伊洛瓦底盆地D区块及周缘古近系物源分析

缅甸D区块是伊洛瓦底盆地中西部与Letpanto油田相邻的区块,具有一定的油气勘探潜力,对物源方向的认识存在不同观点。笔者利用沉积物砾石成分、砂岩骨架成分、地球化学元素分析方法,旨在明确伊洛瓦底盆地D区块及周缘古近纪物源方向和类型,进而指导本区沉积相与油气资源勘探研究。砾石分析结果显示,存在自西向东方向的物源,古新世物源来自中、酸性火成岩,始新世来自浅变质岩、中性及基性火成岩。砂岩骨架成分分析显示,古近纪地层物源均来自弧造山带,既有大陆切割、未切割、过渡型岛弧来源,也有再旋回造山带来源。主量、微量、稀土元素分析结果判断物源区构造背景均属于大陆岛弧和主动大陆边缘,具有安山岩物源区特征。综合分析认为,本区古近纪物源演化具有一定继承和相似性,物源主要来自盆内链状岛弧和东部掸邦高地,喜马拉雅造山带不可能从北部直接提供物源。推测北部喜马拉雅造山带通过伊洛瓦底江从东部进入,为盆地提供物源。

Provenance Analysis of the Paleogene Strata in Block D and Peripheral in Irrawaddy Basin

Myanmar block D located in the midwest of the Irrawaddy basin,adjacent to Letpanto field,has a certain prospect of oil.There are many different views on provenance of sedimentary among previous study results.Our aims are to make clear the direction and type of the Palaeogene provenance of the block D and the Periheral in the Irrawaddy basin,then to guide the research on facies and the oil and gas exploration by the analytical method of identification of gravel composition,statistical analysis of sandstone fragment components and the analysis of sedimentary geochemistry.The analysis results of patrtical granularity of the gravels,obtained by optical microsope,suggest that there could be one provenance which is the east of the Irrawaddy basin.The rock source of the Palaeocene was consisted of intermediate and acidic rock,but the Eocene provenance came from epimetamorphic and intermediate-basic rock.The analysis of sand detrital composition statistics revealed that provenance of Paleogene strata was derived from the mixed source,contained recycled orogen and the transitional,dissected and undissected arc.The major element,rare-earth element (REE),trace element geochemical analyses show that tectonic settings are all belong to the continental arc and active continental margin and provenances have andesite characteristic.Conbined with previous analysis,it is concluded that the Palaeogene provenance has certain inheritance and similarity.Provenances were mainly from the chain-like island arc in the basin and the highlands of the Shan Plateau in the eastern of basin.The hypothesis that sediments were directly derived from the Himalayan orogen through the northern of the Irrawaddy basin has been denied by the analysis results.It could be that sediments were provided through Irrawaddy River from the east of the basin into the sedimentary province.