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A tale of two blocks: New insights on the evolution of the Zambales Ophiolite
Complex, Luzon Island, Philippines
Graciano P. Yumul Jr. 1 , Carla B. Dimalanta 2 , Karlo L. Queaño 3 , Decibel V. Faustino-Eslava 4 Edanjarlo J. Marquez 5 , Noelynna
T. Ramos 2 , Keisuke Ishida 6 , Shigeyuki Suzuki 7 , Ricky C. Salapare 2 , Michael Peter M. Sanchez 8 , Juan Miguel R.
Guotana 8 , Rose Ann B. Concepcion 2
Introduction
For the past decades, our research team has been involved in the
studies of ophiolitic sequences across the Philippine archipelago
(e.g. Yumul et al., 1998; Tamayo et al., 2001; Suerte et al., 2005; Andal
et al., 2005; Faustino et al., 2006; Dimalanta et al., 2009). Recent
investigations have been done to better constrain the emplacement
history of one of the more studied ophiolites in the region, the
Zambales Ophiolite Complex (ZOC). Geological, petrological and
paleontological data presented here provide new insights on the
tectonic evolution of the ophiolite terrane.
Zambales Ophiolite Complex (ZOC)
The ZOC is a complete crust-mantle sequence that occurs as a
north-south trending ridge in western Central Luzon (Figure 1).
Previous works regard this ophiolite to have been formed during
the Eocene on the basis of fossil assemblages observed from the
pelagic Aksitero Formation that overlies the ZOC along the western
foothills of southern Zambales Range (Amato, 1965; Villones, 1980;
Schweller et al., 1983). The Eocene age derived from fossils is
supported by the K-Ar dating of diabase and granodiorite dikes in
Coto Mine that yielded 46.6 (±5.1) Ma to 44 (±3.5) Ma (Fuller et al.,
1989) and by the U-Pb dating of tonalite (Acoje Block) and
leucocratic tonalite and hornblende quartz diorite (Coto Block) that
yielded 45.1 (±0.6) Ma to 44.2 (±0.9) Ma (Encarnacion et al., 1993),
respectively. Thus, an Eocene age had been adopted for the entire
ZOC.
Two blocks of contrasting petrological and geochemical
characteristics comprise the ZOC: the Acoje and the Coto Blocks.
The Acoje Block exhibits an island arc signature whereas the Coto
Block is of transitional mid-oceanic ridge basalt to island arc
signature. The difference between these two blocks is further
highlighted by the chromite types they host. The Acoje Block
1
Monte Oro Resources and Energy Inc. Makati City, Philippines; 2 National Institute of Geological Sciences, University of the Philippines - Diliman, Quezon
City, Philippines; 3 School of Civil, Environmental, and Geological Engineering, Mapúa Institute of Technology, Intramuros, Manila, Philippines; 4 School of
Environmental Science and Management, University of the Philippines - Los Baños, Laguna, Philippines; 5 Department of Physical Sciences and Mathematics,
University of the Philippines – Manila, Padre Faura, Manila, Philippines; 6 Institute of Socio-Arts and Sciences, University of Tokushima, Japan; 7 Department
of Earth Sciences, Okayama University, Japan; 8 Department of Civil Engineering, Adamson University, Manila, Philippines
INTERRIDGE NEWS 27 VOL.21, 2012