Extensional-tectonic processes have generated extensive magmatic activity that produced volcanic/plutonic rocks along an E-W-trending belt across north-western Turkey; this belt includes granites and coeval volcanic rocks of the Alaçamdag volcano-plutonic complex. The petrogenesis of the Early Miocene Alaçamdag granitic and volcanic rocks are here investigated by means of wholerock Sr-Nd isotopic data along with field, petrographic and whole-rock geochemical studies. Geological and geochemical data indicate two distinct granite facies having similar mineral assemblages, their major distinguishing characteristic being the presence or absence of porphyritic texture as defined by K-feldspar megacrysts. I-type Alaçamdag granitic stocks have monzogranitic-granodioritic compositions and contain a number of mafic microgranular enclaves of monzonitic, monzodioritic/monzogabbroic composition. Volcanic rocks occur as intrusions, domes, lava flows, dykes and volcanogenic sedimentary rocks having (first episode) andesitic and dacitic-trachyandesitic, and (second episode) dacitic, rhyolitic and trachytic-trachydacitic compositions. These granitic and volcanic rocks are metaluminous, high-K, and calc-alkaline in character. Chondrite-normalised rare earth element patterns vary only slightly such that all of the igneous rocks of the Alaçamdag have similar REE patterns. Primitive-mantle-normalised multi-element diagrams show that these granitic and volcanic rocks are strongly enriched in LILE and LREE pattern, high ( 87 Sr/ 86 Sr) i and low e Nd(t) ratios suggesting Alaçamdag volcano-plutonic rocks to have been derived from hybrid magma that originated mixing of co-eval lower crustal-derived more felsic magma and enriched subcontinental lithospheric mantle-derived more mafic magmas during extensional processes, and the crustal material was more dominant than the mantle contribution. The Alaçamdag volcano-plutonic complex rocks may form by retreat of the Hellenic/Aegean subduction zone, coinciding with the early stages of back-arc extension that led to extensive metamorphic core-complex formation.

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Garnet-bearing xenoliths are observed within a trachytic dome extrusion in the Hisarlıkaya region (Ankara). These garnets exhibiting greenish-reddish-dark brown colour and ranging in sizes up to one cm were examined in terms of mineralogical, geochemical and gemmological characteristics. Mineralogical studies indicate that these garnets (And 88-93 Grs 7-12) are linked to solid solution series which are dominantly andradite with lower content of grossular. According to major, trace and rare earth element (REE) analysis, the representative garnet crystal shows high CaO, Fe 2 O 3 , Al 2 O 3 , MgO, MnO, V, W and light rare earth elements (LREE) concentrations. These high concentrations might indicate the mobility of these elements during skarn formation related with contact metamorphism, material exchange occurring via hydrothermal fluids, site geometry of the crystal, ionic radius of cations and charge balance. The Hisarlıkaya garnets display dodecahedron-trapezohedron crystal habits with good translucency, glassy, transparent features and also optical isotropic character. Their refractive indices are high (>1.78), and specific gravities range from 3.66 to 3.67 g/cm 3. These garnets are not suitable for use as gemstones since they cannot be cut or processed considering all the mineralogical properties of garnets.

Triassic granitoids related to Palaeo-and Neo-Tethyan events occur widely in the metamorphic terranes largely affected by the Alpine orogeny. A first recorded unmetamorphosed plutonic body intruded into the Palaeotethyan mélange in western Turkey, called the Karaburun granodiorite, is composed of two small intrusive stocks that were emplaced between 240 and 220 Ma. It is compositionally diverse, ranging from granodiorite and tonalite to diorite. These rocks show heterogeneous compositions with 54 to 65 wt % SiO 2 and are calc-alkaline in character. They are also subalkaline with molar ratios of Al 2 O 3 /(Na 2 O + K 2 O) from 0.74 to 1.00 and are metaluminous. Most samples are diopsidenormative (0.36-8.64), with Na 2 O > K 2 O. Chondrite normalized rare earth element (REE) patterns show various degrees of light REE (LREE) enrichment, with La N = 57.79 to 99.59 and (La/Yb) N = 5.98-7.85 and Eu negative anomalies (Eu/Eu* = 0.62-0.86). These rocks have coherent patterns in ocean ridge granite (ORG) normalized trace-element plots, marked by variable enrichment in K, Rb, Ba, Th, Ce and depletion in Ta and Nb, similar to I-type granites from subduction zones. In primitive mantle-normalized multi element variation diagrams, the granodiorites show pronounced depletions in the high-field-strength elements (HFSE; Nb, Ta, Zr), Sr, P, and Ti. Trace-element modeling of the Karaburun granodiorite suggests an origin through partial melting of the subduction-modified mantle wedge with minor contribution of crustal components through a process of strong fractional crystallization (FC) combined with slight assimilation-fractional crystallization (AFC). Exposures of typical continental-arc granodiorites in the Karaburun Mélange support the validity of the subduction-accretion model that implies the presence of an active continental margin following closure of the Palaeotethyan Ocean during the Triassic.