TECTONIC AND GEOCHEMICAL CHARACTERISTICS AND RESERVED CONDITIONS OF AMANTLE SOURCE GAS ACCUMULATION ZONE IN EASTERN CHINA

Along both sides of the Tancheng-Lujiang Fracture Zone in eastern Chin a, a series of mantle source gas pools constitute a massive-scale tect onic accumulation zone in NNE direction, with the mantle geochemical c haracteristics of high concentrations of CO2 and He, high He-3/He-4-Ar -40/Ar-36 ratio system and high delta(13)C(co2) ratios (the main frequ ency, -3.4 parts per thousand-4.6 parts per thousand), showing no diff erence from the tectonic framework of the area. In the area, the tecto nic environment is a rift formed as a result of diapiric mantle inject ion and crust thinning to form graben-type basins and lithospheric fra ctures. The mantle-derived volcanic rocks and inclusions are well-deve loped and a high geothermal zone (mantlesource) exists in the area. Th e characteristics of the three components (solid, liquid and gas) of m antle, concentrated all over the same tectonic space zone, show that t he rift system is of a good tectonic environment or passage for mantle degassing and gas migration. The main types of the gas pools are volc ano, fault-block, anticline, buried hill and so on, but most of them a re combination traps closely related with fracture. For the mantle sou rce gas pools, rift is an optimum tectonic region, and nearby lithosph eric fracture, mantle source volcanic rocks or basement uplifts are a favourable structural location when reservoir-caprock association deve lops.