GEOLOGICAL SOCIETY OF THE PHILIPPINES

PALAWAN PALEOMAGNETISM:  REVIEW OF PRINCIPAL RESULTS

 

J. N. Almascoa, K. Rodolfoa, M. Fullerb* and G. Frostb,
a    Department of Earth & Environmental Sciences,
      University of Illinois, Chicago, Illinois, 60670-7059, USA.
b    Hawai’i Institute of Geophysics and Planetology,
      School of Ocean and Earth Science and Technology,
      University of Hawaii, Honolulu, Hawaii, 96822, USA.
__________________________
*    Corresponding Author


ABSTRACT

       Paleomagnetic studies have been carried out on Palawan and on the island of Busuanga to the north. Results from the Cretaceous Espina Basalts of the Calatuigas Ophiolite in the South Palawan Block (SPB) pass a fold test, yield normal and reversed directions with a magnetic intensity and AF demagnetization characteristics consistent with a primary TRM. The mean direction is 293.9o and an inclination of 5.8o, with a k of 37.7 and an a95 of 12.6o. This suggests that these ophiolites have moved northward and rotated counterclockwise by 66o + 13o with respect to the geocentric axial dipole (GAD) field. It also suggests that they were obducted from the south.

        Paleomagnetic directions from the Jurassic Busuanga Cherts and the Cretaceous Guinlo Formation from the island of Busuanga in the North Palawan Block (NPB) and from the Guinlo on the main island of Palawan are indistinguishable, fail regional fold tests, and have AF demagnetization characteristics consistent with secondary magnetization. Their inclinations are statistically indistinguishable at a 95% significance level, but variation in declination suggests differential local rotation about a vertical axis. The paleolatitude is comparable to that of regions of pervasive Cretaceous remagnetization in the South China borderland and may reflect similar remagnetization, consistent with the NPB’s proposed South China origin.

 

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