CONTINENTAL FLOOD
BASALTS
(EMEISHAN FlOOD BASALT)
Author: Q. Kalimashe (219325731)
Module: Code: GGL412
Assignment no.: 1
Year: 2023
1
Contents
Introduction ................................................................................................................................................. 3
Geological Background................................................................................................................................. 4
Methodology ................................................................................................................................................ 5
Results .......................................................................................................................................................... 9
Discussion .................................................................................................................................................. 15
Reference ................................................................................................................................................... 17
List of Figures
Figure 1: (a) Reconstruction of Pangea during Middle – Late Permian. (b) Distribution of Emeishan flood
basalts in SW China in a rhombic pattern and (c) shows a map of the Sichuan basin that was intruded by
the Emeishan basalts on the southwestern side. ............................................................................................ 4
Figure 2: Harker diagrams of major elements plotted against MgO to show the evolution of magma
during the early stages of crystallization. The plutonic trends of the TiO2, P2O5 and FeO graphs show the
presence of cumulates in the study area. ....................................................................................................... 9
Figure 3 Harker diagrams of major elements plotted against SiO2 to show the evolution of magma during
the late stages of crystallization. The plutonic trends of the TiO and FeO graphs indicate the presence of
cumulates in the study area. ........................................................................................................................ 10
Figure 4: TiO2 vs Zr plot(s) showing two distinct trends (left) and the high Ti and low Ti (right). .......... 12
Figure 5: Rare earth elements in ELIP representing the high Ti (Left) and low Ti (Right) clusters. ......... 12
Figure 6: Rare earth elements in ELIP representing the high Ti (Left), low Ti (Middle) and very low Ti
(Right) clusters. ........................................................................................................................................... 13
Figure 7: Diagrams showing trace element trends in High (Left), Low (Middle) and very Low (Right) Ti
basalts of the study area .............................................................................................................................. 13
Figure 8 ....................................................................................................................................................... 14
2
Introduction
Large igneous provinces (LIP) are geological structures that form from rapid and voluminous
eruptions and are usually as a result of rising mantle plumes from the deep interior of the Earth
and upwelling beneath the base of the lithosphere. These provinces hosts minerals and
hydrocarbons and an important role in events such as continent break up, mass extinctions and
environmental catastrophes.
Emeishan Flood Basalts (EFB) /Emeishan large igneous province (ELIP) is one of the well-studied
large igneous provinces, it is located in Southwestern China and it extends over a rhombic area of
approximately 2.5 x 105 km2. The thickness of the of the basalts range from 5000m in the west to
several hundred meters in the east. After numerous studies on the geochemistry, geochronology,
geophysics, crustal uplift and paleo environment, it has been widely accepted that the province
originated from a mantle plume and that it erupted approximately 245 million years ago, this
coincides with the Gaudalupian mass extinction.
The geochemistry of these provinces are usually well studied to better understand the areas. In this
paper, the major elements found in EFB were plotted against magnesium oxide and silicate oxide
to study the evolution of magma of this area. The magma was then divided into high Ti and Low
Ti, these magmas were then analyzed for the rare earth and trace elements present in them. Lastly,
the rocks were dated using the most common dating method, U – Pb in zircons. The results
obtained from all these analysis provided a better understanding of the study area.
The aims of this study are to:
1. Study tthe evolution of magma using Harker diagrams
2. Characterize the degree of melting, depletion of the mantle source and determine if Garnet
was present in the mantle source using rare earth elements.
3. Characterize metasomatism and contamination (if there was any) using trace elements
4. Date the basalts using U – Pb in zircons.
3
Figure 1: (a) Reconstruction of Pangea during Middle – Late Permian. (b) Distribution of Emeishan flood basalts in SW China in
a rhombic pattern and (c) shows a map of the Sichuan basin that was intruded by the Emeishan basalts on the southwestern side.
