西天山松湖铁矿区火山岩地球化学特征、成岩时代及其地质意义

Geochemistry and Geochronology of the Volcanic Rocks in the Songhu Iron Deposit of Western Tianshan Mountains and Their Geological Significance

阿吾拉勒成矿带位于新疆西天山伊犁地块东北缘,是一条极其重要的铁、铜、金多金属成矿带。松湖铁矿床位于该成矿带西段,矿区出露的地层主要为一套钙碱性系列的火山岩,岩石类型有安山岩、安山质火山碎屑、少量英安岩、流纹岩及等质的火山碎屑岩。铁矿体赋存于安山岩及安山质火山碎屑岩中。安山岩中锆石U-Pb谐和年龄为(343.2±2)Ma,属早石炭世维宪期。该组火山岩具有相似的稀土元素及微量元素地球化学特征,暗示它们应为同源岩浆演化的产物。其微量元素组成具有富集大离子亲石元素(Rb、Ba、Th、K等)和轻稀土元素、亏损高场强元素(Nb、Ta和Ti)的特点,显示活动大陆边缘火山岩特征。矿区安山岩的Nd同位素组成具有亏损型特征(εNd(t)=+2.09^+3.39,平均值为+2.59),而Sr同位素组成为富集型((87Sr/86Sr)i=0.7056~0.7060),显示其岩浆源区应为莫霍面附近的岛弧型地壳根部。

Located at the northwest edge of Yili plate in Western Tianshan Mountains, Xinjiang, the Awulale metallogenic belt is one of the significant polymetallic iron, copper and gold belts discovered in recent years. The Songhu iron deposit is one of the volcanic type iron deposits in the western part of the belt and is hosted in the 2nd member of the Carboniferous Dahalajunshan Group. This paper focused on the petrology, petrography, geochemistry and geochronology of the volcanic rocks exposed in the ore district and tried to constrain their tectonic settings and petrogenesis. Some conclusions have been reached： （1） These volcanic rocks mainly consist of andesite and dacite, with minor rhyolite and volcaniclastic rocks, and belong to the calc-alkaline series. （2） The U-Pb age of zircons in the andesite is （343.2±2） Ma （MSWD=1.8）, suggesting the Visean Age. （3） Trace element patterns show enrichment of LILE （Rb, Ba, Th, K etc.） and LREE, and depletion of HFSE （Nb, Ta, Ti）. These＆amp;nbsp;characteristics suggest that these volcanic rocks might have been formed in the active continental margin arc and produced by cognate magma. （4） These volcanic rocks are characterized by relatively highεNd（t） values （＋2.09 - ＋3.39） and high initial ^87Sr/^86Sr ratios （0.7056-0.7060）. The Nd-Sr isotopic characteristics indicate that their magma source was the roof of continental arc crust near the Moho surface.