Geochemistry of Permian potassic mafic volcanic rocks in western Awulale Mountains
Geochemistry of Permian potassic mafic volcanic rocks in western Awulale Mountains
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发表时间：
2013
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通讯作者：
L. Yon
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作者：
L. Yon
位于新疆北部伊犁河畔的阿吾拉勒山是中亚造山带的重要组成部分。本文重点研究了广泛分布于阿吾拉勒山西段（琼布拉克、卡查克让和托巴西萨依）的二叠纪钾质镁铁质火山岩的常量、微量元素和同位素地球化学特征。提出：（1）阿吾拉勒山西段的镁铁质火山岩为钾玄岩。钾质基性火山岩经历了相当程度的分异演化，铁镁指数为23.3 ~ 64.1。(2)元素地球化学研究表明，阿吾拉勒山西段下二叠统钾质基性火山岩形成于后碰撞弧环境。这表明早二叠世本区的地球动力学体制由挤压向伸展转变。微量元素模式以及La/Yb和Nb/Y比值显示出大离子亲石元素的显著富集和高场元素的贫化，Nb、Ta、Ti，表明受板块俯冲的强烈影响。本次研究还表明，阿吾拉勒钾基性火山源区除尖晶石、辉石、橄榄石和少量石榴石外，还含有一定量的含水矿物角闪石或金云母，即，原始岩浆形成于尖晶石橄榄岩和石榴石橄榄岩过渡带中，深度大于70 km。(3)微量元素地球化学研究表明，阿吾拉勒山源区西段南北部钾基性火山岩具有明显的差异：南部托巴斯萨依钾基性火山岩比北方喀查克让和琼布拉克富水，受板块俯冲影响较大。
Awulale Mountians, located in Yili terrane in north Xinjiang, is an important part of Central Asian Orogenic Belt. This paper focuses on the major, trace elements and isotope geochemistry characteristic of the Permain potassic mafic volcanic rocks, which are widely distributed in the western part of the Awulale Mountains(Qiongbulake, Kachakerang and Tobasisayi). We propose that:(1) The mafic volcanic rocks in the western part of Awulale Mountains are shoshonite. The potassic mafic volcanic rocks experienced a considerable degree of differentiation and evolution with iron magnesium index ranging from 23.3 to 64.1.(2) Element geochemistry shows that, the Lower Permian potassic mafic volcanic rocks formed in post-collisional arc environment in the western part of the Awulale Mountains. These suggest that the geodynamic regime of this region changed from compression toextension in the Early Permian. Tracce element patterns as well as La/Yb and Nb/Y ratios show significant enrichment in large ion lithophile elements and depletion in high field elements, e.g., Nb, Ta, Ti, suggesting strong influence from plate subduction. This studies also show, Awulale potassic mafic volcanic source region also contains a certain amount of hydrous minerals amphibole or phlogopite, in addition to spinel, pyroxene, olivine, and a small amount of garnet, i.e., primitive magmas formed in spinel peridotite and garnet peridotite transition zone at depths greater than 70 km.(3) The trace element geochemistry show that, potassic mafic volcanic rocks in the north and south of the western part of the Awulale Mountains source region are significantly different: the southern Tobasisayi potassic mafic volcanic rocks were more water-rich compared to the northern Kachakerang and Qiongbulake, indicating more influence from plate subduction.