Researches:

Article title: Enhanced arc magmatic productivity of the Western Pacific island arcs deduced from gravity-derived arc crustal growth rates
Authors: N. E. Parcutela, R. S. Austria, C. B. Dimalanta, G. T. V. Valera,J. A. S. Gabo-Ratio, B. D. Payot, L. T. Armada, K. J. F. Sangalang, and G. P. Yumul Jr.
Publication title: Frontiers in Earth Science 11, February 2023

Abstract:
Island arcs are postulated as the juvenile components that contribute to the growth of continental crust. Growth rates of arc crusts were previously computed using crustal thicknesses derived from seismic data. Consequently, crustal growth rates of oceanic island arcs are also constrained by the limited seismic data availability. This work presents the first comparison of gravity-derived magmatic growth rates of Western Pacific oceanic island arcs. We used the statistical correlation between Bouguer anomalies and seismic-derived crustal thicknesses to generate an empirical formula. The new empirical formula was utilized to estimate the crustal thicknesses of oceanic island arcs using Bouguer anomalies from the EGM2008 global gravity model. The resulting crustal thicknesses were employed to compute the magmatic growth rates of western Pacific island arcs and the Philippine island arc system. The latest magmatic growth rate estimates show that the magmatic productivity of Western Pacific island arcs, which are directly associated with Pacific Plate subduction, is significantly higher (28–60 km ³ /km/m.y). The growth rate of the Pacific island arcs is higher compared to the magmatic growth rate computed for the other oceanic island arcs (12–25 km ³ /km/m.y), which are derived from the subduction of other oceanic lithospheres (i.e., the Philippine Sea Plate; Caribbean Sea Plate; and Eurasia-South China Sea slabs). This is attributed to the variation in the ages of the subducting plates. The Pacific Plate, being older, is associated with higher degrees of serpentinization and sediment cover, which introduce more volatiles inducing more robust partial melting of the mantle wedge
Full text link https://tinyurl.com/ywnbdbzd

Article title: Band processing of Landsat 8-OLI multi-spectral images as a tool for delineating alteration zones associated with porphyry prospects: A case from Suyoc, Benguet, Philippines
Authors: N.E. Parcutela, C.B. Dimalanta, L.T. Armada, R.S. Austria, J.A. Gabo-Ratio, and G.P. Yumul Jr.
Publication title: IOP Conference Series Earth and Environmental Science 1071(1):012022, August 2022

Abstract:
The Mankayan Mineral District in Luzon is marked by several porphyry and epithermal mineralizations. The possibility of blind porphyry mineralization in Mangga, Basig, and Palidan was forwarded based on the results of recent ground magnetic surveys in Suyoc, Mankayan, Benguet. These areas exhibited the diagnostic magnetic anomaly patterns expected of porphyry copper deposits. This signature, a magnetic core surrounded by a non-magnetic rim, is due to the alteration haloes common to porphyry systems. The magnetic core corresponds to the potassic zone dominated by iron-oxide-bearing minerals (e.g., magnetite). Meanwhile, the abundance of non-magnetic clay minerals at the periphery of the mineralized region corresponds to propylitic-argillic alteration zones. Delineation of alteration zones using remote sensing was done to further support the suggested mineralization prospects. Mixture tuned matched filtering (MTMF) was carried out to reduce the effects of vegetation cover from Landsat 8 data. Principal Components Analysis (PCA) was applied to generate bands exploiting the greatest difference between the clay and magnetite alterations with background earth materials. A classified composite map depicts the altered regions. The three sites previously identified from magnetic anomalies also display the expected alterations. Another prospect in the Lapangan area is being proposed based on magnetic anomalies and mapped alterations.
Full text link https://tinyurl.com/bdzbupj9

Article title: Arc-crustal compression and its effects on the underlying mantle geometry as elucidated from the potential field signatures of the buckled Cretaceous Cebu lithosphere, Philippines
Authors: Nathaniel E. Parcutela, Rurik S.P. Austria, Carla B. Dimalanta, Leo T. Armada, Graciano P. Yumul Jr.
Publication title: Tectonophysics 831(5):229341, April 2022

