黄山-镜儿泉铜镍成矿带地层时代的厘定及其地质意义探讨

本文对东天山黄山-镜儿泉岩浆铜镍硫化物成矿带原来古生物地层学方法厘定的早石炭统干墩组和晚石炭统梧桐窝子组的碎屑锆石进行了激光等离子质谱(LA-ICP-MS)U-Pb年代学研究。干墩组碳质板岩、变质砂岩和变质长石石英砂岩中的碎屑锆石U-Pb年龄分别为301~491 Ma、307~426 Ma和313~461 Ma,最年轻锆石的加权平均值分别为307.1±3.7 Ma、310.4±2.2 Ma、315.0±10 Ma,表明干墩组最大沉积年龄为晚石炭世。而梧桐窝子组变质砂岩和变质凝灰岩的碎屑锆石年龄为384~448 Ma和393~448 Ma,最年轻锆石的加权平均值分别为386.5±5.8 Ma、394.6±4.5 Ma,确定其最大的沉积年龄为早—中泥盆世。这与近年来对侵位于这些地层的火成岩体的锆石U-Pb年龄一致,说明康古尔-雅满苏岛弧带至少从中泥盆世就开始发育。中—下泥盆统梧桐窝子组与上石炭统干墩组地层之间上泥盆统—下石炭统地层厚度约为10 km,说明侵位于这两套地层中的含铜镍硫化物镁铁-超镁铁岩体分别代表了岩浆通道系统的深部岩浆通道相和浅部岩浆房,整个岩浆通道系统的纵向规模大约为10 km。

Determination of sedimentary ages of strata in the Huangshan- Jingerquan mineralization belt and its geological significance

U-Pb ages of the detrital zircons from Gandun and Wutongwozi Formations along the Huangshan-Jingerquan Ni-Cu metallogenic belt were determined using LA-ICP-MS(laser ablation-inductively coupled plasma-mass spectrometry).The U-Pb ages of detrital zircon from the Gandun carbonaceous slate,meta-sandstone,and meta-arkose are 301~491 Ma,307~426 Ma and 313~461 Ma,respectively.The weighted mean ages of the youngest zircons of these three samples are 307.1±3.7 Ma,310.4±2.2 Ma,315.0±10 Ma,respectively,indicating that the maximum sedimentary age of the Gandun Formation is Late Carboniferous.The U-Pb ages of detrital zircons from the Wutongwozi metasandstone and meta-tuff are 384~448 Ma and 393~448 Ma,respectively.The weighted mean ages of the youngest zircons of the two samples are 386.5±5.8 Ma and 394.6±4.5 Ma,respectively,suggesting a sedimentary event in the Early-Middle Devonian.This is consistent with recent zircon U-Pb ages of the plutons emplaced in the Wutongwozi Formation.The new U-Pb ages of the detrital zircons from the Gandun and Wutongwozi Formations demonstrated that the subduction along the Kanguer-Yamansu arc belt was initiated in the Middle Devonian.The Upper Devonian-Lower Carboniferous strata between the Wutongwozi and Gandun Formations are~10 km thick.This implies that the magma conduit system for the Ni-Cu sulfide mineralization extended at least 10 km in vertical direction;the Ni-Cu sulfide-bearing mafic-ultramafic intrusions emplaced in the Wutongwozi and Gandun Formations represent magmatic conduit in the depths and the magma chambers in the shallow levels,respectively.