Petrologic Characteristics And Petrogenesis Of The Nigzong Intrusion, Honghe County, Yunnan Province

Research area locates at a combining site, which is Anterior Margin nappe structure Ailaoshan Orogen and Changdu- Simao Basin, belonging to South of Sanjiang Metallogenetic Belt. Giving the development of magmatic activities and complex tectonic evolution, we concentrate on the Niangzong Rock Mass which breaks from late Triassic volcanics. Original data of petrology provide us a method to study the tectonic-magmatic process.Based on the field investigations, the platform appears to be a elliptical typhon prolongateing along NW-SE and inclining along NE. It intruded into the sand-mudstone of Waigucun formation from upper Trassic system without clear contact zones, however bearing xenoliths. It is little erosed compex massif.Petrology studies show thatit is a kind of rhyolite porphyry, whose phenocryst is of directional flow, high-temperature melt and micro-crack. It is believed formed in shallow-supershallow conditions.Petro-geochemistry data exhibited that the Rock Massif is aluminium high K cacl alkine- shoshonite series rich in Si, K and Al, and fall into collsion-deceleration volcanics.Primitive mantle standard of the trace elements is simial to arc volcanics, which is relatively rich in Rb,Th,U,K,La,Ce, and depleted in Ta,P,Ti,Sr.,REE characteristics are similar to collsion volcanics, suggesting fractional crystal ion is some high.Its original source is alike the S-type granite and form in syno-collision back-arc condition. So it is believed that the Niangzong complex massif is the production of partional melting of the crustal sedimentary of late Triassic, and cooled rapidly to form shallow-supershallow collision granite.