Geochemical Characteristics and Geological Significance of Ultrabasic Rocks in Jiuzila Ophiolitic Mellitic Rocks in Dangxiong County,Xizang
By study the petrological and geochemical characteristics of the ultrabasic rocks in the ophiolite complex in Jiuzhaila area,the results show that the ultrabasic rocks in Jiuzhaila area are gabbro,with strong ser-pentinization.The major elements show high Mg(MgO=45.51％～46.42％),high Si(SiO2=43.93％～46.52％),poor Al(Al2O3=0.52％～0.86％)and low Fe(FeOT=8.33％～8.84％).The REE distribution model normalized by chondrite shows a trend of slightly enriched light rare earth to the right,with(La/Yb)N ranging from 0.32～9.42,with a relatively light negative Eu anomaly(Eu/Eu*=0.15～1.99)and a rela-tively light positive Ce anomaly(Ce/Ce*=0.71～1.14).The trace elements are obviously enriched in large ion lithophile elements K,Rb,P,relatively enriched in Rb,Ta,poor in Hf,Sm,Yb,belonging to a typical mafic ultrabasic rock.The minimum age of LA-ICP-MS zircon U-Pb in the sample is 119 Ma.Combined with the re-gional tectonic setting,the Tethys Ocean represented by the ophiolite in Shiquanhe area may be a local ocean basin with an independent evolutionary process,which began to subduct in the Early Jurassic and closed in the Early Cretaceous,and represents a series of interarc and backarc basin induced by the southward subduction of the Tethys Ocean.
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维普
