Meta-bauxite deposit in the Tavsanli Zone, NW Turkey: A new locality for gem-quality diaspore formation

The tectonic units of Sakarya Zone (Pontides) and Tavs,anli Zone (Anatolides) are exposed in the Mihaliccik area of central Anatolia. A Cretaceous accretionary complex that forms the Izmir-Ankara-Erzincan suture zone separates the units. Within this region, the Tavs,anli Zone is made up of a coherent series and tectonically overlying late Cretaceous me & PRIME;lange, which has undergone blueschist facies metamorphism. Coherent series consist of strongly retrogressed schists and conformably overlying platform-type thick marbles, known as the Ino & BULL;nu marbles. The Ino & BULL;nu marbles contain meta-bauxite lenses in the lower levels, which can be classified as karstic bauxites deposited in the karst holes within the original limestone. Considering the general stratigraphy of the Tavs,anli Zone, a middle Jurassic age can be envisaged for the bauxite formation. Geochemical data suggest that the bauxites were largely derived from redeposited argillic sediments, with minor and variable inputs from the weathering of intermediate to acidic rock. The mineral assemblage of the meta-bauxite consists of diaspore, chloritoid, muscovite, paragonite, Al-spinel (hercynite), magnetite, hematite and ilmenite. In addition, apatite, rutile, monazite, xenotime and zircon occur as accessory minerals. Limonite, goethite, akaganeite and kaolinite also formed during the latest stage of alteration. P-T conditions for the meta-bauxites are estimated as 20-27 kbar and 330-470 degrees C that are indicative of formation under high-P / low-T blueschist facies conditions. The meta-bauxites are cut by veins of diaspore, muscovite-paragonite, goethite, calcite and ankerite, and include gem-quality diaspore crystals up to 6 cm long. Textural evidence indicates that the diaspore formation is related to the extraction of aluminium from the meta-bauxite body and migration of Al-rich fluids into the shear zones during the last stage of the high-P metamorphism. During exhumation of the Tavs,anli Zone, these veins were brecciated by brittle deformation and the fractured minerals were cemented by granoblastic calcite and ankerite during the latest stage of the vein formation

Geochemistry and petrology of the Early Miocene lamproites and related volcanic rocks in the Thrace Basin, NW Anatolia

The extensional Thrace basin (NW Anatolia) contains an association of early Miocene diopside–leucite–phlogopite (Do?anca) and diopside–phlogopite (Korucuköy) lamproites with Oligocene medium-K calc-alkaline andesites (Ke?an volcanics), early Miocene shoshonitic rocks (Alt?nyaz? trachyte) and middle Miocene Na-alkaline basalts (Be?endik basalts). The Do?anca lamproite (K2O = 5.1–5.5 wt.%; K/Na = 2.78–2.89; MgO = 11.4–11.8 wt.%) consists of olivine (Fo71–86), diopside (Al2O3 = 1.0–5.0, Na2O = 0.2–0.6), phlogopite (TiO2 = 1.1–9.4, Al2O3 = 11.1–13.9), spinel (Mg# = 22.9–32.6; Cr# = 64–83.4), leucite, apatite, zircon, Fe–Ti-oxides and magnetite in a poikilitic sanidine matrix. The potassic volcanic units (lamproites and trachytes) in the region have similarly high Sr and low Nd isotopic compositions (87Sr/86Sr(i) = 0.70835–0.70873 and 143Nd/144Nd(i) = 0.51227–0.51232). The major and trace element compositions and Sr–Nd–Pb isotopic ratios of the shoshonitic, ultrapotassic and lamproitic units closely resemble those of other Mediterranean ultrapotassic lamproites (i.e., orogenic lamproites) from Italia, Serbia, Macedonia and western Anatolia. The Be?endik basalts show intraplate geochemical signatures with an Na-alkaline composition, an absence of Nb negative anomalies on primitive mantle-normalized multi-element diagrams, as well as low Sr (~ 0.70416) and high Nd (0.51293) isotopic ratios; and include olivine (Fo72–84), diopside, spinel, Fe–Ti-oxides and magnetite.The Oligocene Ke?an volcanics were emplaced in the earlier stages of extension in Thrace, and represent the typical volcanic products of post-collisional volcanism. The continental crust-like trace element abundances and isotopic compositions of the most primitive early Miocene ultrapotassic rocks (Mg# up to 74) indicate that their mantle sources were intensely contaminated by the continental material. By considering the geodynamic evolution of the region, including oceanic subduction, crustal accretion, crustal subduction and post-collisional extension, it is suggested that the mantle sources of the potassic volcanic units were most likely metasomatized by direct subduction of continental blocks during accretion and assemblage of various Alpine tectono-stratigraphic units. Overall, the magma production occurred in an extensional tectonic setting that controlled the core-complex formation and related basin development, with the middle Miocene Be?endik basalts being derived from asthenospheric sources during the late stages of extension

CELADONITE FROM SMYRNA (İZMİR-TÜRKİYE): DID VITRUVIUS GET RIGHT?

Green earth pigments were widely used in the ancient Mediterranean area during the Roman period. Two green pigments were mentioned by Roman authors: the creta viridis and appianum. The former was cited by Vitruvius who indicated that it was coming from Smyrna (current Izmir) and it has been speculated that it could correspond to the green earth of Cyprus, with Smyrna only being the transfer port; the other pigment was cited by Pliny and thought to originate in Monte Baldo in Northern Italy. However, neither author mentions the important green earth deposit in Cyprus. As celadonite has been widely detected in wall paintings from all over the empire, most analysts attributed it to Cyprus deposit. In this paper, the geological and historical occurrence of celadonite green earth in Izmir (Smyrna) area is being investigated. Celadonite bearing green colored volcanic blocks and columns have been found in some historical building in Izmir. The material would have most probably quarried from a location 1.5 km south of Smyrna Agora. The green powder that appeared during stone processing may have been used as a green pigment. However, the green pigment is yet to be investigated in excavation studies of Roman wall painting from the area of Smyrna. It is presented here the existence of celadonite formation in Smyrna by petrographic, XRD, SEM studies of green volcanic rock and compared with celadonite materials from Cyprus and Monte Baldo. The data confirm the occurrence of celadonite in the area and that it has close similarity with Cyprian celadonite.</p