The Late Paleoproterozoic A-Type Granites in the Jiao-Liao-Ji Orogenic Belt, North China Craton: Petrogenesis and Implications for Post-Collision Extension

The Paleoproterozoic Jiao-Liao-Ji Orogenic Belt is a part of the Eastern Block, North China Craton. The Shuangcha rock mass has been recently recognized in Laohe group of Jiao-Liao-Ji Orogenic Belt, and it consists of mainly porphyritic monzonitic granite and porphyritic K-feldspar granite. We present detailed studies of petrography, geochronology and geochemistry of Shuangcha rock mass to constrain the petrogenesis and tectonic evolution features of the Jiao-Liao-Ji Orogenic Belt. The mineral of the Shuangcha granite consists of K-feldspar, plagioclase, quartz and a small amount of biotite ( 350 ppm) and 10,000Ga/Al ratios (average 2.69), which are typical features of A-type granite. The Shuangcha A-type granites can be further subdivided into A2-type subgroup based on some geochemical features, such as high Y/Nb ratios (0.99~3.14, average 1.84). Petrographic and geochemical studies have shown that the Shuangcha granites were the product of partial melting of quartzo-feldspathic rocks under a high temperature (>899°C), low pressure and anhydrous environment. Based on geochemical studies of Shuangcha granites, spatial and temporal distributions of regional magmatism and metamorphism records, the Jiao-Liao-Ji Orogenic Belt was in a typical post-collision extension setting in late Paleoproterozoic period (1.82~1.88 Ga) probably triggered by the slab breaks off.