3 Weighted Mean
440
081006-3a Weighted Mean
box heights are 1σ
box heights are 1σ
510
Mean = 475.5 ± 9.6 Ma
Systematic Error = 1.7%
MSWD = 1.3 (2σ)
550
530
Mean = 472.7 ± 10.4 Ma
Systematic Error = 1.7%
MSWD = 1.04 (2σ)
510
490
Best age
Best age
490
470
470
450
430
450
410
390
E
430
081006-5 Weighted Mean
box heights are 1σ
F
370
081106-4 Weighted Average
box heights are 1σ
515
500
Mean = 481.5 ± 7.9 Ma
Systematic Error = 1.3%
MSWD = 0.34 (2σ)
505
490
Best age
Best age
495
480
470
460
450
485
475
Mean = 473.6 ± 7.3 Ma
Systematic Error = 1.3%
MSWD = 1.5 (2σ)
465
455
Figure 17. Additional Weighted Mean Plots. A) 080806-1, B) 080806-2, C) 080906-3, D)
081006-3a, E) 081006-5, F) 081106-4. All uncertainties are reported at the 1-sigma level, and
include only measurement errors. Systematic errors would increase age uncertainties by 1-2%.
U concentration and U/Th are calibrated relative to NIST SRM 610 and are accurate to ~20%.
Common Pb correction is from 204Pb, with composition interpreted from Stacey and Kramers
(1975) and uncertainties of 1.0 for 206Pb/ 204Pb, 0.3 for 207Pb/ 204Pb, and 2.0 for 208Pb/
204Pb. U/Pb and 206Pb/ 207Pb fractionation is calibrated relative to fragments of a large Sri
Lanka zircon of 564 ± 4 Ma (2-sigma). U decay constants and composition as follows: 238U =
9.8485 x 10 -10, 235U = 1.55125 x 10 -10, 238U/ 235U = 137.88.
A
B
081106-5a Weighted Mean
081206-6 Weighted Average
box heights are 1σ
500
500
490
490
480
480
Best age
Best age
box heights are 1σ
470
C
470
460
460
450
Mean = 471.6 ± 8.2 Ma
Systematic Error = 1.5%
MSWD = 0.92 (2σ)
Mean = 470.3 ± 7.7 Ma
Systematic Error = 1.3%
MSWD = 1.7 (2σ)
450
D
440
081206-4 Weighted Mean
440
081206-8a Weighted Mean
box heights are 1σ
box heights are 1σ
500
510
490
490
480
470
Best age
Best age
530
Mean = 476.4 ± 9.8 Ma
Systematic Error = 1.6%
MSWD = 1.5 (2σ)
Mean = 473.4 ± 8.2 Ma
Systematic Error = 1.6%
MSWD = 1.13 (2σ)
470
450
460
430
450
410
440
Figure 18. Additional Weighted Mean Plots. A) 081106-5a, B) 081206-4, C) 081206-6, D)
081206-8a. All uncertainties are reported at the 1-sigma level, and include only measurement
errors. Systematic errors would increase age uncertainties by 1-2%. U concentration and U/Th
are calibrated relative to NIST SRM 610 and are accurate to ~20%. Common Pb correction is
from 204Pb, with composition interpreted from Stacey and Kramers (1975) and uncertainties of
1.0 for 206Pb/ 204Pb, 0.3 for 207Pb/ 204Pb, and 2.0 for 208Pb/ 204Pb. U/Pb and 206Pb/ 207Pb
fractionation is calibrated relative to fragments of a large Sri Lanka zircon of 564 ± 4 Ma
(2-sigma). U decay constants and composition as follows: 238U = 9.8485 x 10 -10, 235U =
1.55125 x 10 -10, 238U/ 235U = 137.88.
Latitude
Longitude
Type
U-Pb Zircon Age (Ma)
080806-1
30.7099
67.5655
Tonalite
477.4
080806-2
30.7126
67.5613
Tonalite
470.8
080906-1
30.7186
67.5483
Migmatite
585.5
080906-3
30.7213
67.5398
Tonalite
475.5
080906-4
30.7213
67.5332
Tonalite
477.1
081006-3A
30.7228
67.5278
Granite
472.7
081006-4
30.7240
67.5235
Tonalite
489.9
081006-5
30.7241
67.5206
Diorite-Gabbro
473.6
081106-2
30.7261
67.5008
Granodiorite
468.7
081106-4
30.7152
67.5038
Granodiorite
481.5
081106-5A
30.7160
67.4635
Granodiorite
470.3
081206-4
30.6428
67.5000
Granodiorite
476.4
081206-6
30.6372
67.4906
Granodiorite
471.6
081206-8A
30.6354
67.4849
Granodiorite
473.4
±
±
±
±
±
±
±
±
±
±
±
±
±
±
7.09
7.19
9.97
9.63
8.41
10.4
9.09
7.28
8.42
7.90
7.71
9.82
8.18
8.23
Table 1. Geochronology samples with locations, rock type and U-Pb zircon ages
(Ma). Rock Type is based on units from Figure 1 when elemental values were not
analyzed.