Geological Background
The Emeishan basalts lie on the western edge of the Yangtze Craton, South Western China with
the Longmenshan thrust and the Ailaoshan – Red river slip fault as its northwestern and
Southwestern boundaries, respectively (Figure 1). Geochronological studies suggested that the
emplacement of the province was initiated in the Late Permian (259 Ma) with a rapid eruption that
lasted for, approximately, 2 Ma in the main parts of the province. The initiation was widely
attributed to a mantle plume and the supporting evidence (such as rapid emplacement, voluminous
flood basalt eruptions and high mantle potential temperature estimates) was extracted from
geochemical, geological and geophysical studies. ……… believed that the origin of the EB was a
rift origin, however, ………. Argued that if the EB were because of a rift origin the rift should be
much larger today. Also, studies showed that the earth’s surface was uplifted by more than 1300
m in the center before the EB erupted and this was far more powerful than a rift could’ve been.
4
Emeishan basalts uncomfortably overlies the late Permian – middle Permian carbonation
formations such Maokou limestones, these formations belonged to polycyclic superimposed
sedimentary basin called the Sichuan basin. The basin was formed on the Precambrian crystalline
basement, it had 19 formations with the main formations being the Maokou, Longtan and
Changxing formations. The depositional environment of these formations was predominantly open
and shallow water. The basin was accommodated in the lower marine carbonate sequence (from
Neoproterozoic – Middle Triassic) and the upper continental clastic sequence from the late Triassic
to Eocene. Several localized outcrops of the Permian basalts were reported in the southwestern
and central areas of Sichuan basin.
Biostratigraphic correlations of the Maokou limestones suggested that a significant crustal doming
and surface uplift resulted from the impingement of the plume head on the lithosphere. The doming
area was divided into inner (Panxi region), intermediate and outer zones based on the extensiveness
of erosion and surface uplift. The inner zone had the thickest crust which then progressively
thinned from the intermediate to the outer zone. Furthermore, …………. Reported that the NE
basalts were different from the western basalts, this suggested that the basalts could have originated
from heterogonous mantle sources with varying degrees of crustal contamination.
Recent studied suggested that the carbon and sulfur that were degassing from the Emeishan mantle
plume contributed to the end of the Gaudalupian abrupt climatic changes and mass extinction
event. These suggestions conformed to the age of that this province is the world’s largest host of
Fe – Ti – V oxide mineral deposits and an important host of Ni – Cu – (PGE) sulphides. In the
inner zone there are abundant giant orthomagnatic Fe – Ti V oxide deposits which contribute to
35.2% and 6.7% of the total global production of these metals. Studies showed that there were
economical and sub economical Ni – Cu – (PGE) and PGE deposits in the inner and outer zones.
Methodology
In this study, secondary data was used to study the Emeishan large Igneous Province. The data
was collected from the website GEOROC (https://georoc.eu/georoc/new-start.asp) and this was
done by opening a folder titled “Precompiled files”, then the “locations” folder and lastly, the
“continental flood basalts” folder. In this folder an excel file named “2023-03WSTPOX_EMEISHAN.csv” was downloaded. The file was launched in excel, all of the data was
the first column and this was fixed by marking the first column then clicking on “text to column”,
under the data tab, then “delimited” on the first page and “next” on the last page. This was followed
by copying the “Unique ID” and pasting it in column A.
Data Sorting and Screening
For sorting and screening of the data, a new sheet (called working sheet 1) was created and data
was copied from the raw data sheet and pasted onto this sheet. This was done to have backup of
the raw data in case the data was manipulated incorrectly. In working sheet 1, the abbreviations
and references in row 2418 and 2420 – 2521, respectively, were deleted. The second step was
sorting the data according to the rock type column, this was followed by deleting 60 sedimentary
5
samples, 1 vein and 86 metamorphic samples, leaving only the plutonic and volcanic samples
behind. The columns titled “location, latitude min, latitude max, land or sea, elevation max, sample
name, min age (yrs), max age (yrs), geol, eruption data and drilling data (X – AB)” were hidden,
this was done because this data wasn’t useful for the analysis of this study so removing hiding it
helped minimize the data on the working sheet and to avoid any confusions. The Unique ID column
was copied and pasted in column A.
