petrogenesis of high-k, calc-alkaline and shoshonitic intrusive ......dabie-sulu orogenic belt...
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78
Petrogenesis of high-K, calc-alkaline and shoshonitic intrusive rocks in the Tongling area, Anhui Province
(eastern China), and their tectonic implications
Cailai Wu1,†, Shuwen Dong2, Paul T. Robinson1, B. Ronald Frost3, Yuanhong Gao1, Min Lei1, Qilong Chen1, and Haipeng Qin11State Key Laboratory of Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China2Chinese Academy of Geological Sciences (CAGS), Beijing 100037, China3Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming 82072, USA
ABSTRACT
The Mesozoic intermediate-silicic intru-sive rocks in the Tongling area, Anhui Prov-ince, eastern China, include a high-K, calc-alkaline series and a shoshonitic series . Rocks of the calc- alkaline series comprise more than 90% of the total and consist chiefl y of gabbro-diorite , granodiorite, quartz monzo-diorite, and porphyritic quartz monzodiorite. These rocks are associated with important skarn-type copper-iron deposits. They con-tain three types of enclaves: mica-rich vari-eties that appear to be residues of partially melted pelitic rock, mafi c quartz monzo-diorite, and microdiorite. The shoshonitic series consists of pyrox ene monzodiorite, monzonite, and quartz monzonite, which are commonly asso ciated with skarn-type gold deposits. Enclaves in these rocks are typi-cally pyroxene-rich or amphibole-rich vari-eties or amphibole gabbros. Zircon sensitive high-resolution ion micro probe (SHRIMP) U-Pb age data suggest that the granodiorites, quartz monzo diorites, and gabbro-diorites of the calc-alkaline series were generated at ca. 146–142, 143, and 140 Ma, respectively. The shoshonitic rocks range in age from 143 to 136 Ma. Although there is some overlap in reported ages of the two series, contact rela-tions indicate that the shoshonitic rocks post-date the calc-alkaline varieties. On the basis of the geochemistry of the two series and the character of their enclaves, the shoshonitic series is thought to have formed primarily by differentiation of a mantle-derived, weakly contaminated, alkali basalt magma, whereas the high-K, calc-alkaline series refl ects mix-
ing of differentiated mantle and crustal melts, followed by assimilation–fraction crystalliza-tion (AFC) processes. The magmatic activity may have been related to reactivation of the Tongling-Deijiahui structural zone in re-sponse to rapid, highly oblique subduction of the paleo–Pacifi c plate beneath South China.
INTRODUCTION
The Tongling district, which is situated in the eastern part of the Yangtze River basin in Anhui Province, is an ancient copper capital of China and one of the most important metal-bearing districts in the country (Fig. 1A). The polymetallic district is ~40 km long in an E-W direction and 20 km wide, with a total area of ~800 km2 (Fig. 1B). Within the district, there are 76 intermediate-silicic intrusive bodies and 54 known ore deposits (Wu et al., 2010a). The intrusive rocks are mostly intermediate dio-rites, monzonites, and quartz monzonites that form an early high-K, calc-alkaline series and a slightly later shoshonitic series. The ore depos-its are predominantly skarn type with copper, iron, and gold mineralization, accompanied by minor strata-bound types in the host carbon-ates (Zhao et al., 1999; Zhai et al., 1992). Some porphyry-type mineralization is also present, but it generally occurs only in the deeper parts of the intrusions (Pan and Dong, 1999). The total reserves in this district have been esti-mated to be 500 Mt copper and 150 t gold (Wu et al., 2010a).
Because of their associated copper and gold deposits, the intrusive rocks have been studied for many years (e.g., Chang and Liu, 1983; Tang et al., 1998; Xing and Xu, 1995, 1996; Zhou et al., 1993; Wu et al., 1996, 2000, 2003), but there is no agreement regard-
ing the petro genesis of the two series. Several processes have been proposed for the origin of these rocks: (1) assimilation of country rock by alkaline basaltic magma (Mao, 1990), (2) fractional crystallization of lower-crustal melts (Wu, 1986), (3) assimilation of lower-crustal material by alkaline basaltic magma followed by fractional crystallization (Xing and Xu, 1995), (4) partial melting of basaltic lower crust to form tonalitic intrusive rocks (Zhang et al., 2001), and (5) mixing of mantle-derived magmas with those formed by partial melting of basaltic lower crust (Wang et al., 2003). In this paper, we reexamine the origin of these granitoids using new sensitive high-reso lution ion microprobe (SHRIMP) U-Pb ages, whole-rock geochemistry, and the com-positions of the various enclaves hosted in the gran itoids. We review all of the recent data on the ages of the rocks and their enclaves (X.S. Xu et al., 2004; Du et al., 2004, 2007; Yang et al., 2007; Zhang et al., 2006; Wu et al., 2001; Wang et al., 2004a, 2004b, 2004c; X.C. Xu et al., 2008), but the validity of some ages is uncertain, because different dating techniques have yielded different ages for the same intru-sive body (Zhou et al., 1987;Wu et al., 1996). For example, 40Ar-39Ar dating of biotite from some of the Tongling rocks has yielded ages of 140–137 Ma for granodiorite, 137–136 Ma for quartz monzodiorite, 138–137 Ma for pyroxene monzodiorite, and 134 Ma for gabbro-diorite (Wu et al., 1996, 2001), but these ages only record the time at which the intrusive bod-ies cooled through ~300 °C, the Ar-Ar clo-sure temperature of biotite (Cliff, 1985). A few zircon SHRIMP U-Pb ages have recently become available (Yang et al., 2008; X.C. Xu et al., 2008), but these studies all focused on individual bodies . Here, we report new zircon
For permission to copy, contact editing@geosociety.org© 2013 Geological Society of America
GSA Bulletin; January/February 2014; v. 126; no. 1/2; p. 78–102; doi: 10.1130/B30613.1; 12 fi gures; 10 tables.
†E-mail: wucailai@126.com
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Petrogenesis of intermediate-acid intrusive rocks and zircon SHRIMP U-Pb dating in the Tongling area, Anhui Province (eastern China)
Geological Society of America Bulletin, January/February 2014 79
A
B
Figure 1. Geological sketch map of Tongling area, Anhui, China. R—Tertiary system; K2, K1—Upper and Lower Cretaceous system; J3—Upper Jurassic system; J1–2—Middle and Lower Jurassic system; T22-T23—Middle Triassic system; D3-T21—Upper Devonian system–Middle and Lower Triassic system; S—Silurian system; «—dating sample locations.
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80 Geological Society of America Bulletin, January/February 2014
SHRIMP ages for four plutons and discuss the petrogenesis of the intrusive rocks and their enclaves, as well as the tectonic environment in which they formed.
GEOLOGICAL SETTING
The continental core of China is composed of the South China block and the North China craton, which were welded together along the Dabie-Sulu orogenic belt between ca. 250 and 220 Ma. The South China block was formed by collision and amalgamation of the Yangtze and Cathaysian blocks at ca. 880 Ma. The Tongling area lies in the Yangtze polymetal-lic belt located in the northeastern part of the Yangtze block (Chang et al., 1991; S. Xu et al., 1992; Pan and Dong, 1999) (Fig. 1A). It is nearly perpendicular to the Tan-Lu fault, a major left-lateral, strike-slip fault that offsets the Dabie ultrahigh-pressure (UHP) metamor-phic belt several hundred kilometers to the northeast (Fig. 1A). The exact age of initiation of the Tan-Lu fault is uncertain, but 40Ar-39Ar dating of amphibole in ductile shear zones in the southern part of the fault suggests it was activated no later than 143 Ma, in response to rapid, highly oblique subduction of the paleo–Pacifi c plate beneath southeast China (Zhu et al., 2005). Gravity and aeromagnetic data suggest that the Tongling district is underlain by a regional, deep-seated, structural feature, the Tongling-Deijiahui structural zone (E-W dashed line in Fig. 1B; Chang et al., 1991, 1996; Lu et al., 2003). This feature is consid-ered by Wang and Cong (1998) to be an east-ward extension of the Xiaotian-Mozitan deep fault, which separates the Huaiyang arc fl ysch belt from the Dabie arc complex west of the Tan-Lu fault. We suggest that the magmatism and mineralization in the Tongling district may have been initiated during reactivation of this feature by transtensional movement on the Tan-Lu fault. Such reactivation may have caused crustal thinning and mantle upwelling, leading to partial melting of the upper mantle and lower crust, ultimately producing exten-sive intermediate-silicic magmatism in the region. Subduction of the paleo–Pacifi c plate also triggered extensive Jurassic and Creta-ceous magmatic activity elsewhere in south-east China and reactivated many preexisting faults and fracture zones (Wong et al., 2009).
Very few basement outcrops occur in the Yangtze block, and the Tongling area is domi-nated by a sequence of Paleozoic and Trias-sic marine carbonate, clastic, and siliceous sedimentary rocks, locally overlain by Cre-taceous to Middle Tertiary continental clastic and volcanic rocks (Xu and Zhou, 2001). The
Paleozoic and Triassic sedimentary rocks form a series of complex, NE-trending folds with thrust faults along their limbs (Zhai et al., 1996), many of which are cut by NW-trending brittle faults (Fig. 1B). Several possible base-ment faults, including the major Tongling-Deijiahui structural zone, have been identifi ed from geophysical data, and their intersections are thought to partially control the location of the Mesozoic intrusions (Ren et al., 1992; Zhai et al., 1996; Chang et al., 1996; Tang et al., 2004).
Seventy-six individual intrusions have been identifi ed in the Tongling area (Fig. 1B). Most of these are small stocks and dikes, gener-ally with outcrop areas of 0.05–3 km2, locally accompanied by small sills, apophyses, and veins. They are hosted mostly in Silurian to Triassic carbonates and quartz sandstones, and less commonly in siliceous rocks. The intrusive rocks are divided into a high-K, calc-alkaline series and a shoshonitic series on the basis of their petrochemistry.
