Magmatism in the Pamir: tracing crustal and mantle processes

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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).