THE CHARACTERISTICS AND TECTONIC ENVIRONMENT OF VOLCANIC ROCKS IN CHAHE AND MAOMIHE OF JINGGU,YUNNAN PROVINCE

A suite of volcanic rocks,which consist of andesites-dacites-rhyolites and mugearites, were extruded on the Chahe and Maomihe at the late Triassic period-early Jurassic period. The volcanic rocks are mostly calc-alkalic and alkalic series. Four volcanic cycles have been recognized on the section from the bottom to the top. The thickness of Chahe volcanic rocks is 972.72 meter and Maomihe 709.69 meter.The volcaniclastic rocks in Chahe account for (39.11%) and 48.6% in Maomihe. The structure of the main lava is porphyristic with porphyristic crystals of plagioclase and amphibole which can reach a maxmum amount of 55%. The volcanic rocks have standard quarts. The amount of the lanthanon increases abruptly from 64.38 to (277.09). δEu approaches 1. (La/Yb)_N is changed from 2.51 to 16.89. The distribution model is right oblique in the orientation. The distribution model of the trace element is the sawtooth seriel. The Si, P and Ti elements are evidently rare in comparison with the mantle-derived rocks. The ration of w(Zr)/w(Y) and (w(Ti))/w(Yb) is more than 3.5 and less than 500. w(TiO_2)% 0.67% on the average, w(K_2O) 2.99%.Therefore the volcanic rocks in Chahe and Maomihe belong to the continental arc environment. The sediments have complex conglomerates, sandstones, carbonate rocks and mudstones. The area belongs to the transional eruptive environment from the coastal region to the shallow sea.