摘要
卡拉麦里俯冲增生杂岩带是中亚造山带西南部东准噶尔造山带重要的组成部分,记录了古亚洲洋俯冲—增生的漫长演化历史。然而关于卡拉麦里古大洋的初始俯冲时间尚不清楚。本文报道了分布在该带中早泥盆世斜长花岗岩的锆石U-Pb年代学、地球化学和锆石Hf同位素数据,结合曾发现斜长角闪岩的变质底板,对卡拉麦里古大洋内起始俯冲时限进行了约束。采用LA-ICP-MS锆石U-Pb定年方法获得清水西两件斜长花岗岩样品的锆石U-Pb年龄分别为400.8±1.7 Ma和401.4±3.4 Ma,形成时代为早泥盆世。样品具有高SiO_(2)、Na_(2)O和低TiO_(2)、Al_(2)O_(3)、K_(2)O、Sr、Rb和REE含量,稀土元素表现为轻稀土元素略亏损的配分型式,微量元素则表现为类似弧岩浆的富集大离子亲石元素Rb、Ba及亏损高场强元素Nb、Sr、P、Ti元素的特征,这些特征与俯冲带弧前斜长花岗岩一致。加之具有较高的锆石εHf(t)值(+7.9~+9.2)及较低的(La/Yb)_(N)值(0.61~0.78)和Sr/Y比值(1.73~2.69)的特征,揭示了清水西斜长花岗岩可能来源于低压条件下大洋堆晶辉长岩的部分熔融,并有俯冲流体的参与。结合区域地质背景,我们提出早泥盆世斜长花岗岩可能形成于洋内岛弧环境,代表了卡拉麦里古大洋洋内初始俯冲的地质记录,并进一步限定了其洋内俯冲的起始阶段可能发生在早泥盆世中晚期(401~403 Ma)。
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 SiO_(2) and Na_(2)O contents,and low TiO_(2),Al_(2)O_(3),K_(2)O,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 zirconɛHf(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 lowpressure 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).
作者
黄岗
周建波
尹福光
宇峰
徐岩
HUANG Gang;ZHOU Jianbo;YIN Fuguang;YU Feng;XU Yan(College of Earth Sciences,Jilin University,Changchun,Jilin 130061,China;Civil-Military Integration Center of China Geological Survey,Chendu,Sichuan 610036,China;Key Laboratory of Mineral Resources Evaluation in Northeast Asia,Ministry of Natural Resources,Changchun,Jilin 130061,China;Xining Natural Resources Investigation Center,China Geological Survey,Xining,Qinghai 810000,China;Shaanxi Geology and Mining Regional Geological Survey Academe Co.,Ltd.,Xianyang,Shaanxi 712000,China)
出处
《地质学报》
北大核心
2025年第7期2311-2329,共19页
Acta Geologica Sinica
基金
国家自然科学基金项目(编号42488201,42230303)
中央返还两权价款资金项目(编号Y15-1-LQ02)联合资助的成果。
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
plagiogranite
Early Devonian
initial subduction
Karamaili subduction-accretionary complex belt
East Junggar orogenic belt
