Abstract:

Yinchangping granite porphyry intrusive outcrops around the southwestern segment of the Yangtze block, which is between the Xianshuihe-Xiaojiang alkaline rock zone and Jinshajiang-Ailaoshan alkali-rich porphyry rock zone. The major elements of this area show high alkaline, high ratio of Na2O/K2O and lower TiO2, presenting typical geochemical characteristic of high-K calc-alkaline rocks. Trace elements characteristics include LILE, LREE (with enrichments) and transitional elements (Cu, Ni and Co), as well as significant “Ta-Nb-Ti” negative anomaly and indistinctive Eu anomaly. LA-ICP-S zircon U-b dating shows that the emplacement age of Yinchangping granite porphyry is (37.39±0.33) Ma: εHf(t) value is in the range of  -1.8+1.8 with twostage Hf model age of 9961226 Ma; εNd(t) value is a little low within the range of -7.4-3.6; (87Sr/86Sr)i (0.706077 0.706231) is high; 207Pb/204Pb(15.56715.574) and 208Pb/204Pb(38.32138.335) present a typical characteristic of orogenic zone. All these analyses suggest that Yinchangping granite porphyry intrusion belongs to the Anninghe alkaline rocks zone  which is formed in the environment of near continental arc, where there is not only the geochemical characteristic of EM I-M II type source enrichment in mantle but also the porphyritic magma formed in “crust-antle mixed layer”. Yinchangping granite porphyry is the acid component at the end of fractional crystallization in Anninghe alkaline rock zone.

Key words:  zircon U-Pb ages, geochemistry, Sr-Nd-Pb istopes, granite porphyry, Yangtze block