North Luzon and the Philippine Sea Plate Motion Model: Insights Following Paleomagnetic, Structural, and Age-Dating Investigations Karlo L
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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, B05101, doi:10.1029/2006JB004506, 2007 North Luzon and the Philippine Sea Plate motion model: Insights following paleomagnetic, structural, and age-dating investigations Karlo L. Queano,1,2 Jason R. Ali,1 John Milsom,1,3 Jonathan C. Aitchison,1 and Manuel Pubellier4 Received 15 May 2006; revised 28 October 2006; accepted 15 November 2006; published 5 May 2007. [1] Results of one of the most comprehensive paleomagnetic and supporting geological programs ever carried out in offshore SE Asia on North Luzon, northern Philippines, are reported. Six new results, based on 66 sites, are reported from a total collection of 243 individual sites. Declinations in the data subset are sometimes scattered, likely reflecting combinations of major plate and local rotations in both clockwise and counterclockwise directions, and thus have a somewhat limited value for tectonic modeling. The inclination data are, however, much more valuable and can be best explained if North Luzon traveled as part of the Philippine Sea Plate for most of its history, a scenario which is compatible with the known geology of the eastern Philippines and broader region. In the proposed model, for all of its Eocene-Pliocene history, North Luzon is placed on the western edge of the Philippine Sea Plate, effectively always just to the west of the site where the Benham Plateau formed 40 Ma. The paleomagnetic data indicate a substantial northward migration of the area since the start of the Neogene, with an earlier interval stretching back to at least the mid-Early Cretaceous when this part of the plate occupied equatorial latitudes. Post-15 Ma motion of the plate has involved the indentation of the Palawan microcontinental block into the western side of the Philippine Archipelago. Deformations induced by this process offer the most likely explanation for the scattered declinations observed in North Luzon and areas a short distance to the south. Citation: Queano, K. L., J. R. Ali, J. Milsom, J. C. Aitchison, and M. Pubellier (2007), North Luzon and the Philippine Sea Plate motion model: Insights following paleomagnetic, structural, and age-dating investigations, J. Geophys. Res., 112, B05101, doi:10.1029/2006JB004506. 1. Introduction strike from 5 cm/yr in the north to 10 cm/yr in the south) 6 2 between Eurasia and the West Philippine Basin [e.g., Seno [2] The 4.7 10 km Philippine Sea Plate (PSP) has  et al., 1993]. played a key role in the tectonic evolution of SE Asia and [3] Various workers have modeled the Luzon-Philippine the western Pacific. Its importance for regional tectonic Sea Plate link in quite different ways. This freedom is very modeling becomes obvious when one considers that it has likely a result of the limited information base that is formed the eastern boundary to the collage of much smaller available for the northern Philippines. In comparing different plates-blocks and tectonic systems which have occupied SE proposals, as a reference point we use the Benham Plateau Asia for a large portion of the Cenozoic [e.g., Rangin et al., (16.5°N, 125.0°E), an oceanic plateau that formed 40 Ma 1990; Hall, 2002; Pubellier et al., 2003a, 2003b]. Luzon on the western side West Philippine Basin just south of the island in the northern Philippines sits just to the west of the ‘‘Central Basin Fault.’’ Today the plateau sits immediately to present-day Philippine Sea Plate, the two being separated by the east of the East Luzon Trough (Figure 1). the East Luzon Trough. The trough represents a short sector [4] Rangin et al. [1990] placed Luzon at 43 Ma in a of the much longer ( 2400 km) double subduction zone position relative to the Benham Plateau very similar to that which runs between Halmahera (S) and Taiwan (N) and it occupies today, plotting this part of the then actively which accommodates convergence (currently varying along spreading West Philippine Basin just south of the equator. The PSP as a whole subsequently had to undergo a 40°CW 1Department of Earth Sciences, University of Hong Kong, Hong Kong, rotation for the plateau to reach its current position. Lee and China. 2Now at Mines and Geosciences Bureau, Quezon City, Philippines. Lawver [1995], on the other hand, although proposing 3Also at Gladestry Associates, Gladestry, UK. similar relative positions for the plateau and North Luzon, 4Laboratoire de Ge´ologie, Ecole Normale Supe´rieure URA 1316 du had them occupying almost their present-day latitudinal CNRS UMR 8538, Paris, France. positions and orientations throughout much of the Cenozoic. [5] The 45 Ma reconstruction of Hall et al. [1995a, Copyright 2007 by the American Geophysical Union. 