昆秦接合部海西期苦海—赛什塘分支洋的存在及其证据

张智勇; 殷鸿福; 王秉璋; 王瑾; 张克信

昆秦接合部海西期苦海—赛什塘分支洋的存在及其证据

1.
中国地质大学地球科学学院, 湖北武汉 430074
2.
青海省地质调查院, 青海西宁 810012

基金项目:

教育部优秀博士论文基金项目“造山带混杂岩区非史密斯地层研究———以青海东昆仑和拉脊山混杂岩带为例” 200228

中国地质调查局项目“1:25万兴海幅地质填图” 19961300010122

“1:25万冬给措纳湖幅地质填图” 19961300010121

详细信息

作者简介:
张智勇(1964-), 男, 地质高级工程师, 在读博士, 主要从事青藏高原区域地质填图与研究

中图分类号: P53
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出版历程
- 收稿日期: 2003-10-18
- 刊出日期: 2004-11-25

Presence and Evidence of Kuhai-Saishitang Branching Ocean in Copulae between Kunlun-Qinling Mountains

1.
Faculty ofEarth Sciences, China University ofGeosciences, Wuhan 430074, China
2.
Geological Survey Institute ofQinghai, Xining 810012, China

摘要

摘要: 在昆仑与秦岭造山带东、西接合部位, 通过详细填图与解剖发现海西期在苦海—赛什塘一带, 存在一条NEE向与东昆仑布青山—阿尼玛卿洋相连通的分支小洋盆, 称为苦海—赛什塘分支洋.晚泥盆世—石炭纪是苦海—赛什塘分支洋扩张时期, 出现大量似洋壳物质, 雪穷、错扎玛洋脊型蛇绿岩是该时期的物质表现, 蛇绿岩组合中的⁴⁰Ar/ ³⁹Ar年龄(368.6± 1.4) Ma, 与布青山-阿尼玛卿洋扩张洋盆形成时期相吻合.扩张形成的苦海—赛什塘分支洋蛇绿岩组合显示属于发育不成熟的有限小洋盆.扩张作用表现之一是大量记录在裂解块体岩片和结晶基底中的构造热事件, 如龙通斜长角闪岩、角闪石低温坪年龄(358.9± 3.2)Ma(⁴⁰Ar/ ³⁹Ar)、羊曲云母石英构造片岩黑云母坪年龄(387.3± 2.3)Ma(⁴⁰Ar/ ³⁹Ar)、苦海黑云斜长片麻岩等时线年龄(336± 2.2)Ma(Rb- Sr)、扎那合惹斜长角闪岩角闪石低温坪年龄(376.9± 0.9)Ma(⁴⁰Ar/ ³⁹Ar)等反映了裂解时限; 其次是侵入裂解块体岩片中的拉龙洼辉绿岩墙群辉石³⁹Ar/ ⁴⁰Ar坪年龄为398.4 Ma, 反映初始扩张始于泥盆纪.早-中二叠世分支洋发展进入俯冲消减阶段, 早期沿柴达木微陆块东南缘形成了早二叠世岛弧火山岩(264 Ma)和纳木龙俯冲型花岗岩(267 Ma), 晚期随着俯冲作用加剧, 发生中高压相变质, 并沿消减带逐步形成俯冲增生杂岩楔.晚二叠世在柴达木和若尔盖微陆块相互作用下, 发生弧-陆碰撞对接, 昆秦接合部地区苦海—赛什塘分支洋闭合, 弧-陆碰撞过程形成了晚二叠世搓卡碰撞型含白云母花岗岩和格曲组同碰撞磨拉石沉积.
- 昆秦接合部 /
- 苦海—赛什塘 /
- 海西期 /
- 分支洋 /
- 多岛小洋盆
Abstract: A branching ocean basin, to be known as the Kuhai-Saishitang branching ocean, has been discovered in the area between the Kunlun and Qinling Mountains, China. The Kuhai-Saishitang branching ocean was discovered by detailed mapping and analysis, which revealed an ophiolite complex in a north-north-east orientated branching basin connected to the (Buqingshan) -Animaqing ocean. The basin includes Xueqiong and Cuozama MOR-type ophiolites which indicate that spreading of the basin took place in the Late Devonian-Carboniferous. This is supported by an Ar⁴⁰/Ar³⁹ age for the ophiolite complex/compound (which compound?) of (368.6±1.4) Ma, which is contemporaneous with the formation of the Buqingshan- (Animaqing) ocean. The ophiolite present indicates that the oceanic lithosphere of the Kuhai-Saishitang basin formed in a small, immature ocean basin. One behavior of expansion is tectonic hot event heavy recorded in cracking block slice and crystal base, for instance, amphibole ⁴⁰Ar/³⁹Ar low temperature plateau age of amphibolite in Longtong area is (358.9±3.2) Ma, biotite ⁴⁰Ar/³⁹Ar plateau age of mica-quartz tectonic schist in Yangqu area is (387.3±2.3) Ma, Rb-Sr isochrone age of biotite plagioclase-gneiss in Kuhai area is (336±2.2) Ma, amphibole ⁴⁰Ar/³⁹Ar low temperature plateau age of amphibolite in Zanaheruo is (376.9±0.9) Ma, these ages reflect cracking time limit. The pyroxene ³⁹Ar/⁴⁰Ar plateau age of diabase in cracking slice in Lalongwa is 398.4 Ma which reflects that expansion began in the Devonian. There is evidence of the formation of a volcanic island arc in the Early Permian (264 Ma) and subduction occurring along the south-east edge of the (Chaidamu) minor continental block in the Early-Middle Permian (267 Ma). The subduction is marked by the presence of subduction-type granite which was altered by middle-high pressure metamorphism as the strength of the subduction increased. Also associated with the subduction zone is a hyperplasia mélange wedge. In the Late Permian, the interaction of the Chaidamu and Ruoergai minor continental blocks caused arc-continent collision which resulted in the closure of the Kuhai-Saishitang branching ocean and the formation of collision-type mica-containing granite in the Cuoka area and the deposition of syn-collision molasse sediments of the Gequ Group.
- joint area between Kunlun and Qinling Mountains /
- Kuhai-Saishitang /
- Hercynian /
- branching ocean /
- archipelagic oceanic basin

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图 1 昆秦接合部区域构造略图

1.蛇绿岩; 2.东昆仑昆南混杂岩带; 3.西秦岭苦海—赛什塘混杂岩带; 4.东昆仑布青山混杂岩带; 5.阿尼玛卿混杂岩带; 6.滑脱带; 7.横推(走滑) 断层; 8.逆冲带

Fig. 1. Sketch of area structure in the joint with Kunlun-Qinling

下载: 全尺寸图片幻灯片

图 2 海西期苦海—赛什塘分支洋演化

Fig. 2. Evolution on Hercynian branching ocean in Kuhai-Saishitang

下载: 全尺寸图片幻灯片

表 1 秦昆接合部海西期岩浆事件及造山过程

Table 1. Hercynian orogenic process and magmatic event on the Kunlun marches with Qinling

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