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Geochemistry Of Intrusive Rocks In Jiangzi-Kangmar Region,tibet

Posted on:2016-10-17Degree:MasterType:Thesis
Country:ChinaCandidate:Y W WangFull Text:PDF
GTID:2180330461956191Subject:Mineralogy, petrology, ore deposits
Abstract/Summary:PDF Full Text Request
Gyangze County-Kangma County area belongs to the Himalayas, southern magmatic belts, study issues related to magmatic rock geochemistry of the region is weak.On the 1:50,000 mapping work, based on the geochemistry, isotope age, petrogenesis, tectonic background, etc. the author researched the monzogranite in Kangma Complex Rocks and the basic rock and intermediate rock emplaced in Mesozoic strata, and finally obtained the following understanding:(1) Contents of Monzogranite in Kangma Complex Rocks: Si O2-72.33~73.68%; Al2O3- 14.34~15.04%; the ratio of K2O/Na2O-1.04~1.47; which belongs to Belongs potassium quality, peraluminous, calc-alkaline rock series, with high Si O2, K2 O, low Fe2O3, Mg O, Mn O, A/CNK greater than 1.4, and it is similar with typical Upper crustal source S-type granites. Trace elements show that rich LILE Rb, rich high-strength field elements Th, Ce, Hf, depleted LILE elements of high-strength field elements K, Ba; varying degrees of depleted high Ta, Nb, Zr, Sm, Y, Yb, with Rb-Th peaks and Nb-Ta trough to show its contamination by the lower crust. Rare Earth Elements ΣREE of 215.39×10-6~405.33×10-6, ΣLREE/ΣHREE ratio of 9.66~ 10.3,distribution patterns of rightist;(La/Yb)N-10.09~12.85 LREE enrichment; δEu-0.36~0.6, with negative Eu anomaly. Show on its attributes eutectic formed crust. Kangma Complex Rocks is acidic Complex long-term evolution of the multi-stage secondary magmatism formed through a variety of tectonic environments. As main components of Kangma Complex Rocks, the cooling ages of the monzogranite is Early Ordovician(485.0 ± 1.8Ma), and relates to the extensional tectonic environment after Pan-African event.(2) Contents of Basic Rock(including Gabbro, Diabase Gabbro, Diabase, Diabase Porphyry):Si O2-43.07%~50.2%,(Na2O/K2O)-1.28~49.17,(Na2O+K2O)-1.55%~ 5.31%; major elements Fe O, Mn O and Mg O were positively correlated; Si O2, Ti2 O, Na2 O, K2 O, P2O5 and Mg O were negatively correlated, and there is no obvious law in Al2O3、Fe2O3、Ca O and Mg O, all of which show that it is the result of the middle part of the lower crust melting, with the feather of alkaline, within tholeiitic basalts board. Trace Elements show that all samples are enrichment of LILE enrichment and loss of HFSE in different levels. The contents: ∑REE-42.84×10-6~318.16×10-6,∑LREE/∑HREE- 1.52~7.52,δEu-0.78~1.18 with the feather of weak Eu anomaly, which shows that it is the product of lower crust- the middle part of the molten magma mantle. The cooling crystallization age of the Basic Rock is in Early Jurassic(177Ma), when the Brahmaputra has northward subduction, and it show that plate of the passive margin of northern India, in the preamble of oceanic crust occurs Yexia care stretch upper mantle upwelling caused by lower crust- upper mantle partial melting occurred due to moderate.(3) Contents of Intermediate Rock(Diorite, Diorite-porphyrite): Si O2-52.34%~63.54%, with features of potassic rocks, calc-alkaline rocks; and the major elements is obvious law, which displays its shell source magma differentiation weak form; varies degrees of enrichment of LILE,;depletes HFSE; ΣREE to 210.77 × 10-6~446.92×10-6,ΣLREE/ΣHREE 7.02~26.73,LREE enrichment, δEu-0.67~0.77,a moderate negative Eu anomaly, all of those feathers show that the under partial melting of crustal magma weak high differentiation form. The cooling crystallization age of the Intermediate Rock is in Early Cretaceous(126Ma), when the Brahmaputra northward subduction occurs oceanic round the north and the Indian plate passive margin has been more long-term evolution. Intermediate Rock should be caused in overall stretch of passive continental margin mantle upwelling continued to lead to lower crustal section shallower lithospheric melting.
Keywords/Search Tags:Tibet, Monzogranite, Basic Rock and Intermediate Rock, Geochemistry, Petrogenesis, Tectonic Environment
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