| Abstract: | Geology setting and petrological features Qiangtang composite plate is located between Xijinwulan—Jinshajiang and Bangonghu—Nujiang suture zones, with the total area of several ten thousand square kilometers. The exposed rocks are mainly Paleozoic, Mesozoic marine sedimentary rocks.. Around Zhabu—Shuanghu area, there exits a post late Triassic uplift, in which middle Devonian low\|intermediate degree metamorphic rocks with solid chronological evidence have been found. However, in central Qiangtang, debate is still there in several aspects, such as there is crystalline basement or not, basement features, and the pre\|Devonian evolution of Qiangtang plate, etc. (Cai Li et al.,1997)Duguer gneiss is the only proved gneiss in Qiangtang region upto now, which is exposed at Duguer mountain (peak, 6208m above sea level), Gaize county, and is confined by faults. An E—W oriented thrust fault zone is its south boundary, which is more than 200m wide and makes the gneiss overthrust on upper Carboniferous strata and Tertiary red beds southwardly. On the east and north sides of the gneiss are upper Carboniferous strata. The gneiss occurs as a triangle form with a long E—W trending bottom line (about 20km) and a height about 10km in S—N direction, which is the main part of Duguer Duguer mountain.Duguer gneiss consists of two rocks types, i.e. granitic gneiss (the dominant component) and amphibole\|plagioclase gneiss. The latter one occurs as a group of nearly E—W trending dikes with clear boundary, which are obviously late basic dikes that intruded into granite. Granitic gneiss is composed of porphyroclast granitic gneiss, banded granitic gneiss, gneissoid granite and granitic mylonite. Both granitic and amphibole\|plagioclase gneisses have been undergone same type and same degree metamorphism and deformation. The typical mineral assemblage of the former gneiss include quartz(30%), microcline(25%),plagioclase(30%), two mica (biotite +muscovite,13%) and the accessory minerals such as zircon, magnetite, and apatite etc. The main oxide contents of the granitic gneiss are (average of three samples) 73 53% SiO\-2, 12 9% Al\-2O\-3, 1 57% FeO, 0 52% MgO, 3 24%Na\-2O and 0 22% K\-2O. The REE distribution pattern shows typical features of granite, i.e. LREE enrichment, HREE depletion and rather strong negative Eu anomaly. |
