A Study On Geochemistry And Thermochronology Of Granite In Dongan-Tangwanghe Area, Heilongjiang Province

Dongan-Tangwanghe area is at the north of xiao xing an ling, between Songnen and Jiamusi block. In this paper, The typical granites in Dongan gold mining area, Pingdingshan gold mining ara and Cuihongshan molybdenum tungsten ploymetallic mining area have been carried on the detailed field geological investiagtion, rock mass petrology, zircon U-Pb chronology, element geochemistry study and the discussion of magmatic origin of the three rock mass and the tectonic background of it formed. At the same time, the three rock mass in the studied area have been carried on the zircon and apatite fission track therchronology study and the fission track thermal history simulation of apatite samples, analysis the thermal history evolution process and the mechanism of uplift and denudation since early Jurassic combined with other isotope age, but it still needs more research to demonstrate on many issues.Rock geochemical study shows that the Pingdingshan rock mass formed in late Palezoic(259±1Ma), high in potassium calc-alkaline series of weakly peraluminous, relatively poor calcium, iron, magnesium and the type I to type A transitional biotite granite rock mass, source area substance comes from partial melting of the lower crust. It is formed in the process of the north china plate and Siberia plate collision collage combined with the development of intracontinental collision. Cuihongshan rock mass formed in the late Triassic(200±1Ma), for high in potassium calc-alkaline series of standard aluminum-weakly peraluminous transition of poor calcium, iron, magnesium rock, source area material is crust-mantle mixed type with shell source is given priority to. Formed under the stretching mechanism after the final closure of Gu Ya Zhou ocean in the procession of the north china plate and Siberia plate collision orogenic, and it is the type A monzonitic granite rock mass. Dongan rock mass formed in early Jurassic(188±1Ma), for high in potassium calc-alkaline series of weakly peraluminous poor calcium, iron, magnesium rock. It is formed In the mechanism of continues subduction of the Pacific plate, A type of coarse alkali granite with crustal material is given priority to and part of the mantle source material.Because of AFT and ZFT value of three kinds of granite is far less than the formation age of the rock mass, apatite fission track length distribution are showed nearly short and wide unimodal distribution,and the length of the track is far less than the standard initial track of apatite fission track length 16.3um, sample values of single particle age are relatively decentralized, it illustrates that the apatite experience slow cooling in the process of annealing process in the long geological history. Cuihongshan rock mass AFT is greater than the Pingdingshan rock mass, Pingdingshan rock mass AFT is greater than the Dongan rock mass, this kind of differences of fission track ae reflect the uneven pattern of tectonic uplift in the study area, it shows that Cuihongshna rock mass experience earlier uplift since late Mesozoic and uplift to the apatite fission track annealing temperature at the bottom of the isothermal surface early.AFT values of rock samples in the study area and height of sample reflects obvious positive correlation, It shows that as the progress of the uplift and the cooling effect of rock mass, the higher sample relatively uplift to the bottom of the part of the fission track annealing early; part of apatite fission track age values do not have positive correlation with the altitude of rock samples, it is likely to be local suffered from small-scale tectonic movement after the rock mass lift through 110±10°C isothermal surface depth, make the thrust nappe of the rock mass occurrence locality and lead to sample an uplifting and denudation.The history simulation of apatite fission track of apatite samples has been made on three kinds of granite rock mass,in combination with zircon fission track age, biotite K-Ar age and zircon U-Pb age, show that rock mass has experienced uneven cooling process;different stages of cooling rate, the uplift rate and quantity of the three kinds of rock mass are also calculated,Overall performance for the three stages of the inhomogeneity of the uplift;combined with the average denudation velosity, Regional denudation depth for the study area since the early Jurassic is at about 6.5Km; The three uneven uplift stage is likely to be the result of the subduction of the Pacific ocean block and large-scale asthenosphere mantle-derived magma upwelling with the intracontinental orogeny.