SiO2
080206-1
080306-1b
080306-6
080406-2
080406-5
080406-7
080506-4
080606-4a
080606-4b
080606-5
080706-2
080706-5a
080706-5b
080806-4
080906-1
080906-3
081006-3a
081006-3b
081106-1
081106-6
081106-7
081206-3a
081206-8a
081206-8b
48.35
49.25
47.66
44.59
55.43
49.02
63.35
75.57
60.42
48.99
59.56
53.79
49.25
52.56
73.80
58.54
73.83
49.99
65.62
76.54
65.41
71.72
68.51
48.81
TiO2
0.867
0.668
0.453
0.105
1.379
1.292
1.033
0.068
1.209
0.866
0.786
0.854
0.989
1.256
0.722
0.861
0.115
0.920
0.692
0.032
0.632
0.247
0.516
1.556
Al2O3 FeO*
17.51
4.22
19.00
21.97
18.41
18.28
16.42
13.02
17.06
15.24
16.53
18.51
14.86
18.38
11.69
16.74
12.62
16.78
15.31
12.09
15.15
13.59
14.63
17.29
10.85
16.40
9.27
6.78
10.14
12.41
7.83
1.06
8.49
9.60
7.21
8.67
12.85
9.57
4.33
7.47
1.06
9.64
5.45
0.40
5.42
1.95
4.16
12.42
MnO
MgO
CaO
0.193 7.45 11.41
0.337 20.62
6.22
0.208 9.79 11.63
0.115 11.69 13.36
0.189 4.48
0.87
0.240 4.98
9.27
0.176 3.11
1.49
0.050 0.54
1.18
0.265 4.67
1.07
0.183 8.59 12.96
0.131 3.25
5.87
0.204 4.22
6.96
0.253 7.12 10.65
0.160 4.27
6.57
0.060 1.61
0.93
0.177 3.67
5.84
0.016 0.29
1.34
0.207 6.53 10.17
0.087 1.72
4.30
0.012 0.08
1.18
0.123 1.79
4.65
0.039 0.71
2.05
0.088 1.30
4.18
0.314 4.32
9.16
Na2O K2O
0.95
0.28
1.01
0.64
1.60
2.16
2.23
2.18
1.35
1.65
2.46
2.63
1.44
2.16
1.83
2.49
1.64
2.17
2.94
1.84
2.84
2.15
2.96
2.97
0.25
0.11
0.22
0.10
4.86
0.69
2.64
4.63
3.07
0.19
1.98
2.34
0.59
2.62
3.01
2.17
6.46
1.20
1.95
5.80
2.27
5.48
1.71
1.49
P2O5 Sum
0.118
0.012
0.049
0.012
0.053
0.277
0.062
0.082
0.054
0.071
0.165
0.435
0.048
0.254
0.127
0.143
0.042
0.189
0.189
0.021
0.157
0.048
0.115
0.261
Table 2. Whole rock major elements (wt %). FeO* is the total Fe as FeO.
