Accretion of an early Paleozoic Alaska-type arc onto northern North China: Implications for continental growth of the Central Asian orogenic belt

The accretionary orogenesis of the Central Asian orogenic belt is essential for understanding the reconstruction and growth of the Asian continent. The origin and accretion of the Bainaimiao arc along the northern margin of North China remain controversial. Here, a comprehensive study of field geology, geochemistry, and geochronology was performed on plutons and an ophiolite-bearing accretionary complex in the Ganqimaodu region, Inner Mongolia. Geochemical data indicate that ca. 445-431 Ma plutons were generated in an intra-oceanic arc and represent the western extent of the Bainaimiao arc. Field mapping and zircon U-Pb dating revealed that the ophiolitic melange contains ca. 470-435 Ma tectonic blocks of ultramafic rocks, gabbros, plagiogranites, and metavolcanic and siliceous rocks in a matrix of intensely foliated quartz schist. The pillow basalt-limestone sequence might have originated from a seamount and then been incorporated into the accretionary complex. Northward subduction of the South Bainaimiao Ocean was responsible for the early Paleozoic tectonic evolution of the Bainaimiao arc, based on the spatial-temporal configuration of arc magmatism and accretionary complexes. Integration of new data with previous studies indicates that the Bainaimiao arc was an Alaska-type arc with various components of intra-oceanic and continental arcs. We suggest that a scissor-like arc- continent collision led to the accretion of the Bainaimiao arc onto the northern margin of North China, which played a fundamental role in the continental growth of the southern Central Asian orogenic belt.