To understand subduction initiation, study forearc crust: To understand forearc crust, study ophiolites

• DOI: 10.1130/l183.1
• Publication Date: 2012-05-17T17:20:31Z
• Authors: R.J. Stern; M. Reagan; O. Ishizuka; Y. Ohara; S. Whattam
• Keywords: Forearc; Seafloor Spreading; Convergent boundary; Eclogitization; Obduction; Volcanic arc

Articulating a comprehensive plate-tectonic theory requires understanding how new subduction zones form (subduction initiation). Because initiation is tectonomagmatic singularity with few active examples, reconstructing challenging. The lithosphere of many intra-oceanic forearcs preserves high-fidelity magmatic and stratigraphic record initiation. We have heretofore been remarkably ignorant this record, because the "naked forearcs" that expose crustal sections are distant from continents lie in deep trenches, it difficult expensive to study sample via dredging, diving, drilling. Studies Izu-Bonin-Mariana convergent margin indicate there was accompanied by seafloor spreading what ultimately became forearc margin. encompassed ∼7 m.y. for complete transition initial eruption voluminous mid-ocean-ridge basalts (forearc basalts) normal arc volcanism, perhaps consistent long might take slowly subsiding sink ∼100 km mantle motions evolve upwelling beneath infant downwelling front. Many ophiolites chemical features formation above plate margin, most those formed forearcs, where they were well positioned be tectonically emplaced on land when buoyant crust jammed associated zone. propose strategy better understand thus studying ophiolites, which preserve stratigraphy, as seen forearc; we call these "subduction rule" ophiolites. This opens door on-land geologists contribute fundamentally