大别山北部漫水河灰色片麻岩的锆石U-Pb年龄及其地质意义  

Zircon U-Pb age and its geological implications of the gray gneiss to the northern Manshuihe in the North Dabie Mountains

作　　者：江来利[1] 刘贻灿[1] 吴维平[1] 李惠民[2] 方中[3] 

机构地区：[1]安徽省地质调查院,安徽合肥230001 [2]天津地质矿产研究所,天津300170 [3]南京大学地球科学系,江苏南京210093

出　　处：《地球化学》2002年第1期66-70,共5页Geochimica

基　　金：国家自然科学基金(40072070;49572150)

摘　　要：北大别杂岩主要由灰色片麻岩和斜长角闪岩组成。通过对大别山北部霍山漫水河花岗闪长片麻岩的锆石U-Pb年龄测定,得到中元古代、早三叠世和晚侏罗世3组年龄数据。中元古代的年龄老于灰色片麻岩集中在新元古代的锆石U-Pb上交点年龄,指示漫水河北部片麻岩中有古老锆石捕掳晶;早三叠世年龄指示该片麻岩中有印支期变质作用形成的锆石;晚侏罗世年龄表明灰色片麻岩中有燕山早期形成的岩浆锆石。根据北大别杂岩的构造背景、变质作用及地球化学特征,认为北大别杂岩中的部分灰色片麻岩形成于燕山早期的花岗闪长岩,它们可能源自或混染了经过早三叠世变质作用的扬子陆块俯冲基底。本文的结果表明,北大别杂岩既不是形成于白垩纪的岩浆杂岩,也不完全是形成于新元古代的TTG岩系,其中的部分灰色片麻岩为形成于燕山早期的花岗闪长岩,即在白垩纪大规模岩浆作用前的燕山早期,北大别曾有过一次岩浆作用。The North Dabie Complex is composed mainly of gray gneisses and amphibolite. Three sets of zircon U Pb age are obtained from the gray gneisses to the northern Manshuihe, Huoshan County in the North Dabie Mountains, they are Mesoproterozoic, Early Triassic and Late Jurassic. The Mesoproterozoic age is older than the upper intercept ages of the Neoproterozoic zircon U Pb from the gray gneisses in the North Dabie Complex, indicating that the gneisses to the northern Manshuihe contains old zircon xenocrystals. The concordia ages of (217.8±8.9) Ma and (155.9±8.4) Ma suggest that there are metamorphic zircons formed during Early Triassic and magmatic zircons produced during Late Jurassic from the gray gneisses, respectively. According to the tectonic setting, metamorphism and geochemical characteristics of the North Dabie Complex, part of the gray gneisses may be granodiorite formed during Late Jurassic, and which may be derived from or contaminated with the Triassic metamorphic subducted basement of the Yangtze continental block. It is suggested that the North Dabie Complex is neither the Cretaceous magmatic complex, nor completely the Neoproterozoic TTG gray gneisses; some of them may be granodiorite formed during Late Jurassic. In other words, there happened a magmatic event in Late Jurassic before the Cretaceous extensive magmatic event in the Northern Dabie Mountains.

关 键 词：北大别杂岩 灰色片麻岩 锆石U-PB定年 大别山 构造背景 变质作用 

分 类 号：P588.345[天文地球—岩石学]