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- W1968117968 abstract "Constraints on the evolution of the northeastern Caribbean plate boundary and the tectonic development of the Puerto Rico Trench have been derived from a study of rocks and sediments dredged from thirty-six localities within and surrounding the trench. Marble, calc-schist, mica-schist, greenschist, amphibolite, magnesian schist and serpentinite crop out below the trench—slope break (∼ 3500 m) along the steep inner-trench wall for over 400 km. At shallower depths, limestone, calcilithite, and minor amounts of chert and sedimentary rock were sampled. Potassium—argon ages of two of the metamorphic rocks are 63 ± 3 and 66 ± 5 m.y.B.P. Rocks dredged from Mona Canyon, directly behind the inner-trench wall, are primarily igneous rocks, volcanic breccia, limestone and calcilithite that have been only slightly metamorphosed. Middle Eocene to Miocene (or younger) shallow-water limestones are interbedded and overlie the volcanogenic rocks. The outer-trench wall (oceanic side) is composed of tholeiitic basalts, serpentinite and deep-sea sediments commonly recovered from the Atlantic oceanic crust. Mineral assemblages and phase relations in the metamorphic rocks are similar to those observed in many subaerially exposed mélanges believed to be subduction complexes. The conditions of metamorphism within the Puerto Rico Trench metamorphic complex are estimated to have been between 400 and 550°C and 3 to 7 kbar. Chemical analyses of the dredged samples suggest that: (1) The metamorphic rocks from the inner-trench wall were primarily island-arc igneous rocks or sediments derived from them. (2) Protoliths of the marbles and calc-schists were apparently biogenic carbonates and pelagic sediments with an arc-derived sedimentary component. (3) Basalt and serpentinite from the outer-trench wall are geochemically similar to oceanic tholeiites (MORB) and ultramafics. (4) Only two greenschists from the inner-trench wall have geochemical characteristics similar to MORB. (5) Magnesian schists and serpentinite from deep along the inner wall have either been severely affected by metasomatism or represent metamorphosed ultramafic rocks from beneath the Greater Antilles. Our results indicate that, unlike a number of arc-trench systems in the Pacific, a great deal of arc-derived material has been accreted to the inner-trench wall and that the amount of oceanic crust incorporated into the subduction wedge was relatively minor. Directly west of the inner-trench wall, metamorphic rocks, marble and limestone identical to those dredged, crop out in a “blueschist belt” in northern Hispaniola. Behind the trench, to the south, low-grade metavolcanics in Puerto Rico appear to be continuous across Mona Passage to central Hispaniola. This belt parallels the higher-grade complex within the trench, and as such constitutes a paired metamorphic belt that extends for more than 500 km along the northern Caribbean plate boundary. The development of this belt is related to the inception of the Puerto Rico Trench in the middle to late Cretaceous due to the southerly subduction of the Atlantic plate beneath the Caribbean plate. Eastward movement of the Caribbean plate relative to the North American plate in the late Cretaceous and early Tertiary initiated transcurrent and tensional faulting which enhanced the uplift of the metamorphosed subduction wedge. Local tectonic readjustments which began in late Eocene time created the grabenlike trench observed at present and caused at least 3500 m of subsidence along the innertrench wall north of Puerto Rico, since Miocene time." @default.
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- W1968117968 date "1980-02-01" @default.
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- W1968117968 title "Chemistry, origin and tectonic significance of metamorphic rocks from the Puerto Rico Trench" @default.
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- W1968117968 doi "https://doi.org/10.1016/0025-3227(80)90069-9" @default.
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