Magmatism in the Pamir: tracing crustal and mantle processes

古地幔岩石圈的对流减薄、软流圈的抬升和岩石圈的熔融、板片剥离以及几个陆内俯冲带上方的岩浆活动是目前对青藏高原岩浆活动起源的构造解释。帕米尔高原的岩浆活动预计也会有类似的原因。我们在TIPAGE束第一阶段的工作表明，帕米尔地区含有几个新生代岩浆套，它们可能与印度-亚洲碰撞带构造演化的不同阶段有关。A套包括镁铁质到长英质、火山岩和深成岩，可能覆盖45-20 Ma，并可能标志着印度在亚洲以下的长期陆内俯冲。B套由玄武岩至安山岩组成，年龄约为20 Ma，可能与印度的板岩-卷曲作用有关。C套包括约20-10 Ma的钾质/超钾质岩石，中到长英质岩石，可追踪印度岩石圈的断裂及其对亚洲大陆岩石圈的影响。在这个项目中，我们将阐明这种岩浆活动在时间和空间上的分布，它的岩石学、性质和地球化学成分，它的源区的组成和时间演化，熔融条件，以及它与与大陆内俯冲、地壳增厚、伸展和折返相关的变形和变质历史的成因耦合；我们在其他子项目中解决的所有方面。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；我们还将尝试与西藏的岩浆活动进行对比。在方法上，我们将采用岩浆岩石学、常量元素和微量元素相结合的方法，并结合当地的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).