| China Geological Survey Chinese Academy of Geological Sciences | Host |
| 科学出版社 | Publish |
| Citation: |
HONG Jun, JI Wenhua, ZHANG Haidi, LIU Mingyi, MA Zhongping, LI Yanguang, ZHANG Huishan. 2017. Petrogenesis of Murgab gabrro-diorite from Pamir:Evidence from zircon U-Pb dating, Hf isotopes and lithogeochemistry[J]. Geology in China, 44(4): 722-736. doi: 10.12029/gc20170406
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Petrogenesis of Murgab gabrro-diorite from Pamir:Evidence from zircon U-Pb dating, Hf isotopes and lithogeochemistry
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Abstract
Located in the central part of Pamir, Tajikistan, near the Rushan-Pshart suture zone, the Murgab pluton separates the middle Pamir from southern Pamir. Petrologically, the pluton consists of gabrro and diorite which intruded into the epimetamorphic detrital rocks of late Proterozoic (?). LA-ICP-MS zircon U-Pb dating shows that the age of gabbro and that of diorite is 232±1.5 Ma and 231.5±1.9 Ma respectively, which represents the formation age of this pluton. The εHf (t) values of the zircon are in the range of 4.8-12.1 and 6.4-10, with a weighted average of 8.1±1.5 (MSWD=6.5) and 7.9±0.8(MSWD=2.4), suggesting that its original rock was derived from mantle materials. The one-stage Hf model ages (TDM1) are 477-621 Ma, 391-672 Ma respectively indicating an original rock of Cambrian-Precambrian basement. The lithogeochemical data shows that gabbros are characterized by rich Mg and, poor Al and alkali, thus belonging to low-potassium rocks, whereas the diorites are rich in Si, Al and poor in Mg, Ti, hence belonging to calc-alkaline to high K calc-alkaline rocks. The gabbros and diorites share similar REE and trace elements features, which are characterized by high total REE content and rich LREE with slight normal Eu anomaly. The trace elements are characterized by rich LILEs and poor HFES. Based on geochemical characteristics, the authors infer that the pluton formed in an island-arc environment. The subduction was continuing during late Triassic, which indicates that the Rushan Ocean basin was closed at least later than 232 Ma.
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Keywords:
- Pamir /
- Murgab complex /
- zircon LA-ICP-MS U-Pb dating /
- zircon Hf isotopes
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References
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HONG Jun, JI Wenhua, ZHANG Haidi, LIU Mingyi, MA Zhongping, LI Yanguang, ZHANG Huishan. 2017. Petrogenesis of Murgab gabrro-diorite from Pamir:Evidence from zircon U-Pb dating, Hf isotopes and lithogeochemistry[J]. Geology in China, 44(4): 722-736. doi: 10.12029/gc20170406
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Figure 1.
Simplified geological map of the Murgab area, southeast Pamir (modified after Geological Map of Soviet Union at the scale of 1: 200 000 published in 1967)
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Figure 2.
Macroscopic and microscopic photographs of Murgab gabrro and diorite
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Figure 3.
SiO2-K2O diagram (a) and SiO2-(Na2O+K2O) diagram (b) of Murgab gabrro and diorite
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Figure 4.
Chondrite-normalized REE patterns (a) and primitive mantle (PM)-normalized spider diagram (b) of Murgab gabrro and diorite
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Figure 5.
Representative CL images of zircons from Murgab mafic complex, Pamira-Diorite; b-Gabbro
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Figure 6.
U-Pb concordia diagram (a, c) and 206Pb/238U age diagram (b, d) of zircons from diorite and gabbro of Murgab complex, Pamir
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Figure 7.
Columnar distribution of εHf(t) values of zircons (a) and one-stage Hf model age (b) from Murgab gabbro