HIGH-PRESSURE AND ULTRAHIGH-PRESSURE METAMORPHIC BELTS - SUBDUCTION, RECRYSTALLIZATION, EXHUMATION, AND SIGNIFICANCE FOR OPHIOLITE STUDY
- DSpace Home
- →
- Геология России
- →
- ELibrary
- →
- View Item
JavaScript is disabled for your browser. Some features of this site may not work without it.
HIGH-PRESSURE AND ULTRAHIGH-PRESSURE METAMORPHIC BELTS - SUBDUCTION, RECRYSTALLIZATION, EXHUMATION, AND SIGNIFICANCE FOR OPHIOLITE STUDY
Ernst W.G.
xmlui.dri2xhtml.METS-1.0.item-citation:
Special Paper of the Geological Society of America, 2003, 373, С. 3, 365-384
Date:
2003
Abstract:
Alpine-type orogenic belts are produced by short-lived subduction of an ocean basin and the underflow of continental crust, resulting in suturing. Old, relatively competent sialic basement and superjacent units characterize these complexes; ophiolites, chiefly enriched mid-ocean ridge basalt and suprasubduction-zone complexes are common in some belts, but are rare in others. Metamorphism of deeply subducted (60-140 km) parts of the orogen ranges from high pressure to ultrahigh pressure , and is not paired. Coeval calcalkaline arc rocks are uncommon. In contrast, paired Pacific-type orogenic belts develop within and landward from long-lived subduction zones. They consist of an outboard trench + accretionary prism deposited on oceanic crust, and an inboard volcanic-plutonic continental margin or island arc. The trench assemblage consists of graywacke + shaley mélanges, minor but widespread deepwater cherts and/or carbonates, and ubiquitous disaggregated ophiolites, especially normal mid-ocean basalt and ocean island basalt varieties, all recrystallized under high-pressure conditions at depths of 15-70 km. A massive, coeval calcalkaline arc dominates the subparallel terrane landward from the trench, and high temperatures characterize the associated metamorphism. In both high-pressure-ultrahigh-pressure Alpine and high-pressure Pacific-type metamorphic terranes, outboard thrust faults chiefly dip landward beneath the stable, nonsubducted plate, and fold vergence is seaward, reflecting similar convergent plate-tectonic settings; inboard, antithetic thrusting characterizes some contractional realms. High pressures and low temperatures in these belts attest to dynamic subduction-zone conditions. Because of their structural integrity, some Alpine-type microcontinents, island arcs, or continental promontories are carried down as much as 140 km, well into the brittle-ductile transition region, before decoupling from the sinking mantle lithosphere. In sharp contrast, incompetent Pacific-type graywacke + shale terranes generally separate from descending oceanic lithosphere at much shallower depths. The ascent of packets of subducted material as thin aspect-ratio sheets 1-5 km thick, combined with normal faulting above and subduction-zone thrusting below, promotes conduction cooling and partial preservation of decompressing high-pressure and ultrahigh-pressure metamorphic complexes. Worldwide, subduction-zone terranes consist of dominantly of small masses of high-density mafic blueschist-eclogite and/or anhydrous peridotitic lenses surrounded by voluminous, low-density quartzofeldspathic ± serpentinitic material, hence the bulk terrane density is less than that of unaltered, dynamically displaced mantle; exhumation to mid-crustal levels is largely buoyancy driven. Partial preservation of high-pressure-ultrahigh-pressure relict phases reflects rapid ascent combined with mineralogic armoring and a general lack of catalytic aqueous fluid. Exposure of rising high-pressure and ultrahigh pressure metamorphic belts is a consequence of erosional decapitation and gravitational collapse of the subduction complex. Many exhumed high-pressure-ultrahigh- pressure sheets are of relatively small volume, and for these, only modest amounts of sedimentary debris are provided to successor basins.
Files in this item
This item appears in the following Collection(s)
-
ELibrary
Метаданные публикаций с сайта https://www.elibrary.ru
Search DSpace
Browse
-
All of DSpace
-
This Collection