The high-K, calc-alkaline rocks occur as NE-trending stocks in Carboniferous dolomitic limestone and Permian to Triassic carbon-ate rocks. Mineralized skarns hosting copper deposits are well developed in the carbonates (Chang and Liu, 1983), and these may represent remobilization of stratiform sulfi de deposits (Xu and Zhou, 2001). Many of the stocks lie along, or near, the axes of anticlines, but some irregu-lar bodies appear to have been emplaced at fault intersections. The calc-alkaline bodies contain abundant enclaves, chiefl y composed of micro-diorite, mafi c quartz monzodiorite, and mica-ceous material. Based on fi eld relationships, these rocks predate the shoshonitic bodies and have 40Ar-39Ar cooling ages ranging from 140 to 137 Ma for granodiorite, 137–136 Ma for quartz monzodiorite, and 134 Ma for gabbro-diorite (Wu et al., 2000).
The shoshonitic intrusive bodies are pyrox-ene monzodiorites that occur as NW- to NE-trending dikes or stocks. They typically have sharp contacts with the host Triassic carbonates and exhibit a preferred orientation of tabular plagioclase grains aligned parallel to the intru-sive contacts. The host carbonates have locally been converted to marble, scapolite, and skarn. All of these intrusive bodies contain abundant enclaves, including spinel pyroxenite, horn-blendite, hornfels, marble, and skarn. Some of the shoshonitic bodies were intruded along contacts between the high-K, calc-alkaline bodies and the host country rocks. The shosho-nitic rocks are commonly associated with gold, silver, lead, and zinc deposits. Their 40Ar/39Ar cooling ages range from 137 to 136 Ma (Wu et al., 2000).
LITHOLOGY OF THE INTRUSIVE ROCKS AND THEIR ENCLAVES
The high-K, calc-alkaline series rocks range in composition from gabbro-diorite through quartz monzodiorite and granodiorite to aplitic granite. Most of these rocks have hypidiomor-phic granular textures, except for the gabbro-diorites, which have gabbroic-diabasic textures, and some granodiorites with porphyritic tex-tures. The rock-forming minerals are plagio-clase, quartz, amphibole, biotite, and potassium feldspar, most of which range from 1.2 mm to 2.2 mm in size. Some porphyritic granodiorites have plagioclase phenocrysts up to ~6 mm. Many of the plagioclase grains have diffuse cores crowded with opaque inclusions; others contain inclusions of apatite. Some alkali feld-spar phenocrysts are rimmed by plagioclase, suggesting magma mixing (cf. Hibbard, 1991). These rocks contain three types of enclaves, which are different from those in the shoshonitic series. Their main features are:
(1) Mica-rich enclaves: These enclaves occur mainly in the granodiorites. They are black, elliptical bodies that range from 4 to 8 cm in their long direction, and they consist chiefl y of biotite (>80 modal%) and plagioclase (15%), with minor cordierite and almandine garnet. Accessory minerals include magnetite, pyrite, chalcopyrite, and sphalerite. Texturally, the enclaves consist of plagioclase phenocrysts imbedded in a granular mosaic of biotite. These enclaves are interpreted as partially melted resi-dues of metamorphic country rock.
(2) Mafic quartz monzodiorite enclaves: These enclaves occur in granodiorites and quartz monzodiorites. They are light gray in color, angular in shape, and 8–30 cm across. They have sharp contacts with the host rocks and are generally concentrated along intrusive contacts, suggesting that they represent a chilled border phase. The mineralogy of these enclaves is similar to that of the host rocks, i.e., plagio-clase + amphibole + alkali feldspar + quartz + biotite, but they contain a higher percentage of dark minerals, such as amphibole and bio-tite. Typical specimens have hypidiomorphic-granular textures and consist of 50–60 modal% plagioclase, 15%–20% euhedral amphibole, and 5%–10% quartz, accompanied by minor potas-sium feldspar and biotite.
(3) Microdiorite enclaves: These enclaves occur chiefl y in granodiorites but are also pres-ent in some quartz monzodiorites and porphy-ritic granodiorites. They are dark gray in color and vary in shape from ellipsoidal or spherical to irregular, fl ame-like forms. These enclaves generally range from 20 to 50 cm in diameter, with the largest up to 140 cm. They are typically
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Petrogenesis of intermediate-acid intrusive rocks and zircon SHRIMP U-Pb dating in the Tongling area, Anhui Province (eastern China)
Geological Society of America Bulletin, January/February 2014 81
distributed in the middle of the intrusive bodies, locally occurring in swarms or belts, and they have gradational contacts with the host rocks. These enclaves mostly contain the same miner-als as the host rocks, and some of the crystals have reaction rims, suggesting possible min-gling of magmas. Some enclaves are compos-ite features with dark central zones and lighter rims, probably also refl ecting magma mix-ing events. The minerals in these enclaves are plagio clase (40–50 modal%), amphibole (20%–30%), biotite (5%–8%), potassium feldspar (3%–7%), and quartz (3%–5%), with accessory apatite, titanite, zircon, magnetite, pyrite, and chalcopyrite. They have typical microgranular textures and locally contain plagioclase pheno-crysts with compositions similar to those of the groundmass grains. Some of the phenocrysts straddle the boundary between the enclave and host rock, and some have distinct, ellipsoidal cores with more calcic compositions than the rims. Plagioclase in the groundmass is typically reversely zoned and contains many inclusions of apatite. Some quartz contains abundant inclu-sions of fi brous amphibole. Such textures sug-gest that the enclave magma cooled rapidly in the host magma (Di et al., 2003).
The shoshonitic series includes pyroxene monzodiorite, monzonite, and quartz monzo-nite, all of which have idiomorphic-hypidiomor-phic granular textures. The main rock-forming minerals (which range from 1.5 to 2.2 mm in size) are clinopyroxene, plagioclase, potassium feldspar, and quartz, accompanied by subor-dinate biotite and amphibole. In addition, the rocks contain abundant, fi ne-grained (0.01–0.5 mm) accessory minerals such as magnetite, zircon, titanite, and apatite. Sulfi de minerals, including chalcopyrite, pyrite, sphalerite, and bornite, are also common.
Three types of enclaves also occur in these rocks: pyroxene-rich, amphibole-rich, and amphibole gabbro enclaves. The pyroxene- and amphibole-rich enclaves are coarser grained than the host rocks, but the minerals in the enclaves and host rock have the same compo-sitions. The amphibole gabbro enclaves are medium grained and have typical allotriomor-phic and hypidiomorphic textures, suggesting that they may have formed by mixing of mafi c and felsic magmas.
(1) Pyroxene-rich enclaves: These mainly occur in the pyroxene monzodiorites. They form black, irregular clots, 4–7 cm across, composed chiefl y of clinopyroxene (90–95 modal%), with subordinate spinel (2%–3%), amphibole (1%–2%), and accessory biotite, apatite, magnetite, and pyrite. Most of the enclaves have abundant, relatively large (3–5 mm), euhedral to rounded crystals of pyroxene in a matrix of the same
composition. All have sharp contacts with the host rock. We interpret these to be accumula-tions of early-formed pyroxene crystals that solidifi ed before they were dispersed by a new pulse of similar magma.
(2) Amphibole-rich enclaves: These occur in the monzonites and pyroxene monzodiorites. They are black, spherical or ellipsoidal, and 20–30 cm across. They consist chiefl y of amphi-bole (90–95 modal%) accompanied by minor clinopyroxene, biotite, and pyrite. Most of these enclaves have textures and grain sizes similar to those of pyroxene-rich varieties. Likewise, they all have sharp contacts with the host rocks, and they are typically marked by thin reaction rims of very fi ne-grained diopside. In some samples, tabular plagioclase in the host rock is oriented parallel to the enclave boundary. These enclaves are also interpreted as accumulations of amphi-bole dispersed by intrusion of a more mafi c magma as indicated by the pyroxene rims.
(3) Amphibole gabbro enclaves: These mainly occur in the monzonites and quartz monzonites. They are black, spherical clots ranging from 5 to 15 cm in diameter, composed of amphibole (60–70 modal%) with subordinate plagioclase (15%–27%), minor biotite (1%–3%), and traces of pyroxene and apatite. These enclaves have allotriomorphic to hypidiomorphic textures. On the basis of their textures and mineralogies, these enclaves most likely formed by mixing of mafi c and felsic magmas.
ANALYTICAL METHODS
Zircon SHRIMP U-Pb Dating
Four samples, HCJZK1, SYSZK3, FHS2, and YSZ3, each ~2 kg, were collected for zircon separation. The samples were crushed to 60–100 mesh, rinsed, and air-dried. Magnetic minerals were removed with a hand magnet, and the dense minerals were separated with heavy liquids. Zir-con grains were then handpicked under a binoc-ular microscope, mounted in epoxy along with zircon standard R33 (Black et al., 2004), and ground to about half their thickness. The zircon grains were photographed in refl ected light and imaged in cathodoluminescence mode (CL) to determine their internal structures and to select points for analysis. All of the analyses were carried out using the Stanford/U.S. Geological Survey (USGS) SHRIMP-RG (sensitive high-resolution ion microprobe, reverse geometry) facility. Age uncertainties are cited at the 95% confi dence level for the selected populations, and the internal precision for single analyses in tables and fi gures is 1σ. The age calculations were performed using the software Isoplot and Squid (Ludwig, 2001, 2003).
