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The Petrography, Geochemical Characteristics And Tectonic Implications Of Lvhepu,Hebei

Posted on:2015-02-13Degree:MasterType:Thesis
Country:ChinaCandidate:K BiFull Text:PDF
GTID:2250330428466987Subject:Geological Engineering
Abstract/Summary:PDF Full Text Request
Formed in the lower crust, the granulite clearly recorded tectonic environmentevolution of the lower crust and even the crust-mantle boundary. In conjunction withpetrographic, geochemical aspects of their knowledge of research,it has an importantsignificant scientific in terms of that it can restore the evolution of craton.The Hongqiyingzi Gr research region is located in the north of ShangYi-Congli-ChiCheng-Taimiao-PingQuan fault zone, whose overall trend is almosteast-west,with covering the middle part of the northern margin of North China Craton,and rock types are mainly (pomegranate) Biotite Plagioclase Gneiss and amphiboliteplagioclase.Some geologist thought Hongqiyingzi Gr was the formation of terrigenoussediment,terrigenous deposits of Paleoproterozoic before. But in its southern tipinside-research found a large amount of degeneration eclogite and other tectonic lens,so that we believe that this should be the Archean ocean crust and ophiolite belt.However, during the past two years, the research region has been continuouslyresearch, some scholars also believed that here is the subduction and closure of thepaleo Asian Ocean in the process of. The tectonic background ofthe region’scontroversial. It makes that the structural environment of the region has been disputedagain.This paper mainly through the study of granulite samples of northern area ofHebei Province we have a certain discussion about characteristics of identifiedpetrographic, geochemical aspects of their characteristics of research, its terms of theoriginal rock type, tectonic environment, and the formation mechanism. It’s aneffective constraint for the metamorphic process during the evolution late ofPaleozoic geological in this region. The research of the tectonic processes hasscientific value in this research region.The main results are as follows:(1) The petrographic study has shown that the mineral assemblage in early high-pressuregranulite facies metamorphism is Cpx+Grt+Pl+Qtz and in later hornblende facies metamorphismis Grt+Amp+Pl+Qtz respectively. However, the retrogressive metamorphism is incomplete.(2) According to the garnet-hornblende geological thermometer, the retrogressivemetamorphism temperature of amphibolite facies is between520-570℃. The petrochemistry studyhas shown that the initiation of Lvhebu granulite formed in the back arc basin.(3) The hornblende facies metamorphic granulite and the serpentinite in situ formed a seriesof ophiolite suite. The existing chronology data indicate that the researched region is a Palaeozoicoceanic remnant.In the Carboniferous, the researched region had experienced stretching plate motions.Large-scale thermal events lead to intense regional retrograde metamorphisms. Thedecompression with a temperature decrease in the process of reaching the surface, the granuliteexperienced hornblende facies retrogressive metamorphism. However, the rapid uplift made theretrogressive metamorphism incomplete. The disintegration and interpenetration on the wayreturning to surface made the granulite lenticularly interpenetrate in the crevice of the gneissprotolith. The gneissosity structure was formed by the function of stress after returning to thesurface, which could explain why the gneissosity structure grew around the granulite. In the late Paleozoic, the Paleozoic evolution history of northern North China was completed with theclosure of the small ocean basin.
Keywords/Search Tags:granulite, petrography, geochemistry, tectonic setting
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