Geochemistry and tectonic settings of basalts from the Tangbale ophiolite
The Tangbale ophiolite consists of serpentinized harzburgite,lherzolite,dunite,podiform chromitite,basalt,gabbro,and abyssal radiolarian chert and occurs in the Kulumudi terrane,which is situated on the southern margin of West Junggar,northwest China.We report here the geochemical data obtained for basalt blocks embedded in the Tangbale ophiolite with the aim of constraining the tectonic setting.The basalts are tholeiitic in composition with SiO2 varying from 44.89%to 46.46%,high total Fe2O3(10.02%-11.03%),low abundances of P2O5(<0.11%)and MgO(4.76%-7.00%),with Mg#varying from 31 to 46.The basalts have total(K2O+Na2O)varying from 3.69%to 4.12%,and are relatively enriched in Na(NaO2/K2O=6.7-10.4).The basalt samples have low rare earth element concentrations(∑REE=(63.0-93.1)×10-6),and their Chondrite-normalized rare earth element patterns can be divided into two groups:the one group is characteristized by slightly enriched light rare earth element(LREE)and less differentiated heavy rare earth element(HREE)((La/Yb)N=2.97-4.56),similar to those of the E-MORB;the other is characterized by slightly depletion of LREE and less differentiated HREE((La/Yb)N=0.67-0.89),similar to those of N-MORB.The overall basalt samples show weak or no Eu anomalies(Eu/Eu*=0.91-1.07),enrichment of LILEs(Rb,K and Ba),depletion of HFSEs(Ti,Zr and Hf),and obvious negative anomalies for Nb and Ta.The basalts from the Tangbale ophiolite likely derived from a spinel lherzolite mantle source in a suprasubduction zone setting.Combined with previous research data,our results demonstrate that West Junggar was in an intra-oceanic subduction regime in the Cambrian.
万方数据
维普
