摘要
桐柏山是秦岭 -大别山造山带的重要组成部分 .新近的构造学和岩石学详细研究表明 ,该区广泛分布有大量的、大小不一的榴辉岩及退变质榴辉岩块体 ,构成一个延展长约2 0 0km和宽约 4 0km的高压变质带 .由榴辉岩或退变质榴辉岩、遭受过高压变质作用的沉积和火山岩、由榴辉岩退变质而成的片麻岩和片岩、以及面理化的含榴或不含榴的花岗岩组成的高压变质单位 (HP) ,在组成及变质演化特征方面 ,均与大别—苏鲁地区的高压单位类似 .构造上 ,显示一典型的西北美型变质核杂岩 .分隔开由桐柏杂岩组成的核部杂岩单位 (CC)及上覆的高压单位的km尺度的伸展拆离带 ,具有下和中伸展拆离带的复合性质 ,是在高压变质作用期后伸展体制下形成的 .桐柏山高压变质带是与大别山地区的高压变质带相联接的 ,据其岩石学、构造学及相关的主要构造边界展布特征 ,推测该高压变质带穿过南襄盆地有继续向东秦岭延伸的趋势 .桐柏山高压变质带是东秦岭造山带与大别—苏鲁超高压和高压变质带间的构造纽带 .
The Tongbai Mountains is an important component part of the Qinling-Dabieshan orogenic belt. The recent detailed researches in tectonics and petrology show that a great amount of eclogites or retrograded eclogites in different sizes, widely distributed in the Tongbai mountains, constitutes a high-pressure metamorphic belt, around 200 km long and 40 km wide. The high-pressure metamorphic unit is generally composed of the following four different major lithologies: (1) eclogites and retrograded eclogites; (2) HP-metamorphosed sedimentation and volcanic rocks; (3) gneissic or schistose rocks resulting from retrogressive HP eclogites; and (4) foliated garnet-bearing granites or garnet-free granites. The rock assemblages and metamorphic evolution of this high-pressure unit are similar to those in the Dabie-Sulu ultrahigh pressure (UHP) and high-pressure metamorphic belts. The regional structural pattern of the HP metamorphic belt in the Tongbai Mountains corresponds perfectly to a Cordilleran-type metamorphic core complex where three crustal-scale, gently-dipping, normal-sense detachment zones were developed. The composite detachment zone resulted possibly from both the lower detachment zone and the middle detachment zone is presently sandwitched between the core complex unit (CC) below, and the high-pressure metamorphic unit (HP) above. The structures controlling the present spatial distribution of HP metamorphic rocks were dominantly products of an extensional process following the Triassic HP metamorphism. Both structural considerations and concordant field relations suggest that the Tongbai HP metamorphic unit is an important part of the Dabie-Sulu UHP and HP metamorphic belts. Its western extension overlain by the Mesozoic to Cenozoic sedimentary rocks may have crossed the Nanxiang basin to the Eastern Qinling. The new findings and ideas should be employed for the reconstruction of the evolution of the whole Qinling-Dabie orogenic belt. The Tongbai high-pressure metamorphic belt serves as a structure lining the Eastern Qinling orogen with the Dabie-Sulu UHP and HP metamorphic belts.
出处
《地球科学（中国地质大学学报）》
EI
CAS
CSCD
北大核心
2001年第6期551-559,共9页
Earth Science-Journal of China University of Geosciences
基金
国家重点基础项目 (No :G19990 75 5 0 6)
国家自然科学基金项目 (No .49972 0 67
No .40 0 730 0 5 )
关键词
桐柏山
高压变质带
变质核杂岩
伸展拆离带
构造边界
构造纽带
榴辉岩
Tongbai mountains
high-pressure metamorphic belt
metamorphic core complex
extensional detachment zone
tectonic boundary
structural linkage.
