EARLY CRETACEOUS METAMORPHIC CORE COMPLEXES AND EXTENSIONAL DOMES AS A RESULT OF PARALLEL EXTENSION TECTONICS IN EASTERN EURASIAN CONTINENT

Early Cretaceous metamorphic core complexes (mcc's) and extensional domes (ed's) are distributed in a vast area of ca. 2000 km (NW)×ca. 4000 km (NE) from east China to Lake Baikal in Russia in eastern Eurasian continent. Ed's (A-type, B-type or transitional type) are dominantly localized at preexisting crustal weaknesses (e.g. along the preexisting Sulu-Dabie orogenic belt), while the mcc's occur either in the cratonic interior or along orogenic belt. The extensional structures share many characteristics. 1) Extensional basins predating mcc/ed formation evolved into supradetachment basins during progressive extension. The tectonic extension predated regional and local magmatisms, when present, of mainly crustal sources. 2) The extensional structures have almost identical kinematic directions for consistent WNW-ESE tectonic extension. 3) Their ages of formation are peaked at ca. 125±5 Ma. 4) The thermal evolution of the mcc's and ed's is variable, either slow-rapid or rapid-slow cooling, which is probably related to magmatic involvement. 5) A transformation of the lithospheric mantle occurred in some places at 122-120 Ma, which may have contributed to the lithospheric thinning of the North China craton.

Integrated studies on the extensional structures, geochemistry of syn-kinematic granitic rocks suggest that extension of the lithosphere triggered the magmatisms from both the crust and the mantle. The Early Cretaceous tectono-magmatic evolution of the eastern Eurasian continent is governed by the Parallel Extension Tectonics (PET). In the PET, detachment faulting in both the crust and lithospheric mantle resulted in the loss of some of the subcontinental roots, gave rise to the exhumation of the mcc's and ed's, and triggered transformation of the lithospheric mantle, plutonic emplacement and volcanic eruptions of hybrid magmas.

The Aegean, the Cordilleran and the eastern Eurasian extensional domains are in general related to plate convergence, but attributed to different tectonic processes. Advancing subduction and subduction roll-back are the dominant dynamic factors triggering the tectonic extension. Extensional structures in eastern Eurasian continent were related to Paleo-Pacific plate subduction, which provides a general architecture of the extensional tectonics of a rifted continent.