Academic
Publications
ORIGIN AND EVOLUTION OF THE HIGH-PRESSURE META IGNEOUS ASSEMBLAGE NEAR ST. MICHALIS, SYROS, GREECE

ORIGIN AND EVOLUTION OF THE HIGH-PRESSURE META IGNEOUS ASSEMBLAGE NEAR ST. MICHALIS, SYROS, GREECE,ANDREI SINITSIN

ORIGIN AND EVOLUTION OF THE HIGH-PRESSURE META IGNEOUS ASSEMBLAGE NEAR ST. MICHALIS, SYROS, GREECE   (Citations: 2)
BibTex | RIS | RefWorks Download
INTRODUCTION Metamorphic rocks of the island of Syros in the Cyclades, a group of Greek islands located in the southern Aegean, are the product of the Alpine Orogeny. This orogeny was initiated by convergence among Africa, Eurasia, and several microplates between them (Smith and Woodcock, 1982). Northward-directed under-thrusting of one such fragment, the Apulian microplate, beneath Eurasia was most likely responsible for eclogite/blueschist facies metamorphism of rocks now exposed on Syros and other Cycladic islands (Avigad and Garfunkel, 1991). This subduction may have begun as early as the Cretaceous (Brö cker and Enders, 1999). Although Syros is mostly composed of a thick pelitic schist-marble succession, several meta-igneous bodies with the mineralogy associated with high-pressure low-temperature metamorphism are embedded in the northern, central, and western parts of the island (Okrusch and Brö cker, 1990). OBJECTIVES This study concentrates on the geochemistry and history of the diverse high-pressure, low- temperature, meta-igneous rocks in the complex located near the village of St. Michalis in the northeastern corner of Syros. This meta-igneous assemblage includes (from most to least abundant) coarse-grained metagabbros, blueschists, fine-grained clinopyroxene-garnet rocks, meta-igneous rocks with a gneissic fabric, meta-breccias, serpentinite, and a small felsic body thought to be a jadeitite. The majority of the diverse rocks composing the St. Michalis assemblage appear to form large coherent meta-igneous bodies, but some also occur as tectonic blocks in serpentinite melange zones. The two wide (at least 50 m) coastal zones of meta-breccia bound on two sides the smaller of the metagabbro bodies and contain dominantly meta-igneous blueschist and clinopyroxene-garnet rock clasts. The entire assemblage appears to be tectonically separate from the marble-schist succesion (Okrusch and Brö cker, 1990). The diversity of rock types in the assemblage suggests that there might also be fault surfaces within it, separating blocks that may have been juxtaposed either during subduction or exhumation. METHODS Chemical analyses of major, minor, trace, and rare earth elements have been obtained for eighteen of the samples in an attempt to constrain the origin and petrogenetic history of the St. Michalis assemblage. Are these meta-igneous rocks genetically related or were they assembled from completely separate protoliths prior to or during the subduction? The results of these analyses suggest that these meta-igneous rocks had at least three chemically different, separate source magmas, and that the major variations in mineralogy are most likely the result of these chemical differences. These data may also provide an answer to the question of whether the two areas of meta-breccia are tectonic in origin or if they in fact were created through the emplacement of the metagabbro pluton. In addition, mineral composition data are being gathered on the SEM/EDS (Scanning Electron Microscope/Energy Dispersive Spectrometer). These data will be used to characterize differences in mineral compositions among various rock types and to constrain the metamorphic evolution of these meta-igneous rocks, especially the conditions of the high-pressure, low- temperature metamorphism. PETROGRAPHY Although the St. Michalis assemblage is composed of many different rock types, three are by far the most abundant: metagabbros, clinopyroxene-garnet rocks, and blueschists. Metagabbros contain mostly coarse-grained (5-20 mm) green clinopyroxene (40%), fine-grained epidote (40%), coarse-grained (5-20 mm) amphibole (15%), and rutile (5%), although an iron-rich variety with more glaucophane than omphacite can also be found in few locations. Fine-grained (up to 2 mm) clinopyroxene-garnet rocks are characterized by clinopyroxene (40-60%), quartz (typically 25-30%; sample 21A is the one exception that has less silica and as the result contains far less quartz), and garnet (10-15%). These rocks also usually contain a white mica (paragonite or phengite), rutile/titanite, and apatite. The significant amount of quartz found in clinopyroxene-garnet rocks suggests that their protolith was probably not basaltic, but a different, more felsic igneous rock type. Blueschists are composed of mostly fine-grained glaucophane (50-70%) and coarse-grained (1-5 mm) garnet porphyroblasts (20-30%), with smaller amounts of epidote, rutile, and white mica. All three of these rock types are foliated where they contain elongate or platy minerals. Meta-
Cumulative Annual
View Publication
The following links allow you to view full publications. These links are maintained by other sources not affiliated with Microsoft Academic Search.
Sort by: