引用本文：高慧,曹玉亭,刘良,王超,康磊,杨文强,陈晓宏.2020.南阿尔金木纳布拉克地区石英闪长岩的成因：来自地球化学特征、锆石U- Pb定年和Lu- Hf同位素组成的制约[J].地质学报,94(8):2262-2278. GAO Hui,CAO Yuting,LIU Liang,WANG Chao,KANG Lei,YANG Wenqiang,CHEN Xiaohong.2020.Origin of quartz diorite in the Munabulake area, South Altyn Tagh: constraints from geochemical characteristics, zircon U- Pb dating and Lu- Hf isotopic composition[J].Acta Geologica Sinica,94(8):2262-2278.
Abstract:The article mainly focusses on the petrology, geochemistry, zircon chronology and Lu- Hf isotope analysis of the quartz diorite that is exposed in the Bashikourgan rock group in the Munabulake area on the west side of the South Altyn Tagh. Whole rock geochemical research indicates that the quartz diorite has SiO2 content of 55. 94%~57. 38%, exhibits the characteristics of high ratio of Na2O/K2O=1. 19~1. 60 and quasi- aluminium (A/CNK=0. 92~0. 95). On the REE partition diagram, all samples show weak or no obvious Eu anomaly, enriched LREE pattern and defected HREE pattern. On the primitive mantle- normalized spider diagram, samples are relatively enriched in large ion lithophile elements (LILE), such as Rb, Th and K, and depleted in high field strength elements (HFSE), such as Nb, Ta, Sr, P and Ti, showing the characteristics of quasi- aluminous I- type granites of crustal high- K calc- alkaline to calc- alkaline series. The zircon crystals in the quartz diorite are euhedral and mostly show long columnar shape with clear oscillatory zones. Zircon U- Pb dating by LA- ICP- MS obtains the age of 455. 5±1. 3 Ma, which is inferred to represent the formation age of quartz diorite based on the internal structure of CL image of zircon. This age is identical to the high- pressure granulite facies retrograde metamorphic age of HP/UHP rocks from the South Altyn Tagh, and is also identical to the third stage of the magmatism (460~451 Ma) in early Paleozoic in the South AltynTagh. All spots of zircons have ε Hf( t )=-6. 29~-1. 35 and T DM C=1512~1823 Ma, which is similar to early Paleozoic granite of the Southern AltynTagh ( T DM C=1331~1789 Ma, ε Hf( t )=-8. 8~-0. 4), suggesting that they were derived from the consistent source rock, which was accreted in Middle Mesoproterozoic- Paleoproterozoic. According to the geochemical characteristics, the quartz diorite was inferred to have formed by partial melting of the basalt in the lower crust, with mantle magma mixed in during the formation process. Based on the results of our studies we conclude that the quartz diorite from the Munabulake area in the South AltynTagh was produced when the metamorphic basalt partially melted and mixed with mantle due to the loss of the pressure, followed by intrusion and crystallization into the crust during the subduction when the continental crust turns back.