Abstract:
The occurrence of long wavelength Moho undulations in continental and oceanic lithospheres is attributed to lithospheric buckling. This has been reported for Cretaceous or older lithospheres under compressional regimes. However, there is very limited data on lithospheric buckling of oceanic island arcs. The region where the Cretaceous Cebu arc is under compression due to the impingement of the Palawan micro-Continental Block (PCB) to the Philippine Mobile Belt (PMB). The configuration of the inferred buckled Cretaceous Cebu arc lithosphere is derived from geologic and combined onshore and airborne gravity and magnetics datasets. Subsurface modeling using gravity data revealed the presence of mantle upwelling beneath Central Cebu. This could be considered as one of the crests of long-wavelength Moho undulations commonly attributed to a buckled lithosphere. The oceanic basement was also modelled to determine its configuration. Euler solutions derived from magnetic data showed that the contact between the arc crustal units of the Cansi Volcanics and Pandan Formation is affected by short wavelength folding with wavelengths ranging from 5 to 15 km. The younger arc crustal units are affected by tighter folding with wavelengths ranging from 1 to 5 km. The occurrence of a buckled arc lithosphere is being considered for the first time in this area. The consistent NE-SW folding axes inferred for the folding events strongly suggest that these are consequences of the Middle Miocene collision involving the Philippine Mobile Belt and the Palawan micro-Continental Block.
Full text available upon request to the author/s

Article title: Magnetic field characterization of Macolod Corridor (Luzon, Philippines): New perspectives on rifting in a volcanic arc setting
Authors: Rurik S.P. Austria, Nathaniel E. Parcutela, Edd Marc L. Reyes, Leo T. Armada, Carla B. Dimalanta, Graciano P. Yumul Jr.
Publication title: Tectonophysics 822(1):229179, December 2021

Abstract:
The Macolod Corridor (MC) is a NE-SW trending zone of Quaternary volcanism which perpendicularly bisects the Luzon Arc. This peculiar zone of volcanism is in a junction of different tectonic elements. This led to several models of formation associated with subduction or crustal extension-related processes. New information about its subsurface structure can provide constraints in resolving outstanding questions on its tectonic development. However, elucidating the origin and deep structure of the MC has been problematic due to the extensive young volcanic deposits that blanket the area. In this study, ground magnetic and aeromagnetic datasets are merged to characterize the magnetic signature in the MC. Short wavelength and high amplitude anomalies suggest complex interactions of magnetic bodies within the region. Edge detection techniques reveal linear magnetic anomalies with NE-SW, NW-SE, and E-W trends in the Corridor. These may indicate rift structures at depth. Analytic signals show maximum amplitudes over volcanic centers suggesting maximum magnetic property contrasts due to deep structural controls. Euler solutions cluster in the NE-SW, NW-SE, and E-W trends. These may correspond to conjugate structures at depth suggesting the primary role of the NW-SE shearing between the bounding Philippine Fault and the Sibuyan Verde Passage Fault. Clustering of solutions in a graben-like pattern is also observed beneath volcanic complexes indicating an extensional regime. The MC is also characterized by a shallow magnetic basement as reflected in the Curie point depths. This may be attributed to high heat flow associated with active volcanism and probably crustal thinning. These results skew our interpretation to a rift-related origin of the MC. Thus, it is interpreted to be the manifestation of the continuum of tectonic processes including near-field influences (shearing between the two bounding faults) and far-field influences (arc-continent collision and resulting northwestward translation of the Philippine Mobile Belt).
Full text available upon request to the author/s

Article title: Interpretation of ground magnetic data in Suyoc, Mankayan Mineral District, Philippines
Authors: Creszyl Joy J. Arellano, Leo T. Armada, Carla B. Dimalanta, Karlo L. Queaño, Eric S. Andal, Graciano P. Yumul Jr.
Publication title: Resource Geology 71(4), July 2021

