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The nature of magmatism at Palinpinon geothermal field, Negros Island, Philippines: implications for geothermal activity and regional tectonics


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Rae, AJ, Cooke, DR, Phillips, D and Zaide-Delfin, M 2004 , 'The nature of magmatism at Palinpinon geothermal field, Negros Island, Philippines: implications for geothermal activity and regional tectonics' , Journal of Volcanology and Geothermal Research, vol. 129, no. 4 , pp. 321-342 , doi: 10.1016/S0377-0273(03)00280-4.

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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 (40Ar/39Ar) 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, calcalkaline, 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 ( less than 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 (less than 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.

Item Type: Article
Authors/Creators:Rae, AJ and Cooke, DR and Phillips, D and Zaide-Delfin, M
Keywords: Palinpinon geothermal field; hydrology; magmatism; 40Ar/39Ar geochronology; adakites; slab melts
Journal or Publication Title: Journal of Volcanology and Geothermal Research
ISSN: 0377-0273
DOI / ID Number: 10.1016/S0377-0273(03)00280-4
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