摘要
首次对藏东南原称的瓦浦组进行系统的岩石化学研究 ,发现它包括了两套不同时代和大地构造环境下形成的火山岩。瓦浦组火山熔岩由下部的玄武岩夹玄武安山岩和上部的流纹岩组成 ,是古特提斯洋盆中的洋岛火山岩 ,其时代初定为早二叠世—晚二叠世早期。在觉马—巴格和扎西所见的岩层是以钙质浊积岩为主的火山 -沉积岩系 ,火山岩为岛弧拉斑玄武岩 ,属晚三叠世早期活动大陆边缘产物。上述发现为碧土带是复杂的造山带拼贴体。
The geological survey in early 90's discovered the Bitu ophiolite in southeast Xizang(Tibet),which comprehends the Bitu tectono magmatic zone a complicated orogenic collage;and named the Wapu Formation which is Late Triassic sediments interlayered with andesites.Our study,the first systematic work of petrochemistry on the volcanic rocks,reveals that the Wapu Formation may include two volcanic suites with varied tectonic settings and ages.The volcanic rocks in Wapu and Jushui consist of,in ascending order,basalt as well as sub ordinate basaltic andesite,continent erupted rhyolite,tuff and volcaniclastic rocks.The petrochemistry features indicate the tectonic setting of an oceanic island,which may be one of Hawaiian type,and erupted in Early Permian early Late Permian.The volcano sedimentary strata,with principal part calcareous turbidites and outcroping at Juema Bage and Zhaxi,are products of an active continental margin:the island arc tholeiite recording a subduction of the major oceanic basin of Paleotethys in early Late Triassic.The Jushui,Xueba and other oceanic islands have been discovered in southeast Xizang,the recognition of Wapu oceanic island supports further evidence for the major oceanic basin of Paleotethys being an archipelago.The volcano sedimentary rock formation comprehends a relative wide back arc basin in early Late Triassic,which can be well comparable with that in southwest Yunnan:an active continental margin of Mariana type during that time.
出处
《现代地质》
CAS
CSCD
北大核心
2000年第1期21-28,共8页
Geoscience
基金
国家自然科学基金重点项目 !(项目号 :492 3 2 0 3 0和4973 2 10 0 )
关键词
藏东南
火山岩
大地构造环境
岩石形成
瓦浦组
Paleotethys,oceanic island,active continental margin,southeast Xizang
