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Suprasubduction zone ophiolites and Archean tectonics

¹ Department of Geology, Miami University, Oxford, Ohio 45056, USA
² Department of Earth Sciences, University of Windsor, Windsor, Ontario N9B 3P4, Canada

Correspondence: *E-mail: dileky@muohio.edu

The first 20% of the full text of this article appears below.

The internal structure and geochemistry of many Phanerozoic ophiolites show a complex pattern of igneous accretion that involved multiple stages and sources of melt evolution and life cycles in suprasubduction zone (SSZ) environments (Shervais, 2001; Dilek and Flower, 2003). Some of the most extensively studied Tethyan ophiolites appear to have developed, for example, in arc-forearc settings within restricted marginal basins, which were nested in older, preexisting oceans (Ishikawa et al., 2002; Dilek et al., 2008). The subduction of the ocean floor in these older basins, combined with slab rollback processes, facilitated ophiolite development in the extending upper plate within relatively short time spans (<10 m.y.). The SSZ ophiolites generated during these arc-trench rollback cycles commonly have structurally and geochemically heterogeneous crustal components attesting to the progressive evolution of their mantle melt sources. We discuss here that SSZ ophiolites, albeit with different internal structure and stratigraphy, are part of Archean greenstone belts, suggesting the operation of plate tectonic–like processes as early as 3.8 Ga in the Archean.

The Middle Jurassic Mirdita ophiolite (MO) in northern Albania contains a ~12-km-thick oceanic lithosphere with SSZ affinity. Different dike generations and lava units within the sheeted dike complex and in the extrusive sequence of the MO show a geochemical progression from older mid-oceanic ridge basalts (MORB) and basaltic andesites to younger dikes and lavas with compositions of basaltic andesite, andesite, dacite, and rhyolite. These more evolved rocks display island arc tholeiite (IAT) signatures characterized by progressive depletion in increasingly incompatible elements. Even younger dikes and lavas higher in the sequence have boninitic compositions, suggesting that their magmas were produced from partial melting of highly depleted, ultra-refractory harzburgites (Dilek et al., 2008). These late-stage dike and lava rocks show enrichment in the most-incompatible elements that likely resulted . . . [Full Text of this Article]