Data recalculation
In this part of the assignment, a new column with the heading “FeOT was recalculated” was created
and Iron oxide was recalculated using the IF function:
IF(AJ2>0,AJ2,AI2+(AH2*0.899))
Then another column with the heading “test major’’ was created at the end of the major elements
And the following test was used for the whole column:
AND(AC3>0,AH3>0,AL21,AM3>0)
Following this the data from the column titled “H2O” to “LOI (wt%)” were shifted to the right and
major elements were coped and pasted (with values) in this space. The columns with B2O3, NiO,
Al2O3, Fe2O3, FeO and FeOT were deleted.
Then another column labelled “total” this column was used to calculate the total of the major
elements using the SUM function
=SUM(AT2:BC2)
9 new columns were inserted to recalculate the major elements, this was done by using the formula:
=(AT2/$BD2)*100
And the sum of these recalculated major elements was calculated in the last column using the SUM
function (values were 100).
Harker diagrams
The first step here was to create a Harker diagram, using data from the sheet called “working sheet
1”. SiO2 was on the x – axis and MgO was on the y – axis. From this data a limit was chosen at
SiO2 40 wt%. The data was then sorted out as a function of SiO2 recalculated and the samples with
a SiO2 concentration that was ≥ 40 were selected (138 samples) and sorted as a function of rock
type. In the selected samples, the plutonic and volcanic samples were highlighted with different
colors and they were plotted on scatter plots (Harker diagrams) as two different series. For the 8
major elements, a SiO2 and MgO Harker diagram was created (these diagrams were plotted on a
new sheet renamed “Graphs”). The graphs were copied and pasted in PowerPoint where they were
edited to make them look presentable.
6
Trace elements and Rare earth elements
A new limit at 5 MgO wt% in the MgO vs TiO2 Harker diagram was chosen. A new worksheet
called “working sheet 2” was created. Data was copied from working sheet 1 and pasted on that
sheet. The sheet was then sorted according to MgO. From this data, a new diagram of TiO2 vs
MgO was created. The graph had 2 distinct trends, a trendline was added and its formula was
added. The plotted samples were sorted as a function of Zr. and a new column (test 1) was created,
in this column x from the trendline formula was calculated. Then another column for test 2 was
created where the value of zr was subtracted from test 1.
The next step was sorting the data as a function of test 2 and separating the positive values (in
blue) from the negative values (by highlighting them green). From this plot, two distinct clusters
were identified, one at 3 – 5 wt% TiO2 and 200 – 500 wt% Zr and the second cluster 1 – 2 wt%
TiO2. The clusters were classified as high Ti and low Ti respectively. The data was sorted
according to Zr and the samples that fall within the selected ranges were plotted on a diagram. For
the high cluster, after selected 3 – 5 wt% TiO2 the selected data (high cluster) was sorted as a
function of Zr and only samples within 200 – 500 wt % zr were plotted as the high cluster.
For the rare earth elements and trace elements, a new worksheet was created (normalizing
worksheet). The first thing was to sort out the trace elements in this sheet by creating 27 new
columns and the data was copied from the disordered data and pasted in the new columns in the
right order. The rest of the trace elements (excluding REE) and duplicated columns were deleted.
The next step was to normalize the data, this was done by creating 27 new column again and using
the primitive mantle composition (provided in moodle):
=BS6/FA$4
Using the normalized data, a few samples of high Ti, low Ti and Vwet low Ti were plotted in three
different diagrams for the trace elements and REE. The y axis were set to be logarithmic scale and
the diagrams were pasted on PowerPoint for further editing.
Isotopes
Data was collected from the website GEOROC and this data was “fixed as explain above”. The
next step was to calculate 206Pb/238U and 207Pb/235U using the equation:
t=𝜆
1
206
𝑃𝑏 206
ln ( 𝑈 238 + 1) = 𝜆
1
207
𝑃𝑏 207
ln ( 𝑈 235 + 1)
For a range of age from 500 000 000 million years to 4000 000 000. Then the Zircon data was
plotted on this graph and it plotted within the range of 240 – 280 million years ago and because of
this, a new graph was plotted and which ranged from 200 000 000 million years to 400 000 000.
