新疆卡拉麦里地区早石炭世火山岩地球化学特征及构造意义

Geochemical Characteristics and Tectonic Significance of Early Carboniferous Volcanic Rocks of Kalamaili,Xinjiang

卡拉麦里断裂带西段南侧下石炭统山梁砾石组中基性火山岩分布广泛,呈夹层整合产出。岩石具有变化的Si O2（49.43%～59.08%）、Mg O（3.81%～6.28%）、K2O（0.16%～1.55%）含量,高Ti O2（1.18%～2.49%）、Na2O（2.89%～5.44%）、P2O5（0.21%～0.92%）含量,为玄武岩、玄武安山岩及安山岩,属钙碱性系列。样品具相对高的HFSE含量（Ti,Zr,Y）和高的La/Nb（1.96～2.98）、Zr/Y（3.65～9.36）比值,微量元素原始地幔标准化蛛网图显示岩石富集大离子亲石元素Rb,Ba,K和U,Pb,相对亏损高场强元素Nb,Ta和Ti,在球粒陨石稀土元素配分图上,LREE轻微富集,（La/Yb）N=2.04～10.11,弱的负Eu异常（δEu=0.87～0.95）,显示出该火山岩兼有板内玄武岩和火山弧玄武岩的地球化学特征。结合区域地质背景研究认为,山梁砾石组中火山岩形成于后造山伸展的构造背景,是由先前被俯冲流体交代过的富集地幔发生部分熔融,并有俯冲沉积物参与,经历一定的结晶分异作用和地壳混染后喷出地表而形成,且该区在晚石炭世早期伸展运动最为强烈,火山活动达到顶峰。

Shanlianglishi Formation strata volcanic rocks are widely distributed in western fault zone of Kalamaili. Studies show that the rocks are basalt,andesite and basaltic andesite,calc-alkaline series with SiO 2content of samples ranging from 49. 43% to 59. 08%,TiO 2（ 1. 18% ～ 2. 49%）,P2O5（ 0. 21% ～ 0. 92%） and Mg O（ 3. 81% ～ 6. 28%）. Samples have relatively high HFSE content（ Ti,Zr,Y） and also high La /Nb（ 2. 98 ～1. 96）,Zr / Y（ 9. 36 ～ 4. 01） ratio. The primitive mantle normalized trace element spider shows samples enriched LILE（ Rb,Ba,K,U） and Pb,but relatively depleted Nb,Ta and Ti. Rare earth element distribution of REE shows slightly enriched LREE,（ La / Yb）N= 1. 93 ～ 9. 59,and that Eu is weakly negative anomaly（ δEu = 0. 87 ～0. 95）. Combined with geochemical characteristics of WPB and VAB. Shanlianglishi Formation strata formed in the stretched after collision environmen. After partial melting of the enriched mantle that was previously metasomatized by the subduction fluid and with participation of the subduction sediment,magma experienced a certain degree of fractional crystallization and contamination by earth crust,and then erupted to form the Shanlianglishi Formation strata volcanic rocks. In eraly Late-Carboniferous,extensional movement was the most intense volcanic activity,which reached its peak in this area.