Whole-Rock Chemical Analysis
Thirty-six relatively fresh whole-rock and six enclave samples were selected for complete whole-rock chemical analysis at the Chinese Geological Experiment and Testing Center, Academy of Geological Sciences, Beijing. Major oxides and Sr, Ba, Zn, Rb, Nb, Zr, and Ga were determined by X-ray fl uorescence spec-trometry (XRF) on glass discs using National Standard GB/T 14506-1919. Total iron as Fe2O3 was determined by XRF, and FeO contents were determined by titration. Rare earth ele-ments (REE) and other trace elements, includ-ing Cu, Pb, Th, U, Hf, Ta, Sc, Cs, V, Co, Cr, and Ni, were determined by inductively coupled plasma–mass spectrometry (ICP-MS) with an Agilent 7500a system using National Standard LY/T 1253-1999. The analytical precision for the major oxides is better than 1%, whereas that for most trace elements is 5%.
Mineral Analysis
The compositions of plagioclase, potassium feldspar, amphibole, biotite, and pyroxene were determined on a Superprobe 733 at the Mineral-ogy Laboratory of the China University of Geo-sciences, Beijing, with an acceleration voltage of 15 kV and a beam current of 0.02 mA using natural and synthetic minerals for standards (Tables 3–7). The accuracy of the reported val-ues is 1%–5%, depending on the absolute ele-ment concentrations. Oxygen abundances in the silicate minerals are based upon stoichiometry (Deer et al., 1992).
ANALYTICAL RESULTS
Zircon SHRIMP U-Pb Dating
Each dated sample is described in this sec-tion, and the analytical results are presented in Table 1.
Sample HCJZK1Sample HCJZK1 is from a drill core (hole
ZK1) of the Huchengjian gabbro-diorite of the high-K, calc-alkaline series. The rock is dark gray in color and is characterized by abundant pyroxene and plagioclase phenocrysts of simi-lar size. The matrix has a diabasic texture and consists of tabular plagioclase with fi ne-grained interstitial pyroxene and magnetite (see Table 2 for a chemical analysis of this rock).
Zircon grains from this sample are prismatic, with length:width ratios generally between 1:1 and 2:1. CL images are uniformly gray with no evidence of zoning (Fig. 2A). Their U contents range from 524 to 1545 ppm, and Th ranges from 661 to 2752 ppm, yielding Th/U ratios of 1.3–2.7, indicating an igneous origin (Table 1).
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Wu et al.
82 Geological Society of America Bulletin, January/February 2014
TAB
LE 1
. ZIR
CO
N S
EN
SIT
IVE
HIG
H-R
ES
OLU
TIO
N IO
N M
ICR
OP
RO
BE
(S
HR
IMP
) U
-Pb
ISO
TO
PIC
DA
TA F
OR
INT
RU
SIV
E R
OC
KS
OF
TO
NG
LIN
G, A
NH
UI P
RO
VIN
CE
, CH
INA
Spo
t nam
e
206 P
b C(%
)U
(ppm
)T
h(p
pm)
232 T
h/23
8 U
206 P
b R(p
pm)
Dis
c.(%
)To
tal 2
38U
/206
Pb
% e
rrTo
tal 2
07P
b/20
6 Pb
% e
rr20
6 Pb/
238 U
% e
rr20
7 Pb/
206 U
% e
rr
206 P
b/23
8 U a
ge
(Ma)
1σ e
rrH
CJZ
K1-
10.
2378
314
011.
8514
.7−2
545
.65
0.5
0.05
001.
90.
0219
0.5
0.04
812.
614
01
HC
JZK
1-2
0.03
812
1055
1.34
15.5
−50
45.0
00.
50.
0486
1.8
0.02
220.
50.
0474
2.2
142
1H
CJZ
K1-
30.
0110
5227
052.
6620
.2−6
944
.77
0.5
0.04
881.
60.
0223
0.5
0.04
692.
414
21
HC
JZK
1-4
0.10
1046
1716
1.69
20.4
−20
44.1
10.
40.
0497
1.5
0.02
260.
40.
0483
2.0
144
1H
CJZ
K1-
50.
0115
4527
521.
8430
.5−1
743
.53
0.4
0.04
911.
40.
0230
0.4
0.04
841.
614
61
HC
JZK
1-6
0.15
1207
2151
1.84
23.2
−744
.64
0.5
0.05
011.
50.
0224
0.5
0.04
872.
014
31
HC
JZK
1-7
0.03
1092
1673
1.58
21.1
−34
44.4
70.
40.
0492
1.5
0.02
250.
40.
0479
2.0
143
1H
CJZ
K1-
80.
0753
372
51.
4110
.120
45.1
90.
60.
0494
3.1
0.02
210.
60.
0494
3.1
141
1H
CJZ
K1-
90.
2252
466
11.
309.
9−1
445
.38
0.6
0.05
062.
20.
0220
0.7
0.04
843.
214
01
HC
JZK
1-10
0.01
887
1471
1.71
17.2
−24
44.2
10.
50.
0490
1.8
0.02
260.
50.
0482
2.0
144
1H
CJZ
K1-
110.
0385
112
881.
5616
.6−2
643
.95
0.5
0.04
921.
80.
0227
0.5
0.04
822.
114
51
SY
SZ
K03
-10.
2721
316
30.
794.
16
44.9
81.
00.
0510
3.4
0.02
221.
00.
0490
4.4
141
1S
YS
ZK
03-2
0.13
1086
1118
1.06
20.9
044
.68
0.4
0.04
991.
50.
0224
0.4
0.04
891.
814
31
SY
SZ
K03
-30.
1195
976
70.
8318
.827
43.9
00.
50.
0498
1.7
0.02
280.
50.
0498
1.7
145
1S
YS
ZK
03-4
0.47
503
529
1.09
9.4
−13
45.7
70.
60.
0525
2.2
0.02
170.
70.
0484
4.2
139
1S
YS
ZK
03-5
0.24
955
1705
1.84
18.3
−30
44.7
60.
50.
0508
1.7
0.02
230.
50.
0480
2.8
142
1S
YS
ZK
03-6
0.38
419
740
1.82
7.8
1746
.00
0.7
0.05
182.
50.
0217
0.7
0.04
933.
713
81
SY
SZ
K03
-70.
4328
427
91.
025.
4−9
244
.71
0.9
0.05
232.
90.
0222
0.9
0.04
637.
414
21
SY
SZ
K03
-80.
0165
966
11.
0412
.34
46.0
20.
60.
0489
2.0
0.02
170.
60.
0489
2.0
139
1S
YS
ZK
03-9
0.53
189
133
0.73
3.6
7045
.24
1.0
0.05
313.
50.
0220
1.0
0.05
104.
614
01
SY
SZ
K03
-10
0.24
367
461
1.30
7.2
−58
43.6
20.
80.
0508
2.9
0.02
280.
90.
0472
5.0
146
1S
YS
ZK
03-1
10.
0983
914
161.
7416
.2−8
344
.38
0.5
0.04
821.
80.
0225
0.5
0.04
652.
514
41
FH
S2-
10.
8330
479
0.27
22.6
4211
.54
0.5
0.06
481.
30.
0866
0.5
0.06
451.
453
13
FH
S2-
20.
0751
842
90.
8510
.0−1
5144
.48
0.6
0.04
952.
40.
0224
0.7
0.04
474.
614
31
FH
S2-
30.
6422
020
10.
9421
.519
8.78
0.6
0.06
771.
30.
1137
0.6
0.06
651.
669
14
FH
S2-
40.
2547
342
20.
929.
065
45.1
40.
70.
0508
2.3
0.02
220.
70.
0508
2.3
141
1F
HS
2-5
0.66
225
204
0.94
4.3
−20
45.2
41.
00.
0541
3.3
0.02
191.
00.
0483
7.0
140
1F
HS
2-6
0.22
540
361
0.69
10.6
−91
43.9
80.
60.
0507
2.1
0.02
260.
60.
0463
4.3
145
1F
HS
2-7
0.07
573
481
0.87
10.9
−75
45.0
50.
60.
0483
2.1
0.02
220.
60.
0467
2.7
142
1F
HS
2-8
0.05
515
452
0.91
9.9
−98
44.5
10.
60.
0493
2.2
0.02
240.
70.
0461
5.1
143
1F
HS
2-9
0.39
346
255
0.76
6.6
1144
.81
0.8
0.05
192.
70.
0222
0.8
0.04
924.
814
21
FH
S2-
100.
5823
111
50.
524.
4−2
744
.70
1.0
0.05
353.
30.
0222
1.0
0.04
816.
814
21
FH
S2-
111.
5223
311
00.
497.
513
426
.55
0.8
0.06
302.
40.
0375
0.8
0.05
874.
523
52
YS
Z3-
10.
3035
729
0.08
6.9
−134
44.2
50.
70.
0513
2.6
0.02
240.
80.
0451
6.0
144
1Y
SZ
3-2
0.79
242
240.
104.
8−9
143
.42
0.9
0.05
523.
10.
0228
1.0
0.04
638.
314
61
YS
Z3-
30.
1125
026
0.11
5.0
−50
43.1
11.
10.
0499
3.2
0.02
311.
10.
0475
4.2
148
2Y
SZ
3-4
0.39
294
180.
065.
8−4
843
.68
0.8
0.05
212.
90.
0228
0.9
0.04
754.
914
51
YS
Z3-
51.
3826
077
0.31
99.0
42.
250.
50.
1617
0.4
0.44
340.
50.
1615
0.4
2330
12*
YS
Z3-
61.
2133
136
0.11
7.0
4940
.85
0.8
0.05
082.
90.
0245
0.8
0.05
082.
915
61
YS
Z3-
73.
3818
293
0.53
62.9
132.
480.
60.
1614
0.7
0.40
280.
60.
1612
0.7
2104
13*
YS
Z3-
80.
1833
623
0.07
6.7
842
.78
0.8
0.05
052.
80.
0233
0.8
0.04
933.
314
91
YS
Z3-
90.
4230
828
0.09
6.1
−65
43.2
40.
80.
0524
2.9
0.02
300.
90.
0470
6.5
147
1Y
SZ
3-10
0.24
357
370.
117.
0−7
443
.82
0.8
0.05
092.
