Origin and geodynamic relationships of the Late Miocene to Quaternary alkaline basalt volcanism in the Pannonian Basin, eastern-central Europe

摘要

Alkaline basaltic volcanism has been taking place in the Carpathian-Pannonian Region since 11 Ma and the last eruptions occurred only at 100-500 ka. It resulted in scattered low-magma volume volcanic fields located mostly at the margins of the Pannonian basin. Many of the basalts have compositions close to those of the primitve magmas and therefore can be used to constrain the conditions of the magma generation. Low degree (2-3%) melting could occur in the convective asthenosphere within the garnet-spinel transition zone. Melting started at about 100 km depth and continued usually up to the base of the lithosphere. Thus, the final melting pressure could indicate the ambient lithosphere-asthenosphere boundary. The asthenospheric mantle source regions of the basalts were heterogeneous, presumably in small scale, and included either some water or pyroxenite/eclogite lithology in addition to the fertile to slightly depleted peridotite. Based on the prevailing estimated mantle potential temperature (1300-1400oC) along with number of further observations we exclude the existence of mantle plume or plume fingers beneath this region. Instead, we propose that plate tectonic processes controlled the magma generation. The Pannonian basin acted as a thin-spot after the 20-12 Ma syn-rift phase and provided suction in the sublithospheric mantle, generating asthenospheric flow from below the adjoining thick lithospheric domains. A near vertical upwelling along the steep lithosphere-asthenosphere boundary beneath the western and northern margin of the Pannonian basin could result in decompressional melting producing low-volume melts. The youngest basalt volcanic field (Perşani) in the region is inferred to have been formed due to the dragging effect of the descending lithospheric slab beneath the Vrancea zone that could result in narrow rupture at the base of the lithosphere. Continuation of the basaltic volcanism cannot be excluded as inferred from the still fusible condition of the asthenospheric mantle. This is reinforced by the detected low-velocity seismic anomalies in the upper mantle beneath the volcanic fields.