Accretionary processes of the central segment of Beishan: Constraints from structural deformation and 40Ar-39Ar geochronology

The Beishan Orogenic Belt is a key area for understanding the accretionary tectonics of the southern Central Asian Orogenic Belt. The pervasively deformed metamorphic complexes and associated intrusive rocks from the central segment of Beishan are keys to illuminating the accretionary history of Beishan Orogenic Belt. In order to put constraints on the timing of metamorphism-deformation for the rocks in the central Beishan, this study carried out field geological, microstructural and 40Ar-39Ar geochronological studies on these rocks. The rocks from the central Beishan have undergone widespread ductile shearing deformation. Biotite 40Ar-39Ar dating on four samples yield respective plateau ages of 323.1 +/- 3. 6Ma, 296.0 +/- 3. 7Ma, 261.2 +/- 3. 1Ma and 209.2 +/- 4.0Ma, which are younging from the north to the south. Combined with the spatial-temporal distribution of major litho-tectonic units, these data reveal a northward subduction of oceanic plate (Niujuanzi Ocean) and southward accretion of the orogen during the Paleozoic-Early Mesozoic in the central segment of Beishan. The last orogenic pulse of the Beishan may have extended to the Triassic.