97.94
98.12
99.29
99.37
97.42
98.61
98.34
98.39
97.65
98.34
97.94
98.62
98.05
97.81
98.12
98.09
97.42
97.81
98.25
97.99
98.45
97.99
98.16
98.60
La
Ce
080206-1
10.09
22.58
080306-1b
2.27
7.50
080306-6
9.50
23.54
080406-2
1.38
2.99
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
Ba
Th
Nb
Y
Hf
Ta
U
Pb
Rb
Cs
Sr
Sc
Zr
2.98 12.69
3.15 1.02
3.09 0.49
2.87 0.58 1.57 0.22 1.39 0.22
134.21
1.70
2.05 14.06 1.21 0.10 0.34
5.03
5.60 0.07 288.61 40.62
38.73
1.24
6.18
1.94 0.35
2.18 0.40
2.58 0.52 1.46 0.21 1.36 0.21
13.36
0.38
0.93 12.43 0.60 0.06 0.07
0.49
1.98 0.06
21.71 64.63
14.25
3.08 12.55
2.92 0.70
2.80 0.48
3.04 0.61 1.76 0.27 1.73 0.27
41.22
0.15
2.72 15.76 0.95 0.14 0.04
3.92
1.17 0.02 162.27 36.42
28.04
0.37
0.41 0.21
0.44 0.08
0.49 0.10 0.27 0.04 0.25 0.04
21.76
0.30
0.34
1.60
3.36 0.18 173.43 14.50
6.22
080406-5
79.46 166.35 18.54 69.19 11.81 2.52
8.46 1.00
4.51 0.74 1.67 0.20 1.25 0.22
929.21 26.68 12.94 17.05 7.37 0.39 0.47 26.00
98.42 0.68 169.53 23.40 252.28
080406-7
16.19
6.49 1.10
6.78 1.37 3.72 0.53 3.27 0.51
162.61
19.79 0.81 210.27 49.25 192.52
636.94 23.41 15.44 31.07 6.86 0.80 1.05 19.78
38.96
1.59
5.48 24.47
6.27 1.69
080506-4
59.09 124.28 14.13 52.61 10.48 1.82
8.67 1.28
6.86 1.27 3.21 0.42 2.40 0.37
080606-4a
18.93
2.42 0.35
1.84 0.34 0.85 0.12 0.71 0.11 1125.29
080606-4b
68.37 149.76 16.40 61.06 12.17 1.87 10.12 1.50
36.93
3.88 14.05
2.82 2.15
8.02 1.45 3.63 0.49 2.81 0.44
1.45
5.80
2.41 0.20 0.03 0.08
8.40 33.13 5.07 0.48 0.51
0.82
6.36
8.34 1.39 0.07 4.27 47.62
69.10 1.16 132.90 17.62 230.34
81.58 0.51 225.55
1.41
47.72
547.28 24.48 18.15 35.76 7.17 0.71 1.88 18.06 118.86 1.89 111.36 21.57 245.64
080606-5
4.30
11.15
1.64
7.76
2.41 0.85
3.06 0.57
3.83 0.82 2.27 0.34 2.08 0.32
23.89
0.15
2.33 20.28 1.39 0.15 0.07
1.31
080706-2
21.79
51.32
6.80 29.87
8.17 1.56
8.25 1.43
8.62 1.71 4.52 0.62 3.54 0.51
405.63
3.41
9.94 41.32 4.82 0.36 0.26
8.69
407.06
1.17 13.38 54.73 1.69 0.60 0.33 10.30
080706-5a
19.29
52.76
7.75 35.69 10.34 1.94 10.77 1.84 11.14 2.24 5.96 0.81 4.67 0.68
080706-5b
8.37
18.68
2.32
9.95
2.78 0.97
3.53 0.70
4.75 1.04 2.98 0.44 2.81 0.44
67.93
080806-4
15.91
36.34
4.76 20.68
5.16 1.41
5.21 0.84
5.04 1.00 2.61 0.37 2.23 0.34
493.47
1.47
3.73 25.16 1.14 0.22 0.27
1.06 10.46 24.39 8.14 0.46 0.32
4.91
1.37 0.04 105.87 47.74
43.21
73.58 0.91 163.86 33.92 177.65
91.50 1.43 183.70 51.76
52.22
4.88 0.07 105.56 51.30
29.44
9.02 119.23 1.80 194.21 29.67 311.69
080906-1
42.23
85.67 10.31 39.02
8.17 1.60
7.22 1.19
7.00 1.40 3.86 0.57 3.55 0.55
481.85 15.64 12.92 36.13 9.03 0.78 5.33 20.38
98.21 0.84 132.26 10.96 315.27
081006-3a
42.14
86.45
9.86 37.71
8.47 1.53
7.98 1.31
7.91 1.55 4.08 0.56 3.23 0.46
347.47
87.35 1.31 155.59 44.40 171.79
080906-3
4.85
7.71
0.80
0.56 1.01
0.46 0.07
0.42 0.09 0.30 0.05 0.37 0.08 1127.35
0.79
1.21
5.47 22.72 2.40 0.33 0.59
