冈底斯带南部新特提斯洋早期俯冲有关岩浆特征与成矿分析

发布时间：2018-04-25 12:37

本文选题：冈底斯南缘 + 早中生代岩浆岩　；参考：《地球化学》2017年06期

【摘要】：冈底斯南缘经历了新特提斯洋俯冲及其后的陆陆碰撞,发育众多后碰撞环境的斑岩铜矿床,而与洋壳俯冲有关斑岩型矿床却发现不多,目前仅有雄村斑岩型铜金矿床。本工作在冈底斯南缘东西向200多千米范围内发现多个铜矿化岩体及火山岩。岩体锆石U-Pb年龄显示其侵位于早中侏罗世。这些铜矿化岩体及火山岩多发育脉状帘石化蚀变,而其周围新生代岩基多未发生蚀变及矿化,显示矿化及蚀变早于新生代岩基;而磁铁矿-赤铁矿-黄铜矿矿物组合表明铜矿化与岩浆磁铁矿的氧化还原过程有关,矿化时代与岩体基本同期。矿化岩体多富含角闪石,发育磁铁矿-赤铁矿组合,显示岩浆富水氧化特征,而岩浆期榍石、磷灰石及石英中发育原生流体包裹体,显示富水岩浆较早出溶挥发分。综合区内早中生代岩浆岩的时空分布,冈底斯南缘存在东西向的侏罗纪弧岩浆岩带。该套岩浆岩具有典型弧岩浆地球化学特征,锆石?Hf(t)值(+10~+16)显示近亏损地幔端元的源区特征。上述证据表明,冈底斯南缘在早中生代发生了大范围的岩浆活动和同期铜矿化,新生下地壳或亏损地幔源区可提供良好的Cu金属来源,高氧化富水的母岩浆有利于亲铜元素的富集与成矿,为斑岩铜矿床形成的有利条件。据此,我们提出冈底斯南缘在早中侏罗世可能存在一个包括雄村斑岩型铜金矿床在内的高氧化岩浆岩和矿化带,其与新特提斯洋洋壳在侏罗纪俯冲引发的大规模的岩浆活动相关,该带具备良好的斑岩铜矿找矿前景。鉴于冈底斯南缘在白垩纪之后经历了大规模抬升和剥蚀,在该地区寻找新的俯冲型斑岩铜金矿床应主要集中在早中侏罗世火山岩出露区。
[Abstract]:The southern margin of Gangdes experienced the new Tethys ocean subduction and subsequent continental collision, and developed many porphyry copper deposits in the post-collision environment, but few porphyry deposits related to oceanic crust subduction. At present, only Xiongcun porphyry copper-gold deposit is found. In this work, several copper orebodies and volcanic rocks have been found in the range of more than 200 km from east to west in the southern margin of Gangdis. The zircon U-Pb age indicates that the intrusion occurred in the early and middle Jurassic. Most of these copper orebodies and volcanic rocks developed vein-like anodized alteration, but there was no alteration and mineralization in the surrounding Cenozoic rock base, indicating that the mineralization and alteration were earlier than that of the Cenozoic rock base. However, the combination of magnetite, hematite and chalcopyrite indicates that copper mineralization is related to the redox process of magmatic magnetite, and the mineralization age is basically the same as that of the rock mass. The mineralized rock bodies are rich in amphibole and developed magnetite hematite assemblage, which shows that magma is rich in water and oxidized, while primary fluid inclusions are developed in sphene, apatite and quartz of magmatic epoch, which indicates that the water-rich magma produced early dissolved volatile matter. The distribution of early Mesozoic magmatic rocks in the Synthetical area shows that there is a Jurassic arc magmatic belt in the southern margin of Gangdis. This suite of magmatic rocks is characterized by typical arc magmatic geochemistry, and the zircon Hftt values (10-16) show the source features of the near-depleted mantle end elements. The above evidence indicates that extensive magmatism and copper mineralization occurred in the early Mesozoic on the southern margin of Gangdis, and that the source region of the new lower crust or depleted mantle can provide a good source of Cu. The high oxidized and water-rich parent magma is favorable for the enrichment and metallogenesis of copperophile elements and is a favorable condition for the formation of porphyry copper deposits. Therefore, we suggest that there may be a high-oxidized magmatic rock and mineralization zone in the southern margin of Gangdis, including the Xiongcun porphyry copper-gold deposit in the early and middle Jurassic. It is related to the large-scale magmatic activity caused by the Jurassic subduction of the NeoTethys oceanic crust and has a good prospect of porphyry copper deposit prospecting. In view of the large-scale uplift and denudation in the southern margin of Gangdis after the Cretaceous, the exploration of new subducted porphyry copper-gold deposits in this area should be mainly concentrated in the early and middle Jurassic volcanic outcrops.
【作者单位】：中国科学院广州地球化学研究所中国科学院矿物学与成矿学重点实验室;中国科学院大学;中国科学院广州地球化学研究所同位素地球化学国家重点实验室;钦州学院广西北部湾海洋灾害研究重点实验室;
【基金】：中国科学院战略性先导科技专项(B类)(XDB03010302) 科技部国家重点研究计划(2016YFC0600407)
【分类号】：P588.1;P618.2

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