Applicability of the subduction initiation rule to accreted oceanic crustal terranes of the Circum-Caribbean region
Abstract
The 'subduction initiation rule' (SIR) [Whattam, S. A., Stern, R.J. 2011. The 'subduction initiation rule': a key for linking ophiolites, intra-oceanic forearcs and subduction initiation. Contrib. Mineral. Petrol. DOI 10.1007/s00410-011-0638-z] demonstrates that Tethyan-type ophiolite and Izu-Bonin-Mariana forearc lava compositions evolve from early-MORB-like to VAB-like affinities over the course of SI. We have compiled data from oceanic complexes exposed along the apparent periphery of the Caribbean Large Igneous Province (CLIP) in the Circum-Caribbean/Central American region in order to test the applicability of the SIR to accreted oceanic terranes in the Circum-Caribbean realm. Oceanic complexes crop out in Guatemala, Cuba, Venezuela, Costa Rica and Panama and perhaps the best-documented sequences in the region are from Panama. Here, recent geochemical, stratigraphic and radiometric dating studies of Panamanian oceanic crustal terranes illustrate a temporal and stratigraphic transition from oceanic basement interpreted as CLIP to late proto-arc and arc sequences. SI likely commenced by ~75 Ma as the oldest basaltic 'proto-arc' sequences, which encompass the remnant Sona-Azuero Arc in western Panama, are 73-68 Ma; younger (66-40 Ma) 'arc' sequences comprise the remnant Chagres-Bayano Arc system in eastern Panama. Chagres-Bayano Arc lavas and related intrusives exhibit progressively lesser REE abundances and significantly deeper HFSE-depletions (Nb, Zr, Ti; e.g., mean [Nb/Ce]PM = 0.56) than those of the Sona-Azuero Arc (mean [Nb/Ce]PM = 0.73). Moreover, Ti/V, Cr/Y and Zr/Y relations effectively discriminate the older, MORB-like Sona-Azuero Arc lavas (e.g., Ti/V = 15-33, mean = 25) from those of the younger Chagres-Bayano Arc (Ti/V = 6-25, mean = 14). Explanations for the MORB-like affinities of the proto-arc sequences entail either anomalously high thermal gradients in the subplateau lithosphere due to (remnant) plume-source region interaction or melting of a 'mixed' plume source upon SI; i.e., the Sona-Azuero Arc system is interpreted as representing the transition from Galapagos plume to SI circa 75 Ma. It must be noted however that the chemotemporal progression of Panamanian oceanic crustal terranes mimic those of Tethyan-type ophiolites and IBM forearc lithosphere, neither of which require anomalous thermal or plume contributions upon SI. Panamanian oceanic crustal terranes follow the SIR and thus may share a common petrogenetic origin with SI-related Tethyan-type ophiolites and intra-forearc lithosphere. The shift from MORB-like to VAB-affinities over time is simply the result of progressive subduction zone enrichments and source depletions over the course of SI.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.V53B2622W
- Keywords:
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- 1031 GEOCHEMISTRY / Subduction zone processes;
- 8140 TECTONOPHYSICS / Ophiolites