Extensional to compressive Mesozoic magmatism at the SE Eurasia margin as recorded from the Meratus ophiolite (SE Borneo, Indonesia)

Abstract

-The Meratus ophiolitic series (SE Borneo) present a specific assemblage that have recorded (I) a continental extensional episode mostly seen within the peridotites and 2) later subduction-relat ed magmatic events marked by the emplacement of calc-alkaline magmas. These events relate the magmatic activity and geodynamic evolution of the SE Eurasia margin in Mesozoic times. The ophiolitic series comprise ultramafic rocks with minor metavolcanic rocks. The ultramafic rocks include dominant Iherzolites and pyroxenites with rather scarce harzburgites and dunites. Spinel peridotite, mineral chemistry data and bulk rock Rare Earth Element (REE) abundances show that most rocks underwent a low degree of partial melting. However, a few samples display significant depletions in Light REE (LREE), which are interpreted as the result of fractional melting under shallow conditions. Plagioclase-bear ing peridotites are characterized by high REE abundances which also point to a very low degree of melting followed by reequilibration in the plagioclase facies, as seen from phase chemistry data. These peridotites are locally crosscut by dikelets containing high-temperatur e Kand Cr-rich amphiboles. Lavas closely associated with the Meratus peridotites have REE compositions ranging from the ones typical of enriched MORB (E-MORB) to normal MORB (N-MORB) types. We believe that the Meratus peridotites represent a fragment of subcontinental lithospheric mantle that locally suffered a low degree of fractional melting during the last stages of a continental rifting phase, in agreement with the presence of metamorphic K-and Cr-rich amphiboles in the peridotites. The E-MORB basalts might result from the melting of an enriched subcontinental lithosphere thermally eroded during the rifting phase by rising asthenosphere which might have produced N-MORB volcanic rocks. Back-arc basin basalts (BABB) now associated with E-MORB and N-MORB have also been found in the metamorphic soles of the peridotites. These rocks would have formed in a back-arc basin now accreted to the eastern margin of Eurasia. The latter are partly covered by calc-alkaline magmatism (Alino Formation). The ophiolitic series was later crosscut by calc-alkaline melts (Manunggul Formation). The Meratus ophiolitic series hence displays a dual origin. They witness I) a continental episode mostly seen within the peridotites, and 2) later subductionrelated events marked by the emplacement of calc-alkaline magmas. © Elsevier, Paris ophiolite I geochemistry I peridotites I continental margin I South East Asia Resume -L'ophiolite des Meratus (SE de Borneo Indonesie) : temoin d'un magmatisme extensif puis co';pressif Ie long de la marge sud-est eurasienne. Cet article montre que I'ophiolit~des Meratus (SE de Borneo, Indonesie) represent~un ancien fragment du manteau lithospherique souscontmental forme au cours des derniers stades de rifting Ie long de la marge SE eurasienne probablement au debut du Mesozoi'que, puis tardivement obductee comme Ie temoigne Ie magmatisme calco-alc...

Along‐ridge petrological segmentation of the mantle in the Oman ophiolite

“…The theoretical evolution after partial melting [Arai, 1994a] shows a trend beginning from the Fertile MORB Mantle (FMM). Domains represent mineral compositions of fore-arc harzburgites [Ishii et al, 1992], abyssal peridotites [Dick and Bullen, 1984], and back-arc Cpx-free harzburgites [Monnier et al, 1995[Monnier et al, , 1999a[Monnier et al, , 1999b[Monnier et al, , 2000[Monnier et al, , 2003. [Snow and Dick, 1995].…”