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Early Cretaceous arc volcanic rocks, diorite intrusions and an associated large porphyry deposit occur in the Cebu Island, Central Philippines. In this paper, we studied the diorite porphyries associated with Cu-Au mineralization in the Kansi region, where Early Cretaceous arc volcanic rocks are widely distributed. Zircon U-Pb age reveals that the diorites were formed at ca. 110 Ma, close to the formation age of Lutopan diorites in the famous Atlas porphyry Cu-Au deposit (109–101 Ma), and younger than those of the arc volcanics in this region (126–118 Ma). The Kansi diorites and Lutopan diorites are both calc-alkaline high-Mg adakites with high Sr/Y ratios. Their major elements define similar variation trends in Harker diagrams, suggesting that they were probably generated from a uniform source but experienced different degree of partial melting or fractional crystallization. The Kansi diorites are characterized by LREE enrichment, HREE depletion, no Eu negative anomaly, with enrichment of Pb, Sr, Zr and Hf and depletion of Nb, Ta, and Ti. They are probably generated by the partial melting of subducted oceanic crust, followed by a certain degree of mantle interaction and crustal contamination. The highly depleted Sr-Nd-Pb-Hf isotopes of the Kansi diorites are close to the Amami Plateau basalt and tonalite, indicating the dominance of a Pacific-type MORB in the source. The Cu-Au mineralization-related Kansi diorites are characterized by high oxygen fugacities more than ΔFMQ +2, indicating quite a good potential for porphyry Cu-Au mineralization in the region. Finally, in our tectonic model, the successive generation of arc volcanic rocks and adakites in the Cebu Island are responses to the subduction and rollback of the paleo-Pacific Plate to the proto-Philippine Sea Plate (PSP) in the Early Cretaceous. 相似文献
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Abstract. The Philippines is generally accepted to be the center of the international trade of stony corals for ornamental use. Despite existing legal bans on the collection and export of stony corals in the Philippines, the coral trade continues to date, particularly in Cebu. This paper reports on the specific market demand for stony corals in Cebu and the effects of commercial collection based on the results of a quantitative study of two shallow coral reef areas subjected to large differences in collection effort. Comparison of the measured coral community parameters suggests selective population changes and reduced abundance of exploited coral populations as a result of commercial collection. Estimates of the natural mortality, fishing mortality and yield are presented for the two sampled populations of Pocillopora verrucosa , utilizing the method of GRIGG (1976). Based on the study results and a review of reported coral growth rates and coral colony size at reproductive maturity, the potential for resource management of stony corals on a sustainable yield basis is - discussed. 相似文献
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