The Philippine Archipelago’s
Cenozoic Evolution: A Reflection of the North Luzon-Benham Plateau
Tie-up
Karlo L.
Queaño1, Jason R. Ali2, Jonathan Aitchison2,
Graciano P. Yumul Jr. 3
1Lands
Geological Survey Division, Mines and Geosciences Bureau, North
Avenue
2Department of Earth Sciences-The University of Hong Kong
3Department of Science and Technology, Bicutan, Taguig
City
This
study represents one of the most comprehensive paleomagnetic work
ever carried out in North Luzon. Reliable (α95 ≤ 15o)
paleomagnetic results are reportedfrom six out of the 13 rock units
from which a total of 243 individual sites were sampled. The
declination data are of limited use, with many outcrops recording
both local and regional-scale movements. The inclination data are,
however, much more valuable and can be best explained if North Luzon
travelled as part of the Philippine Sea Plate for most of it
history. 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 observed inclinations of primary magnetization suggest
that Luzon occupied low, sub-equatorial latitudes for a reasonable
portion of the early Cenozoic, substantially migrating northwards
since the start of the Neogene.
With a
Philippine Sea Plate origin, this study considers arc development
for Luzon as being attributed to a “permanent” east-directed
subduction. This contrasts with the long-held view of an “arc
polarity reversal” origin for Luzon. In addition, the
reconstructions show that the Palawan microcontinental
block-Philippine Mobile Belt collision occurred in the Late Miocene,
somewhat later than is commonly envisaged. The indentation of the
Palawan microcontinental block into the western side of the
Philippine Archipelago induced deformation in the region. This
process offers the most likely explanation for the scattered
declinations observed in North Luzon and areas a short distance to
the south. Partial subduction of the Palawan block beneath Central
Cordillera likely caused significant uplift of the Central
Cordillera starting in the Late Miocene. |