The graph has increments of 20 000 000 from 200 000 000 to 500 000 000 million years, this was
zone to zoom in on the area where the data plotted from to allow more accurate dating results.
7
8
Results
The evolution of magma in the Emeishan igneous province was shown by the SiO2 and MgO
Harker diagrams in figure 1 and 2 below. The MgO diagrams ranged from 30 wt% to 0 wt% with
an uneven sample distribution while the SiO2 diagrams ranged from 40 – 80 wt% with an uneven
distribution as well. There seemed to be two main cluster points on both sets of diagrams, for the
MgO diagrams majority of the samples plotted from MgO 10 – 4 wt% (only 17% of the range)
resulting in the formation of felsic clusters, while the remaining few samples plotted from 30 wt%
to 10 wt%, a much bigger range, and were evenly distributed across the mafic range. Conversely,
for the SiO2 diagrams majority of the samples formed a big cluster at SiO2 40 – 55 wt% suggesting
a mafic magma and fewer samples plotted 65 – 80 wt% thus suggesting a less felsic magma.
On both sets of diagrams, the volcanic data showed narrow trends, indicating that the major
elements have similar parental magma compositions, however, the plutonic samples showed some
variability with the TiO2, FeO and P2O5 samples. From MgO 6 wt% - 4 wt%, P2O5 and TiO2
showed a cluster at 1 – 3 wt% and 6 – 10 wt%, respectively, and FeO showed cluster from MgO
30 - 10 wt% (Figure 1). These enriched plutonic trends suggested that the rocks were cumulates
and studies have shown that the intrusions in this area are high in Titanium and Iron thus explaining
the high TiO2 and FeO2 cumulate clusters. Also, the volcanic rocks
25
Al2O3 wt%
B
E D C
A
Plutonic
TiO2 wt%
carbnatites and friends
Volcanic
0
5
10
15
20
25
30
35
25
30
35
MgO wt%
20
P2O5 wt%
SiO2 wt%
F
85
80
75
70
65
60
55
50
45
30
40
15
10
5
250
0
5
10
15
20
SiO2 wt%
K2O wt%
CaO3 wt%
20
10
9
8
7
6
5
4
3
2
1
40
3.5 0
3
2.5
2
1.5
1
0.5
12
0
0
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15
10
5
10
15
20
5
10
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20
A
SiO225
wt%
30
35
25
30
35
25
30
35
MgO wt%
8
6
4
20
0
5
10
15
20
25
30
SiO2 wt%
5
10
15
20
0
35
FeOtotal wt%
Na2O wt%
B
C
2
5
09
8 0
7
6
5
4
3
2
1
0
0
F E D
25
30
15
10
5
0
35
0
5
10
15
20
MgO wt%
MgO wt%
Figure 2: Harker diagrams of major elements plotted against MgO to show the evolution of magma during
the early stages of crystallization. The plutonic trends of the TiO2, P2O5 and FeO graphs show the presence
of cumulates in the study area.
9
A
B C
D
E
A
F
35
Volcanic
Plutonic
25
20
15
10
5
300
40
50
60
70
80
90
70
80
90
SiO2 wt%
P2O5 wt%
Al2O3 wt%
25
20
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250
40
50
60
SiO2 wt%
K2O wt%
CaO wt%
20
15
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90
8 40
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E
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60SiO2 wt% 70
80
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70
SiO2 wt%
80
90
SiO2 wt%
8
6
4
2
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70
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SiO2wt%
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60
SiO2 wt%
FeOtotal wt%
Na2O wt%
B C D
TiO2 wt%
MgO wt%
30
8
7
6
5
4
3
2
1
10
0.9 40
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
12
0
10 40
0
20
18
16
14
12
10
8
6
4
2
0
SiO2%
40
50
60
Figure 3 Harker diagrams of major elements plotted against SiO2 to show the evolution of magma during
the late stages of crystallization. The plutonic trends of the TiO and FeO graphs indicate the presence of
cumulates in the study area.
