论赣东北—皖南晚元古代沟弧盆体系

THE LATE PROTEROZOIC TRENCH-BASIN-ARC SYSTEM IN NORTHEASTERN JIANGXI-SOUTHERN ANHUI PROVINCES

赣东北—皖南的元古界可分为3种岩石组合,分别属于不同的、但互有联系的构造古地理单元。赣东北—浙西火山岩带的野外地质和岩石化学特征表明它曾是一条岛弧带。对该带以北元古代浊积岩沉积特征的分析揭示了弧后盆地的发育历史。根据该带以南元古代岩石建造类型,推测其可能代表弧前及海沟地区。通过各种构造古地理分析,推断了岛弧带与弧后盆地的关系并运用沟弧盆体系的模式探讨了晚元古代构造古地理发展历史。

The late Proterozoic can be divided into three rock sequences in northeastern Jiangxi and southern Anhui provinces which represent three palaeogeographic units.The first sequence is called the Dengshan Group which is distributed from northeastern Jiangxi to western Zhejiang, comprising a volcanic series with an isotopic age of 818 Ma 122 samples illustrate a continuous change in chemical composition and, particularly, andesite is an important part in the volcanic series. In Pearce's and Wood's diagrams the majority of the volcanic rocks show an affinity to island arc. So the Dengshan Group might occur in an island arc belt.The second is called the Shangxi Group, which is represented by turbidite distributed from northeastern Jiangxi to southern Anhui. A lot of turbidite facies strata have been recognized, which may be divided into two turbidite facies associations. Association Ⅰ, lying in the north includes D, C and G facies, and association 11, B_2 and C facies, lying in the south. It is cleer that associations Ⅰ and Ⅱ reflect respectively the outer-and inner-fan positions, by which a northward developing turbidite fan is recognized in a backarc basin.The third sequence, called the Qigong Group or Tieshajie Group, crops out along the railway form Jiangxi to Zhejiang, comprising carbonate, argillaceous, siliceous and volcanic rocks. It is regarded as a trench and fore-are formation.According to the above-mentioned analysis, a late Proterozoic trench-arc basin system can be reconstructed.