70.
0227
0.8
0.04
684.
914
51
YS
Z3-
110.
2938
645
0.12
7.6
7243
.33
0.7
0.05
132.
60.
0231
0.7
0.05
132.
614
71
Not
e:20
6 Pb C
and
206
Pb R
are
com
mon
and
rad
ioge
nic
port
ions
, res
pect
ivel
y.*2
06P
b/20
7 Pb
age.
-
Petrogenesis of intermediate-acid intrusive rocks and zircon SHRIMP U-Pb dating in the Tongling area, Anhui Province (eastern China)
Geological Society of America Bulletin, January/February 2014 83
TAB
LE 2
. WH
OLE
-RO
CK
GE
OC
HE
MIC
AL
AN
ALY
SE
S O
F IN
TR
US
IVE
RO
CK
S A
ND
EN
CLA
VE
S O
F T
HE
TO
NG
LIN
G D
IST
RIC
T
Hig
h-K
, cal
c-al
kalin
e se
ries
Sam
ples
HC
JZK
1S
ML3
MJ1
JGS
2JG
S9
DT
S2
QS
J1D
GS
1JT
4D
BZ
3D
BZ
1T
EB
D1
TE
BD
2T
GS
1R
ocks
GB
DG
BD
QM
DP
QM
DQ
MD
QM
DQ
MD
QM
DQ
MD
QM
DQ
MD
QM
DQ
MD
QM
DS
iO2
52.6
454
.53
54.3
960
.21
61.8
863
.66
59.0
160
.86
60.1
059
.95
59.1
560
.29
61.7
262
.62
TiO
21.
150.
900.
820.
580.
550.
570.
720.
770.
640.
750.
750.
650.
670.
56A
l 2O3
17.3
217
.70
15.5
316
.11
16.2
815
.69
16.4
915
.75
16.1
516
.26
16.5
016
.44
16.5
216
.82
Fe 2
O3
3.59
2.72
3.81
1.50
2.32
1.82
2.54
2.16
3.13
2.74
2.23
0.72
2.07
1.32
FeO
5.36
5.73
2.48
2.50
2.62
4.07
3.12
3.44
2.84
2.75
2.19
3.46
3.83
1.95
MnO
0.18
0.18
0.12
0.07
0.07
0.12
0.11
0.12
0.06
0.06
0.06
0.13
0.13
0.07
MgO
3.45
3.06
2.09
1.29
1.36
1.43
2.40
2.12
1.34
2.69
2.53
1.73
1.77
1.47
CaO
8.09
6.72
6.75
5.58
4.63
4.06
5.69
5.81
4.92
6.42
6.36
7.66
5.15
5.86
Na 2
O3.
673.
773.
284.
074.
254.
034.
184.
384.
245.
005.
483.
964.
134.
97K
2O
2.17
2.18
2.80
3.39
3.23
3.01
3.01
2.82
2.99
2.70
1.96
3.38
2.79
2.94
P2O
50.
410.
390.
370.
240.
240.
230.
450.
330.
250.
310.
280.
290.
300.
27LO
I0.
571.
063.
231.
540.
980.
761.
840.
691.
290.
851.
130.
840.
680.
48S
0.12
0.09
0.01
0.10
0.02
0.21
0.67
0.16
0.52
0.27
0.27
0.02
0.07
0.01
CO
20.
220.
384.
992.
291.
020.
550.
560.
341.
080.
500.
900.
560.
200.
14To
tal
98.9
499
.41
100.
6799
.47
99.4
510
0.21
100.
7999
.75
99.5
510
1.25
99.7
910
0.13
100.
0399
.48
ALK
6.0
6.1
6.6
7.8
7.7
7.1
7.4
7.3
7.5
7.7
7.6
7.4
7.0
8.0
Na 2
O/K
2O
1.7
1.7
1.2
1.2
1.3
1.3
1.4
1.6
1.4
1.9
2.8
1.2
1.5
1.7
Fe*
0.71
0.72
0.74
0.74
0.77
0.79
0.69
0.71
0.81
0.66
0.62
0.69
0.76
0.68
Fe#
0.61
0.65
0.54
0.66
0.66
0.74
0.57
0.62
0.68
0.51
0.46
0.67
0.68
0.57
MA
LI–2
.26
–0.7
9–0
.72
1.97
2.93
3.02
1.54
1.42
2.39
1.28
1.11
−0.3
21.
792.
07A
SI
0.77
0.87
0.77
0.8
0.87
0.92
0.83
0.77
0.86
0.72
0.74
0.69
0.88
0.78
AI
0.14
0.14
0.14
0.13
0.13
0.12
0.13
0.12
0.13
0.11
0.1
0.13
0.13
0.12
An
43.9
43.9
41.1
31.3
30.5
31.7
3328
.831
.124
.824
33.8
34.4
26.2
Cr
48.6
38.3
2064
.162
.198
61.2
67.4
53.8
86.7
45.7
129.
171
.236
.9N
i12
.610
.411
.711
.310
.310
.913
.210
.38.
813
.911
.010
.910
.913
.4V
191
160
124
7068
6658
8682
112
9073
7859
Co
23.8
2115
.99.
99.
512
.311
.415
.310
.210
9.4
9.3
137.
8R
b66
6795
8786
8778
6295
4131
9270
74S
r70
372
356
689
390
276
311
9898
175
778
075
283
677
810
99Y
26.4
18.4
18.3
12.5
12.9
14.5
17.8
19.8
20.5
16.9
17.8
19.7
1913
.8Z
r21
215
673
192
132
245
262
171
178
226
256
186
181
184
Nb
19.2
13.3
17.7
15.9
16.3
16.9
15.9
15.5
15.8
14.7
15.5
17.1
16.9
16B
a63
965
160
891
411
3110
3692
892
388
110
4578
890
191
410
45H
f5.
213.
54.
124.
125.
175.
035.
284.
843.
784.
824.
165.
66.
15.
6Ta
0.92
0.36
0.68
0.71
0.79
1.05
0.97
0.86
0.67
0.91
0.85
0.77
0.97
0.72
(con
tinue
d)
-
Wu et al.
84 Geological Society of America Bulletin, January/February 2014
TAB
LE 2
. WH
OLE
-RO
CK
GE
OC
HE
MIC
AL
AN
ALY
SE
S O
F IN
TR
US
IVE
RO
CK
S A
ND
EN
CLA
VE
S O
F T
HE
TO
NG
LIN
G D
IST
RIC
T (c
ontin
ued
)
Hig
h-K
, cal
c-al
kalin
e se
ries
Sam
ples
HC
JZK
1S
ML3
MJ1
JGS
2JG
S9
DT
S2
QS
J1D
GS
1JT
4D
BZ
3D
BZ
1T
EB
D1
TE
BD
2T
GS
1R
ocks
GB
DG
BD
QM
DP
QM
DQ
MD
QM
DQ
MD
QM
DQ
MD
QM
DQ
MD
QM
DQ
MD
QM
DT
h6.
607.
5612
.06
9.73
10.1
711
.14
9.44
8.72
8.50
9.41
10.2
211
.66
9.82
8.93
U1.
322.
262.
102.
302.
702.
022.
832.
482.
402.
352.
872.
602.
601.
35C
u75
4128
7363
3690
122
221
43
1512
240
Zn
131
115
8644
5595
6876
6233
4087
9457
Pb
52.2
53.5
2421
.114
.819
34.3
21.8
41.5
11.6
16.6
27.1
25.3
10.8
Sc
0.28
12.2
39
5.23
5.14
5.89
5.36
8.34
6.12
9.63
9.2
7.35
7.66
5.56
Ag
0.2
0.29
0.1
0.1
0.1
0.1
0.2
0.2
0.3
0.2
0.1
0.3
0.1
0.3
As
33.2
10.3
2.8
3.6
24.
35.
67.
827
.82.
72.
94.
63.
32.
5B
i1.
60.
30.
20.
30.
20.
80.
40.
91.
70.
80.
70.
90.
30.
2S
b0.
200.
710.
240.
300.
300.
520.
380.
840.
210.
800.
740.
740.
420.
20G
a28
.417
18.6
1919
.622
.618
.216
.720
.517
15.7
19.2
18.4
22.2
Li31
.720
.825
.49.
510
.716
.89.
113
.68.
79.
79.
213
.816
.613
Be
1.9
1.94
2.51
2.15
2.18
2.13
2.26
2.18
1.9
1.88
1.96
2.39
2.19
2.28
Mo
2.4
1.6
1.0
1.4
1.2
2.5
1.6
1.2
2.2
0.8
1.0
2.5
1.0
1.5
La37
.928
.645
.335
.134
.734
.438
.439
.439
.734
.537
.841
.040
.739
.1C
e73
.055
.785
.365
.065
.564
.779
.278
.372
.265
.475
.180
.276
.876
.2P
r9.
86.
69.
67.
37.
47.
39.
38.
68.
97.
58.
99.
18.
78.
8N
d34
.70
25.2
033
.60
25.7
025
.90
26.4
031
.40
33.4
030
.70
27.2
031
.90
31.9
031
.10
31.4
0S
m7.
935.
256.
484.
865.
005.
026.
246.
336.
455.
446.
216.
346.
066.
05E
u1.
861.
441.
581.
251.
271.
322.
111.
691.
431.
451.
581.
621.
531.
54G
d5.
933.
974.
503.
333.
413.
428.
245.
254.
483.
934.
314.
614.
384.
04T
b1.
150.
630.
660.
530.
610.
630.
990.
690.
840.
610.
740.
720.
760.
67D
y5.
333.
713.
682.
612.
642.
964.
563.
803.
993.
413.
653.
953.
832.
92H
o1.
070.
670.
690.
440.
470.
530.
940.
700.
800.
610.
680.
750.
680.
51E
r3.
141.
831.
811.
101.
111.
332.
