BPP Teknologi, Indonesia

Based on a newly identified magnetic anomaly pattern and radiometric age determination it is assumed that the floor of the eastern Celebes Sea was generated by seafloor spreading. The crustal age of 43 Ma at ODP Site 767 and 770 allows to place chron 20 along latitude 5 degrees 30'N. The Celebes Sea crust also moved over a hot spot along an east-west path which was still active around 40 Ma as the age of a basalt from the hot-spot trace, i.e. a seamount chain near latitude 3 degrees N, indicates. If the underlying crust is assumed to be 43 Ma old it would be lying within chron 20. The new anomaly pattern places a central seafloor spreading anomaly at 4 degrees N. It was created possibly at 39 Ma (chron 18). Positive magnetic anomalies north and south of chron 20 are identified as chron 21 and provide the highest age of the eastern Celebes Sea crust, i.e. ca. 48 Ma, and a spreading rate of 4 cm/a. The central seafloor anomaly is somewhat obscured by a long northwest-trending wrench fault, thought to be a consequence of transpressive tectonic processes as bathymetric features and upthrusted basaltic basement suggest. The existence of a large crustal splinter within the accretionary wedge off southwestern Mindanao obviously is responsible for a high thermal conductivity which in turn could have enhanced heat flow (108.1 mW/m (super 2) ) and methanogenesis (405 ppb). The heat flow of 102.8 mW/m (super 2) at the deformation front of the Mindanao wedge and the high methane concentration of 5555 ppb suggests tectonically induced fluid transport within the wedge. High methane concentrations between 8044 and 49006 ppb at the lower slope off Sulawesi and in the North Sulawesi Trench are accompanied by high heat flow values of up to 97 mW/m (super 2) . Heat flow is significantly lower upslope (26.2 mW/m (super 2) ). This general heat flow distribution pattern is seen over a large portion of the accretionary wedge. The elevated heat flow values and high methane concentrations near the deformation front most likely result from heat transport by fluids squeezed out from vertically and laterally compacting sediments. The reduced heat flow towards the coast is compatible either with a cooling effect of slow subduction of the oceanic crust, or stacking of cool slabs of compacted sediments. A subduction of oceanic crust with a heat flow around 60 mW/m (super 2) over a period of more than 3 million years would have produced the low heat flow values of the upper slope if the wedge consists of claystone with a low thermal conductivity (1.2-1.7 W/mK). Even in the low-heat flow area isolated fluid venting is possible. Lateral variations in the heat flow pattern (e.g. broadening of the anomalies in the west) may be due to different thermal regimes within the subducted crust.