Chemistry, origin and tectonic significance of metamorphic rocks from the Puerto Rico Trench
In: Marine Geology. Elsevier: Amsterdam. ISSN 0025-3227; e-ISSN 1872-6151, more
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| Keywords |
Chemistry > Geochemistry
Earth sciences > Geology > Tectonics > Plate tectonics
Mineralogy
Plate boundaries
Rocks > Metamorphic rocks
Subduction zones
Trenches (pipelines)
ASW, Puerto Rico Trench [Marine Regions]
Marine/Coastal |
| Authors | | Top |
- Perfit, M.R.
- Heezen, B.C.
- Rawson, M.
- Donnelly, Th.W.
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| 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 36 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 melanges believed to be subduction complexes. These conditions of metamorphism within the Puerto Rico Trench metamorphic complex are estimated to have been between 400 and 550C and 3 to 7 kbar. Chemical analyses suggest that: (1) The metamorphic rocks from the inner-trench wall were island-arc igneous rocks or derived sediments. (2) Protoliths of the marbles and calc-schists were biogenic carbonates and pelagic sediments with an arc-derived sedimentary component. |
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