451.
952.
311.
711.
791.
842.
051.
15T
m0.
480.
290.
370.
260.
210.
290.
310.
270.
390.
360.
390.
340.
230.
27Y
b2.
301.
802.
672.
101.
861.
502.
091.
910.
811.
751.
691.
160.
721.
71Lu
0.35
0.28
0.41
0.32
0.30
0.25
0.27
0.28
0.12
0.27
0.27
0.19
0.11
0.27
Σ RE
E18
513
619
715
015
015
018
718
317
315
417
518
417
817
5E
u*/E
u0.
800.
940.
860.
910.
900.
930.
910.
880.
780.
920.
890.
880.
870.
91R
b/S
r0.
090.
090.
170.
100.
090.
110.
060.
060.
130.
050.
040.
110.
090.
07B
a/R
b9.
89.
76.
410
.513
.212
.011
.914
.89.
325
.525
.49.
813
.114
.2S
r/Y
26.6
39.3
30.9
71.4
69.9
52.6
67.3
49.5
36.9
46.2
42.2
42.4
40.9
79.6
(con
tinue
d)
-
Petrogenesis of intermediate-acid intrusive rocks and zircon SHRIMP U-Pb dating in the Tongling area, Anhui Province (eastern China)
Geological Society of America Bulletin, January/February 2014 85
TAB
LE 2
. WH
OLE
-RO
CK
GE
OC
HE
MIC
AL
AN
ALY
SE
S O
F IN
TR
US
IVE
RO
CK
S A
ND
EN
CLA
VE
S O
F T
HE
TO
NG
LIN
G D
IST
RIC
T (c
ontin
ued
)
Hig
h-K
, cal
c-al
kalin
e se
ries
(HA
C)
Enc
lave
s (H
AC
)
Sam
ples
TG
S2
FH
S2
FH
S1
NH
C1
ST
J3S
TJ5
QT
Y1
QT
Y2
SJD
LC1
XQ
T4
YS
Z3
TG
S3
FH
SB
4T
EB
DB
6R
ocks
QM
DG
DG
DG
DG
DG
DG
DP
GD
PG
DP
GD
PG
DP
GV
MD
EM
QM
ES
iO2
62.7
463
.12
63.5
862
.85
64.2
364
.33
61.1
661
.72
63.7
763
.59
58.1
975
.37
59.5
854
.50
TiO
20.
550.
560.
570.
600.
500.
480.
520.
420.
490.
320.
470.
110.
930.
90A
l 2O3
16.7
315
.48
16.2
616
.13
16.3
816
.40
16.3
416
.08
15.5
314
.49
15.1
412
.69
16.3
515
.09
Fe 2
O3
2.52
2.12
2.12
1.72
1.87
1.53
1.25
0.55
2.23
1.05
2.11
0.51
4.13
3.19
FeO
2.42
3.06
2.90
1.55
2.58
2.74
2.68
2.09
2.94
2.18
2.76
0.97
3.29
5.14
MnO
0.11
0.08
0.09
0.07
0.08
0.07
0.03
0.05
0.07
0.10
0.11
0.04
0.09
0.20
MgO
1.44
1.22
1.46
1.44
1.22
1.23
1.06
0.73
1.33
0.89
1.38
0.16
2.65
4.69
CaO
4.72
3.94
4.18
5.03
3.60
3.94
3.96
4.48
4.14
4.36
6.46
1.64
3.44
7.42
Na 2
O4.
813.
934.
754.
685.
065.
094.
565.
124.
111.
411.
463.
873.
853.
82K
2O
2.72
3.23
3.01
3.33
2.53
2.70
2.78
3.41
3.10
3.88
2.71
3.96
2.51
2.33
P2O
50.
280.
250.
250.
230.
210.
210.
230.
180.
220.
170.
220.
030.
430.
24LO
I0.
581.
310.
622.
200.
750.
662.
862.
160.
923.
103.
520.
241.
770.
76S
0.01
0.16
0.02
0.34
0.09
0.36
0.65
0.21
0.33
0.33
0.03
0.04
0.96
0.82
CO
20.
271.
810.
360.
260.
950.
952.
203.
080.
824.
275.
690.
160.
100.
57To
tal
99.9
010
0.27
100.
1710
0.43
100.
0510
0.69
100.
2810
0.28
100.
0010
0.14
100.
2599
.79
100.
0899
.67
ALK
7.6
7.4
7.8
8.2
7.7
7.9
7.8
9.0
7.4
5.7
4.6
7.9
6.5
6.3
Na 2
O/K
2O
1.8
1.2
1.6
1.4
2.0
1.9
1.6
1.5
1.3
0.4
0.5
1.0
1.5
1.6
Fe*
0.77
0.8
0.76
0.68
0.77
0.76
0.78
0.77
0.79
0.77
0.77
0.9
0.73
0.62
Fe#
0.63
0.71
0.67
0.52
0.68
0.69
0.72
0.74
0.69
0.71
0.67
0.86
0.55
0.52
MA
LI2.
843.
323.
613.
054.
063.
93.
574.
273.
131.
01−2
.52
6.23
3−1
.3A
SI
0.88
0.92
0.88
0.8
0.94
0.9
0.94
0.8
0.89
1.02
0.9
0.93
1.11
0.69
AI
0.12
0.13
0.12
0.12
0.11
0.11
0.12
0.12
0.12
0.17
0.17
0.1
0.13
0.11
An
28.3
31.2
26.1
2525
.33
24.4
529
.21
2029
.83
63.2
667
.52
17.4
21.6
747
.92
Cr
57.3
122.
258
79.3
129.
410
4.1
74.5
51.6
74.3
23.1
19.2
25.2
16.2
83.9
Ni
11.1
9.9
10.0
12.6
13.0
12.0
14.8
12.1
10.1
5.8
6.9
9.1
6.2
17.9
V61
6672
5759
5465
5463
3554
1713
220
7C
o11
9.4
8.4
11.3
9.8
10.7
10.4
1310
.66.
38.
76.
615
.124
Rb
7213
411
475
7270
7885
112
167
105
6511
576
Sr
1040
699
809
961
1188
1019
705
703
697
204
448
292
690
593
Y15
.516
.117
.413
.211
.911
.88.
28.
614
.713
16.5
7.2
27.6
13.7
Zr
189
187
187
196
175
172
122
118
162
161
4312
113
618
4N
b16
.917
.517
.713
18.8
17.9
16.1
15.3
16.8
18.2
13.5
12.6
145
Ba
1098
819
898
941
1056
951
681
803
898
726
489
695
797
829
Hf
5.9
6.13
6.78
3.98
54.
54.
215.
274.
75.
15.
43.
9n.
d.n.
d.Ta
0.85
0.88
1.26
0.82
0.67
0.56
0.75
0.81
0.76
0.82
0.61
0.67
n.d.
n.d.
(con
tinue
d)
-
Wu et al.
86 Geological Society of America Bulletin, January/February 2014
TAB
LE 2
. WH
OLE
-RO
CK
GE
OC
HE
MIC
AL
AN
ALY
SE
S O
F IN
TR
US
IVE
RO
CK
S A
ND
EN
CLA
VE
S O
F T
HE
TO
NG
LIN
G D
IST
RIC
T (c
ontin
ued
)
Hig
h-K
, cal
c-al
kalin
e se
ries
(HA
C)
Enc
lave
s (H
AC
)
Sam
ples
TG
S2
FH
S2
FH
S1
NH
C1
ST
J3S
TJ5
QT
Y1
QT
Y2
SJD
LC1
XQ
T4
YS
Z3
TG
S3
FH
SB
4T
EB
DB
6R
ocks
QM
DG
DG
DG
DG
DG
DG
DP
GD
PG
DP
GD
PG
DP
GV
MD
EM
QM
ET
h9.
3711
.35
9.95
7.81
11.6
911
.42
9.59
10.2
611
.69
16.4
48.
4116
.08
15.0
09.
00U
1.12
2.67
2.25
2.57
2.15
2.19
2.60
2.80
2.56
1.38
1.50
2.42
n.d.
n.d.
Cu
1327
514
038
2568
9344
85
712
760
420
2Z
n91
4258
6771
4317
764
3859
7398
7114
8P
b20
.819
.718
.131
.217
7.3
16.3
31.1
24.1
15.7
19.4
60.8
109
12.5
12.7
Sc
5.4
6.13
6.4
4.21
4.7
4.58
5.65
4.86
6.12
2.21
6.41
1.51
n.d.
n.d.
Ag
0.1
0.5
0.3
0.1
0.09
0.1
0.4
0.19
0.12
0.12
0.13
0.23
0.63
0.56
As
1.4
3.3
3.6
2.5
2.9
12.7
516.
24.
42.
811
.747
.81.
85.
2B
i0.
27.
30.
40.
40.
30.
41.
41.
10.
40.
30.
13.
10.
30.
1S
b0.
240.
460.
401.
381.
300.
301.
200.
470.
530.
430.
5410
.50
0.40
0.61
Ga
24.4
20.9
20.9
21.1
23.2
2220
.822
.519
.718
.517
25.2
19.7
15.9
Li24
.910
.98.
415
.216
.714
.818
.515
.810
.19.
826
10.9
20.5
37.2
Be
2.39
2.39
2.46
2.23
2.43
2.27
2.14
1.98
2.2
2.58
1.84
3.07
1.5
0.96
Mo
0.9
3.3
2.1
1.2
1.4
2.2
3.1
1.3
1.6
1.8
0.6
1.2
2.1
3.6
La40
.538
.239
.937
.341
.443
.332
.429
.533
.836
.426
.317
.057
.026
.3C
e78
.871
.375
.768
.280
.984
.562
.258
.264
.262
.651
.727
.811
3.9
47.2
Pr
9.1
8.2
8.6
7.4
9.3
9.6
7.0
6.6
7.4
6.6
6.2
3.0
12.8
5.2
Nd
32.7
028
.90
30.7
025
.90
32.7
033
.60
24.6
023
.20
25.9
021
.10
23.0
09.
