Paleomagnetism of the Samar Ophiolite: Implications for the Cretaceous sub-equatorial position of the Philippine island arc

Abstract

Samar island in the eastern part of Central Philippines is underlain by a complete ophiolite suite, the Samar Ophiolite. We present the first geochronological and paleomagnetic data for the Samar Ophiolite. Whole rock K–Ar dating of two basalt samples yielded an age of 100.2±2.7Ma and 97.9±2.8Ma. Thirteen sites in four localities yielded characteristic remanent magnetization with in situ direction of D=340°, I=−24°, k=15, α95=11° and tilt-corrected direction of D=342°, I=−27°, k=15, α95=11°. These values suggest that the ophiolitic basement rocks of Samar formed in the Late Cretaceous at a paleolatitude of 14°S±6°. The paleolatitude is several degrees south of the sub-equatorial positions calculated for the three other Mesozoic ophiolites of the Philippine Mobile Belt (PMB) whose paleomagnetism had been previously studied. The PMB ophiolites in eastern and central Philippines share a common age, geochemistry and paleolatitude with the Halmahera Ophiolite, suggesting that they originated from a Mesozoic supra-subduction zone that spanned a few degrees north of the equator to around 15°S.