摘要
西准噶尔庙尔沟岩体中发育大量近南北向岩脉,脉体中可见暗色闪长质包体。脉体主要为石英闪长(玢)岩,包体主要为闪长岩。石英闪长岩和闪长岩LA-ICP-MS锆石U-Pb年龄分别为298.0±3.7 Ma和299.4±2.5 Ma,属晚石炭世晚期-早二叠世早期。岩石属钙碱性系列,具有中等的SiO_2(53.58%～57.89%)含量、较高的MgO(3.09%～4.83%)、Mg~#(44.69～54.12)、TiO_2(1.17%～1.66%)、Cr(51.24×10^(-6)～126.1×10^(-6))、Ni(35.91×10^(-6)～57.55×10^(-6))含量及K/Na值(0.35～0.70),富集大离子亲石元素(K、Rb、Ba和U)和轻稀土元素,亏损高场强元素(Nb、Ta和Ti),具弱负铕异常(δEu=0.67～1.08),类似于日本中新世Setouchi火山岩带及西准噶尔哈图地区赞岐岩,其源区应为受流体交代的亏损地幔。俯冲板片脱水所产生的流体在上升过程中与地幔楔发生反应,导致角闪石-尖晶石橄榄岩地幔源区发生2%～5%的部分熔融而形成具赞岐岩地球化学特征的庙尔沟岩脉。研究认为,西准噶尔南部地区在早二叠世早期仍为与俯冲消减相关的岛弧环境,多期次俯冲增生作用可能是造成西准噶尔南北俯冲时限差异的主要原因。
NS-trending dikes which contain dioritic enclaves widely occur in the Miaoergou pluton,West Junggar,Xinjiang.The dikes are composed of quartz diorite and quartz diorite porphyrite.LA-ICP-MS zircon U-Pb ages of the quartz diorite and diorite are 298.0±3.7 Ma and 299.4±2.5 Ma,respectively,corresponding to the end of the Late Carboniferous to beginning of the Early Permian.The dikes and enclaves have similar geochemical properties with island arc features.They are calc-alkaline,with moderate SiO2(53.58%to 57.89%),high MgO(3.09%to 4.83%,Mg#values ranging from 44.69 to 54.12),TiO2(1.17%to 1.66%),Cr(51.24×10-6 to 126.1×10-6),Ni(35.91×10-6 to 57.55×10-6)contents and K/Na ratios(0.35 to 0.70).Moreover,all samples are enriched in large-ion lithophile elements(LILEs:e.g.K,Rb,Ba and U)and light rare earth elements,but strongly depleted in high field strength elements(HFSEs:e.g.Nb,Ta and Ti),with insignificant Eu anomalies(δEu=0.67 to 1.08).In contrast,the dikes and enclaves in the Miaoergou pluton show geochemical signatures similar to those of the Cenozoic sanukitoids in Setouchi volcanic belt of SW Japan and the sanukitoids in the Hatu area,West Junggar.The source of the dikes might be the depleted mantle previously metasomatized by fluids released from subduction slabs.These sanukitic dikes may be generated by interaction of the mantle wedge with fluids derived from dehydration of the subducting oceanic slab,resulting in 2%to 5%partial melting of amphibole-spine peridotite.The identification of the sanukitic dikes in the Miaoergou pluton,together with previous studies,suggest that the southern West Junggar region was still dominated by subduction-related island arc setting at the beginning of the Early Permian,and multi-stage subduction-accretionary orogeny may account for the difference of subduction duration between the north and the south of West Junggar.
作者
段丰浩
李永军
支倩
万阈
任毅
DUAN Fenghao;LI Yongjun;ZHI Qian;WAN Yu;REN Yi3REN Yi(School of Earth Science and Resources,Chang’an University,Xi’an 710054,Shaanxi,China;Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits,MLR,Xi’an 710054,Shaanxi,China;No.7 Geological Party,Xinjiang Bureau of Geology and Mineral Resources,Wusu 833000,Xinjiang,China)
出处
《大地构造与成矿学》
EI
CAS
CSCD
北大核心
2018年第4期759-776,共18页
Geotectonica et Metallogenia
基金
国家自然科学基金项目(41402044
41303027
41273033
41202044)
新疆地勘专项基金项目(Y14-5-LQ06
Y15-1-LQ01)
中央高校基本科研业务费专项资金-长安大学优秀博士学位论文培育资助项目(300102278713)联合资助
关键词
赞岐岩
晚石炭世晚期-早二叠世早期
岛弧
多期次俯冲增生
西准噶尔
sanukitic dikes
the end of the Late Carboniferous-the beginning of the Early Permian
island arc setting
multi-stage subduction-accretionary orogeny
West Junggar
