Geochemistry Characteristics And Formation Environment Of The Zanzongcuo Ophiolite In The Shuanghu County,Tibet

The Banggong-Nujiang suture zone is located in the middle of the QingHai-Tibet plateau and The Zanzongcuo ophiolite lies in Zanzongcuo,Shuanghu county,Tibet.On the base of field geological survey and which combinate mineralogy,petrology and petrogeochemistry methods to study on Zanzongcuo ophiolite.The formation environment and magma source property of Zanzongcuo ophiolite are simply investigated.According to the basal field geology survey,Zanzongcuo ophiolite included serpentinizated mantle peridotite,cumulated diamitite,mafic dike,pillow/massive lavas and radiolarian chert.The above rock units are mainly outcropped in the form of tectonic slab which is distributed in the Zanzongcuo region.The mantle peridotite in Zanzongcuo ophiolite is characterized by lower REE content than primitive mantle and depleted mantle,which displayed the wide and gentle "V" or "U" type of variation.The light rare earth elenmt are slight depleted and Eu element is negative anomaly.The gabbro unit rock displayed the deplement of light rare earth elemrnt.The heavy rare earth element distribution plots are differented but overall looks like flat.The REE distribution patterns of gabbro indicate which is similar to those of N-MORB or E-MORB ree distribution curve.The spider diagram of trace element ratio show Nb,Ta,Zr,Hf elements are negative anomaly.The rare earth elements are high content and the rare earth element distribution patterns of the basalt show light rare erath elements are steep while the heavy rare earth elements are relatively flat.The Eu element is obvious positive anomaly.The Zanzongcuo basalts rare earth element distribution pattern is closed to the ocean island basalt mode.The element of Zr and Hf are depleted while the large ion lithophile elements Rb,Ba are enriched.The spider diagram of trace element primitive mantle normalized ratios are"Unimodal uplift" type and which are similar to the Hawai ocean island basalt spider diagram forms.The characteristics of major elements and trace elements in the mantle peridotite and the gabbro reveal the formation inviroment are analogous to N-MORB construction environment and the basalts show the OIB construction environment.The element abundance of total rock and the features of Sr/Nd element isotopic geochemistry which indicate the Zanzongcuo region basalts magma source are not contaminated by the earth crust substance and the basalts magma source are mixed by depleted mantle and I enrichment mantle.The abundance of Th,Ta,La,Nb inactive rare earth elements and those ratios of each other which indicate the Zanzongcuo ophiolite have the same traits with the middle ocean ridge.The result of gabbro SHRIMP analytical test which manifest the Zanzongcuo ophiolite was formed in the earlyLate Jurassic.