Magma underwent fractional crystallization and the process was summarized in table 1 below.
During phase A nothing happened, the concentration of major elements in the magma remained
constant and no minerals were formed. During early crystallization FeO decreased and mafic
minerals crystalized, starting with Olivine, and in the late stages of crystallization felsic minerals
crystalized with Albite being the last one to crystalize.
10
Table 1: An interpretation of the Harker diagrams accompanied by a description of the fractional
crystallization process.
MgO wt%
SiO2 wt%
Phase A
35 - 30
40 - 45
Phase B
30 - 10
45 - 48
Phase C
10 - 6
48 - 50
Phase D
6-4
50 - 55
Phase E
4-3
55 - 65
Phase F
3-0
65 – 80
Al2O
CaO
FeO
TIO2
Na2O
K2O
P2O5
Constant
Constant
Constant
Constant
Constant
Constant
Constant
Decrease
Decrease
Decrease
Decrease
Decrease
Increase
Decrease
Decrease
Depleted
Decrease
Depleted
Decrease
Decrease
Depleted
Olivine
Clinopyroxene
Orthopyroxene
Anorthite
Apatite
Ilmenite
Albite
-
Increase
Increase
Decrease
Increase
Decrease
Decrease
Decease
Decrease
Decrease
Increase
Increase
Decrease
Increase
Increase
Increase
Increase
Increase
Increase
Increase
Increase
Decrease
Minerals that crystalize
X
X
X
X
X
X
X
X
-
X
X
X
X
X
Hi – Ti and Low – Ti in Rare Earth Elements and Trace elements
Continental Flood Basalts were classified as High Ti and Low Ti using the TiO2 vs Zr plot. Both
these elements are immobile and incompatible hence the positive correlations in figure 3 below.
The TiO2 vs Zr graph (on the left in figure 3) showed two distinct trends, one with low Zr and high
Ti and the other with high Zr and low Ti. These two trends were separated with a limit and the
high Zr, low Ti plot was used for further investigations. From this trend, two distinct clusters were
observed (See figure 3, right), the first one between 1 – 2 Ti wt% and the second one between 3 –
5 Ti wt% and between 200 – 500 Zr wt%. These clusters were identified as the low Ti and high
Ti, respectively, and were used to plot rare earth elements and trace elements.
11
500
600
High Zr
Zr (ppm)
400
y = 52.308x - 48.462
High Ti
400
350
Zr (ppm)
500
300
450
Ti-rich samples (ore?)
Series2
Low Ti
Linear (Series2)
300
250
200
Low Ti
150
200
100
100
Low Zr
50
0
0
0.0
0.0
5.0
10.0
TiO2 wt%
15.0
20.0
1.0
2.0
3.0
TiO2 wt%
4.0
5.0
6.0
Figure 4: TiO2 vs Zr plot(s) showing two distinct trends (left) and the high Ti and low Ti (right).
Rare Earth Elements (REE) were plotted on three graphs as show in figure 4 and 5 below. The one
on the right represents high Ti while the one on the left represents low Ti. The high Ti graph had
a steeper slope, its magma was more enriched in LREE than HREE while the opposite phenomena
held true for low Ti elements. Despite the pronounced difference in the general slope of the high
and low Ti elements, it is imperative to not that, for both graphs, the slopes indicated by the HREE
was very similar thus making it difficult to tell which melt is more depleted in HREE. To overcome
this analysis hiccup a third graph with very low Ti samples was plotted (Figure 5, right) and this
graph made is easier to see that the Low Ti melt was more depleted in HREE than the high Ti.
Also, in figure 5 positive and negative anomalies were observed for SM.
Rare Earth Elements High Ti
Rare Earth Elements Low Ti
100
100
10
10
1
1
LA CE PR ND SM EU GD TB DY HO ER TM YB LU
LA CE PR ND SM EU GD TB DY HO ER TM YB LU
Figure 5: Rare earth elements in ELIP representing the high Ti (Left) and low Ti (Right) clusters.
