Serpentinite emplacement in southwestern Puerto Rico indicates a complex plate boundary history between the Caribbean and North America plates. In this study we investigate the kinematics of shear planes within the serpentinite to improve constraints on the tectonic evolution of the region. Shear planes collected within the Monte del Estado and Río Guanajibo serpentinites reveal two predominant groups. One group comprises northwesterly-striking thrust faults and easterly-striking left-lateral faults. A second group comprises northwesterly-striking right-lateral faults and easterly-striking thrust faults. These shear zones reveal two shortening directions that trend NE-SW and N-S. The N-directed shortening is interpreted be older and subsequent stress reactivated the shear planes. The SW-directed shortening is attributed to transpression that caused contraction, uplift, and left-lateral shearing of serpentinite. A subsidiary younger group comprising fewer faults consists of northerly-directed thrusts and northwesterly-directed left-lateral faults and may be related to the last transpressional deformation within Puerto Rico.
Thin-section observations show that porphyroclastic peridotite with pyroxenes that are kinked, show deformation lamellae, undulose extinction, and define foliation and lineation. Olivine shows a granuloblastic texture, and many crystals are strain-free and show polygonization indicating recrystallization. These textures indicate high temperature deformation that formed prior to serpentinization. Crystal-plastic deformation, recorded by serpentine mylonite and serpentine veins, was followed by brittle faulting. These structures demonstrate that the serpentinite was deformed and uplifted by tectonic stresses at the Caribbean-North America plate boundary zone and not by diapirism as a result of buoyancy differences within the crust.
In southwestern Puerto Rico serpentinite emplacement has been described as first by collisional processes and second by diapirism. Structure mapping of the Monte del Estado and Río Guanajibo serpentinite bodies indicate that serpentinite was emplaced by thrusts verging towards the southwest in early Tertiary time. The thrust faults are mostly blind and produced fault-propagation folds in the overlying Late Cretaceous and Tertiary volcano-sedimentary cover. Low-angle thrusts are exposed in places at the southern contact of the Monte del Estado and Río Guanajibo serpentinite bodies and are interpreted to form part of the transpression that occurred in middle Tertiary at the boundary of the Caribbean-North America plates.
| Identifer | oai:union.ndltd.org:PITT/oai:PITTETD:etd-08072008-214549 |
| Date | 30 October 2008 |
| Creators | Laó-Dávila, Daniel Alberto |
| Contributors | Thomas H. Anderson, William Harbert, Edward G. Lidiak, Grenville Draper, Ian Skilling |
| Publisher | University of Pittsburgh |
| Source Sets | University of Pittsburgh |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.library.pitt.edu/ETD/available/etd-08072008-214549/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Pittsburgh or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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