Persistent shallow magnetic inclination in the past 5 million years with implications for regional tectonics in the Philippines

• Published in: Journal of Asian Earth Sciences: X Vol. 5; p. 100048
• Main Authors: Faustino-Eslava, Decibel V., Shibuya, Hidetoshi, Dimalanta, Carla B., Yumul, Graciano P., Macuroy, Jonathan T.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.06.2021; Elsevier
• Subjects: Luzon; Paleosecular variation of lavas (PSVL); Philippines; Shallow inclination anomaly; Paleosecular variation of lavas (PSVL); Shallow inclination anomaly; Luzon; Philippines
• ISSN: 2590-0560; 2590-0560
• DOI: 10.1016/j.jaesx.2021.100048

[Display omitted] •A time-averaged geomagnetic field was derived from volcanic rocks in Luzon.•Rocks between 1 ka to 4.3 Ma consistently registered shallow inclination anomalies.•Inclination anomalies ranged between ~8° to 14° shallower than the GAD model.•The VGP scatter is comparable to other near-equatorial regions including Java. Despite the growing knowledge on geomagnetic paleosecular variations, the region around the Philippine archipelago remains to be a huge data gap in this regard. This work looked into rock magnetic information from <5 Ma volcanic rocks of Luzon Island to provide data for the statistical characterization of the time-averaged field in the region. A total of 21 sites with ages from 1 ka to 4.3 Ma yielded 13 normal, 7 reversed, and 1 intermediate polarity dataset. These were aggregated with previously published work to form a combined dataset of 59 normal + reversed sites with a mean virtual geomagnetic pole at 321.1°E and 83.7°N with α95 = 3.4, and an angular standard deviation of about 14.6°. This amount of scatter is slightly larger than that predicted by Model G but relatively comparable with other near-equatorial regions such as Java and Ecuador. This work is a first examination of paleomagnetic data from the Philippines in relation to the long-term behavior of the magnetic field in this part of Southeast Asia. The long-ranging shallow inclination observed may also have implications on how paleomagnetic data are interpreted for tectonic studies in the region.