Occurrence, petrography and genesis of tourmalinite at lake Bafa district

Tourmalinites consist of conformable layers made up primarily of quartz and abundant tourmaline; tourmaline typically exceeds 15% to 20% of rock volumes. A few tourmalinites display sedimentary structures such as graded bedding, cross bedding, slump and flame structure and rip-up clasts. Such geological features provide important constraints for assessing the origin of these rocks. Tourmalintes with tourmalines of schorl (Fe-rich)- dravite (Mg-rich) series is an abundant rocktype of the Menderes Massif of western Anatolia. Tourmalinites have at least eight modes of occurances as; (1) as tourmalinites (stratabound and/or stratiform laminated quartz-tourmaline rocks containing > 15-20% tourmaline by volume)- as locally significant but discontinuous lenses or intercalations within mica-quartz (± garnet) schist; (2) as euhedral to anhedral crystals disseminated within mica schist or paragneiss; (3) as weakly concentrated, fine-to medium- grained, anhedral to subhedral crystals within the vast felsic gneiss unit that is considered to be the oldest unit of the Menderes crystalline sequence; (4) as eye- shaped concentrations/nodules and in massive lenses (the latter in zones of weakness) within the felsic gneiss unit; (5) as euhedral crystals, some very large in pegrnatoid (leucosomes) and pegmatites; (6) as subhedral to anhedral crystals or clots, with quartz, as intrafolial pods or segregations within garnet-mica schist; (7) in bands of anhedral to subhedral crystals within strongly sheared granitic gneiss; (8) as joint- and fracture- fillings, with quartz in veins or layers and as country-rock replacements accompanying sulfide mineralization near the margin of unmetamorphosed, post kinematic granite.IV Study area comprises two different locations which are Karahayit and Yeşilköy, at the south of the Menderes Massif. In the Karahayit area tourmaline zones or bands occur in a biotite-quartz schist unit, southwest of Karahayit villige (Muğla-Milas) and also about 2 km east of Lake Bafa. In the Yeşilköy area, between Yeşilköy villige and Lake Azap, north of Lake Bafa, there is single, approximately two-meter- thick outcrop of garnetiferous tourmalinite within a mica-schist unit. Studied tourmalinites at Karahayit and Yeşilköy are composed predominantly of quartz and tourmaline. However, preserved sedimentary features in Karahayit tourmalinite includes laterally continuous rnilimeter-scale quartz and tourmaline laminae, tourmaline-rich rip-up clasts, distinct angular quartz grains (in one outcrop), graded bedding (in thin section) (Mittwede et al., 1997). Magnetite-rich iron formation also occurs in this sequence. Samples from tourmalinites of Karahayit and Yeşilköy areas were investigated as petrographically and geochemically. In thin section, mineral composition of the tourmalinites consist of quartz and tourmaline with a trace amounts of biotite- muscüvite-zifcorı-apatite-sferı and opaque minerals. The tourmalines are mostly brown (dark to very pale), with minor blue, amber and green hue. The different colors most likely reflect different chemical compositions and may represent different stages of tourmaline formation (Jiang et al., 1998). Most of tourmalines from tourmalinites of Karahayit and Yeşilköy areas display optical zonation. Furthermore, the tourmalinites at Yeşilköy are conspicuously garnetiferous. However in a few tourmalinite samples at Karahayit subhedral garnet crystals are observed. Garnet crystals include abundant quartz and tourmaline inclusions. Microprobe analyses of tourmalines from study area indicate that tourmalines have an intermediate composition between schorl and dravite. Whole-rock chemical analyses of tourmalinites from Karahayit and Yeşilköy area show large variations for Si02 (%43. 56-91. 86), Al2O3(%6.05-27.40), Fe2O3(top)(%3.28-13.01), MgO(%0.27-6.71), CaO(%0.04-0.73), Na2O(%0. 14-3.27),,K2O(%0.02-4.30), TiO2(%0.06-1.36) ve MnO(%0-0.035). However, the tourmalines plot apparently Ca-poor metapelites and rnetapsammites (8 field of Henry and Guidotti (1985)) and Mainly 4,5 and 6 fields of Henry and Guidotti (1985) at Al-Fe(top)-Mg and Ca-Fe(top)-Mg diagrams. Geochemical studies of Yeşilköy and Karahayit tourmalinites and stream- sediment samples from Mittwede et al. (1995) suggest that there is no significant metalic mineralization in the vicinity. Nevertheless, Karahayit and Yeşilköy tourmalinites record an unusual chemical-sedimentary depositional environment, indicating either exhalative activity or subseafloor replecament of clastic sediments by boron-rich hydrothermal fluids, or both.