板内拉张环境下地壳熔融和酸性岩浆生成的数值模拟

GYIG OpenIR > 研究生 > 学位论文

	板内拉张环境下地壳熔融和酸性岩浆生成的数值模拟
	章清文
导师	朱丹
	2014
学位授予单位	中国科学院研究生院
学位授予地点	北京
学位名称	硕士
学位专业	地球化学
关键词	沉积补偿不均一拉张板内环境酸性熔体生成地壳熔融
摘要	地壳熔融和酸性岩浆的生成需要为地壳供给大量热量，确定熔融所需热量的来源对于厘定板内环境下酸性岩浆作用的成因至关重要。目前多认为地壳熔融是由高温幔源岩浆的底侵引发的，这种观点也得到多学科资料的支持。然而底侵观点未能很好地解释大规模酸性和基性大火成岩省之间在时空分布上的不相关性及S型花岗岩的成因。同时，前人对底侵进行数值模拟的结果忽略了长英质熔体难以从源区中高效分离形成可流动岩浆的事实，因而高估了镁铁质岩浆底侵可能生成的长英质岩浆量。为了解决这些问题，提出岩石圈的不均一拉张和拉张裂谷内沉积物的快速加积可使地壳内部形成较高的地温梯度，进而造成以变沉积岩为主要成分的上地壳的大规模熔融和相关S型酸性岩浆作用。如果在不均一拉张过程中岩石圈局部减薄且地表负地形（如裂谷盆地）被沉积物快速充填增厚，那么拉张过程中残留上地壳就会被上涌软流圈直接加热。针对上述思想，使用数值模拟的方法（有限差分法）对岩石圈在其拉张过程中热状态的演化和熔融状况经行了研究。结果表明，如果给定一个符合地质事实的岩石圈拉伸速度和沉积速率，在岩石圈的不均一拉张过程中地壳可以发生熔融且生成显著数量的长英质熔体。此外，如果假定沉积盆地内有足够量的沉积物且岩石圈伸展存在大规模的局部减薄，那么不同拉伸速度可能导致不同类型的岩浆活动：岩石圈在一个缓慢的拉伸速度下无熔融发生或仅有少量的镁铁质熔体生成，原因在于在此条件下由于热传导作用显著岩石圈地温梯度较低，同时软流圈减压熔融受到抑制；岩石圈快速局部减薄有可能导致双峰式岩浆作用的发生。
其他摘要	Crustal melting and the generation of silicic melt require massive heat supplied to the crust. Therefore, the source of heat is the key to understanding the genesis of silicic magmatism in an intraplate setting. It is generally accepted that this heat is derived from the hot, mantle-derived mafic magma underplated into the crust or at the Moho level. However, the underplating model, though to some extent supported by some evidences, is difficult to explain the irrelevant occurrence between the large-scale silicic and mafic magmatism and the origin of S-type granitic magma that involves the melting of sedimentary protolith in the upper crust. In addition, results of previous numerical modeling of underplating overestimate the amount of silicic magma generated by ignoring the difficulty for silicic melt to extract from its source to form mobile magmas. To address these issues, a supplementary thermal model is presented that considers the combined effects of the depth-dependent extension of the lithosphere and the depositional thickening (or thickness compensation )of the crust. We propose that the residual upper crust can be directly heated by the upwelling asthenosphere if the lithosphere is largely necked, and if the crust is thickened by rapid sediment input (e.g., in rift basins ). The results of the numerical experiments indicate that crustal anatexis does occur and that a significant amount of felsic melts can be generated during depth-dependent extension, given a geologically realistic stretching velocity and deposition rate. Moreover, given a sufficient amount of sediment within the sedimentary basin and large-scale lithospheric necking, different types of magmatism can occur under varying stretching velocities: (a )no melt or only limited mafic melt is generated at a slow stretching velocity due to the low geotherm that fails to induce crustal anatexis and the suppressed asthenospheric decompression melting or (b )bimodal magmatism caused by the rapidly necking of the lithosphere.
学科领域	矿床地球化学
语种	中文
文献类型	学位论文
条目标识符	http://ir.gyig.ac.cn/handle/352002/5899
专题	研究生_研究生_学位论文
推荐引用方式 GB/T 7714	章清文. 板内拉张环境下地壳熔融和酸性岩浆生成的数值模拟[D]. 北京. 中国科学院研究生院,2014.

条目包含的文件
文件名称/大小	文献类型	版本类型	开放类型	使用许可
板内拉张环境下地壳熔融和酸性岩浆生成的数（2025KB）			暂不开放	使用许可	请求全文