2.87
7.04 12.04 37.55 4.74 0.50 0.33 11.07
2.83 3.44 0.06 0.41 25.59 141.21 0.50 162.36
081006-3b
19.74
43.64
5.66 23.08
5.24 1.49
4.79 0.76
4.51 0.92 2.49 0.35 2.27 0.36
227.46
3.59
081106-1
30.38
61.42
7.16 26.90
5.34 1.09
4.34 0.66
3.63 0.70 1.80 0.25 1.46 0.24
187.05
9.40 10.55 16.07 5.47 0.58 0.47 17.26
7.69
1.12 104.36
33.03 1.11 243.58 33.40
77.70
91.34 2.05 144.36 13.98 194.58
081106-6
9.61
18.21
2.02
7.15
1.42 1.03
1.21 0.19
1.06 0.21 0.52 0.07 0.44 0.08
873.88
4.42
081106-7
33.95
70.20
8.14 30.97
7.15 1.39
6.95 1.20
7.47 1.50 3.97 0.54 3.08 0.44
469.40
5.64 10.37 35.93 4.58 0.47 0.44 10.38
081206-3a
35.13
67.56
6.94 22.17
3.17 0.79
2.07 0.28
1.50 0.29 0.80 0.12 0.74 0.12 1116.13
9.35
3.61
081206-8a
26.87
51.58
5.88 21.40
4.17 1.02
3.62 0.59
3.58 0.72 2.02 0.30 1.98 0.32
227.41
9.99
8.02 18.78 4.00 1.09 2.60 13.47
89.17 3.27 182.85
081206-8b
28.64
66.83
8.66 35.55
8.12 2.31
7.74 1.26
7.73 1.55 4.18 0.58 3.65 0.56
168.11
1.36
9.86 38.37 4.38 0.53 0.67 11.21
45.77 1.64 208.45 41.13 165.22
0.73
5.46 2.50 0.08 0.33 31.30 114.57 0.45 124.84
7.59 3.33 0.18 0.30 22.35 132.55 1.18 166.29
Table 3. Whole rock trace element (ppm) concentrations.
0.77
59.66
81.03 1.27 166.23 22.56 166.09
3.62 110.05
9.09 136.86
Rb ppm Sr ppm
080206-1
080306-1b
080306-6
080406-2
080406-5
080406-7
080506-4
080606-4a
080606-4b
080606-5
080706-2
080706-5a
080706-5b
080806-4
080906-1
080906-3
081006-3a
081006-3b
081106-1
081106-6
081106-7
081206-3a
081206-8a
081206-8b
5.11
2.03
0.98
3.15
92.79
19.83
n/a
0.30
105.19
1.22
69.88
82.29
4.48
120.51
96.08
84.84
139.33
33.63
83.84
n/a
77.20
118.50
82.57
40.30
300.13
19.94
165.11
189.29
164.39
215.49
n/a
229.61
108.29
106.06
169.66
185.19
305.30
186.73
132.02
150.70
164.77
252.12
149.67
n/a
165.63
140.03
130.09
204.09
Rb/Sr
0.0170
0.1019
0.0059
0.0166
0.5645
0.0920
n/a
0.0013
0.9713
0.0115
0.4119
0.4444
0.0147
0.6454
0.7277
0.5630
0.8456
0.1334
0.5601
n/a
0.4661
0.8462
0.6347
0.1975
87
86
Rb/ Sr
0.048957
0.293183
0.017092
0.047838
1.626365
0.264709
n/a
0.003711
2.802282
0.032940
1.186903
1.279696
0.042210
1.859226
2.097391
1.621186
2.436081
0.383634
1.613174
n/a
1.341699
2.437782
1.826962
0.568179
2σ (Sr)
1.68E-04
1.70E-05
2.13E-05
2.12E-05
2.44E-05
3.84E-05
n/a
1.74E-05
1.89E-04
2.96E-05
4.84E-04
2.00E-04
1.99E-05
4.00E-04
1.86E-05
1.85E-05
6.25E-05
1.56E-05
3.33E-04
n/a
1.56E-05
1.40E-04
1.27E-05
4.32E-04
87
86
Sr/ Sr(i) Sm ppm Nd ppm
0.706495
0.709437
0.709059
0.708283
0.716832
0.710862
n/a
0.723477
0.721820
0.705224
0.721731
0.713793
0.709339
0.714030
0.716358
0.711233
0.709848
0.706962
0.712277
n/a
0.709169
0.709271
0.705745
0.710623
2.86
n/a
2.69
0.37
6.77
6.10
8.36
n/a
8.06
2.23
2.75
3.63
6.61
4.62
7.62
7.93
0.28
4.68
5.16
1.29
4.36
1.82
2.82
5.10
12.15
n/a
6.05
1.47
41.74
24.72
44.37
n/a
42.50
7.55
8.26
13.67
23.55
18.55
39.65