5046
.40
20.7
0S
m6.
375.
445.
844.
445.
905.
984.
504.
324.
943.
754.
531.
908.
204.
30E
u1.
621.
341.
391.
391.
381.
411.
091.
021.
200.
901.
250.
541.
601.
20G
d4.
313.
653.
874.
203.
513.
552.
782.
713.
342.
433.
361.
417.
604.
90T
b0.
680.
550.
630.
490.
490.
490.
470.
470.
600.
400.
520.
211.
200.
60D
y3.
283.
223.
502.
532.
572.
531.
811.
862.
932.
373.
221.
216.
003.
50H
o0.
590.
580.
630.
490.
410.
400.
300.
310.
530.
470.
580.
241.
200.
60E
r1.
371.
541.
671.
351.
060.
990.
620.
691.
381.
351.
650.
672.
901.
40T
m0.
210.
310.
330.
190.
130.
110.
150.
110.
190.
320.
290.
110.
480.
26Y
b1.
211.
401.
611.
151.
451.
001.
161.
301.
301.
741.
951.
342.
701.
20Lu
0.20
0.22
0.26
0.14
0.23
0.16
0.25
0.21
0.21
0.27
0.30
0.22
0.40
0.20
ΣRE
E18
116
517
515
518
118
813
913
014
814
112
565
262
118
Eu*
/Eu
0.90
0.88
0.85
0.98
0.86
0.87
0.88
0.86
0.86
0.86
0.95
0.98
0.61
0.80
Rb/
Sr
0.07
0.19
0.14
0.08
0.06
0.07
0.11
0.12
0.16
0.82
0.23
0.22
0.17
0.13
Ba/
Rb
15.3
6.1
7.9
12.5
14.7
13.7
8.8
9.5
8.0
4.3
4.7
10.7
6.9
10.9
Sr/
Y67
.143
.446
.572
.899
.886
.486
.081
.747
.415
.727
.240
.625
.043
.3(c
ontin
ued
)
-
Petrogenesis of intermediate-acid intrusive rocks and zircon SHRIMP U-Pb dating in the Tongling area, Anhui Province (eastern China)
Geological Society of America Bulletin, January/February 2014 87
TAB
LE 2
. WH
OLE
-RO
CK
GE
OC
HE
MIC
AL
AN
ALY
SE
S O
F IN
TR
US
IVE
RO
CK
S A
ND
EN
CLA
VE
S O
F T
HE
TO
NG
LIN
G D
IST
RIC
T (c
ontin
ued
)
)O
HS(
sevalcnE
)O
HS(
seirescitinohso h
S)
AC
H(s ev alcn
E
Sam
ples
FH
SB
7JG
6X
QT
3C
S1
DS
8D
S4
XS
1X
S5
SJC
1S
A1
SM
LM
BS
6B
MS
2C
SB
1R
ocks
MR
EP
MD
PM
DM
zQ
MQ
MQ
MQ
MD
QM
QM
QM
PC
EH
CE
HG
ES
iO2
42.0
750
.81
55.5
257
.32
56.3
261
.69
58.8
561
.58
59.3
557
.46
62.3
041
.96
34.8
240
.94
TiO
21.
881.
210.
871.
050.
990.
650.
710.
680.
790.
700.
480.
402.
452.
45A
l 2O3
20.4
417
.16
16.6
016
.67
16.4
115
.59
16.1
615
.83
15.6
815
.99
16.0
212
.13
13.1
411
.98
Fe 2
O3
5.91
2.71
3.84
0.97
2.96
0.82
1.97
1.36
2.25
3.42
1.00
2.79
7.15
9.20
FeO
9.47
5.55
3.32
4.54
5.07
3.98
2.47
2.93
3.91
3.02
2.80
3.97
9.16
8.34
MnO
0.24
0.14
0.18
0.08
0.16
0.08
0.10
0.09
0.11
0.12
0.10
0.28
0.18
0.20
MgO
6.04
3.26
1.91
1.73
2.55
2.09
1.89
2.24
2.49
1.05
0.99
11.4
78.
576.
86C
aO3.
909.
636.
896.
275.
843.
906.
474.
655.
666.
002.
2118
.41
13.4
810
.88
Na 2
O2.
593.
734.
494.
704.
413.
904.
353.
764.
274.
460.
971.
881.
912.
51K
2O
5.06
3.10
3.11
3.36
2.93
5.10
4.75
4.72
3.77
3.19
10.1
21.
160.
952.
05P
2O
50.
160.
560.
450.
350.
340.
210.
310.
220.
310.
290.
191.
851.
721.
90LO
I1.
310.
761.
100.
501.
011.
060.
701.
130.
991.
321.
692.
682.
870.
84S
0.03
1.30
0.04
0.84
0.83
1.02
0.86
0.45
0.20
0.21
1.08
0.37
0.52
1.09
CO
20.
140.
341.
512.
550.
050.
230.
200.
500.
382.
620.
800.
492.
550.
84To
tal
99.2
410
0.26
99.8
310
0.93
99.8
710
0.32
99.7
910
0.14
100.
1699
.85
100.
7599
.84
99.4
710
0.08
ALK
7.8
7.0
7.8
8.3
7.5
9.2
9.3
8.7
8.2
8.0
11.4
1.7
3.1
4.7
Na 2
O/K
2O
0.5
1.2
1.4
1.4
1.5
0.8
0.9
0.8
1.1
1.4
0.1
0.7
2.0
1.2
Fe*
0.7
0.7
0.78
0.75
0.75
0.68
0.69
0.64
0.7
0.85
0.78
0.36
0.64
0.71
Fe#
0.61
0.63
0.63
0.72
0.67
0.66
0.57
0.57
0.61
0.74
0.74
0.26
0.52
0.55
MA
LI3.
84−2
.86
0.73
1.84
1.53
5.2
2.68
3.91
2.41
1.72
9.14
−17.
3−1
1.4
−6.4
9A
SI
1.23
0.65
0.73
0.75
0.8
0.83
0.68
0.81
0.75
0.75
0.98
0.36
0.49
0.5
AI
0.22
0.14
0.13
0.13
0.12
0.15
0.14
0.15
0.13
0.12
0.26
0.12
0.12
0.1
An
40.8
339
.929
.626
.730
.523
.222
.328
25.7
27.3
53.6
7268
.349
.03
Cr
180.
724
.531
.818
.493
.820
9.6
115.
116
3.2
46.6
55.1
47.5
24.4
22.2
18.2
Ni
79.5
14.4
9.9
12.5
13.4
14.3
11.4
12.4
13.2
11.9
7.1
9.0
9.2
8.5
V30
717
812
812
814
373
8582
100
106
5262
5753
5C
o37
.529
.413
.69.
821
.214
.711
.214
.516
.610
.18.
88.
212
.646
.7R
b32
193
107
6087
162
104
130
8710
22.
7950
6277
Sr
669
1116
1109
952
720
665
940
719
1031
903
638
300
773
682
Y25
.924
.923
.320
.918
.513
.817
.615
.121
2016
.97.
620
.628
.5Z
r20
226
919
420
115
915
919
017
217
820
118
224
6977
Nb
2321
.118
.615
.717
.917
.118
.917
17.5
1816
.96
86
Ba
1684
752
944
788
789
966
944
972
916
943
1055
280
322
373
Hf
n.d.
6.23
5.7
5.19
4.71
5.74
5.2
5.6
4.2
4.9
5.5
n.d.
n.d.
n.d.
Tan.
d.0.
940.
720.
880.
951.
210.
750.
830.
540.
860.
86n.
d.n.
d.n.
d.(c
ontin
ued
)
-
Wu et al.
88 Geological Society of America Bulletin, January/February 2014
TAB
LE 2
. WH
OLE
-RO
CK
GE
OC
HE
MIC
AL
AN
ALY
SE
S O
F IN
TR
US
IVE
RO
CK
S A
ND
EN
CLA
VE
S O
F T
HE
TO
NG
LIN
G D
IST
RIC
T (c
ontin
ued
)
)O
HS(
sevalcnE
)O
HS(
seirescitinohs oh
S)
AC
H(sevalcn
E
Sam
ples
FH
SB
7JG
6X
QT
3C
S1
DS
8D
S4
XS
1X
S5
SJC
1S
A1
SM
LM
BS
6B
MS
2C
SB
1R
ocks
MR
EP
MD
PM
DM
zQ
MQ
MQ
MQ
MD
QM
QM
QM
PC
EH
CE
HG
ET
h35
.00
11.0
111
.14
9.20
11.6
311
.54
10.7
410
.50
11.2
29.
409.
666.
007.
0011
.00
Un.
d.3.
362.
182.
622.
542.
962.
322.
162.
422.
052.
21n.
d.n.
d.n.
d.C
u83
356
1412
697
192
7314
195
137
2891
133
289
Zn
335
7415
187
9653
5857
101
9810
930
321
212
1P
b12
.226
.536
.632
.823
29.9
22.3
23.3
47.3
61.5
93.6
13.4
11.2
12.8
.d.n.d.n
.d.n87.5
53.0185.7
30.753.6
57.982.8
33. 799.0 1
. d.nc
S Ag
0.11
0.42
0.15
0.7
0.3
0.4
0.7
10.
20.
30.
50.
160.
320.
27A
s0.
54.
92.
54.
49.
87.
77.
37.
