花岗岩体的累积生长与高结晶度岩浆的分异

发布时间：2018-08-16 19:41

【摘要】：花岗岩成因研究是认识大陆地壳形成和分异的有效方式。野外地质和地球物理观测、岩石学和地质年代学研究以及热演化模拟证明,很多花岗岩体是在数百万年甚至更长的时间跨度内、由多次岩浆累积添加侵位而成的。地壳内可能不存在岩基尺度的大岩浆房,具有流动能力的岩浆体一般规模很小(宽度1000m)。1000m宽的岩浆体冷凝到固相线只需要数千年时间。复式岩体的形成一般要经历三个阶段,即源区岩浆沿岩墙的上升、在脆-韧性地层界面处岩墙转化为岩床以及无数的岩床的垂向堆垛导致侵入体长大。存在于上地壳的岩浆储库,特别是多次先后侵位产生的岩浆体,主体上是晶粥体,其晶体含量高,粘度大,活动性弱,不利于发生对流、分异和混合。当幔源镁铁质岩浆大规模注入到地壳时,使粘稠的晶粥状岩浆受到加热,熔体含量增大,岩浆的粘度降低,引起岩浆体内部的成分分异和不同成分的岩浆之间的混合;当逐渐加厚的熔体层产生了足够大的浮力后,特别是有挥发份加入后,就会快速上升,甚至穿透上部的晶粥体,触发大规模的火山喷发。幔源岩浆的通量越大,地壳岩浆的活动性也越强,大规模的长英质岩浆聚集就可能发生大喷发,形成超级火山。本文提出,只有将侵入岩与火山岩相结合、长英质岩石与镁铁质岩石相结合,重点从侵入体形成的时间长短、岩浆相互作用的规模和频率、岩浆通量的演变、高结晶度的岩浆分异机理、侵入岩与火山岩的关系、地幔热和物质的贡献、挥发份在岩浆分异和火山喷发中的作用等方面入手,开展野外地质、岩石学、地球化学、同位素年代学及岩浆动力学的综合研究,才能深入认识花岗岩的成因机制,深化对大陆地壳形成和演化过程的理解。
[Abstract]:The study of granite genesis is an effective way to understand the formation and differentiation of continental crust. Field geological and geophysical observations petrological and geochronological studies and thermal evolution simulations show that many granites were emplaced by multiple magma accumulation over a period of millions of years or more. In the crust, there may be no large magma chamber of rock base scale, and it takes only thousands of years for the magmatic body with flowing capacity to be condensed to the solid line in a very small scale (width 1000m) .1000m wide. The formation of complex rock mass usually goes through three stages, namely, the magma of source area rises along the rock wall, the rock wall transforms into rock bed at the interface of brittle and ductile strata and the vertical stacking of countless rock beds leads to the intrusion body growing up. The magmatic reservoir in the upper crust, especially the magmatic body produced by multiple emplacement, is mainly composed of crystalline porridge, which is characterized by high crystal content, high viscosity and weak activity, which is not conducive to convection, differentiation and mixing. When the mantle-derived magma is injected into the crust on a large scale, the viscous porridge magma is heated, the melt content increases, and the viscosity of the magma decreases, which results in the composition differentiation in the magmatic body and the mixing between the different compositions of the magma. When sufficient buoyancy is produced in the thickened melt layer, especially when volatiles are added, it will rise rapidly and even penetrate the upper porridge, triggering a large-scale volcanic eruption. The greater the fluxes of mantle magma, the stronger the activity of crustal magma, and the larger the accumulation of felsic magma, the larger the eruption and the formation of super volcanoes. In this paper, it is suggested that only by combining intrusive rocks with volcanic rocks, felsic rocks with mafic rocks, emphasis should be placed on the time of formation of intrusions, the scale and frequency of magmatic interaction, and the evolution of magmatic fluxes. The mechanism of magmatic differentiation with high crystallinity, the relationship between intrusive rocks and volcanic rocks, the contribution of mantle heat and matter, the role of volatile matter in magmatic differentiation and volcanic eruption, etc., and the development of field geology, petrology, geochemistry, etc. Only through the comprehensive study of isotopic chronology and magmatic dynamics can the genetic mechanism of granites be deeply understood and the understanding of the formation and evolution of continental crust be deepened.
【作者单位】：中国地质大学地球科学学院全球大地构造研究中心地质过程与矿产资源国家重点实验室;
【基金】：国家自然科学基金项目(41272079) 中国地质调查局项目(DD20160030)联合资助
【分类号】：P588.1

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