GEOCHEMISTRY OF CENOZOIC VOLCANIC ROCKS FROM TENGCHONG, WESTERN YUNNAN

Tengchong Cenozoic volcanic rocks, which consist of basaltic trachy-andesite, trachy-andesite, and basaltic andesite, belonging to the high-K and calc-alkaline series, are continental intraplate volcanic rocks erupted after the Tethys Ocean was closed. They are distributed near the collision zone of the Indian plate and the Eurasian plate. The geochemical features of the rocks can be used to define the tectonic properties and magma sources. The systematic geochemical study of the typical rock samples by XRF and ICP-MS shows that the rocks are characterized by high K₂O, CaO, low TiO₂, and high Mg # (averaging about 46). REE shows a LREE-enriched pattern with significantly negative Eu. Large ion lithophile elements (LILE) and high field strength elements (HFSE) are enriched compared to the primitive mantle, and the LILE have higher enrichment than the HFSE. Th shows a significantly positive anomaly. The geochemical composition of the studied volcanic rocks is similar to the volcanic arc magma, suggesting that the magmatic activity was triggered by the subduction of the Indian plate down to the Eurasian plate. Characteristic element ratios show that the magma may be derived from the subduction-related EMⅠmantle.