12
Rare Earth Elements High Ti
Rare Earth Elements Low Ti
100
100
10
10
Rare Earth Elements Very Low Ti
100
10
1
LA
CE
PR
ND
SM
EU
GD
TB
DY
HO
ER
TM
YB
LU
1
LA CE PR NDSM EU GD TB DYHO ER TMYB LU
1
LA CE PR ND SM EU GD TB DY HO ER TM YB LU
0.1
Figure 6: Rare earth elements in ELIP representing the high Ti (Left), low Ti (Middle) and very low Ti
(Right) clusters.
Figure 6 showed the trace element trends in the high, low and very low Ti basalts. The three
diagrams showed a fairly consistent trend of abnormalities in all of their samples. The steepness
of the graphs decreased progressively from high Ti to low Ti. High and Low Ti showed negative
and positive anomalies for U, negative anomalies for Ba, Ce, Sr and Eu and positive anomalies for
Ta, Zr and Ho. Very low Ti had a negative anomaly for U as well, one sample with a positive
anomaly for Sr and a depletion in HREE from Tb – Yb.
Trace Elements High Ti
Trace Elements Low Ti
100
100
10
10
Trace Elements Very Low Ti
100
10
1
1
1
0.1
Figure 7: Diagrams showing trace element trends in High (Left), Low (Middle) and very Low (Right) Ti
basalts of the study area
Isotopes
U-Pb dating was used to date the basalts of the ELIP using a range from 100 000 000 million years
to 450 000 000 million years as shown on figure 8 (Right). This range was selected so that all of
the samples could be plotted and because previous studies dated the basalts from this area to 220
– 280 million years ago so this was the best range. On the right of figure 7 is a graph showing
zoomed in of the years where the samples plotted up to 350 000 000 million years with majority
of the samples plotting between 2.2 Ga and 3.2 Ga. On the left of figure 7The high Ti and Low Ti
plotted within the same range and there was no evidence of metamorphism. However, there were
samples that plotted lower than the expected range.
13
1
0.1
0.9
0.09
4.0 Ga
0.8
3.5 Ga
0.6
206Pb/238U
206Pb/238U
0.7
3.0 Ga
0.5
2.5 Ga
0.4
0.3
Series1
2.0 Ga
0.2
Plutonic
1.5 Ga
0.1
0.08
Series1
0.07
Plutonic
Volcanic
0.06
0.05
3.2 Ga
0.04
0.03
2.2 Ga
Volcanic
0.02
0.5 Ga
0.01
0
0
10
20
30
207Pb/235U
40
50
60
0
0
0.1
0.2
0.3
0.4
0.5
207Pb/235U
Figure 8
14
0.6
0.7
0.8
0.9
Discussion
Major elements
The Harker diagrams in figure 1 and 2 represent the evolution of magma and they were interpreted
in table 1. The interpretation in table one may be further interpreted to determine the type of rocks
that may have formed in the selected study area. In phase B olivine and pyroxene crystalized
suggesting the formation of komatiite and peridotite rocks, in phase C mostly pyroxene crystalized
and this suggested the formation of gabbro and basalt. It is also imperative to note that had the
highest number of samples which would explain why the rocks in this area were referred to as
basalts. Phase D was characterized by the crystallization of clinopyroxene, anorthite, apatite and
ilmenite and this phase suggested the formation of basalt, diorite and andesite. Lastly, phase E was
characterized by the formation of albite and the continued formation of the minerals in phase C.
These minerals suggested the formation of rhyolite and granite. These results correlated with the
results that were obtained by Tong Hou in a similar study that he carried out.
The Magma of the ELIP belonged to, both, the tholeiitic and alkali magma series. This was seen
from the change in the Alkali content where it started off with very high alkali content, indicating
an alkaline magma series, and as crystallization progressed, the alkaline content decreased
resulting in the transition to a more tholeiitic series (Table 1).
