Birth, death, and resurrection: The life cycle of suprasubduction zone ophiolites

Suprasubduction zone (SSZ) ophiolites display a consistent sequence of even ts during their formation and evolution that suggests that they form in res ponse to processes that are common to all such ophiolites. This sequence in cludes the following: (1) birth, which entails the formation of the ophioli te above a nascent or reconfigured subduction zone; this stage is typically characterized by the eruption of arc tholeiite lavas and the formation of layered gabbros and sheeted dike complex; (2) youth, during which is contin ued melting of refractory asthenosphere (depleted during birth) occurs in r esponse to fluid flux from the subducting slab, with extensional deformatio n of the older plutonic suite, eruption of refractory lavas, and the intrus ion of wehrlite-pyroxenite; (3) maturity, with the onset of semistable arc volcanism, typically calc-alkaline, as the subduction zone matures and stab ilizes, and the intrusion of quartz diorite and eruption of silicic lavas; and (4) death, which is the sudden demise of active spreading and ophiolite -related volcanism, which in many cases is linked to collision with an acti ve spreading center and the onset of shallow underthrusting of the buoyant spreading axis; expressed as dikes and lavas with oceanic basalt compositio ns that crosscut or overlie rocks of the older suites; (5) resurrection, wi th emplacement by obduction onto a passive margin or accretionary uplift wi th continued subduction. The early stages (1-3) may be diachronous, and eac h stage may overlap in both time and space. The existence of this consisten t progression implies that ophiolite formation is not a stochastic event bu t is a natural consequence of the SSZ tectonic setting.