0148-0227/07/2006JB004506$09.00 1995b] and Hall [2002] was very different, with northern B05101 1of44 B05101 QUEANO ET AL.: NORTH LUZON AND THE PHILIPPINE SEA PLATE B05101 Figure 1 2of44 B05101 QUEANO ET AL.: NORTH LUZON AND THE PHILIPPINE SEA PLATE B05101 and central Luzon situated some 1000 km ENE of Sabah gence (8 cm/yr), the depth of the Wadati-Benioff zone (northern Borneo) in the northern part of the West Philip- (<200 km), the age of volcanic rocks and the lack of any pine Basin but with the Benham Plateau emplaced at 40 Ma well-developed accretionary prism, this plate boundary is near to, but south of, the spreading axis. By the time widely believed to have initiated 3–5 Ma [Karig, 1975; spreading had ceased (33 Ma), the plateau was about Cardwell et al., 1980; Hamburger et al., 1983; Ozawa et al., 1500 km away from North Luzon and the two were then 2004]. This implies that prior to the Pliocene, parts of the shown as traveling along parallel trajectories until the Luzon Philippine archipelago, including northern Luzon, formed Trough formed at around the Mio-Pliocene boundary. Only part of the Philippine Sea plate. then did the Benham Plateau start moving toward North [8] Intense deformation affects the PMB, with the sinis- Luzon. Deschamps and Lallemand [2002] generally fol- tral Philippine Fault transecting the archipelago from Luzon lowed the Hall et al. [1995a, 1995b] Philippine Sea Plate to eastern Mindanao for more than 1200 km [Aurelio et al., kinematic model, but placed North Luzon in the southern 1991]. The fault system accommodates a lateral component part of the West Philippine Basin at 45 Ma, separated from of the oblique convergence between the Philippine Sea Plate Borneo by a major N-S fault that was later to become the and Eurasian Plate, with the other component being Manila Trench. absorbed by subduction along the Philippine Trench, under a shear partitioning mechanism [Fitch, 1972; Barrier et al., 2. Tectonic Setting 1991; Aurelio, 2000]. This mechanism implies synchronous formation of the trench and fault. [6] The central part of North Luzon lies 800 km SE of [9] A summary of ages and tectonic events around the the main Asian landmass in southern China, trapped at the Philippine Mobile Belt is shown in Figures 1 and 2. margins of the Eurasian and the Philippine Sea plates. Relative to Eurasia, the Philippine Sea Plate moves WNW, rates varying from about 10 mm/yr at the southern 3. Geology of Northern Luzon tip to about 5 mm/yr near Taiwan, the Euler pole being [10] Regional geological studies on North Luzon date located near to Japan [Seno et al., 1993]. The NW-SE back more than a century, with the work of Becker [1899] oblique convergence between these plates is currently being (as cited by Billedo [1994]), Corby et al. [1951], Durkee absorbed by two oppositely dipping subduction zones: the and Pederson [1961], Christian [1964]; Caagusan [1977], Manila Trench to the west and the East Luzon Trough- Japan International Cooperation Agency–Metal Mining Philippine Trench to the east (Figure 2). These subduction Agency of Japan (JICA-MMAJ ) [1977], Japan International zones extend southward by approximately 1500 km, delin- Cooperation Agency–Metal Mining Agency of Japan– eating a 400-km-wide deformation zone that Gervasio Mines and Geosciences Bureau (JICA-MMAJ-MGB) [1966] named the Philippine Mobile Belt (PMB). The [1990], Billedo [1994] and Florendo [1994] providing much Manila Trench connects with the Negros-Sulu-Cotobato of the key information. On the basis of physiographic and trench system along which the marginal basins (i.e., South morphostructural features, the region can be divided into China Sea, Sulu Sea and the Celebes Sea) on the eastern four major zones: (1) Cagayan Valley Basin; (2) northern edge of the Eurasian Plate are being subducted [Rangin and Sierra Madre–Caraballo Range (including Palaui Island); Pubellier, 1990; Ringenbach et al., 1993]. These subduction (3) southern Sierra Madre and; (4) Central Cordillera zones continue on as collision zones in Taiwan, Mindoro, (including the Ilocos foothills) (Figure 3). Figures 4 and 5 Panay and Mindanao islands where continental fragments of provide a summary of the stratigraphy and magmatic events Eurasian affinity (parts of the Palawan microcontinental of North Luzon. block) have been transferred to the PMB [Lewis and Hayes, 1984; Rangin, 1989; Pubellier et al., 1991; Quebral et al., 3.1. Cagayan Valley Basin 1996] (Figure 2). Wolfe [1981] and Lewis and Hayes [1984] [11] The Cagayan Valley Basin separates the Central proposed that subduction along the Manila Trench started Cordillera and Sierra Madre mountain ranges. It is bounded 15 Ma. However, Malettere [1989] noted that the island in the north by the ENE-WSW Sicalao Ridge, also referred arc volcanism presumably related to the activity along the to as Sicalao-Cassigayan High [Durkee and Pederson, Manila Trench in western Luzon commenced sometime 1961] or Cassigayan Ridge [Florendo, 1994], and in the earlier. south by the Caraballo Range.