Early Devonian Post-collisional Granitic Magmatism in the North Qilian Orogenic Belt,Western China:Insights into Lithospheric Delamination and Orogenic Collapse  

作　　者：WANG Qian ZHAO Xilin MENG Yuanku YU Shengyao LIU Yanan 

机构地区：[1]College of Earth Science and Engineering,Shandong University of Science and Technology,Qingdao,Shandong 266590,China [2]Nanjing Center,China Geological Survey,Nanjing 210016,China [3]Key Laboratory of Submarine Geosciences and Prospecting Techniques,MOE,Institute for Advanced Ocean Study,College of Marine Geosciences,Ocean University of China,Qingdao,Shandong 266100,China [4]Sinopec Qingdao Liquefied Natural Gas Co.,Ltd.,Qingdao,Shandong 266400,China

出　　处：《Acta Geologica Sinica(English Edition)》2024年第2期352-367,共16页地质学报（英文版）

基　　金：supported by the Natural Science Foundation of Shandong Province(Grant No.ZR2022QD055);the Taishan Scholars(Grant No.tstp 20231214);the National Natural Science Foundation of China(Grant No.42372247).

摘　　要：Post-collisional magmatism contains important clues for understanding the reworking and growth of continental crust,as well as lithospheric delamination and orogenic collapse.Early Devonian magmatism has been identified in the North Qilian Orogenic Belt(NQOB).This paper reports an integrated study of petrology,whole-rock geochemistry,Sm-Nd isotope and zircon U-Pb dating,as well as Lu-Hf isotopic data,for two Early Devonian intrusive plutons.The Yongchang and Chijin granites yield zircon U-Pb ages of 394-407 Ma and 414 Ma,respectively.Both of them are characterized by weakly peraluminous to metaluminous without typical aluminium-rich minerals,LREE-enriched patterns with negative Eu anomalies and a negative correlation between P_(2)O_(5) and SiO_(2) contents,consistent with geochemical features of I-type granitoids.Zircons from the studied granites display negative to weak positive ε_(Hf)(t)values(−5.7 to 2.1),which agree well with those of negative ε_(Nd)(t)values(−6.4 to−2.9)for the whole-rock samples,indicating that they were derived from the partial melting of Mesoproterozoic crust.Furthermore,low Sr/Y ratios(1.13-21.28)and high zircon saturation temperatures(745℃ to 839℃,with the majority being>800℃)demonstrated a relatively shallow depth level below the garnet stability field and an additional heat source.Taken together,the Early Devonian granitic magmatism could have been produced by the partial melting of ancient crustal materials heated by mantle-derived magmas at high-temperature and low-pressure conditions during postcollisional extensional collapse.The data obtained in this study,when viewed in conjunction with previous studies,provides more information about the tectonic processes that followed the closure of the North Qilian Ocean.The tectonic transition from continental collision to post-collisional delamination could be constrained to~430 Ma,which is provided by the sudden decrease of Sr/Y and La/Yb ratios and an increase in zircon ε_(Hf)(t)values for granitoids.A two-stage tectonic e

关 键 词：post-collisional magmatism lithospheric delamination extensional collapse North Qilian Orogenic Belt 

分 类 号：P534.44[天文地球—古生物学与地层学] P588.1[天文地球—地质学] P542