• journal_title：Bulletin de la Societe Geologique de France
• Contributor：Christophe Monnier ; Jacques Girardeau ; Hariady Permana ; Jean-Pierre Rehault ; Hervé Bellon ; Jo Cotten
• Publisher：Societe Geologique de France
• Date：2003-
• Format：text/html
• Language：en
• Identifier：10.2113/174.6.529
• journal_abbrev：Bulletin de la Societe Geologique de France
• issn：0037-9409
• volume：174
• issue：6
• firstpage：529
• section：Articles

The Seram-Ambon ophiolitic series comprise peridotites, websterites, gabbros and lavas. Petro-geochemical data show that the peridotites are weakly depleted rocks, except for the rare Cpx-free harzburgites. They underwent a sub-solidus metamorphic re-equilibration in the plagioclase field. The associated websterites and gabbros display various chemical features, allowing to define 3 types of websterites and 2 groups of gabbros. They have mostly BAB characteristics (presence of negative anomalies in Nb, Zr, Ti and Y), except the group 2 gabbros which have N-MORB features and the type 3 websterites which bear adakitic affinities. Lavas also display a variety of compositions, including high-Mg IAT and Mg-rich BABB with sub-alkaline affinities. Both IAT and BABB display high Th/Nb ratios which support an origin close to a continental crust environment.

Our 20 to 15 Ma ⁴⁰K/⁴⁰Ar ages calculated for the BABB and 15-9 Ma for the IAT show that the basin and arc formed in a very short span of time, before their obduction 9–7 Ma ago [Linthout et al., 1997]. Considering the paleogeographic situation in the Miocene [Haile, 1979 ; Haile, 1981] and our data, we propose that the Seram-Ambon ophiolites formed during the early Miocene in a small, short-lived (10 Ma), transtensive basin bordered on its east by an active margin and on its western part by a passive continental margin over which it was later obducted towards the SW direction.