地质学报2025，Vol.99Issue(7)：2311-2329,19.DOI:10.19762/j.cnki.dizhixuebao.2024256
东准噶尔卡拉麦里洋内初始俯冲时限:来自早泥盆世斜长花岗岩的证据
Timing of initial subduction in the Kalamaili Paleo-Ocean,East Junggar:Evidence from the Early Devonian plagiogranite
摘要
Abstract
The Karamaili subduction-accretion complex belt,a key unit within the East Junggar orogenic belt in the southwestern Central Asian Orogenic Belt,records a long evolution history of the subduction-accretion of the Paleo-Asian Ocean.However,the precise timing of the initial subduction of the Karamaili Paleo-Ocean is still unclear.This study presents new geochemical,geochronological,and Hf isotope data for early Devonian plagiogranite from the Karamaili subduction-accretion complex belt.These data,combined with the metamorphic sole of previously discovered amphibolite,help constrain the initiation time of intraoceanic subduction within the Karamaili Paleo-Ocean.LA-ICP-MS zircon U-Pb dating of two plagiogranite samples from the West Qingshui area yielded ages of 400.8±1.7 Ma and 401.4±3.4 Ma,indicating emplacement during the early Devonian.These samples exhibit high SiO2 and Na2O contents,and low TiO2,Al2O3,K2O,Sr,Rb,and REE concentrations.Their arc-like trace-element patterns are characterized by enrichment in LILEs(e.g.,Rb and Ba)and depletion in HFSEs(e.g.,Nb,Sr,Ta,and Ti),with only slight depletion of LREEs,which are most likely similar to those found in fore-arc plagiogranites in the subduction belt.Furthermore,the plagiogranite samples display high zircon εHf(t)values(+7.9 to+9.2)and low(La/Yb)N(0.61～0.78)and Sr/Y(1.73～2.69)ratios.These geochemical signatures suggest a derivation from partial melting of oceanic cumulate gabbro under low-pressure conditions,with the participation of subducted fluids.Considering the regional geological context,we propose that the early Devonian plagiogranites formed in an intra-oceanic island arc setting,which represents the geological record of the initial subduction in the Karamaili Paleo-Ocean and further constrains the initial stage of intra-oceanic subduction to occur in the Early Devonian(401～403 Ma).关键词
斜长花岗岩/早泥盆世/初始俯冲/卡拉麦里俯冲增生杂岩带/东准噶尔造山带Key words
plagiogranite/Early Devonian/initial subduction/Karamaili subduction-accretionary complex belt/East Junggar orogenic belt引用本文复制引用
黄岗,周建波,尹福光,宇峰,徐岩..东准噶尔卡拉麦里洋内初始俯冲时限:来自早泥盆世斜长花岗岩的证据[J].地质学报,2025,99(7):2311-2329,19.基金项目
本文为国家自然科学基金项目(编号42488201、42230303)和中央返还两权价款资金项目(编号Y15-1-LQ02)联合资助的成果. （编号42488201、42230303）