Abstract:
Ground magnetic surveys conducted in Suyoc, Mankayan, Benguet led to the delineation of features related to epithermal and porphyry copper targets in the area. High reduced to equator (RTE) anomalies are observed in areas with epithermal mineralization. The high RTE anomalies are attributed to hydrothermally altered rock with quartz veins. The previously recognized porphyry copper prospect in Palasaan (Mohong Hill) is characterized by low RTE anomaly surrounded by a high RTE anomaly. One explanation for this signature is the possible presence of a magnetic core and the destruction or absence of magnetite in the alteration haloes at the periphery of a porphyry prospect. Areas such as Mangga and Liten exhibit the same magnetic signatures. This distinct magnetic pattern coupled with observed alteration and mineralization signatures led to the interpretation of prospective blind porphyry deposits in these localities. Results of the study reveal the applicability of ground magnetic data in characterizing and extracting a potential area of mineralized zones at a regional scale. The first ground magnetic surveys conducted in Suyoc, Mankayan, Benguet led to the delineation of features related to epithermal and porphyry copper targets in the area. Results of this study reveal magnetic anomalies which may be used in characterizing and determining mineralized areas at a regional scale.
Full text available upon request to the author/s

Article title: Forearc structures and deformation along the Manila Trench
Authors: Leo T. Armada, Shu-Kun Hsu, Carla B. Dimalanta Graciano P. Yumul Jr., Wen-Bin Doo, Yi-Ching Yeh
Publication title: Journal of Asian Earth Sciences: X 4(1), December 2020

Abstract:
The Manila Trench subduction zone is characterized by varying tectonic structures from north to south. Analyses of new seismic reflection data and bathymetric data indicate distinct morphological and deformational patterns in the forearc region. Differences in the nature of the subducting oceanic lithosphere (i.e. seafloor relief related to seamounts and ridges, sediment supply, reactivated features and faults associated with the South China Sea opening) cause along-strike heterogeneity in the Manila Trench and the Luzon forearc region. The northern segment is classified as an accretionary margin while the southern segment is mainly an erosive margin (with a narrow, steep, and often eroded frontal wedge). This sharp contrast is attributed to abundant sediment supply to the trench in the north and to the highly eroded frontal wedge in the south due to scarce sediment supply. The southern trench segment is prone to submarine slope failures and mass wasting processes. The 17°N latitude boundary also separates the forearc basin into the North Luzon Trough and the West Luzon Trough. Associated with this is the initiation of the Scarborough Seamount Chain (South China Sea extinct spreading ridge) subduction at 16°N latitude. A combination of forearc uplift and submarine mass movements attributed to subduction of bathymetric highs near and south of 17°N latitude produced the Stewart Bank. Seamount and other seafloor spreading features induced complex responses arising to diverse forearc architectures in the southern segment. Seamounts and other seafloor spreading-related features in the subducting slab induce slope steepening and significant vertical movement in the frontal wedge and the forearc region, respectively. Deformation associated with the subduction is overprinted by shearing related to the Philippine Fault Zone splay faults with the frontal wedge shortening associated with the ongoing subduction, further complicating the forearc development in the trench and marine forearc region.
Full text available upon request to the author/s

Article title: PHILCRUST3.0: New constraints in crustal growth rate computations for the Philippine arc
Authors: Nathaniel E. Parcutela Carla B. Dimalanta, Leo T. Armada, Graciano P. Yumul Jr.
Publication title: Journal of Asian Earth Sciences: X 4(1), December 2020

