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首页> 外文期刊>Journal of Volcanology and Geothermal Research >The nature of magmatism at Palinpinon geothermal field, Negros Island, Philippines: implications for geothermal activity and regional tectonics
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The nature of magmatism at Palinpinon geothermal field, Negros Island, Philippines: implications for geothermal activity and regional tectonics

机译：菲律宾内格罗斯岛Palinpinon地热田的岩浆作用性质：对地热活动和区域构造的影响

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摘要

The Palinpinon geothermal field, Negros Island, Philippines is a high-temperature, liquid-dominated geothermal system in an active island-arc volcanic setting. This paper presents a regional context for the Palinpinon geology, discusses the petrogenetic evolution of magmatism in the district and assesses the genetic relationships between intrusion and geothermal circulation. The oldest rock formation, the Lower Puhagan Volcanic Formation (Middle Miocene), is part of a volcanic sequence that is traceable throughout the Visayas region and is related to subduction of the Sulu Sea oceanic basin in a southeasterly direction beneath the Sulu arc. Late Miocene to Early Pliocene times mark a period of regional subsidence and marine sedimentation. A thick sequence of calcareous sediments (Okoy Formation) was deposited during this period. Magmatism in Early Pliocene to Recent times coincided with commencement of subduction at the Negros-Sulu Arc. This produced basaltic andesites and andesites belonging to the Southern Negros and Cuernos Volcanic Formations. During this time the Puhagan dikes and the Nasuji Pluton intruded Middle Miocene, Late Miocene and Early-Late Pliocene formations. Based on radiogenic (~(40)Ar/~(39)Ar) dating of hornblende, the Puhagan dikes are 4.1-4.2 Ma and the Nasuji Pluton 0.3-0.7 Ma. This age difference confirms these intrusions are not genetically related. The Early Pliocene age of the Puhagan dikes also confirms they are not the heat source for the current geothermal system and that a much younger intrusion is situated beyond drill depths. Igneous rock formations in southern Negros are the products of regional island-arc magmatism with medium K, calc-alkaline, basaltic to dacitic compositions. Their adakitic affinity implies that the melting of subducted oceanic basalt has influenced magmatism in this region. Considering the regional tectonic history the most likely scenarios for the generation of slab melts are: (1) during the Middle Miocene, by the melting of relatively young (<20 Ma) oceanic crust; (2) during Early Pliocene times, by the initiation of subduction along the Negros-Sulu Trench; and (3) during Late Pliocene times, by the melting of young ( < 10-20 Ma) oceanic crust. The adakitic composition of the magmas at Palinpinon has promoted the formation of a porphyry copper-style magmatic-hydrothermal system that is comparable to mineralised porphyry deposits elsewhere in the Philippines.
机译：菲律宾内格罗斯岛的Palinpinon地热田是一个活跃的岛弧火山环境中的高温，以液体为主的地热系统。本文介绍了Palinpinon地质的区域背景，讨论了该地区岩浆作用的岩石成因演化，并评估了侵入与地热循环之间的遗传关系。最古老的岩层是下普哈甘火山岩层（中新世中部），是整个米沙s地区可追溯的火山岩层的一部分，与苏禄海弧下苏拉海大洋盆地向东南方向的俯冲有关。中新世晚期至上新世早期标志着区域沉降和海洋沉积的时期。在此期间沉积了厚厚的钙质沉积物序列（Okoy地层）。上新世早期至近代的岩浆作用与内格罗斯-苏鲁弧开始俯冲有关。这产生了属于南部内格罗斯和库埃诺斯火山岩层的玄武质安山岩和安山岩。在这段时间内，Puhagan堤防和Nasuji Pluton侵入了中新世，中新世晚期和上新世晚期。根据角闪石的放射成因（〜（40）Ar /〜（39）Ar）测年，Puhagan堤防为4.1-4.2 Ma，Nasuji岩体为0.3-0.7 Ma。这种年龄差异证实了这些入侵与遗传无关。 Puhagan堤防的上新世早期也证实它们不是当前地热系统的热源，而且钻探深度之外还存在着更年轻的侵入。内格罗什南部的火成岩是区域性岛弧岩浆作用的产物，中钾，钙碱性，玄武质到大镁质成分。它们的adadtic亲和力表明，俯冲的海洋玄武岩的融化影响了该地区的岩浆作用。考虑到区域构造历史，最有可能产生板状融体：（1）中新世中期，相对年轻的（<20 Ma）洋壳融化； （2）在上新世早期，通过沿内格罗斯-苏鲁海沟俯冲作用开始俯冲； （3）在上新世晚期，年轻的（<10-20 Ma）洋壳融化。 Palinpinon岩浆的adakitic成分促进了斑岩铜型岩浆热液系统的形成，与菲律宾其他地方的矿化斑岩矿床相当。

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