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These rocks have undergone extensive metamorphism, and represent some of the oldest surface rocks on Earth. Two papers dating the age of the Nuvvuagittuq Greenstone Belt have been published. One paper gave an age of c. 3,750 million years ( Ma ), [ 2 ] while the other gave an age of c. 4,388 Ma. [ 3 ]
retreating subduction: caused by weak coupling between the lower and upper plate which leads to the opening of a back arc basin and the subduction zone being moved by slab rollback. stable subduction: caused by intermediate coupling between the lower and upper plate. The subduction zone generally stays in the same place and the subduction plate ...
This type of subduction (B-type) tends to emplace magmatic arcs on or near the edge of the overriding plate in modern subduction zones, and evidence of contemporary (c. 1300–1200 Ma) island arcs can be found throughout the Grenville orogen.
The increasingly felsic nature of preserved rocks between 3 and 2.5 billion years ago implies that subduction zones had emerged by this time, with preserved zircons suggesting that subduction may have begun as early as 3.8 billion years ago. Early subduction zones appear to have been temporary and localized, though to what degree is controversial.
Ophiolite generation and subduction may also be explained, as suggested from evidence from the Coast Range ophiolite of California and Baja California, by a change in subduction location and polarity. [10] Oceanic crust attached to a continental margin subducts beneath an island arc. Pre-ophiolitic ocean crust is generated by a back-arc basin.
Another proposed cause was subduction of thickened oceanic crust. Magmatism associated with subduction occurred not near the plate edges (as in the volcanic arc of the Andes, for example), but far to the east, along the Colorado Mineral Belt. [2] Geologists call such a lack of volcanic activity near a subduction zone a magmatic gap.
Evidence for this increased subduction activity comes from the abundance of old granites originating mostly after 2.6 Ga. [14] The occurrence of eclogite (a type of metamorphic rock created by high pressure, > 1 GPa), is explained using a model that incorporates subduction. The lack of eclogites that date to the Archean Eon suggests that ...
Accretionary orogens, which were produced by subduction of one oceanic plate beneath one continental plate for arc volcanism. They are dominated by calc-alkaline igneous rocks and high-T/low-P metamorphic facies series at high thermal gradients of >30 °C/km. There is a general lack of ophiolites, migmatites and abyssal sediments.