TWO TYPES OF CENOZOIC HIGH-K MAGMATINSM IN EASTERN TIBET:IMPLICATIONS FOR THE NATURE OF MANTLE SOURCES

Cenozoic high\|K igneous rocks are widely distributed in eastern Tibet. These rocks are exposed as flows, dykes and small intrusions along a narrow north\|south trending zone, which follows Tertiary fold belts and the Batang—Lijiang and Ailao Shan—Red River strike\|slip systems. Although several models were proposed to interpret their petrogenesis (Deng, 1989; Arnaud et al., 1991; Turner et al., 1996; Yin et al., 1995; Miller et al., 1999), their origin still remains hotly debated. Moreover, the published results were only focused on the high\|K igneous rocks resulted from partial melting of an enriched lithospheric mantle. Here, we present the detailed documents to testify the existence of a new kind of high\|K igneous rocks in eastern Tibet.Our new 39 Ar/ 40 Ar age data (Wang et al., 1999) and published age data for high\|K rocks in eastern Tibet show two distinctive magmatic episodes: one between 42Ma and 24Ma, and the other since ca.16Ma. They correspond to two types of high\|K magmatism in eastern Tibet. We name the older and younger groups as types Ⅰ and Ⅱ, respectively.