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40Ar/39Ar and Fission Track constraints on Miocene Tectonics in
the Buruanga Peninsula, Panay Island, Central PhilippinesMonika
Walia1, T. F. Yang1, T. K. Liu1, C. H. Lo1, L. S. Teng1, W. M.
Yuan2, Ling Chung1, G. P. Yumul3, C. B. Dimalanta4 1National Taiwan
University, Taipei, Taiwan2China University of Geosciences,
Beijing, 100083, China3Department of Science and Technology,
Bicutan, Taguig, Metro Manila4National Institute of Geological
Sciences, University of Philippines, Diliman, Philippines
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~7 cm/yr
~9 cm/yr
The Philippines is sandwiched between two oppositely dipping
subduction zones The Philippine island arc is built on oceanic
crust which was modified by several episodes of magmatism
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Age of collisionThe Palawan Microcontinental block, which was
rifted from Mainland Asia started to collide with the Philippine
Mobile Belt during Early to Middle Miocene {Yumul et al., 2003 and
reference therein} Paleomagnetic reconstructions show that the
Palawan microcontinental Block-Philippine Mobile Belt collision
occurred in the Late Miocene, somewhat later than is commonly
envisaged {Queano et al., 2007}
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[from Dimalanta, 2006]
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The rock units are limestone, chert, siliceous mudstone and
quartz-rich sandstone
In the east of the peninsula, pyroclastic flow deposits and
clastic rocks (polymictic conglomerates, arkosic and lithic
sandstones and shale)
Serpentinized peridotites (harzburgite and dunite) in the
northeastern part of the study area
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Field ObservationsQuartz-rich sandstone, siliceous mudstone,
shale
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Field Observations
mudstone-wackestoneMassive to beddedBeds dipping NW
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Field Observations
Plio-Pleistocene (Cruz & Lingat, 1996)Limestone
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Field ObservationsUltramafic rocks
Dunites and harzburgitesHighly serpentinizedHighly fractured
opxserpentine1 mm
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Late Middle MioceneUnits:1. Quartz-poor sandstone, mudstone,
shale2. Conglomerates with harzburgite and gabbro clastsField
Observations
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PN 1: Quartz Diorite
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PN 1: Quartz Diorite
Early Miocene20.8+1 Ma19.5+1 Ma (Bellon & Rangin, 1991)
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PN 5: Intrusive Rock
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PN 7B: Sandstone
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PN 7B: Diorite
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Hornblende Ar
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FISSION TRACK DATA
No.SampleMineral datedNsNs iNiU(ppm)( 2)Central age (Ma 1)P (2)
%1.PN 1Zircon512.5226252.182274436.811.82.5
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RESULTS16.1 Ma10.1 Ma13.6 Ma50.9 Ma
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RESULTS9.3 Ma7.1 Ma16.9 Ma
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40Ar/39Ar RESULTS
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Ar-Ar HornblendeFT ApatiteFT ZirconAr-Ar BiotiteAr-Ar
Hornblende
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Ar-Ar HornblendeFT ZirconAr-Ar HornblendeFT Zircon
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Ar-Ar hornblende ages suggest the time of intrusion of the
diorite bodies in the area ~84 Ma in the eastern part and ~30 Ma in
the western partTectonic activity is recorded by the zircon FT and
Ar-Ar system over a temperature range of ~250 C to ~500 C around
17-20 Ma This may be inferred as the time of collision of the
microcontinent with the mobile belt We interpret the last stage of
cooling recorded by the fission track system as representing the
timing of later successive events/soft collisions ranging from 9-13
Ma In the western coast of the island, apatite ages show partial
resetting and zircon ages are unaffected by the tectonic event
being away from the suture zoneCONCLUSIONS
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Thank you for the attention ~~
*Philippine Island ArcPhilippine Mobile BeltPhilippine Sea
PlateEurasian PlateNorth Palawan Block based on Ramos, 2005