40.24
1.56
21.84
26.65
7.06
19.44
13.08
15.51
22.71
Sm/Nd
0.2350
n/a
0.4443
0.2494
0.1621
0.2469
0.1885
n/a
0.1896
0.2955
0.3327
0.2654
0.2805
0.2492
0.1923
0.1970
0.1812
0.2140
0.1937
0.1835
0.2244
0.1394
0.1816
0.2246
147
144
Sm/
Nd 2σ (Nd)
0.142041
n/a
0.268592
0.150766
0.097996
0.149259
0.113927
n/a
0.114614
0.178681
0.201112
0.160431
0.169591
0.150641
0.116221
0.119071
0.109519
0.129386
0.117093
0.110899
0.135660
0.084266
0.109805
0.135776
1.54E-05
n/a
2.46E-05
1.54E-05
1.74E-05
1.54E-05
1.02E-05
n/a
1.84E-05
2.46E-05
1.23E-05
8.20E-06
3.07E-05
2.66E-05
1.13E-05
1.84E-05
2.87E-05
1.23E-05
1.02E-05
1.54E-05
9.22E-06
1.02E-05
1.84E-05
8.20E-06
143
144
Nd/
Nd(t) ε (Nd)0
0.511882
n/a
0.511495
0.511802
0.511679
0.511764
0.511672
n/a
0.511657
0.512071
0.511460
0.511810
0.511722
0.511731
0.511684
0.511727
0.511725
0.511871
0.511725
0.511724
0.511772
0.511771
0.511763
0.511802
-5.96
n/a
-5.68
-6.98
-12.63
-7.83
-11.8
n/a
-12.04
0
-10.54
-6.23
-7.37
-8.37
-11.4
-10.39
-11.03
-6.96
-10.58
-10.96
-8.51
-11.71
-10.29
-7.9
Table 4. Sr-Nd Isotopes. εNd values are calculated as deviations from a chondritic uniform reservoir in parts per 104, using present
day values of 143Nd/144Nd = 0.512638 and 147Sm/144Nd = 0.1967 (Wasserburg et al., 1981; Faure, 1986). Ages of rocks are from an
average of the Famatinian plutonism (485 Ma) reported by Panhurst et al., (1998), Panhurst et al., (2000), and Stair et al., (2007). n/a
samples were not analyzed.
206
080206-1
080306-1B
080306-6
080406-2
080406-5
080406-7
080506-4
080606-4A
080606-4B
080606-5
080706-2
080706-5A
080706-5B
080806-4
080906-1
080906-3
081006-3A
081006-3B
081106-1
081106-6
081106-7
081206-3A
081206-8A
081206-8B
204
Pb/
Pb
18.510
18.842
18.214
18.225
18.289
18.624
18.434
18.254
18.747
18.459
18.357
18.338
18.489
18.303
18.784
18.320
18.267
18.827
18.477
18.276
18.478
18.307
19.822
18.670
2σ
0.0102
0.0085
0.0102
0.0025
0.0102
0.0102
0.0102
0.0102
0.0102
0.0085
0.0102
0.0102
0.0102
0.0102
0.0102
0.0102
0.0102
0.0102
0.0102
0.0102
0.0102
0.0102
0.0102
0.0102
207
204
Pb/
Pb
15.653
15.699
15.635
15.642
15.658
15.731
15.672
15.663
15.701
15.666
15.688
15.660
15.675
15.640
15.709
15.655
15.642
15.669
15.657
15.654
15.658
15.646
15.797
15.676
Table 5. Whole Rock Pb Isotope Results from the Sierra de Valle Fertil.
2σ
0.0107
0.0101
0.0107
0.0024
0.0107
0.0107
0.0107
0.0107
0.0107
0.0107
0.0107
0.0107
0.0107
0.0107
0.0107
0.0107
0.0107
0.0107
0.0107
0.0107
0.0107
0.0107
0.0107
0.0107
208
Pb
/204
Pb
38.432
39.147
38.070
38.102
39.855
38.558
39.778
38.170
40.039
38.379
39.952
38.214
38.575
38.201
39.392
39.251
38.112
38.768
39.600
38.273
39.092
38.644
39.374
38.911
2σ
0.0267
0.0300
0.0267
0.0094
0.0267
0.0267
0.0267
0.0267
0.0267
0.0300
0.0267
0.0267
0.0267
0.0267
0.0267
0.0267
0.0267
0.0267
0.0267
0.0267
0.0267
0.0267
0.0267
0.0267