福建紫金山矿田深部似斑状花岗闪长岩锆石SHRIMP U-Pb和单矿物^(40)Ar/^(39)Ar年龄及其地质意义  

Zircon SHRIMP U-Pb and Single Mineral ^(40)Ar/^(39)Ar Dating of Granodiorite from the Deep Part of the Zijinshan Orefield in Fujian Province and its Geological Significance

作　　者：黎敦朋[1] 邱小平[1,2] 张文慧[1] 刘文元[1] 于波 

机构地区：[1]福州大学紫金矿业学院,福建福州350108 [2]中国地质科学院地质研究所,北京100037 [3]广东省地质建设工程集团公司,广东广州510080

出　　处：《大地构造与成矿学》2016年第4期783-797,共15页Geotectonica et Metallogenia

基　　金：国家自然科学基金"巨厚层高硫化型低温热液矿床深部铜硫化物成分特征研究"(41172075);国家科技支撑项目"中国东部铁铜铅锌重要矿集区深部资源勘查技术与示范"课题(2009BAB43B04)共同资助

摘　　要：通过对福建紫金山矿田深部与成矿作用有关的主期似斑状花岗闪长岩3组锆石SHRIMP U-Pb和2组角闪石、钾长石^(40)Ar/^(39)Ar测年,获得锆石^(206)Pb/^(238()U加权平均年龄为101.8±1.5 Ma(n=34,MSWD=1.0),代表紫金山矿田深部与成矿作用有关的主期似斑状花岗闪长岩的成岩年龄;同时获得角闪石^(40)Ar/^(39)Ar冷却年龄为100±11 Ma、102.2 Ma,钾长石的^(40)Ar/^(39)Ar冷却年龄为96.3±1.7 Ma、98.5 Ma。依据矿物封闭温度理论,估算紫金山矿田深部与成矿作用有关的主期似斑状花岗闪长岩由锆石结晶至角闪石40Ar/39Ar体系封闭、再到钾长石^(40)Ar/^(39)Ar体系封闭的岩石冷却速率分别是40.7~67.1℃/Ma、116.9~216.3℃/Ma,显示岩石的冷却速率较大;由古地温梯度推算主期似斑状花岗闪长岩结晶(101.8±1.5 Ma)至钾长石^(40)Ar/^(39)Ar体系封闭(96.3±1.7 Ma)期间岩体隆升剥露了约3 km,暗示地壳在这一时期发生了快速隆升剥蚀作用。紫金山矿田深部似斑状花岗闪长岩锆石206Pb/238U年龄佐证了紫金山矿田深部存在一个大岩基,并约束了紫金山矿田斑岩型矿床的成矿时代,单矿物的^(40)Ar/^(39)Ar年龄为矿区的隆升剥露研究提供新资料。The isotopic ages of the main porphyraceous granodiorite at the deep part of the Zijinshan orefield of Fujian province, China, were dated by using in-site zircon SHRIMP U-Pb method and hornblende and potassium feldspar 40Ar/39Ar method. The 206pb/238U weighted average ages of the zircons from three samples are 102.8±1.5 Ma （n=13, MSWD=0.67）, 102.4±1.7 Ma （n=9, MSWD=0.73）, 100.4±1.8 Ma （n=12, MSWD=1.2）, respectively. The three samples as whole yielded a weighted average age of 101.8±1.5 Ma （n=34, MSWD=1.0）, which most likely represents the age of crystallization of the porphyraceous granodiorite. The 40Ar/39Ar dating of two hornblende and two potassium feldspar samples yielded isochron ages of 100±11 Ma, 102.2 Ma, 96.3±1.7 Ma, and 98.5 Ma, respectively. Based on the theory of mineral sealing temperature, the cooling rate of the rocks of the main porphyraceous granodiorite at the deep part of the Zijinshan orefield is estimated to be about 40.7-67.1 ℃/Ma from crystallization of zircon to closure of hornblende 40Ar/39Ar system, 116.9-216.3 ℃/Ma from closure of hornblende 40Ar/39Ar system to closure of potassium feldspar 40Ar/39Ar system. Both of the estimated cooling rates of the rock are rather high. In comparison with the paleogeothermal gradient, the pluton uplift and exhumed 3 km from crystallization （101.8±1.5 Ma） to the closure of potassium feldspar 40Ar/39Ar system （96.3±1.7 Ma）, suggestive of rapid uplift and exhumation during this period. The dating results show that there is a large batholith at the deep part of the Zijinshan ore field which contributed to the porphyry mineralization. Single mineral 40Ar/39Ar dating results provided meaningful constraints on the uplift and exhumation of the deposit.

关 键 词：锆石SHRIMP U-Pb测年 40Ar/39Ar测年 岩石冷却 似斑状花岗闪长岩 紫金山矿田 

分 类 号：P597[天文地球—地球化学]