西藏冈底斯成矿带碰撞期岩浆作用与成矿系列研究

【作者】 张晖；

【导师】 李光明；

【作者基本信息】 中国地质科学院 ， 矿物学、岩石学、矿床学， 2008， 硕士

【摘要】 西藏冈底斯成矿带的铜铁铅锌金等矿产的资源潜力巨大,是我国西部地区一个具有世界级规模铜铁多金属成矿带。已有资料显示,西藏冈底斯成矿带经历了从板块俯冲-碰撞到青藏高原隆升的全过程,成矿带内驱龙、甲马等系列大型、特大型斑岩铜矿床的形成时代为21-13Ma,与印度—欧亚大陆碰撞后伸展阶段的岩浆作用有关,而与印度—欧亚大陆碰撞期(65-41Ma)的成矿作用由于发现矿床点少而未受到重视。一些研究者认为,在欧亚-印度大陆的碰撞阶段,由于处于强烈的构造挤压背景,岩浆活动、成矿流体运移和成矿物质的沉淀受到很大的限制,因此成矿活动不发育,不利于大型矿床的形成。还有一些研究者认为,由于受到碰撞后伸展阶段成矿作用的叠加改造以及中新世以来高原的强烈隆升和剥蚀作用的影响,碰撞阶段的成矿纪录即使存在也难以保存。本文通过对冈底斯成矿带碰撞期花岗质岩浆作用、林子宗群火山作用和以及冈底斯成矿带南缘大型韧性剪切带为主的构造作用的研究,认为冈底斯成矿带印度—欧亚大陆碰撞期(65-41Ma)同样发育有大规模的成矿作用。1、冈底斯构造—岩浆带经历了碰撞前特提斯弧盆系统演化、印度—欧亚大陆碰撞、后碰撞伸展等3个重要的构造演化阶段,各阶段的构造-岩浆作用形成了不同成矿系列,形成了规模巨大的冈底斯成矿带。2、根据板块运动学、古地磁学、地层古生物和区域岩石学的证据,把印度—欧亚大陆主碰撞期时限界定于65-41Ma。3、主碰撞期发育的岩浆活动总体上属于钙碱性中酸性岩浆,具有“I”+“S”花岗岩的特征。岩浆明显具有Eu的负异常,富集不相容元素Rb、Th、U,亏损Nb、Ta、Ti、Sr、P,显示出明显的岛弧-同碰撞岩浆的特点,对岩浆岩型铜铁多金属矿床和斑岩型铜钼矿床的形成有利。4、主碰撞期的构造-岩浆活动在冈底斯成矿带发育①与花岗质岩浆作用有关的铁铜铅锌成矿系列②与火山作用有关的铜金成矿亚系列和③与构造-热液作用有关的铜金成矿亚系列等3个成矿亚系列。5、指出冈底斯成矿带具有发现大型铜铁多金属矿床的成矿地质条件。更多还原

【Abstract】 There is large mineral resource potential such as Cu Fe Pb Zn Au in Gangdese metallogenic belt,Tibet,which is a world-class scale polymetallic metallogenic belt in western China.Gangdese metallogenic belt goes through the entire process from plate subduction-collision to plateau uplift.The large-scale porphyry copper deposit such as Qulong Jiama(21-13Ma) is related to magmatism of India-Eurasian post-collision extensional period. The mineralization during India-Eurasian plate collision period(65-41Ma) has been ignored for a long time.Some researchers believe that during India-Eurasian plate collision period, because of sharp structural compressive,the transfer of ore-forming fluid and the sediment of ore-forming element are restricted badly,so the ore-forming activity is not obvious.Some researchers think that because of superimposed change affected by post-collision extensional mineralization and the uplift and erosion of the plateau since Miocene Epoch,the ore-forming record during collision period is not remained though existed ever.This paper summarized the granite-like magmatism during collision period、the linzizong volcatism and the tectonic activity based on ductile shear zone in southern Gangdese,reached several conclusions as follows:1、The Gangdese tectonic-magmatism belt goes through 3 important periods:pre-collision Tethys arc-basin system、India-Eurasian collision、post-collision extension,there are different mineralization during each period.2、According to the evidence based on plate-movement、paleomagnetic、stratigraphical palaeontology and regional-petrology,the collision period is 65-41Ma.3、The magma during the collision period is calc-alkalic acid-intermediate magma,with "I"+"S" granite characteristics.The magma has a obvious negative anomaly in Eu,rich in incompatible elements such as Rb、Th、U,poor in Nb、Ta、Ti、Sr、P,so it is island-arc-collision magma,which is important to the formation of magma polymetallic deposits and porphyry copper deposits.4、There are 3 metallogenic series during collision period:①Fe Cu series of granite-like magmatism②Cu Au series of volcanism③Cu Au series of tectonic-fluid activity.5、The metallogenic geologic condition is good so we can find large-scale polymetallic deposits in Gangdese metellogenic belt.更多还原