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Unformatted text preview: 1 ERSC 4011 El-Shazly, A. K., 1995 Lab 8 Samples from the Semail Ophiolite As you are aware, the Semail ophiolite consists of (1) Tectonized harzburgites with pods and lenses of dunite, (2) Layered gabbros (3) Isotropic gabbros (4) Sheeted dykes (5) Pillow basalts (6) Radiolarian cherts and pelagic sediments The layered and isotropic gabbros (as well as the mantle sequence) are crosscut by dykes of wehrlite, pyroxenite, troctolite, and uralitic gabbros. The &quot;uralitic gabbros&quot; differentiate into diorites and (probably?) tonalites. Because these tonalites are in many cases extremely leucocratic, they were called &quot;plagiogranites&quot; (although they are not granites at all as they do not contain any K-spar!). Another name used for those leucotonalites is &quot;Trondhjemites&quot;. The &quot;pillow basalts&quot; were found to consist of three different &quot;lavas&quot; erupted at different types and places and designated V1, V2 and V3. These relations are illustrated in Fig. 1 from Christensen and Smewing (1981). Genetically, the Semail ophiolite rocks are considered to have formed by at least two magmatic &quot;events&quot;. The main event culminated in volcanism at the site of a spreading centre and formed the layered and isotropic gabbros, the sheeted dykes and the lower pillow basalts (V1; N-MORB). Later stage of magmatism produced the intrusive gabbros, the palgiogranites??, and culminated in the extrusion of the upper basaltic sequence V2 (E-MORB) in an off-axis position. V3 basalts represent intraplate volcanism, and occur as columnar jointed lava flows characterized by alkalic signatures (Regba et al., 1990). 2...
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This note was uploaded on 02/28/2012 for the course GLY 421 taught by Professor Staff during the Fall '11 term at Marshall.
- Fall '11