We present here a tectonic-geodynamic model for the generation and flow of partially molten rocks and for magmatism during the Variscan orogenic evolution from the Silurian to the late Carboniferous based on a synthesis of geological data from the French Massif Central. Eclogite facies metamorphism of mafic and ultramafic rocks records the subduction of the Gondwana hyperextended margin. Part of these eclogites are forming boudins-enclaves in felsic HP granulite facies migmatites partly retrogressed into amphibolite facies attesting for continental subduction followed by thermal relaxation and decompression. We propose that HP partial melting has triggered mechanical decoupling of the partially molten continental rocks from the subducting slab. This would have allowed buoyancy-driven exhumation and entrainment of pieces of oceanic lithosphere and subcontinental mantle. Geochronological data of the eclogite-bearing HP migmatites points to diachronous emplacement of distinct nappes from middle to late Devonian. These nappes were thrusted onto metapelites and orthogneisses affected by MP/MT greenschist to amphibolite facies metamorphism reaching partial melting attributed to the late Devonian to early Carboniferous thickening of the crust. The emplacement of laccoliths rooted into strike-slip transcurrent shear zones capped by low-angle detachments from c. 345 to c. 310 Ma is concomitant with the southward propagation of the Variscan deformation front marked by deposition of clastic sediments in foreland basins. We attribute these features to horizontal growth of the Variscan belt and formation of an orogenic plateau by gravity-driven lateral flow of the partially molten orogenic root. The diversity of the magmatic rocks points to various crustal sources with modest, but systematic mantle-derived input. In the eastern French Massif Central, the southward decrease in age of the mantle- and crustal-derived plutonic rocks from c. 345 Ma to c. 310 Ma suggests southward retreat of a northward subducting slab toward the Paleotethys free boundary. Late Carboniferous destruction of the Variscan belt is dominantly achieved by gravitational collapse accommodated by the activation of low-angle detachments and the exhumation-crystallization of the partially molten orogenic root forming crustal-scale LP migmatite domes from c. 305 Ma to c. 295 Ma, coeval with orogen-parallel flow in the external zone. Laccoliths emplaced along low-angle detachments and intrusive dykes with sharp contacts correspond to the segregation of the last melt fraction leaving behind a thick accumulation of refractory LP felsic and mafic granulites in the lower crust. This model points to the primordial role of partial melting and magmatism in the tectonic-geodynamic evolution of the Variscan orogenic belt. In particular, partial melting and magma transfer (i) triggers mechanical decoupling of subducted units from the downgoing slab and their syn-orogenic exhumation; (ii) the development of an orogenic plateau by lateral flow of the low-viscosity partially molten crust; and, (iii) the formation of metamorphic core complexes and domes that accommodate post-orogenic exhumation during gravitational collapse. All these processes contribute to differentiation and stabilisation of the orogenic crust.

The South Tibetan Detachment (STD) in the Himalayan orogen juxtaposes low‐grade Tethyan Himalayan sequence sedimentary rocks over high‐grade metamorphic rocks of the Himalayan crystalline core. We document infiltration of meteoric fluids into the STD footwall at ~17–15 Ma, when recrystallized hydrous minerals equilibrated with low‐δD (meteoric) water. Synkinematic biotite collected over 200 m of structural section in the STD mylonitic footwall (Rongbuk Valley, near Mount Everest) record high‐temperature isotopic exchange with D‐depleted water (δD_water = −150 ± 5‰) that infiltrated the ductile segment of the detachment most likely during mylonitic deformation, although later isotopic exchange cannot be definitively excluded. These minerals also reveal a uniform pattern of middle Miocene (15 Ma) ⁴⁰Ar/³⁹Ar plateau ages. The presence of low‐δD meteoric water in the STD mylonitic footwall is further supported by hornblende and chlorite with very low δD values of −183‰ and −162‰, respectively. The δD values in the STD footwall suggest that surface‐derived fluids were channeled down to the brittle‐ductile transition. Migration of fluids from the Earth's surface to the active mylonitic detachment footwall may have been achieved by fluid flow along steep normal faults that developed during synconvergent extension of the upper Tethyan Himalayan plate. High heat flow helped sustain buoyancy‐driven fluid convection over the timescale of detachment tectonics. Low δD values in synkinematic fluids are indicative of precipitation‐derived fluids sourced at high elevation and document that the ground surface above this section of the STD had already attained similar‐to‐modern topographic elevations in the middle Miocene.

In the Rhône Valley near the city of Montélimar, a Mw 4.9 surface-rupturing earthquake occurring on the 11th of November 2019 was linked to the reactivation of the NE–SW trending normal La Rouvière fault as a reverse fault mechanism. Here, we present the first in situ calcite U–Pb data acquired on well-characterized microstructures from core samples from a first exploratory drilling conducted in the NE part of the La Rouvière fault. In agreement with relative chronology data based on microstructural observations, our results allow us to define four main tectonic events: A first event from ~90 to 75 interpreted to reflect a thermal subsidence at the regional scale (Ardèche—South-East basin of France), a second event bracketed between ~60 to 50 Ma related to the N–S trending shortening of the South-East basin, a third tectonic event dated from ~40 to 37 Ma that we interpret to reflect the opening of the Gulf of Lion and European Cenozoic Rift System (ECRIS), and a fourth and final event at ~25 Ma that very likely represents a middle to late stage of the ECRIS. No more recent event has been identified on this fault.

The South Tibetan Detachment (STD) is parallel to the east–west-trending axis of the Himalayan range over >1500 km and represents an untapped source of information for understanding the coupling between multi-scale deformation processes, fluid flow, exhumation of high-grade rocks and topography. Here, we present hydrogen isotope ( δ ² H) geochemistry, quartz c -axis fabric deformation thermometry and electron microprobe micro-analyser data from a strand of the STD exposed in NW India (the Zanskar Detachment). Our data document intense meteoric fluid–rock–deformation interactions within the upper part of the hot (>400°C) mylonitic footwall to the detachment, which was active at 22–20 Ma. Calculated δ ² H _water values ranging from −115 to −95‰ suggest that the Zanskar area was standing at least above 2500–3000 m mean topographic elevation during the early Miocene. When compared with previous data obtained from Mt Everest, our results suggest that high topography along the Himalayan range was diachronous, occurring at c . 20 Ma in the western Himalaya (>3000) and at c . 15 Ma in the Central Himalaya (>5000 m). This study highlights the close relationships between topography, meteoric fluid flow, high heat flux and exhumation of the Himalayan Crystalline Core.