40Ar/
39Ar and Fission Track constraints
on Miocene Tectonics in the Buruanga Peninsula, Panay Island, Central
Philippines
Monika 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, Taiwan
2China University of Geosciences, Beijing, 100083, China
3Department of Science and Technology, Bicutan, Taguig, Metro Manila
4National Institute of Geological Sciences, University of Philippines, Diliman, Philippines
~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
Age of collision
“The 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}
[from Dimalanta, 2006]
The rock units are The rock units are limestone, chert, limestone, chert, siliceous mudstone and quartz-rich siliceous mudstone and quartz-rich sandstonesandstone
In the east of the peninsula, In the east of the peninsula, pyroclastic pyroclastic flow flow deposits and clastic rocks deposits and clastic rocks (polymictic (polymictic conglomerates, arkosic conglomerates, arkosic and lithic sandstones and lithic sandstones and shale)and shale)
Serpentinized peridotites Serpentinized peridotites (harzburgite (harzburgite and dunite) in the northeastern part of and dunite) in the northeastern part of the study area the study area
Field ObservationsField Observations
Quartz-rich Quartz-rich sandstone,sandstone, siliceous siliceous mudstone,mudstone, shaleshale
Field ObservationsField Observations
mudstone-mudstone-wackestonewackestone
Massive to beddedMassive to bedded
Beds dipping NWBeds dipping NW
Field ObservationsField Observations
Plio-PleistocenePlio-Pleistocene (Cruz & Lingat, 1996)(Cruz & Lingat, 1996)
LimestoneLimestone
Field ObservationsField Observations
Ultramafic rocksUltramafic rocks
Dunites Dunites and and harzburgitesharzburgites
Highly Highly serpentinizedserpentinized
Highly fracturedHighly fractured
opx
serpentine
1 mm
Late Middle MioceneLate Middle Miocene
Units:Units:
1. 1. Quartz-poor Quartz-poor sandstone, sandstone, mudstone, shalemudstone, shale
2. 2. ConglomeratesConglomerates with harzburgite and with harzburgite and gabbro clastsgabbro clasts
Field ObservationsField Observations
PN 1: Quartz Diorite
PN 1: Quartz Diorite
Early MioceneEarly Miocene20.820.8++1 Ma1 Ma
19.519.5++1 Ma 1 Ma
(Bellon & Rangin, 1991)(Bellon & Rangin, 1991)
qtz
hbdbt
bt
plg 1 mm
PN 5: Intrusive Rock
PN 7B: Sandstone
PN 7B: Diorite
Hornblende Ar
No. SampleMineral
datedN ρs Ns ρ i Ni
U(ppm)(± 2σ)
Central age
(Ma ± 1σ)P (χ2) %
1. PN 1 Zircon 51 2.52 2625 2.18 2274 436.8 11.8±2.5 <1
2. PN 1 Apatite 45 0.10 174 0.7 1176 17.6 12.6±1.7 <1
3. PN 5 Zircon 16 3.14 365 0.64 74 127.5 50.9±10.3 91.4
4. PN 5 Apatite 20 0.17 91 0.87 470 21.7 16.2±2.4 20.3
5. PN 7B Zircon 31 0.99 1143 1.13 1301 - 8.6±1.9 <1
6. PN 7B Apatite 31 0.05 120 0.33 838 - 13.2±2.1 <1
7. PN 8 Zircon 22 1.91 451 1.21 286 - 16.3±4.2 <1
FISSION TRACK DATA
RESULTS
16.1 Ma
10.1 Ma13.6 Ma
50.9 Ma
RESULTS
9.3 Ma7.1 Ma
16.9 Ma
40Ar/39Ar RESULTSPN-1B (Biotite)
18.49±0.03 Ma 18.69±0.03 Ma
PN-1C (Biotite)
PN-1B (Hornblende)
19.35±0.09 Ma
PN-1C (Hornblende)
30.6±0.19 Ma
PN-8 (Hornblende)
84.07±0.37 Ma
Ar-Ar Hornblende
FT Apatite
FT Zircon
Ar-Ar Biotite
Ar-Ar Hornblende
Ar-Ar Hornblende
FT Zircon
Ar-Ar Hornblende
FT Zircon
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 zone
CONCLUSIONS
Thank you for the attention ~~