Geochemistry And Chronology Of Ultramafites From The Songshugou Area In Qinling

Owing to ultramafites coming from mantle, it contains abundant deep information of geology. This paper chooses-Songshugou dunite body, which is the largest ultramafic intrusion exposing in Qinling area, on the basic of previous researches, to do a systematic research on petrology, geochemistry and LA-ICPMS dating zircon U-Pb of ultramafic intrusions and rocks around it, and probe into its forming property and inviroments. At the same time, to make sure the emplacement time of the body, even to reveal the evolution characteristic of Qinling area. It mainly reaches the following achievements:1) Through the research of petrology and geochemistry, it is found that dunite takes over 85 percent in ultramafic intrusion, which largely contains Mg(39.66%-47.20%) and Fe(733%-11.17%). The containing of Mn. K. Na, P and Ti is less than 0.1 percent respectively. So it has typical characteristic of leaving of mantle rocks, while it doesn't have partly characteristic of melting. Trace element exhibits enrichment of LREE and antipathic elements. Trace element spidergram of obvious right deviation and extremely high containing of Sr, Zr and Hf are different from the negative anomaly of dunite which lies the bottom of ophiolite, but has weak positive anomaly. Above all are different with classical ophiolite.2) Based on the field study, to do a research of petrology and geochemistry of garnet amphibolites in a contact-metamorphic zone and amphibolites in Qinling Group, it is found that amphibolites' transfigurations are complicated, occurrence and structure are similar with gneiss in Qinling Group, these show the ultramafites is in contact with the Qinling Qroup as intrusions. Amphibolites' major elements have the property of MORB and IAT., at the same time trace element distribution mode of level, trace element exhibits weak enrichment of LREE, the positive anomaly of Rb and Ba while the negative anomaly of Zr and Hf. Combining penological and geochemical studies on amphibolites, we suggest that Songshugou dunite body's intruding setting is immature back arc basin. Garnet amphibolites are enrich in trace elements, the containing of Ba, Th, Nb and Ta high respectively, while the containing of Zr and Hf is mezzo, these shows garnet amphibolites' characteristic of OIB. Its trace element spidergram is consistent with basalts of mantle plume in the USA, which shows deep content of the North Qinling Orogenic Belt.3) Garnet amphibolites are accompanied Songshugou dunite body, as a contact-metamorphic zone, received a lot of attention. Using CL and LA-ICPMS methods, this study obtains two metamorphic ages at 506.2±7.4Ma and 510.4±7.5Ma for garnet amphibolites. The two concordant ages constructed the Early Paleozoic intrusion of Songshugou dunite body. The energy of intrusions comes from continents deep dive on two sides of the Songshugou dunite body.