The FeO, TiO2 and P2O5 harker diagrams had increasing clusters that deviated from their
respective trends (Figure 1 and 2), these clusters indicated the enrichment of Fe-Ti-V oxides in
this province.
Zr vs TiO2
Zr vs TiO2 diagrams were used determine the mantle source of ELIP (Figure3) and the diagram on
the left showed two distinct trends, one characterized by a positive slope and another one
characterized by a flat slope with high TiO2. The latter trend suggested the presence of ore deposits
and this suggestion was supported by various previous studies which reported that ELIP hosts giant
Fe – Ti – V oxide ore deposits in mafic intrusions such as Limahe, Baimazhai and Yasngliuping
intrusions. The trend with a positive relationship between TiO2 and Zr was used to characterize
the magma into low Ti and high Ti magma. However, it was imperative to note that the data
showed a continuous TiO2 range thus making it difficult to point out the different types of magma
and also, demonstrating that high Ti and Low Ti magma could be derived from the same mantle
source. Majority of the samples were in the low Ti cluster. The petrogenesis of high and low Ti
has been part of heated debates even though there was a general consensus that the ELIP was
divided into three zones: an inner, intermediate and outer zone, with high Ti being dominant in the
periphery while low Ti and alkaline lava occurred exclusively in the inner zones. …….. Proposed
that the low Ti magma were generated in a plume axis region and the high Ti lava were generated
by melting the mantle at the plume periphery via low degrees of melting due to the thicker
lithosphere.
15
Rare Earth Elements and Trace elements
The samples plotted in the REE diagrams exhibited a uniform primitive/chondrite-normalized
pattern with an apparent enrichment in LREE in high Ti and low Ti samples (Figure 5) and little
to no anomalies. However, high Ti was more enriched in LREE and less enriched in HREE
resulting in the formation of a steep slope. This slope was indicative of low degrees of partial
melting and alkaline magma. The low Ti was less enriched in LREE thus forming a flatter slope
which was indicative of high degrees of melting and tholeiitic magma. During low degrees of
partial melting the most incompatible rare earth elements (LREE) entered the melt immediately.
At higher degrees (greater depth), the least incompatible elements are able to enter the melt easily
as well. High Ti and Low Ti didn’t show the presence of absence of garnet well hence a third
diagram of “very low Ti” was created, this diagram also showed high degree of partial melting,
however, in this graph we were able to see the flat slope from Gd to Lu more clearly. These
elements are incompatible in other minerals but compatible in garnet. Their depletion suggested
the presence of garnet, they were still in the garnet during the melting process.
Among the trace elements, the high Ti samples had consistent abnormalities thus suggesting that
the abnormalities are from the mantle source, maybe a contamination at the source. Similarly, low
Ti and very low Ti samples had positive and negative anomalies for certain elements. This latter
trend suggested that the elements may have been used up during fractional crystallization and or
reintroduced by metasomatism (for fluid mobile elements). Barium had positive and negative
anomalies, this element is fluid mobile, and therefore, the positive anomalies could be attributed
to metasomatism while the negative one remains a mystery because barium is not compatible to
any of the major elements thus meaning fractional crystallization failed to explain that anomaly.
In very low Ti samples we could clearly see the presence of garnet by the flat slope from Gd to
Lu. Despite all the minor difference, it was imperative to note that that all Ti samples followed the
expected characteristic continental crust trend.
Isotopes
The age of Emeishan basalts has been widely accepted at 240 – 280 million years and the results
obtained from this study conform this statement as majority of the samples plot between 240 –
3000 million years. However, there was rocks that plotted bellow than expected range and a few
above it, the presence of the older samples was explained using the resistivity of zircons. Zircons
are resistant thus meaning they can withstand the formation of an igneous province, therefore,
these older zircons could’ve been inherited from the country rock that the magma assimilated from
and survived the geological process. The younger zircons could be accumulates that were
deposited later or maybe there was inconsistency in the collection of the data.
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Reference
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