CB Dimalanta, GP Yumul, MCA de Ungria, National Institute of Geological Science, National Institute of Physics, Natural Science Research Institute, Philippine science, philippine science history, Philippines, SC Halos, Science, UP Diliman
In 1983, Pres. Ferdinand Marcos established a system of national centers of excellence in the basic sciences. The first institutes to be created were the National Institute of Physics (NIP), the National Institute of Geological Sciences (NIGS), and the Natural Science Research Institute (NSRI) at the University of the Philippines (UP) in Diliman and the Institute of Mathematical Sciences (IMS, now the Institute of Mathematical Sciences and Physics, IMSP), the Institute of Chemistry (IC), and the Institute of Biological Sciences (IBS) at the UP’s Los Baños campus.
In this series of blog posts, I will trace the history of the UP Diliman institutes from the perspective of published research. This post in particular, highlights the most exciting research paper from these institutes in the second decade (1993-2003). I divided this post into several parts so that we will not be “sabaw”. Yeah, it is difficult to munch a lot of information in one bite.
So far I have listed 3 papers from NSRI (click here) which are similar in flavor; those papers are genome analyses used in forensic. Here, I list 4 papers from the National Institute of Geological Sciences from this decade.
All papers are from Graciano Yumul and Carla Dimalanta (Hi Maám!).
Two of these papers have impact on mining and all give clues on how the country was formed geologically. All are important to the Islands and its people. This is the reason why I add these papers in my list of 30 for 30.
The authors explain how the crust in the Philippines thickens in the first two papers. They said that the crustal growth in the Philippines is most likely dominated by arc magmatism (volcanic deposition near subduction zone). However, they said that there are significant contribution from the uplift of oceanic crust. The authors were able to estimate the magmatic and amagmatic contributions to the crustal growth of the Islands also.
Crustal thickening in an active margin setting (Philippines): The whys and the hows
Dimalanta, CB, Yumul, Episodes 27, 260-264 (2004).
A synthesis of crustal thickness estimates was made recently utilizing available field, geochemical, seismicity, shear wave velocity and gravity data in the Philippines. The results show that a significant portion of the Philippine archipelago is generally characterized by crust with a thickness of around 25 to 30 kilometers. However, two zones, which arc made up of a thicker crust (from 30 to 65 km) have also been delineated. The Luzon Central Cordillera region is characterized by thick crust. Another belt of thickened crust is observed in the Bicol-Negros-Panay-Central Mindanao region. This paper examines the interplay of tectonic and magmatic processes and their role in modifying Philippine arc crust. The processes, which could account for the observed crustal thicknesses, are presented. The contributions of magmatic arcs as compared to the contribution of the emplacement and accretion of ophiolite complexes to crustal thickness are also discussed.
Magmatic and amagmatic contributions to crustal growth of an island-arc system: the Philippine example
Dimalanta, CB, Yumul, International Geology Review 45, 922-935 (2003). DOI: 10.2747/0020-6822.214.171.1242
The growth of continental crust consists of contributions from both magmatic and amagmatic processes. In the Philippines, the presence of numerous active and potentially active volcanoes and ophiolite/ophiolitic complexes attests to the significant role of arc magmatism and oceanic lithosphere emplacement to crustal growth. However, an estimate of the magmatic and amagmatic contributions to crustal growth has never been attempted previously for this particular island-arc system due to the paucity of geophysical data (e.g., seismic refraction data, seismic velocity models, etc.). This study presents a synthesis of crustal thickness values based on available geophysical and geochemical data. These thicknesses are used to determine the volume of material produced by arc magmatism as well as crustal growth resulting from the amagmatic emplacement of ophiolites. Based on the computations, are magmatism, rather than ophiolite emplacement, has contributed more significantly to crustal growth in the Philippines. Arc magmatism growth rates of 25 to 67 km(3)/km/m.y. are comparable to those of computed arc magmatic addition rates in other island-arc systems in the Western Pacific. Ophiolite accretion rates vary from 2 to 19 km(3)/km/m.y.
The two papers are about areas for mining.
The authors show in the two papers below possible areas of exploration for economically viable metals like gold, copper, chromite, nickle and platinum-group minerals. Mining is still a contentious issue in the Islands.
Distribution, geochemistry and mineralization potentials of Philippine ophiolite and ophiolitic sequences
The Philippines has ophiolite and ophiolitic sequences as major components of its basement complex. They range from complete oceanic crust-mantle sequences (Tethyan typo) to dismembered ones with some lithological suites missing (Cordilleran type). Majority of these sequences manifest subduction-related affinity. Economically viable chromitite, volcanic/ultramafic-hosted massive nickel-copper sulfide and, to a certain extent, platinum-group mineral deposits art, hosted by these ultramafic-mafic rock sequences. Available information shows that subduction-related ophiolite/ophiolitic sequences are better exploration targets fur volcanic- and ultramafic-hosted metallic mineral deposits compared to mid-ocean ridge ophiolites.
Mineralization Controls in Island Arc Settings: Insights from Philippine Metallic Deposits
Yumul, GP, Dimalanta, CB, Maglambayan, VB , Tamayo, RA, Gondwana Research 6, 767-776 (2003). DOI: 10.1016/S1342-937X(05)71023-6
A review of the gold-copper, volcanogenic massive sulfide and ultramafic-hosted (i.e., chromitite, nickel sulfide, platinum-group minerals) deposits in the Philippines is presented. It is critical that a thorough understanding of the spatial and temporal relationship among magmatism, structures and mineralization must be gained if the correct evaluation of the economic potential of a particular deposit is to be done. Structural features conducive to precious and base metal mineralizations are associated with shear zones, extensional jogs and collision zones. In Northern Luzon, alkali and adakitic magmatism are considered good markers for gold-copper mineralization. Volcanogenic massive sulfide deposits are hosted by either ophiolites of marginal basin origin or metamorphic terranes. Exploration works on these deposits have been geared in determining the gold content of the massive sulfides. Chromitite deposits are related with ultramafic rock-hosted deposits. Their occurrence is attributed to crystallization, magma mixing and mantle-melt interaction processes in subduction-related settings. The multiple stages of partial melting responsible for the formation of supra-subduction zone ophiolites result in the generation of second to third stage melts that are enriched in nickel sulfides and platinum group minerals. On the basis of structural, geochemical and tectonic controls, Panay, Mindoro and Central Mindanao and the Sierra Madre, Leyte, and Samar are good exploration targets for precious and base metal deposition in the western and eastern sides of the Philippines, respectively.
These papers from the National Institute of Geological Sciences show that scientific problems of global impact in the field of geology can be done within our backyard.