From Periphery Collision to Intraplate Orogeny: Early Paleozoic Orogenesis in Southeastern Part of South China

Xu Yajun; Du Yuansheng

Abstract：The Early Paleozoic Kwangsian Orogeny in South China is considered to have resulted from the intraplate deforma tion.However the geodynamic mechanism for the intraplate deformation remains unclear.The Early Paleozoic orogenesis is marked by a regional unconformity between pre-Devonian and Devonian strata and multiple stratigraphic unconformities developed within the Early Paleozoic sequence in the local areas of southeast South China.The Kwangsian magmatism,metamorphism and palaeontological variation are dated from 460 to 380 Ma.These events are in age linked to the multiple unconformities between the Ordovician and Devonian sequences.The unconformity between the Late Cambrian and Early Ordovician,named as the Yu'nan Event in the southern margin of South China,is lack of contemporaneous petrological records,except for minor metamorphic rocks dated at 530-480 Ma.The range of this unconformity corresponds with timing of orogenic activity extending along the northern margin of East Gondwana.Derivation of detrital zircons from the Cambrian and Ordovician strata in the southern part of South China suggests that in the Cambrian South China constituted part of the north India and the Sanya Block presented currently in Hainan Island had not been part of South China but rather part of western Australia until the juxtaposition of South China and west Australia in the Early Ordovician.The event removed the Cathaysia Block from any spatial association with an active plate boundary and permitted the stresses sourced from the accretionary orogen in East Gondwana to propagate inboard across the supercontinent.These stresses localized along the site of the weak rheological Nanhua basin and consequently resulted in basin inversion and development of the intraplate Kwangsian Orogeny.The Early Paleozoic orogenesis in the southeastern part of South China evolved from periphery collision in the Yu'nan Event to intraplate orogeny in the Kwangsian Orogeny.