Bezard, R.

Garbe-Schönberg, D.

Hauff, F.

Hoernle, K.

Jicha, B.

Portnyagin, M.

Schaefer, B. F.

Turner, S.

Werner, R.

Yogodzinski, G.

OceanRep

T22E-06: Inception and Early Evolution of the Aleutian ArcTuesday, 12 December 201711:35 - 11:50Constraining the timing and style of subduction initiation in the Aleutian system is critical to model the Cenozoic geodynamic evolution of the Pacific. Until now, the oldest agesfor the Aleutian arc suggest a subduction inception at c.a. 46-47 Ma. However, the compositions of these samples (arc tholeiites and calc-alkaline rocks) are different fromthose of typical early-arc sequences found at extensively studied subduction systems (Izu-Bonin-Mariana), dominated by FABs and boninites. Thus, if the FAB/boninite modelapplies to the Aleutian, the oldest units might not have been recovered yet and the arc inception could have occurred earlier than 47 Ma. To test this hypothesis, we havesampled the lowermost submarine Aleutian sequences at ten forearc and rear-arc localities during the R/V SONNE Cruise 249. We present preliminary whole-rock major andtrace element concentrations, Sr-Nd-Hf-Pb isotopes as well as U-Pb zircon dating on the recovered igneous rocks.The sample compositions range from tholeiitic to calc-alkaline. No boninites were found. Most of the samples show strong subduction signatures. However, the remainingrocks present no or minor arc-type trace element features. These samples are either depleted tholeiites with similar trace element characteristics to FABs or enriched calc-alkaline rocks. Preliminary zircon dating suggests an age of 47.2 ± 1.2 Ma for one of the samples with strong arc signatures, consistent with the oldest published ages for theAleutian so far. However, based on their compositional similarities to FABs, the depleted tholeiites should be older than the arc-type rocks, suggesting that subductioninitiation could have occurred earlier than the above-mentioned age. The absence of boninite could either reflect an incomplete sampling of the early-arc sequences or adifferent initiation style compared to other Pacific subduction zones. Further ages and radiogenic isotope data should refine these interpretations.Plain Language SummaryAuthorsRachel Bezard *GEOMAR Helmholtz Centre for OceanResearch KielKaj HoernleGEOMAR Helmholtz Centre for OceanResearch KielFolkmar HauffGEOMAR Helmholtz Centre for OceanResearch KielMaxim PortnyaginGEOMAR Helmholtz Centre for OceanResearch KielNew Orleans Ernest N. Morial Convention Center - 211-2132017 AGU Fall Meeting https://agu.confex.com/agu/fm17/meetingapp.cgi/Paper/2710961 von 2 19.11.17, 17:20Reinhard WernerGEOMAR Helmholtz Centre for OceanResearch KielGene YogodzinskiUniversity of South CarolinaBrian JichaUniversity of Wisconsin MadisonDieter Garbe-SchönbergUniversity of KielSimon TurnerMacquarie UniversityBruce F SchaeferMacquarie UniversityFind SimilarView Related EventsDay: Tuesday, 12 December 20172017 AGU Fall Meeting https://agu.confex.com/agu/fm17/meetingapp.cgi/Paper/2710962 von 2 19.11.17, 17:20

Inception and Early Evolution of the Aleutian Arc

Inception and Early Evolution of the Aleutian Arc

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