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Abstract:
The Central Asian Orogenic Belt (CAOB), located between the Siberia and Baltica cratons to the north, and the Tarim and North China cratons to the south, is a large and long-lived accretionary orogen that extends from the Urals in the west through Kazakhstan, Magnolia, China to the Okhotsk Sea in Russia, with the ocean closing during Neoproterozoic to the Late Phanerozoic. Quaternary volcanoes and earthquakes are widespread in the northeastern China of eastern CAOB, along with high heat flow background, obviously affected by the subduction of the Pacific slab; however, the range and manner of this subduction effects still remain elusive. Seismogenic depths in northeastern China show that, bounded by the Great Xing’an Range, the seismicity in the west is diffusely distributed in the crust, with a bimodal pattern as the upper and middle/lower crust (15-25 km); while for the east area, the seismicity only occurs in the upper crust (~15 km). Rheological modeling demonstrates, only the rheologically weak crust in the east with wet condition and strong crust in the west with dry condition, can reconcile the observed seismicity, suggesting the control of differential crustal rheology. Combing with other geological and geophysical observations, we propose that the stagnation and associated dehydration of the subducted Pacific slab underneath the northeastern China could account for this rheological contrast. Our findings further confirm that the North-South Gravity Lineament in East China, geographically representative of the Great Xing’an Range-Taihang Mountain, as a large-scale tectonic boundary, marks the westward limit of the subduction.
