PRESSURE-TEMPERATURE CONTOURS AND PT PATHS OF THE EARLY PRECAMBRIAN ROCKS THROUGH THE YINSHAN AREA AND THEIR IMPLICATION TO THE CRUSTAL EVOLUTION

Four distinct litho-tectonic belts (zones) in the Yinshan area, North China, were identified by pressure-temperature contours and litho-tect onic features, such as the Sanggan granulite belt, Jining metasediment ary belt, Wulashan-Daqingshan front tectonic zone and Se' eratengshan belt. This area witnessed two important thermo-tectonic events. The ol der one is c. 2.5 Ga while the younger one c. 1.9 Ga. The Se' ertengsh an Neoarchaean terrane features a clockwise PT path with the decompres sion ranging from >1500 MPa to 800-1000 MPa in the Se' ertengshan belt , which implies an island are setting. The Sanggan belt is a Mesoarcha ean microcontinent reworked by Neoarchaean magma underplating, which s hows an counterclockwise PT path. During the Palaeoproterozoic period, two Archaean continent (arc) collided. The Archaean basement of the S anggan and Wulashan-Daqingshan belts overthrust northwards, the PTt pa ths of basement show a decompression from 1000-1200 MPa to 500-700 MPa . The PT paths of the Jining and Erdaowa Groups show different PTt pat hs: the former shows counterclockwise while the latter clockwise, whic h indicates that the Jining and Erdaowa groups formed in different the rmo-tectonic settings.