GEOCHEMICAL CHARACTERISTICS OF ROCKS AND MINERALS OF BLUESCHISTS AND GREENSCHISTS IN ORDOVICIAN TERRANE IN THE NORTHERN QILIAN MOUNTAINS SUNAN COUNTY,GANSU PROVINCE
北祁连奥陶系地体中蓝片岩、绿片岩岩石矿物化学特征及地质意义

Metavolcanic rocks of Ordovician tectonic terrane mainly make up blu-eschists, greenschists, lavas and tuffs in the Sunan county. Geocbemical characteristics of rocks displays an isosource evolutional system, most of the rocks are basic and intermediate. Their nature belongs to oceanic tholeiitic series. Comparison to bluecchists and greenschists of the Shuksan (Washi-ngto.) indicates that the Sunan samples have similar magmatic differential trend, but the primitive differential level of the Sunan magma is lower, correspond to modern MORB composition of the FAMOUS area (after Owen, 1989) . They are divided into LREE-depleted group and mildly LREE-enri-ched group. Samples of LREE-depleted group are selected for comparison with blueschists and greenschists of the Shuksan, their geological formation setting meaned N-type MORB. According to chemical characteristics of minerals, lawsonites and pumpellyites of the Sunan can be compared with lawsonite zone and pumpellyite zone of the jadeite-glaucophane type facies series in Cazadero (California), high-p metamorphic environment of the Sunan plate movement took place at depths of above 20 km in the underplating subduction zone.