ELEMENTAL GEOCHEMISTRY AND PETROGENESIS OF PERMIAN BASALTS IN LUOJI,SHANGRI-LA

The basalt occurred in the Luoji area of Shangri-la County is studied in the aspects of their petrology and geochemistry and its petrological genesis is discussed.It is showed that the w(SiO2) contents of the basalts vary from 45.08% to 50.50%,and characterized by high w(MgO)(2.86%~14.73%) and w(Na2O+K2O) contents 1.78%~6.34%(Na2OK2O),suggesting that these rocks belong to alkaline basalt series.Chondrite-normalized patterns for the basalts exhibit flat but moderate depletion in HREE(LREE/HREE=1.88~9.61) without Eu anomalies(δEu=0.91~1.10),and the primitive mantle-normalized spidergrams show relatively enrichment in the LILE(Rb,Ba,Sr,and Pb),but depletion in the HSFE(Nb,Ta,Zr and Hf),with obvious wave of Ba and Sr.Based on the above geochemical features,it is proposeg that these basalts were derived from partial melting(5%~20%) of the enriched lithospheric mantle of the garnet-spinel mantle peridotites in the tectonic setting of convergent plates.Meanwhile,the parental magma experienced intense mineral fractional crystallization,including olivine,clinopyroxene,apatite and rutile.Meanwhile t weak crustal contamination occurred during magma ascent.