220
42.7
18.5
3.9
3.2
19.9
Bi
0.1
0.6
0.4
0.5
1.6
1.0
4.2
4.5
0.3
9.0
0.8
0.2
0.2
0.3
Sb
0.05
0.84
0.30
0.72
1.20
0.90
1.50
2.60
0.85
2.00
1.30
0.78
0.62
0.78
Ga
27.9
18.9
22.6
19.6
18.4
23.8
21.3
23.5
18.2
24.7
28.3
10.4
12.2
15.1
Li76
.334
18.6
22.5
16.3
12.7
13.9
15.2
14.8
11.3
21.8
160
132
55.2
Be
3.37
2.5
2.61
2.21
2.26
2.2
2.21
2.19
2.08
2.3
1.6
1.42
1.22
3.65
Mo
3.5
1.6
2.6
2.1
1.9
2.8
2.7
15.9
3.2
6.5
1.0
3.9
3.2
3.8
La10
2.6
51.0
47.8
42.4
38.8
35.8
36.1
35.2
39.7
48.8
36.1
12.6
25.8
36.4
Ce
194.
010
0.9
92.0
72.5
72.8
67.2
71.9
67.5
74.0
88.8
70.5
28.6
58.4
74.5
Pr
18.7
11.9
10.9
11.4
8.3
7.6
8.3
7.8
8.7
11.0
8.1
3.3
8.9
9.7
Nd
75.3
043
.70
39.7
040
.20
30.8
027
.30
29.9
028
.20
31.4
036
.10
28.7
014
.00
37.6
041
.10
Sm
13.3
08.
807.
596.
965.
995.
105.
805.
546.
277.
295.
342.
508.
008.
80E
u1.
502.
261.
951.
761.
621.
221.
481.
411.
551.
601.
390.
602.
402.
20G
d10
.10
6.32
5.28
4.76
4.35
3.46
4.06
3.81
4.52
4.73
3.69
1.90
6.70
10.5
0T
b1.
301.
120.
820.
750.
630.
560.
620.
610.
700.
780.
630.
301.
101.
20D
y6.
405.
174.
664.
183.
872.
903.
573.
164.
193.
943.
351.
504.
707.
00H
o1.
100.
930.
841.
140.
650.
500.
640.
550.
770.
780.
630.
300.
901.
20E
r2.
702.
252.
322.
181.
791.
361.
651.
381.
992.
081.
610.
802.
202.
90T
m0.
310.
250.
360.
310.
270.
220.
320.
160.
310.
360.
250.
120.
350.
41Y
b2.
102.
301.
861.
932.
351.
451.
710.
661.
761.
791.
200.
701.
702.
30Lu
0.40
0.35
0.30
0.31
0.37
0.23
0.28
0.11
0.28
0.25
0.19
0.10
0.30
0.30
Σ RE
E43
023
721
619
117
215
516
615
617
620
816
267
159
199
Eu*
/Eu
0.38
0.89
0.90
0.89
0.94
0.85
0.89
0.90
0.86
0.79
0.92
0.82
0.98
0.70
Rb/
Sr
0.48
0.08
0.10
0.06
0.12
0.24
0.11
0.18
0.08
0.11
0.44
0.17
0.00
0.11
Ba/
Rb
5.2
8.1
8.8
13.2
9.1
6.0
9.1
7.5
10.5
9.2
3.8
5.6
5.2
4.8
Sr/
Y25
.844
.847
.645
.638
.948
.253
.447
.649
.145
.237
.839
.537
.523
.9N
ote:
n.d
.—no
t det
erm
ined
; LO
I—lo
ss o
n ig
nitio
n; A
LK—
tota
l alk
alis
; Fe*
—F
eOT/(
FeO
T +
MgO
); F
e#—
FeO
/(F
eO +
MgO
); M
ALI
—N
a 2O
+ K
2O-C
aO; A
SI—
mol
ecul
ar A
l/(C
a –
1.67
P +
K +
Na)
; AI—
mol
ecul
ar
Al-(
Na
+ K
) >
0; A
n—w
hole
-roc
k no
rmat
ive
anor
thite
; RE
E—
rare
ear
th e
lem
ent.
Roc
k na
mes
: GB
D—
gabb
ro-d
iorit
e; Q
MD
—qu
artz
mon
zodi
orite
; QM
DP
—po
rphy
ritic
qua
rtz
mon
zodi
orite
; GD
—gr
anod
iorit
e; G
DP
—po
rphy
ritic
gra
nodi
orite
; GV
—gr
anite
; PM
D—
pyro
xene
mon
zodi
orite
; Mz—
mon
zoni
te; Q
M—
quar
tz m
onzo
dior
ite; P
CB
—py
roxe
ne-r
ich
encl
ave;
HC
B—
amph
ibol
e-ric
h en
clav
e; H
GB
—am
phib
ole
gabb
ro e
ncla
ve;
MD
E—
mic
rodi
orite
enc
lave
; MQ
ME
—m
afic
quar
tz m
onzo
dior
ite e
ncla
ve; M
RE
—m
ica-
enric
hed
encl
ave.
-
Petrogenesis of intermediate-acid intrusive rocks and zircon SHRIMP U-Pb dating in the Tongling area, Anhui Province (eastern China)
Geological Society of America Bulletin, January/February 2014 89
Eleven grains have ages ranging from 140 ± 1 Ma to 146 ± 1 Ma. After excluding grain 5, which has very high Th and U, the remaining 10 analyses yield a weighted average age of 143 ± 1 Ma (n = 10, mean square of weighted deviates [MSWD] = 2.9; Fig. 3A).
Sample SYSZK03Sample SYSZK03 is a core sample of the
Shujiadian pyroxene monzodiorite of the sho-shonitic series taken from hole ZK03. The rock body occurs as a NE-trending stock with an irregular shape. It is hosted in Silurian silt-stone with veinlet and disseminated gold min-eralization. A large garnet skarn with an area of 2500 m2 occurs in the middle of the stock. The monzodiorite is dark gray, has a hypidio-morphic-granular texture, and consists mainly of plagioclase (An45–55) (60–70 modal%) and diopside (10%–15%), with subordinate biotite, potassium feldspar, and quartz (for a chemical analysis of this rock, see Wu et al., 1996).
Zircon grains from this sample are prismatic, with length:width ratios between 1:1 and 2:1, similar to those of the Huchengjian gabbro-diorite. Most of the grains are uniformly gray in their CL images, although a few display oscilla-tory zoning (such as grain 6) or a banded struc-ture (such as grains 7 and 11; Fig. 2B), which is typical of magmatic zircon (Pidgeon et al., 1998). The grains have U contents ranging from 189 to 1086 ppm and Th ranging from 133 to 1705 ppm, giving Th/U ratios of 0.73–1.84, consistent with an igneous origin (Table 1). Eleven analyzed spots from this sample yielded a cluster of U-Pb ages ranging from 138 ± 1 Ma to 146 ± 1 Ma, with a weighted average age of 142 ± 2 Ma (n = 11, MSWD = 4.1) that is regarded as the crystallization age (Fig. 3B).
Sample FHS2Sample FHS2 is from the Fenghuangshan
granodiorite of the high-K, calc-alkaline series, the largest intrusive body in the area. This body forms a stock with an irregular circular outcrop area of ~10 km2. The rock is light colored and consists chiefl y of plagioclase (45–55 modal%), quartz (15%–20%), and alkali feldspar (10%–15%), accompanied by minor amphibole and biotite. An analysis of this rock is given in Table 2.
Zircon grains in this sample are prismatic, with length:width ratios of 2:1–3:1, and they show good oscillatory zoning in CL images (Fig. 2C). The analyzed grains have U contents ranging from 225 to 573 ppm and Th ranging from 79 to 481 ppm, giving Th/U ratios ranging from 0.59 to 1.13, except for grain 1, which has a ratio of 0.27, still within the range of igne-ous zircon (>0.2). Eleven analyzed grains yield
A
B
C
DFigure 2. Cathodoluminescence (CL) images of zircon from the intrusive rocks in the Tongling district.
-
Wu et al.
90 Geological Society of America Bulletin, January/February 2014
206Pb/208U ages ranging from 140 ± 1 Ma to 691 ± 4 Ma. If grains 1, 3, and 11, which con-tain inherited cores (531 ± 3 Ma, 691 ± 4 Ma, and 235 ± 2 Ma, respectively; Fig. 2C), are rejected, the remaining grains yield a weighted average age of 142 ± 1 Ma (n = 8, MSWD = 1.1; Fig. 3C).
Sample YSZ3Sample YSZ3 is from the Yaoshan porphy-
ritic granodiorite of the high-K, calc-alkaline series, which crops out west of the Fenghuang-shan intrusion (Fig. 1B). It forms a sill with an outcrop area of 3 km2 that is connected to the Xingqiao porphyritic granodiorite in the north-east. The rock is characterized by phenocrysts of plagioclase and quartz, ranging up to 2 cm across, which are set in a fi ne-grained, felsic matrix. A chemical analysis of this sample is given in Table 2.
Zircon grains from this sample are elongate, euhedral prisms with length:width ratios of 2:1–4:1. CL images show that the grains have excel-lent oscillatory zoning, indicating an igneous origin (Fig. 2D). Eleven analyzed points on nine
grains have relatively low contents of U and Th (242–386 ppm and 18–93 ppm, respectively), yielding Th/U ratios of 0.06–0.53, which are considerable lower than zircons from the other samples (Table 1). These low ratios are due pri-marily to very low Th contents (18–93 ppm). Grains 5 and 7, which have inherited cores, have the highest Th values and highest Th/U ratios. The inherited cores in these two grains (with three analyses) yielded 207Pb/206Pb ages of 2330 ± 12 Ma and 2104 ± 13 Ma, respectively, and were discarded. The remaining eight ana-lyzed spots on seven grains yielded 206Pb/238U ages ranging from 144 ± 1 Ma to 149 ± 1 Ma, with a weighted average age of 146 ± 1 Ma (n = 8, MSWD = 0.8), which is considered the age of zircon crystallization (Fig. 3D).
