盆地形成及成矿与地幔流体间的成因联系

文中共讨论以下5个问题:(1)盆地起源于幔壳溃变和膨隆,后者是地幔流体(超临界态(>375℃)HACONS流体,简称幔汁)上涌、渗入、交代、富化、致熔的产物。地幔流体造成油气盆地深部的高热流、异常超高压、伊利水云母化、硅化和地层有机碳的加氢成油作用。(2)盆地成矿可分两大阶段,先是沉积时的同生成矿;地层沉积后还有众多的后生成矿。两者组成“盆地矿套”(杜乐天,2002)。成矿无论同生还是后生,其分布均受断裂控制,都和地幔流体活动有关。(3)黑色页岩的实质是碳-硅-泥三元岩系,和热液成矿中的碳酸盐-硅质-泥质蚀变三元完全相当。此类岩系中总是有几十种亲壳亲幔亲气元素的特殊富集。奇异的是,石油、油页岩、沥青及砂岩型铀矿彼此有完全类似的继承性元素特殊富集。此等元素群不可能都是来自盆地之外蚀源区岩体的风化。研究证明,相当多的元素是地幔流体携带上来的。(4)盆地地层中广泛发育由地幔流体衍生的热液作用。(5)盆地实质上是气盆,全盆地排气。许多气田是地幔流体排气形成的。沙漠(原地型)和天然气田的共生很值得注意,两者皆源于地球强烈排气,导致地下和大气增温,过度蒸发,不易降雨,长期干旱而形成沙漠。

Genetic relationship between basin formation, associated mineralization and mantle fluids

This paper describes the following aspects: (1) Basins are generated by the upwelling of upper mantle into the crust. Upwelling of asthenospheric mantle induces fluid circulation in the crust resulting in high geothermal gradients, and alteration of the rocks with illitization, sericitization and silification, as well as hydrogenation of organic matter to produce hydrocarbons. (2) Basins are associated with the formation of ore deposits. (3) Black shales are carbonaceous-siliceous-argillaceous sedimentary rocks, commonly found in sedimentary basins, oil, oil-shales, bitumens and sandstone-type U mineralization may be present in these basins. These ore components and hydrocarbons are not derived from the weathering of igneous rocks surrounding the basins. Studies reveal that these components are related to deep fluids that are associated with the upper mantle. (4) Intense hydrothermal activity is common in these basins.(5) Genetic relation between desert-formation and mantle outgassing.