Metamorphic Core Complex Structure and Uplifting Mechanism in Lajishan-Hualong Area
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摘要: 中祁连拉脊山、化隆地区的变质核杂岩是由韧性变形的太古宙、元古宙化隆群变质岩系组成核; 由脆-韧性变形和经受了低压变质的中、上寒武统和岩体组成中间层; 由脆性变形和未变质的下白垩统组成盖层.变质核杂岩的组成与结构显示了对称伸展和隆升的特征.23~ 32Ma是快速隆升的时期.主剥离断层剪切位移量约25~ 27km, 并根据矿物对计算, 变质核杂岩的伸展变质温度约625~ 630℃, 变质深度约20km, 变质压力约为0.63GPa, 属偏低压型区域热流变质作用.从青藏高原热壳、热幔、厚壳的演化历史及构造隆升活动来看, 认为拉脊山、化隆变质核杂岩是地幔热隆引起地壳伸展的典型实例, 是研究青藏高原岩石圈结构和高原隆升的重要窗口.Abstract: This paper studies the metamorphic core complex in Lajishan-Hualong area, middle Qilian. Its core consists of Archeozoic and Proterozoic Hualong Group metamorphic complexes undergoing ductile deformation, with its median layers, Middle-Upper Cambrian and mass of magmatic rocks undergoing plastic deformation of low-pressure metamorphism, and overlayers, Lower Cretaceous experiencing minor brittle deformation without metamorphism. The composition and texture of the metamorphic core complex show features of symmetrical extension and uplifting and a rapid uplifting period within 23 to 32 Ma and displacement quantity of normal denudational faults about 25-27 kilometres. The mineral pair calculation measures its extensional metamorphic temperature about 625-630 ℃, the metamorphic depth about 20 km and the metamorphic pressure about 0.63 GPa, which shows that it should belong to a regional thermal current metamorphism of low-pressure type. In the light of long run thermal crustal, thermal mantle, thick crustal evolution and tectonics upwelling of the Qinghai-Tibet plateau, the Lajishan-Hualong metamorphic core complex can be considered as a typical example of crust extension caused by thermal upwelling of mantle. The Lajishan-Hualong area can, therefore, become a window to look into the structure and tectonic upwelling of the Qinghai-Tibet plateau lithosphere.
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Key words:
- metamorphic core complex /
- thermal upwelling /
- extensional tectonic /
- Lajishan
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图 1 拉脊山—化隆一带热隆伸展构造
1.第四系河流冲积; 2.上第三系贵德群; 3.下第三系西宁群; 4.志留系; 5.下奥陶统; 6.中、上寒武统; 7.新太古—古元古化隆群; 8.花岗岩体; 9.志留系花岗闪长岩体; 10.闪长质混杂岩; 11.穹状变质核杂岩体; 12.正断层; 13.逆断层; 14.主折离断层韧性剪切带; 15.伸展拉伸线理产状; 16.剖面位置
Fig. 1. Thermal upwelling structure from Lajishan to Hualong
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