The Development Regularities And Engineering Classification Of Altered Rock In Songzong And Basu Tibet

The uplift of Tibetan Plateau is because of the collision between Eurasian plate and India plate.The geological structure and magma activity is very complex and active.In strong magma activity area of Tibetan plateau, because of the special high-altitude, high in ground stress, Highland heat and high diurnal amplitude,forming a special gneous alteration zone.In this paper, it has done systematic investigation for the distribution characteristics,reason of altered and mechanical properties of the altered rock in Songzong and Basu Tibet, and achieved the following results:(1) Summarizing the main types of altered rocks and spatial distribution, based on the research in the area, and analyzing the combination features of altered rocks through field investigation and laboratory tests. Intrusion of granite generally occurs along the regional faults, and distributes zonally along the strike of the fault in the plane. The combination relationship of the altered rock includes two types:first, the Paleocene (E1) granite intrusions in the late Jurassic (J2-3) sandstone; second, early Cretaceous (Ki) granite intrusions Carboniferous(C1) sandstone.(2) Identifying the reason of alteration in the altered rock mass. The mineral alteration of the altered rocks in research area includes that the biotite altered to chlorite, plagioclase altered to sericite, feldspar altered to muscovite and the recrystallization of quartz. Among them, chloritization generally occurs in biotite granodiorite; sericitization of plagioclase generally occurs both in biotite granodiorite and Jurassic sandstone; however the muscovitization of feldspar mainly occurs in early cretaceous granite; the recrystallization of quartz occurs mainly in Jurassic sandstone and feldspar quartz sandstone under the action of the hot liquid.(3) According to the content of quartz and feldspar in Jurassic sandstone alteration where the mineral to mineral structure is divided into three types:structure of quartz to quartz to quartz (quartz content is 75%～90%, feldspar content< 10%); structure of quartz to feldspar to quartz(quartz content 40%～50%, feldspar content 25%～40%);structure of feldspar to quartz to feldspar (quartz content<40%, feldspar content 40%～60%).(4) Obtaining the mechanics parameters of altered rock mass through uniaxial compression deformation test and summarizing that altered rock belongs to the high compressibility, high strength and breakable metamorphic rocks with high pore.The altered rock can be divided into three levels according to the rock uniaxial compressive strength and secant modulus indicators:high strength rock mass with uniaxial compressive strength of 100-200 MPa,secant modulus of 4.5～5.0×104 MPa;moderate intensity rock mass with uniaxial compressive strength of 50～100 MPa, secant modulus of 2.5～4.5×104 MPa; low intensity rock mass with uniaxial compressive strength of 25-50 MPa, secant modulus of 1 ～2.5×104 MPa.