PRELIMINARY CLASSIFICATION OF THE GENETIC TYPES OF GRANITOIDS IN WESTERN YUNNAN

According to the material sourrce, rock-forming mechanism and tectonic environments, the granitoids in western Yunnan can de divided into the following four genetic tyqes. 1. Anatectic granite It is develoqed in dehind-the-continental magmatic are thrust zones and continental collision zones, with magmatic differentiation, from the early to late time, the size of the rock masses decame small, their depth pecame shallow, the degree of their differentiation increased and late-stage pneumatolytic-hydrothermal alterations were developed, so this type may de further diveded into three subtypes; anatectic emplacement granite, high-level emplacement-differentiation granite and altered granite. Its~87Sr/~88Sr ranges from 0.71168 to 0.74301, indicating that the sialic crust is of anatectic origin. The tin deposits in western Yunnan are all closely related to anatectic highlevel emplacement and altered granites. 2. metamorphic-metasomatie granite It is develoqed in the fronts of obduction continental crust, low-pressure and high-temperature metamorphie zones or dack-arc thrust oshear znes. It may de subdivided into autochthonous migmatitic granite and qaraautochthonous granite. The latter has the characteristics of both migmatitic granite and anatectic emplacement granites. It has a high ratio of ~87Sr/~86Sr （0. 71858—0. 72480）, belonging to the origin to the origin of sialic crustal reconstitution. 3. Syntectic granite It is only develoqed in volcanic island-arc zones on the active continental margins, The magma has undergone an evolution from the ultrabasic to intermediate-acid eomposition, making up a comqlete series of calc-alkaline magmas. It has a low ratio of ~87Sr/~86Sr （0.7056） and shows the features of derivation from the consuming crust and the upper mantle. The intermediate-acid prophyry contains mainly Cu, accompanied by Sn, Mo, pb-Zn and Au. Mantle-derived differentiated granite It is dominated by alkaline complex distributed along the Cenozoic Red River rift zone and alkaiine （Atype） granite is occassionally seen, It is characterized by smaii size shallow level of emplacement, high rock-forming temperature and distinct differentiation, and belongs to the high-alkaline normal series resulting from differentiation and evolution of alkaline ultrabasic and basic rocks. In the alkaline complex of rift origin there often occur Cu and Mo mineralizations associated with W, Pb-Zn and Au mineralizations.