基底岩系对日土-多龙岩浆弧地球化学和成矿地质背景的制约

Magmatic arcs in active margin are closely related to metallogenesis. The geochemistry and geological background of magmatic arc are constraint by the basement rocks. Hyperplasia arcs with accretionary melange as basement rocks are more conducive to the formation of large porphyry-type deposits, but there are fewer such studies. The Duolong large porphyry Cu-Au deposit, Fuoye and Chaima rich magnetite deposits have been found in recent years in the northern margin of the Bangonghu-Nujiang suture, that are considered to be originated from the Mesozoic Rutog - Duolong magmatic arc. Regional geological surveys carried out in Qiangtang reveals that the Permo-Carboniferous rocks to the north of the south Qiangtang terrane are characterized by an accretionary melange belt, and there are some indications that the Mesozoic rocks from north to south in the south Qiangtang terrane are accretionary continental margin. Therefore, whether there is a hyperplasia arc formed in the substrate of the accretionary wedge, is a very important geological problem. This project aims to study the basement rocks of the Rutog - Duolong magmatic arc and its regional differences, constraints on the magmatic arc metallogenesis. This study is helpful for such researchs and to guide the mineral resources explorations in the Duolong metallogenic region.

活动大陆边缘岩浆弧与成矿作用密切相关。不同类型的基底岩系对岩浆弧的成分和成矿作用有一定的制约。以增生混杂带为基底的增生弧更有利于形成大型斑岩型矿床，但此类研究较少。近年来在班-怒带北缘相继发现的多龙大型斑岩Cu-Au矿、弗野和材玛矽卡岩型富磁铁矿等与日土-多龙中生代岩浆弧有成因关系。在羌塘开展的区域地质调查发现，南羌塘北部的石炭、二叠系具有弧前增生混杂带的特征，并且从北向南的中生界也有增生型活动大陆边缘的一些迹象。因此，研究南羌塘南缘是否存在形成于增生楔基底上的增生弧，是十分重要的地质问题。本项目旨在研究日土－多龙岩浆弧的基底岩系及其区域性差异、对岩浆弧成矿作用的制约。研究成果有利于提升本领域研究水平，有助于指导班-怒带多龙整装勘查区地质矿产勘查。

扎普—多不杂（日土—多龙）岩浆弧位于班公湖—怒江结合带北侧的南羌塘多玛地块和侏罗纪盆地中。地表上本带并非一条连续的岩浆岩带，仅出露少量的花岗（斑）岩体和火山岩，主体为小、散、隐伏—半隐伏的花岗岩和花岗斑岩体，与典型的岩浆弧区别较大。本带花岗岩类的侵入时代分为两个明显的时间段,分别为中晚侏罗世（150—170 Ma）和早白垩世（130—110 Ma）。在140—130 Ma之间为约10Ma的岩浆活动间断期。.扎普—多不杂带两期花岗岩的主要岩性为花岗闪长斑岩、花岗岩、花岗闪长岩、石英闪长岩、闪长岩等。两期岩体大部分属于正常钙碱性—钾玄岩系列I型花岗岩类，只有西段的拉热拉新—材玛岩体（J2-3）和吉普岩体（K1）属于强烈分异的I型花岗岩类。这两类花岗岩均显示LREE和LILE相对富集的分配模式。.中、晚侏罗世花岗岩类的在西段（扎普—弗野）和东段（多不杂—利群山）具有类似的Sr、Nd同位素特征。(87Sr/86Sr)i值在西段和东段分别为0.7029～0.7075和0.7063～0.7089。εNd(t) 值分别为−5.39～−1.76 和−6.30～−2.10。西段的早白垩世岩体弗野岩体的(87Sr/86Sr)i 值为0.7082～0.7102 ，εNd(t) 值为−8.98～−7.19。东段的多龙早白垩世含矿斑岩体的(87Sr/86Sr)i值为0.7047～0.7085，εNd(t) 值主要为0.00～−4.00。岩石地球化学研究表明，（1）早白垩世多龙含矿斑岩体和本带中、晚侏罗世花岗岩体的源岩包括班-怒带蛇绿岩中玄武岩成分和羌塘硅铝质古老地壳成分，但多龙斑岩体中幔源成分贡献较大；（2）西段的早白垩世弗野和吉普岩体主要形成于地壳重熔。.该带西段的材玛—弗野远景区内，中侏罗世花岗岩具有形成矽卡岩型和热液型多金属矿床的潜力，早白垩世花岗岩类的成矿潜力较低。东段的多不杂—青草山成矿远景区中青草山—先遣一带的早白垩世花岗斑岩类与多龙成矿斑岩相似的岩石地球化学特征，具有很高的斑岩Cu Au 成矿潜力，加措—利群山一带的中晚侏罗世花岗岩类具有形成矽卡岩型和热液型多金属矿床的潜力。