Abstract:
A revised crustal thickness map for the Philippine island arc, PHILCRUST3.0, has been generated using new gravity data from the EGM2008. The gravity-derived crustal thickness is compared with crustal thickness estimates obtained using the Sr/Y ratios. PHILCRUST3.0 shows that crustal thickness in the Philippines varies from 13 to 33 km. The Philippine arc appears to be at its thinnest in areas underlain by ophiolites and young magmatic arcs. The resulting crustal thickness values are used to revisit the growth rates of the Philippine arc from magmatic and amagmatic contributions. Arc magmatism contributes more significantly to the growth of Philippine crust with rates from specific volcanoes varying from 5 to 35 km3/km/m.y. Despite being relatively young, magmatism associated with the volcanoes of the East Philippine Arc displayed a higher growth rate (32 km3/km/m.y.) compared to volcanoes belonging to older magmatic arcs in the archipelago. This is attributed to the more hydrated oceanic lithosphere subducting beneath the Philippine Trench. PHILCRUST3.0 provides the most complete crustal thickness map of the Philippines to date. This will enable the computation of crustal growth rate in areas within the Philippines where point gravity or geochemical data is not available.
Full text link https://tinyurl.com/3ew5f6p

Article title: Subduction with arrested volcanism: Compressional regime in volcanic arc gap formation along east Mindanao, Philippines
Authors: Graciano P. Yumul Jr. , Leo T. Armada, Jillian Aira S. Gabo-Ratio, Carla B. Dimalanta , Rurik S.P. Austria
Publication title: Journal of Asian Earth Sciences: X 4(1), December 2020

Abstract:
The eastern portion of the Philippine island arc system, from the Bicol Peninsula through Leyte island to the Pacific Cordillera of east Mindanao, is the overriding plate underneath which the West Philippine Basin (part of the Philippine Sea Plate) and Palau Basin oceanic plates subduct along the Miocene-Pliocene to present-day Philippine Trench. Southward younging of the trench, coupled with the presence of the left-lateral Philippine Fault Zone parallel to it, is recognized. Young volcanic centers (<7Ma to present) are well-developed in the Bicol Peninsula and in Leyte island but not in the Pacific Cordillera. There are only two volcanic centers that are exposed in the Pacific Cordillera, the Paco volcanic center in the north and the Leonard Kniassef in the south. There is a 250km volcanic arc gap distance between the two volcanic centers. Reported inland and offshore geologic structures, from onramp structures to thrust faults, and strain rate computations suggest a predominantly compressional regime in the Pacific Cordillera from the Miocene to the present. This is consistent with the hinge advance character of the Philippine Trench and the recognized E-W directed σ1 in this part of the island arc system. It is forwarded that the prevailing compressional regime inhibited the extrusion of lavas leading to the non-formation of surficial volcanic centers between the Paco and Leonard Kniassef volcanic centers. Furthermore, the compression can also partly account for the presence of porphyry copper deposits in this part of Mindanao.
Full text link https://tinyurl.com/4urf38t3

Article title: Mesozoic rock suites along western Philippines: Exposed proto-South China Sea fragments?
Authors: Graciano P. Yumul Jr., Carla B. Dimalanta, Jillian Aira S. Gabo-Ratio, Karlo L. Queaño , Leo T. Armada, Jenielyn T. Padrones, Decibel V. Faustino-Eslava, Betchaida D. Payot, Edanjarlo J. Marquez
Publication title: Journal of Asian Earth Sciences: X 4(1), December 2020

Abstract:
An ancient oceanic crustal leading edge east of mainland Asia, the proto-South China Sea crust, must have existed during the Mesozoic based on tectonic reconstructions that accounted for the presence of subducted slabs in the lower mantle and the exposed oceanic lithospheric fragments strewn in the Philippine and Bornean regions. Along the western seaboard of the Philippine archipelago, numerous Mesozoic ophiolites and associated lithologies do not appear to be genetically associated with the younger Paleogene-Neogene ocean basins that currently surround the islands. New sedimentological, paleomagnetic, paleontological, and isotopic age data that we generated are presented here, in combination with our previous results and those of others, to reassess the geological make-up of the western Philippine island arc system. We believe that the oceanic lithospheric fragments, associated melanges, and sedimentary rocks in this region are exhumed slivers of the proto-South China Sea ocean plate.
Full text link https://tinyurl.com/54jvtf9v