长江中下游初期裂谷及其找矿

CONTINENTAL RIFTS WITH PRIMARY DISCUSSION ON THE INCIPIENT RIFTING AND ORE PROSPECTING IN THE LOWER YANGTZE REACH

大陆裂谷区有着独特的地形地貌、地质、地球物理和壳幔结构特征,本文探讨了其形成和发展过程。在此基础上,提出长江中、下游中生代以后具有大陆裂谷初期阶段的特征,并指出在这个带中找矿应注意的几个问题。

Continental rifts are ready to be discerned by their distinctive features in geo- morphology,geophysics and crust-mantle structures.The whole process of rifting can be divided grossly into four stages:i.e.crustal doming,fault depressing,rift matur- ing and ocean formation.Most of the mineral deposits related to rift magmatism were emplaced under up-doming geological settings at the early stage of rifting, whereas the stratiform and stratabound ones were characteristic of fault depressions. Geomorphologically,the Lower Yangtze Reach appears to be a relative lowlying land with altitude difference of 1000m.Since Mesozoic Era,the area was filled wi- th very thick volcanic rock and red bed which shows a typical graben sag.The magma- tic activity is very strong during this Era resulting in many normal graben rock types which mostly indicates that the faults have cut into upper mantle.Accord- ing to seismic research results,the average thickness of crust of the area is ab- out 24.67 km which is thiner than that of normal crust.