The wide range in Th/U ratios for the zircons both within and between individual samples is puzzling. For example, the analyzed zircons from sample SYSZK have Th/U ratios ranging from 0.73 to 1.84, but they all have very simi-lar ages and all appear to be magmatic in form and internal texture. In contrast, all zircons from sample YSZ3 have low U (182–386 ppm) and
very low Th (18–45 ppm), except for two grains with 93 and 77 ppm Th that are clearly xeno-crysts. Except for these obviously xenocrystic grains, the zircons all appear to be magmatic in origin and are believed to date the time of crys-tallization of the various Tongling bodies.
Geochemistry
Intrusive RocksMost of the analyzed intrusive rocks from the
Tongling district are fresh, with loss on ignition (LOI) < 2 wt% (Table 2). Two samples from the calc- alkaline series (XQT4 and YSZ2) have LOI >3 wt% and are depleted in Na2O, indi-cating moderate alteration. All but these two samples have relatively high total alkalis, with enrichment in K2O, placing them in the shosho-nitic fi eld and upper parts of the calc-alkaline fi eld in the SiO2 versus (Na2O + K2O) diagram (Fig. 4) (Middlemost, 1994; Irvine and Baragar, 1971). On the SiO2 versus K2O diagram (Pec-cerillo and Taylor, 1976) (Fig. 5), they plot in the high-K, calc-alkaline and shoshonite fi elds, respectively. Most of the intrusive rocks (>90%)
A
C D
B
Figure 3. Zircon 238U/206Pb-207Pb/206Pb concordia diagrams for the intrusive rocks in Tongling. MSWD—mean square of weighted deviates.
-
Petrogenesis of intermediate-acid intrusive rocks and zircon SHRIMP U-Pb dating in the Tongling area, Anhui Province (eastern China)
Geological Society of America Bulletin, January/February 2014 91
belong to the high-K, calc-alkaline series and range in composition from mafi c to intermedi-ate, with SiO2 contents between 52.6 and 64.3 wt%, and K2O contents between 2 and 4 wt%; one sample of granite has 75.4 wt% SiO2 and 4 wt% K2O (Table 2). Although rocks of the sho-shonitic series have similar SiO2 contents (50.8–65.2 wt%), they have much higher total alkalis (7.4–11.4 wt%), with K2O contents generally between 3 and 5 wt%. One sample (SML2) has 10 wt% K2O with very low Na2O and slightly elevated LOI (Table 2), suggesting some altera-tion. Rocks from both series are mostly mag-nesian, with only a few ferroan samples (Frost et al., 2001; Frost and Frost, 2008). Both series are alkali-calcic to calc-alkaline on the basis of the modifi ed alkali lime index (MALI) (Frost et al., 2001) (Fig. 6). All of the rocks have ASI values (= Al/[Ca – 1.67P + Na + K]) 0
(Table 2), indicating they are metaluminous (Frost et al., 2001).
In the Harker diagrams, TiO2, Al2O3, Fe2O3, FeO, MgO, CaO, and P2O5 all show relatively systematic decreases in concentration with increasing SiO2, as expected for granitoid mag-mas undergoing fractionation (Fig. 7). However, the granite sample (TGS3) with 75.4 wt% SiO2 is completely separated from the other calc-alkaline rocks (Fig. 7), and its origin is unclear. Except for three samples, Na2O contents range between 3.3 and 5.5 wt% and show no system-atic variation with SiO2; in contrast, K2O shows a positive correlation with SiO2 in both the calc-alkaline and shoshonitic series (Table 2; Fig. 7).
The large ion lithophile elements show con-siderable scatter on the Harker diagrams but generally increase with increasing SiO2 (Fig. 8). An increase in Rb with increasing SiO2 in the shoshonitic series, coupled with nearly constant
Ba, results in a rapid decrease in the Ba/Rb ratio for these rocks. Zirconium shows a broad scatter of values in the calc-alkaline rocks but decreases regularly in the shoshonitic series (Fig. 8), whereas Y decreases systematically as SiO2 increases, resulting in generally posi-tive correlations between Sr/Y ratios and SiO2 contents, particularly in the calc-alkaline series. One anomalous geochemical feature of these rocks is their relatively high Cr contents (up to 129 ppm in the calc-alkaline series and 210 ppm in the shoshonitic series; Table 2). Not only do the rocks have high Cr contents, but there is a crude positive correlation between Cr and SiO2 (Fig. 8). This trend is particularly puzzling because the other transition metals (Ni, Co, V, and Sc) all decrease systematically with increas-ing SiO2. It may refl ect injection of more mafi c melts into the magma chamber.
Rocks of the high-K, calc-alkaline series have ΣREE of 65–197 ppm, with most samples in the range of 140–180 ppm, and they show no systematic change with SiO2 (Table 2). Chon-drite-normalized REE patterns of these rocks are quite uniform, with nearly fl at heavy (H) REE segments and signifi cant light (L) REE enrichment (LREE/HREE = 8.4–19.3; aver-age = 12.5). They have negligible to very weak negative Eu anomalies (Eu*/Eu = 0.78–0.98; Figs. 9A–9B). These patterns are similar to those of average upper-crustal rocks (Taylor and McClennan, 1985).
The ΣREE values in the shoshonitic series range from 155 to 237 ppm, i.e., slightly higher on average than in the high-K, calc-alkaline
Figure 4. Diagram of SiO2-(Na2O + K2O) for the rocks in Tongling (after Middlemost, 1994; Irvine and Baragar, 1971); the dashed line represents that the plot fi eld of more than 400 collected analyses of the intrusive rocks in Tongling. Circles—intrusive rocks of the high-K, calc-alkaline series. Squares—intrusive rocks of shoshonitic series.
Figure 5. Diagram of SiO2-K2O for the Tongling rocks (after Peccerillo and Taylor, 1976). Symbols are the same as those in Figure 4. K—potassium.
Figure 6. Diagram of SiO2 vs. modified alkali lime index (MALI) for the Tongling rocks (after Frost et al., 2001; Frost and Frost, 2008). Symbols are the same as those in Figure 4. A—alkaline series, AC—alkali-calcic series, CA—calc-alkaline series, C—calcic series.
-
Wu et al.
92 Geological Society of America Bulletin, January/February 2014
series, and they show a systematic decrease with increasing SiO2, although the range of SiO2 is quite narrow (50.8–62.3 wt%; Table 2). We inter-pret this trend as possibly refl ecting early crystal-lization of titanite, one of the major carriers of REEs in these rocks. Experiments by Prowatke and Klemme (2006) and measured mineral/glass data (Bachmann et al., 2005; Colombini et al., 2011) demonstrate that distribution coeffi cients for the middle REEs in titanite are very high and hence should lead to noticeable depletion in these elements. We calculated middle (M) REE depletion factors (2Gdn/[Lan × Lun]) for the sho-shonitic rocks, which range from 0.64 to 0.23, compatible with some titanite fractionation. Chondrite-normalized REE patterns for the sho-shonitic rocks are indistinguishable from those of the calc-alkaline series, showing the same fl at HREE portion and LREE enrichment (LREE/
HREE = 11.1–13.9; average = 12.3; Fig. 9C). Likewise, they also have very weak negative Eu anomalies (Eu*/Eu = 0.79–0.92; Table 2).
In the primitive mantle–normalized trace-element diagram, rocks of the high-K, calc-alkaline series show strong enrichment in large ion lithophile elements (LILEs; Rb, Ba, Th, K), marked negative anomalies in Nb and Ti, and weak negative anomalies in P and Nd. The negative Nb suggests a subduction component in the source area, as does the enrichment in LILEs. Most samples also show weak enrich-ment in Sr and Zr (Figs. 10A–10B). Rocks of the shoshonitic series generally have trace-element compositions comparable to the calc-alkaline rocks, except for somewhat higher values for some of the transition elements, par-ticularly Cr, V, and Co, and somewhat lower values of Sr and Ba, refl ecting their more mafi c
character. Despite the higher K2O contents of these rocks, their Rb concentrations overlap those of the calc-alkaline series (Table 2). The primitive mantle–normalized trace-element patterns of the two series are very similar (Fig. 10C).
Figure 7. Harker diagrams for the major elements (wt%). Data are from Table 2. Symbols are the same as those in Figure 4.
Figure 8. Harker diagrams for selected trace elements (ppm). Data are from Table 2. Symbols are the same as those in Figure 4.
-
Petrogenesis of intermediate-acid intrusive rocks and zircon SHRIMP U-Pb dating in the Tongling area, Anhui Province (eastern China)
Geological Society of America Bulletin, January/February 2014 93
EnclavesThe various enclaves range widely in chemi-
cal composition because of their different ori-gins. The microdiorite and quartz monzodiorite enclaves in the high-K, calc-alkaline series have
similar major-oxide compositions, generally close to those of their host rocks, but somewhat enriched in FeOt and MgO (Table 2). The mica-rich enclave is characterized by signifi cantly lower SiO2 and Na2O but higher TiO2, Al2O3,
FeOt, MgO, and K2O than the others. The ΣREEs are quite variable in the calc-alkaline enclaves, being highest in the mica-rich variety; however, all of the enclaves in the calc-alkaline series, except for the mica-rich samples, have similar chondrite-normalized patterns with strong LREE enrichment and very weak nega-tive Eu anomalies (Fig. 9D). These enclaves have rather variable mantle-normalized trace-element patterns but generally show strong enrichment in LILEs and marked negative Nb anomalies, but they lack the positive P anoma-lies of the enclaves in the shoshonitic series (Fig. 10D). The mafi c quartz monzodiorite enclave is similar in composition to its host rock but with higher FeOt and MgO and correspond-ing decreases in most other oxides. On the other hand, the mica-rich enclave contains relatively high contents of transition metals, particularly Cr, Ni, V, and Co, suggesting that it is refractory crustal material that is a relict of crustal partial melting. No metasedimentary rocks of this com-position are currently known in the sedimentary sequence overlying the basement; however, the presence
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