Magmatism in the Pamir: tracing crustal and mantle processes

古代丰富的地幔岩石圈对流变薄，随后软流圈上升和岩石圈融化，板块断裂，以及几个大陆内俯冲带之上的岩浆活动是目前对青藏高原岩浆活动起源的构造解释。帕米尔的岩浆活动也有类似的原因。我们在TIPAGE束第一期的工作表明，帕米尔包含几个新生代岩浆套，这些岩浆套可能与印度-亚洲碰撞带的不同构造演化阶段有关。A套包括基性到长英质、火山岩和深成岩，可能覆盖45至20 Ma，可能标志着印度在亚洲下方长期的大陆内俯冲。B组由玄武岩和安山岩组成，年代约为20 Ma，可能与印度板块回滚期有关。C组含~20 ~ 10 Ma钾质/超古生代中长英质岩石，可追溯印度岩石圈断裂及其对亚洲大陆岩石圈的影响。在本项目中，我们将阐明该岩浆活动的时空分布，岩石学、性质和地球化学组成，源区组成和时间演化，熔融条件，以及与大陆内俯冲、地壳增厚、伸展和掘出相关的变形变质史的成因耦合；我们在其他子项目中讨论的所有方面。我们的目标是将岩浆演化及其提供的地壳和地幔信息完全整合到TIPAGE开发的地球动力学情景中；我们也将尝试与西藏的岩浆活动进行对比。系统地，我们将采用岩浆岩石学结合主微量元素，Sr-Nd-Pb和Hf同位素地球化学以及局部高分辨率地质年代学（U-Th-Pb和Ar-Ar技术）。

Convective thinning of ancient, enriched mantle lithosphere followed by asthenospheric rise and lithosphere melting, slab break-off, and magmatism above several intra-continental subduction zones are the current tectonic interpretations of the origin of magmatism on the Tibet plateau. Similar causes are expected for magmatism in the Pamir. Our work in the 1st phase of the TIPAGE bundle indicates 2 that the Pamir contains several Cenozoic magmatic suites that are potentially related to distinct stages of the tectonic evolution of the India-Asia collision zone. Suite A involves mafic to felsic, volcanic and plutonic rocks that likely cover 45 to 20 Ma and possibly mark long-lasting intra-continental subduction of India beneath Asia. Suite B, comprising basaltic to andesitic rocks dated at ~20 Ma, is potentially related to a phase of Indian slab-roll back. Suite C involves ~20-10 Ma potassic/ultrapotassic, intermediate to felsic rocks that may trace break-off of the Indian lithosphere and its effects on Asian continental lithosphere. In this project, we will elucidate the distribution of this magmatic activity in time and space, its petrology, nature, and geochemical composition, the composition and temporal evolution of its source regions, the melting conditions, and its genetic coupling to the deformation and metamorphic history associated with intra-continental subduction, crustal thickening, extension, and exhumation; all aspects that we address in the other subprojects. Our goal is a full integration of the magmatic evolution and the information it provides on crust and mantle into the geodynamic scenarios developed in TIPAGE; we also will attempt a correlation with magmatism in Tibet. Methodically, we will employ magmatic petrology combined with major and trace element as well as Sr-Nd-Pb and Hf isotope geochemistry along with local high-resolution geochronology (U-Th-Pb and Ar-Ar techniques).