Characteristics and key scientific issues of the"atypical"Caledonian orogeny in South China
The representative Caledonian Orogeny is defined as the late Silurian continent-continent collision and remote-thrusting associated with the closure of the Iapetus Ocean,resulting in a series of regional unconformities,intense metamorphism,deformation and granitic intrusions on the borders of the present Atlantic Ocean.The South China block is also considered to have experienced significant early Paleozoic movements the but bears little resemblance to the classical Caledonian Orogeny.In this paper,we propose the concept and characteristics of the"atypical"Caledonian orogenesis in South China through a comparison with representative Caledonian Orogen:① Large-scale gradually younger westward planar and non-linear granites but lacks of typical arc-affiliated basic rocks and oceanic relics.② Regional amphibolite-greenschist facies metamorphism with an absence of typical high-temperature granulites and linear high-ultrahigh-pressure metamorphic rock belts.③ Spatial differentiation of multi-stages sedimentary formations,yet there were no clear boundaries and continuous transition of sediments within the block at the same stage.We also propose some crucial scientific issues that need further resolution from the perspective of the geodynamic mechanisms:① The contact relationship between Devonian and pre-Devonian strata transitions from high-angle and low/minor angle unconformity to parallel unconformity through east to west devided by Xuefeng Mountains-Jiuling,and the deformation of pre-Devonian formations manifested in different forms of folds with axial traces from nearly E-W-oriented in the south to NE-SW in the north,however,effective means are still needed to eliminate the influence of subsequent Indosinian or Yanshanian movements,which is the basis of further discussion on geodynamic mechanisms.② The positional relationship between South China and other plates during the early Paleozoic,and coupling relation between sedimentary records at the plate scale and the global tectonic.③ Whether the dynamic process of this"atypical"orogenesis corresponds to a model of subduction-collision/oblique strike-slip-collision within South China,intraplate orogens,subduction-collision between South China and East Gondwana,or ocean-continent collision between east and west Cathaysia,remain to be determined.Answering these questions can provide significant insights into the geological processes of the Early Paleozoic orogenesis in South China and possibly serve as a typical example for understanding other"atypical"orogenesis globally.
South ChinaEarly PaleozoicCaledonian"atypical"orogeny
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