Title: Geochemistry of oceanic island diabase from ophiolitic mélange zone in Renbu area: Implications for hotspot within Tethys in southern Xizang (Tibet)
Abstract: The Renbu ophiolitic melange zone locates in the easternmost middle section of the Yarlung Zangbo suture zone, and there are lots of fresh diabase tectonic block outcrops in the melange zone. In order to acquire the tectonic property of the diabase and discuss its petrogenesis, the petrography, mineralogy and whole rock geochemistry are carefully studied. The results show that the diabase samples have relatively low SiO2 content and high total alkalis, and are rich in Ti and P, but poor in Ca, with an average Mg#of 55. All samples belong to alkaline series. The rare earth element (REE) abundances are higher than that of chondrite and all samples show the enrichment distribution patterns of light rare earth elements (LREE), with (La/Yb)N of 9.30~10.9 and no Eu anomaly, indicating LREE clearly being fractionated from the HREE. Large ion lithophile elements (LILE) and high field strength elements (HFSE) are all enriched, and the spider diagram indicates that the normative value of incompatible elements to primitive mantle increases with their incompatibility . Sr-Nd isotopic ratios of the diabase and its congenetic basalts display a evo lution trend from depleted mantle (DM) to enriched mantle Ⅱ(EM Ⅱ). Obviously, the geochemical characteristics of the diabase are similar to those of typical o ceanic island basalts (OIB). In addition, the major elements and compatible elem ents (Cr, Co and Ni, etc.) are uniform wholly, and show very low crystallization differentiation. Immobile incompatible elements (including Th, Ta, Nb, Hf, Zr, Ti, Y and REE), typical trace element ratios and SrNd isotopic compositions su ggest that the diabase almost has no crustal contamination and probably derived from a late-stage outpouring of relatively low-degree partial melts of primiti ve garnet and spinel iherzolite because of mantle plume tails, and is similar to the oceanic islands alkalic basalts of Kerguelen. Therefore, the Renbu OIAB-ty pe diabase probably represents the product from the hotspots in the southern Xiz ang Tethys, moreover, because it is similar to the 90°E Ridge hotspots of the I ndian Ocean in origin, it is believed that the Indian Ocean mantle has inherited some characteristics of the Tethyan Ocean.
Publication Year: 2006
Publication Date: 2006-01-01
Language: en
Type: article
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Cited By Count: 4
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