GEOLOGICAL SOCIETY OF THE PHILIPPINES
NEW ESTIMATES OF ARC MAGMATIC ADDITION RATES: CONSTRAINTS FROM SEISMIC AND GRAVITY DATA
C.B. Dimalanta1,2, A. Taira1, G.P Yumul, Jr.,2 and K Mochizuki3
1 Ocean Research Institute , University of Tokyo, Tokyo Japan
2 Rushurgent working Group, national Institute of Geological Sciences, College of Science, University of the Philippines, Diliman QC
3Earthquake Research Institute, Univerrsity of Tokyo, Tokyo Japan
There have been numerous studies conducted in order to look into the evolution o0f the continental crust. Some suggest that one of the mechanisms, which contribute to the growth of the continental crust, is arc magmatism. It is in this context that Reymer and Schubert (1984) estimated arc magmatic addition rates to the continental crust. Their results suggest that island arc magmatism was producing material at an average rate of 20 – 40 Km3/km/m.y. ( volume per unit width along the strike direction of arc).
This present work utilizes the most recent worldwide marine gravity data, together with improved seismic data from some oceanic island arcs in the western pacific region. The combined gravity and seismic data allows a more accurate image of the subsurface configuration beneath the oceanic island arcs and yields better estimates of crustal volumes created during arc magmatic processes. Oceanic island arcs investigated in this study show crustal thickness ranging from 20 to 30 kilometers. Utilizing this thickness, the relevant crustal volume for each island arc is then estimated. Dividing the crustal volume by the age of initiation of subduction of the arc gives arc magmatic addition rates ranging from 30 to 96 km3/km/m.y. The estimates presented here are nearly twice as high as the previous estimates of arc magmatic addition rates.
The results of this present work show that the arc magmatism is capable of producing considerable volumes of crustal material. Thus, arc magmatism provides a significant contribution to the formation of continental crust, especially within the upper crustal level.
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