Geochemical characteristics and tectonic settings of Carboniferous volcanic rocks from Ludong-Wucaiwan area,Junggar basin.
2009; Science Press; Linguagem: Inglês
ISSN
2095-8927
Autores Tópico(s)Geochemistry and Elemental Analysis
ResumoCarboniferous volcanic rocks from Ludong-Wucaiwan area of Junggar basin mainly composed of basalts,basaltic andesites and andesites occur within Upper Carboniferous Batamayineishan Formation,and are mainly Calc-alkaline series.These rocks have moderate Mg~#(38～57) values,relatively high alkali((K_2O + Na_2 O) = 4.75%～6.16%),TiO_2(0.96%～2.04%) contents and Na_2O/K_2O ratios(2).They are enriched in LREE((La/Yb) N =2.4～4.7),and with slight fractionation of HREE((Gd/Yb) _N = 1.5～1.8),and possess weak Eu anomalies(δEu = 0.89～1.05 ),without significant Ce anomalies.These samples are enriched in LILE but relatively depleted in HFSE,with strong negative Nb-Ta anomalies.They have high La/Nb(2.0～2.8 ),Zr/Y(3.95～7.03 ),but low Th/La(≈0.1 ) ratios.Furthermore,They have relatively low I_(sr)(0.70278～0.70365 ),t _(DM)(0.47～0.67Ga),and highe_(Nd)(t)(+5.69～+8.24).These characteristics,along with the discrimination diagrams,indicate that these volcanic rocks are from extensional setting of post-collisional period,rather than typical intraplate or island arc environments,and they were produced by the ascending and melting of asthenospheric material,and the magmas were contaminated by the arc component formed before Late-Carboniferous in the processes of uplift and emplacement.The arc characteristics carried by the volcanic rocks were inherited from the pre-collisional arc component which had contaminated the source region.
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