Forming age and tectono-petrogenises of the Jiugequan ophiolite in the North Qilian Mountain, NW China

• 来源期刊: 科学通报(英文版)
• 学科: 地球科学
• 关键词: 北祁连山 形成时代 蛇绿岩 构造 北祁连造山带 中国 净重 板块俯冲
• 年，卷（期）: 2010,（18）
• 页码范围: 1899-1907
• 页数: 9页
• 分类号: P315.2 P588.121
• 语种: 英文

摘要

The Jiugequan ophiolite is one of the representative ophiolite fragments in the Early Paleozoic orogenic belt of the North Qilian Mountain.It has been drawn much attention and extensively studied in recent years.In this study,ion microprobe(SHRIMP) U-Pb dating was carried out for zircons from isotropic gabbro from the Jiugequan ophiolite.Eighteen analyses yield a relatively consistent apparent 206Pb/238U ages from 480 to 508 Ma with a weighted mean age of 490±5 Ma(MSWD=1.06),which is believed to be the crystallization age of the gabbro and thus the forming age of the Jiugequan ophiolite.Major and trace element geochemical study indicates that the diabase-basalts from the Jiugequan ophiolite have N-MORB and E-MORB characteristics with some subduction-related signatures.The petrological,geochemical and chronological data enable us to conclude that the Jiugequan ophiolite is most likely to be formed at a spreading center of back-arc basin during the early Ordovician,while the ancient Qilian oceanic plate subducted northwards.The acquisition of forming age and determination of tectonic setting for Jiugequan ophiolite provide significant constraints on the evolution of intra-oceanic subduction system in the North Qilian orogenic belt during the Early Paleozoic era.