| Late Triassic Biotite Monzogranite from the Western
Litang Area, Yidun Terrane, SW China: Petrogenesis
and Tectonic Implications |
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| 作者姓名： | ZHU Yu LAI Shaocong QIN Jiangfeng ZHANG Zezhong ZHANG Fangyi |
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| 作者单位： | State Key Laboratory of Continental Dynamic, Department of Geology, Northwest University, Xi’an 710069, China,State Key Laboratory of Continental Dynamic, Department of Geology, Northwest University, Xi’an 710069, China,State Key Laboratory of Continental Dynamic, Department of Geology, Northwest University, Xi’an 710069, China,State Key Laboratory of Continental Dynamic, Department of Geology, Northwest University, Xi’an 710069, China and State Key Laboratory of Continental Dynamic, Department of Geology, Northwest University, Xi’an 710069, China |
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| 摘 要： | The Late Triassic igneous rocks in the Yidun terrane can provide vital insights into the evolution of Plaeo-Tethys in western China. We present new zircon U-Pb, whole-rock geochemistry, and Sr-Nd-Pb-Hf isotopic data for the Litang biotite monzogranites, Yidun terrane. The biotite monzogranites have a zircon U-Pb age of 206.1±1.0 Ma(MSWD=1.9,n=30), which indicates Late Triassic magmatism. The biotite monzogranites display I-type affinity, high Na_2O(3.38-3.60 wt%) contente,medii SiO_2(67.12-69.13 wt%), and low P_2 O_5 contents(0.10～0.12 wt%). They enriched in Rb,and Ba and depleted in Nb and Ta, with negative Eu anomalies(Eu/Eu*=0.74—0.81). They have evolved Sr-Nd-Pb-Hf isotopic composition, i.e.,(~(87) Sr/~(86 )Sr)i=0.714225 to 0.714763, negative ?_(Nd(t)) values of -2.0 to-2.6 with two-stage Nd model ages ranging from 1.01 to 1.05 Ga, negative ?_(Ht)(t)) values o f-3.4 to-4.1 with two-stage Hf model ages of 1.85 to1.88 Ga, suggesting a matured crustal sources. Their low Al_2O_3/TiO_2 ratios and medium Cao/Na_2O ratios, medium Mg~# and SiO_2 contents, low molar Al_2O_3/(MgO+FeO~T)] values, and high molar Cao/(MgO+FeO~T)] values indicate that the Litang biotite monzogranite was formed by partial melting of metabasaltic rocks. Based on the previous studies, we propose that the Litang biotite monzogranite derived from the westward subduction and closure of the Ganzi-Litang ocean during the Late Triassic-The mantle wedge-derived mafic melts provided sufficient heat for partial melting of ancient metabasalt protolith within the middle-lower crust.
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| 关 键 词： | Late Triassic biotite monzogranite zircon U–Pb dating Sr–Nd–Pb–Hf isotopes Yidun terrane |
| 收稿时间： | 2017/12/5 0:00:00 |
| 修稿时间： | 2018/4/18 0:00:00 |
Late Triassic Biotite Monzogranite from the Western Litang Area,Yidun Terrane,SW China: Petrogenesis and Tectonic Implications |
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| Authors: | ZHU Yu LAI Shaocong QIN Jiangfeng ZHANG Zezhong and ZHANG Fangyi |
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| Abstract: | The Late Triassic igneous rocks in the Yidun terrane can provide vital insights into the evolution of Plaeo‐Tethys in western China. We present new zircon U–Pb, whole‐rock geochemistry, and Sr–Nd–Pb–Hf isotopic data for the Litang biotite monzogranites, Yidun terrane. The biotite monzogranites have a zircon U‐Pb age of 206.1±1.0 Ma (MSWD=1.9, n=30), which indicates Late Triassic magmatism. The biotite monzogranites display I‐type affinity, high Na2O (3.38–3.60wt%) contents, medium SiO2(67.12–69.13wt%), and low P2O5 contents (0.10–0.12wt%). They are enriched in Rb, Th, and Ba and depleted in Nb and Ta, with negative Eu anomalies (Eu/Eu?=0.74–0.81). They have evolved Sr‐Nd‐Pb‐Hf isotopic composition, i.e., (87Sr/86Sr)i=0.714225 to 0.714763, negative εNd(t) values of –2.0 to –2.6 with two‐stage Nd model ages ranging from 1.01 to 1.05 Ga, negative εHf(t) values of –3.4 to –4.1 with two‐stage Hf model ages of 1.85 to 1.88 Ga, suggesting a matured crustal sources. Their low Al2O3/TiO2 ratios and medium Cao/Na2O ratios, medium Mg# and SiO2 contents, low molar Al2O3/(MgO+FeOT)] values, and high molar Cao/(MgO+FeOT)] values indicate that the Litang biotite monzogranite was formed by partial melting of metabasaltic rocks. Based on the previous studies, we propose that the Litang biotite monzogranite derived from the westward subduction and closure of the Ganzi–Litang ocean during the Late Triassic. The mantle wedge‐derived mafic melts provided sufficient heat for partial melting of ancient metabasalt protolith within the middle‐lower crust. |
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| Keywords: | Late Triassic biotite monzogranite zircon U–Pb dating Sr–Nd–Pb–Hf isotopes Yidun terrane |
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