摘要
阿吾拉勒山位于中国新疆伊犁地区,是中亚造山带的重要组成部分。本文对阿吾拉勒山西段琼布拉克、卡查可让和托巴斯萨依等地出露的下二叠统基性火山岩的主元素、微量元素和同位素地球化学特征进行了研究。阿吾拉勒山西段琼布拉克、卡查可让、托巴斯萨依等地出露的基性火山岩为钾质基性火山岩(属橄榄玄粗岩系的橄辉玄粗岩),其镁铁指数从23.3变化到64.1,表明它们经历了相当程度的分异演化;微量元素地球化学特征显示,该类钾质基性火山岩形成于后碰撞弧环境,暗示该地区在早二叠世地球动力学性质由挤压转换为伸展。La/Yb和Nb/Y比值显示,由于源区受到与俯冲有关的流体交代影响,岩石明显富集大离子亲石元素并亏损Nb、Ta和Ti等高场强元素。微量元素地球化学特征还显示,该类钾质基性火山岩的源区除了含有尖晶石、辉石、橄榄石和少量的石榴子石外,还含有一定数量的角闪石或金云母等含水矿物,该类岩石原始岩浆形成于深度大于70 km的尖晶石橄榄岩与石榴子石橄榄岩的过渡区;微量元素地球化学特征显示,阿吾拉勒山西段南北两地钾质基性火山岩的源区组成有明显差异:南部的托巴斯萨依钾质基性火山岩较北部的卡查可让和琼布拉克钾质基性火山岩的源区更加富水,受到俯冲物质的影响更强烈,但源区石榴子石含量相对较少;同位素地球化学特征也显示,琼布拉克和卡查可让等地的钾质基性火山岩εNd(t)值比托巴斯萨依的钾质基性火山岩更低,(87Sr/86Sr)i比值比托巴斯萨依的钾质基性火山岩略高,暗示它们源区的富集程度更高,也表明托巴斯萨依的钾质基性火山岩受软流圈的影响更为强烈。
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 to extension 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.
出处
《地球化学》
CAS
CSCD
2013年第6期544-556,共13页
Geochimica
基金
国家自然科学基金(U1203291
41040029)
中国科学院矿物学与成矿学重点实验室合作研究基金(KLMM20120101)
河南省科技发展计划项目(132400410705)
