大型花岗岩基形成和演化的深部动力学过程：滴水构造、钾质火山作用与地表地质过程

以美国内华达山脉复合岩基为例,系统评述了与大型花岗岩基的形成、演化相关的深部地球动力学过程及构造地貌学响应.在大陆岛弧环境下,基性岩浆的底侵作用促使下地壳发生角闪岩脱水部分熔融,在岩基根部形成高密度的石榴辉石岩,岩基根部最终发生重力失稳,形成滴水构造;在地貌上反映为滴水构造对应区域的沉降和相应的张性构造,在岩浆作用上则表现为软流圈地幔上涌和残余富集岩石圈地幔的低程度部分熔融,形成钾质火山岩.这种高度动态的深部动力学过程是维持大型花岗岩基地区较高高程或促使这些区域高程骤然增加的重要因素.

Root zone processes for the formation and evolution of a large-scale granitic batholith:drip structures,potassic volcanism and Earth surface processes

Taking the Sierra Nevada batholith for example, the authors give a comprehensive review of the root zone processes and tectonogeomorphic responses during the formation and tectonic evolution of a large-scale granitic batholith. In a continental arc environment, the processes responsible for the formation and evolution of a large-scale batholith involve (1) basaltic magma underplating near the lower crust-upper mantle; (2) dehydration and partial melting of lower crustal material, production of a large volume of granitic magma and related high-density garnet pyroxenite at the root of a batholith; (3) occurrence of negative gravity instability; (4) removal of such high-density material beneath a granitic batholith as drips, either spontaneously or induced by nearby deformation; (5) potassic basaltic volcanism by low degrees of partial melting of the residual lithospheric mantle; (6) large-magnitude surface subsidence and tensional deformation directly above the drip structure; and (7) abrupt rise of mountain belts. Highly dynamic drip tectonics as imaged in the southern Sierra Nevada batholith may have been a major factor that maintains the high elevation of the Sierra Nevada mountain range.