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| Titel |
Extreme extension across Seram and Ambon, eastern Indonesia: evidence for Banda slab rollback |
| VerfasserIn |
J. M. Pownall, R. Hall, I. M. Watkinson |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1869-9510
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| Digitales Dokument |
URL |
| Erschienen |
In: Solid Earth ; 4, no. 2 ; Nr. 4, no. 2 (2013-09-24), S.277-314 |
| Datensatznummer |
250084934
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| Publikation (Nr.) |
 copernicus.org/se-4-277-2013.pdf |
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| Zusammenfassung |
| The island of Seram, which lies in the northern part of the
180°-curved Banda Arc, has previously been interpreted as a
fold-and-thrust belt formed during arc-continent collision, which
incorporates ophiolites intruded by granites thought to have been produced by
anatexis within a metamorphic sole. However, new geological mapping and a
re-examination of the field relations cause us to question this model. We
instead propose that there is evidence for recent and rapid N–S extension
that has caused the high-temperature exhumation of lherzolites beneath
low-angle lithospheric detachment faults that induced high-temperature
metamorphism and melting in overlying crustal rocks. These "Kobipoto
Complex" migmatites include highly residual Al–Mg-rich
garnet + cordierite + sillimanite + spinel + corundum granulites
(exposed in the Kobipoto Mountains) which contain coexisting
spinel + quartz, indicating that peak metamorphic temperatures likely
approached 900 °C. Associated with these residual granulites are
voluminous Mio-Pliocene granitic diatexites, or "cordierite granites",
which crop out on Ambon, western Seram, and in the Kobipoto Mountains and
incorporate abundant schlieren of spinel- and sillimanite-bearing residuum.
Quaternary "ambonites" (cordierite + garnet dacites) emplaced on Ambon
were also evidently sourced from the Kobipoto Complex migmatites as
demonstrated by granulite-inherited xenoliths. Exhumation of the hot
peridotites and granulite-facies Kobipoto Complex migmatites to shallower
structural levels caused greenschist- to lower-amphibolite facies metapelites
and amphibolites of the Tehoru Formation to be overprinted by
sillimanite-grade metamorphism, migmatisation, and limited localised anatexis
to form the Taunusa Complex. The extreme extension required to have driven
Kobipoto Complex exhumation evidently occurred throughout Seram and along
much of the northern Banda Arc. The lherzolites must have been juxtaposed
against the crust at typical lithospheric mantle temperatures in order to
account for such high-temperature metamorphism and therefore could not have
been part of a cooled ophiolite. In central Seram, lenses of peridotites are
incorporated with a major left-lateral strike-slip shear zone (the "Kawa
Shear Zone"), demonstrating that strike-slip motions likely initiated
shortly after the mantle had been partly exhumed by detachment faulting and
that the main strike-slip faults may themselves be reactivated and steepened
low-angle detachments. The geodynamic driver for mantle exhumation along the
detachment faults and strike-slip faulting in central Seram is very likely
the same; we interpret the extreme extension to be the result of eastward
slab rollback into the Banda Embayment as outlined by the latest plate
reconstructions for Banda Arc evolution. |
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