Geological Record of Late Eocene to Early Oligocene Lithosphere Delamination along the Jinshajiang–Red River Tectonic Zone

Abstract

Geodynamic processes following the Indo–Eurasian plate collision remain a key research focus, and the Jinshajiang–Red River tectonic zone (JRTZ), situated along this collision boundary, provides critical insights into post-collision tectonic evolution. In this study, we identify a lithological assemblage in the JRTZ, including amphibolite, granite gneiss, and migmatite. These rocks exhibit contrasting geochemical signatures, reflecting multiple source regions: asthenospheric mantle, lithospheric mantle, mafic lower and upper crust. Specifically, amphibolite (28.5 Ma) formed through the partial melting of OIB-like mantle source, whereas S-type granite gneiss (28.2 Ma) originated from the dehydration melting of metamorphosed sedimentary rocks. Amphibole monzonite (28.9 Ma) records the mixing of ancient crustal material with mantle-derived components, while migmatite (37.9 Ma) resulted from deep melting processes of metasedimentary rocks under shear conditions. We propose that the ongoing Indo–Eurasian convergence progressively thickened the crust, ultimately driving large-scale lithospheric delamination between the Eocene and Oligocene. This delamination triggered asthenospheric upwelling, which provided the thermal input required for widespread melting. This lithospheric delamination event started around 38–37 Ma and lasted at least until 28 Ma.

Keywords

asthenosphere / lithospheric delamination / lithospheric mantle / Jinshajiang–Red River tectonic zone / amphibolite

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2025 Geological Society of China