Gravity fields in eastern Halmahera and the Bonin Arc: implications for ophiolite origin and emplacement

Article Abstract:

The eastern part of the island of Halmahera, northern Indonesia, and the Bonin Arc, at the margin of the Philippine Sea Plate, are ophiolites which produce little gravity anomalies. The lack of exposure of the continental basement rocks or of the quartzose sediments in Halmahera indicates that there is no overthrusting of ophiolites onto the continental crust. The Halmahera and Bonin Arc ophiolites have related origins as their crustal structure and thickness are similar. However, the Bonin forearc areas have higher gravity fields unlike any Halmahera structures.

Observations, Gravity anomalies

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Origin of the amphibolite "sole" of the Josephine ophiolite: emplacement of a cold ophiolite over a hot arc

Article Abstract:

The amphibolite sole of the Josephine ophiolite (Madstone Cabin thrust) originated from the footwall of the Madstone Cabin thrust, which contains rocks from the Chetco complex. The underthrusting of a cold Josephine ophiolite by an active magmatic arc produced the emplacement of the ophiolite. The metamorphic soles of the Bay of Islands and Oman Ophiolites are different from those of the basal Josephine sole. The geochemically diverse amphibolites contain both metavolcanically and metaplutonically derived rocks.

Research, Analysis, Geochemistry, Northern California, Amphiboles

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Cenozoic motion of the Philippine Sea Plate: palaeomagnetic evidence from eastern Indonesia

Article Abstract:

The Philippine Sea Plate comprises the whole area north of the Sorong Fault in east Indonesia. A discontinuous 90 deg clockwise rotation, approximately, is observed in the plate as compared to its position in the early Eocene. Palaeomagnetic data collected from 34 sites north of Sorong Fault and 29 sites in the Fault system are used to study the cenozoic motion of the Philippine Sea Plate.

Geological research, Geology, Stratigraphic, Stratigraphy, Cenozoic Era, Philippine Sea

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