Geochemistry of I-type granitoids in the Karaburun Peninsula, West Turkey: Evidence for Triassic continental arc magmatism following closure of the Palaeotethys

• Published in: The island arc Vol. 17; no. 3; pp. 394 - 418
• Main Authors: Erkül, Sİbel Tatar, Sözbİlİr, Hasan, Erkül, Fuat, Helvaci, Cahİt, Ersoy, Yalçin, Sümer, ÖKmen
• Format: Journal Article
• Language: English
• Published: Melbourne, Australia Blackwell Publishing Asia 01.09.2008
• Subjects: active continental margin; Chondrites; mantle wedge; Neotethys; Palaeotethys; Triassic; volcanic arc granitoids; MED, Turkey
• ISSN: 1038-4871; 1440-1738
• DOI: 10.1111/j.1440-1738.2008.00627.x

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 % SiO2 and are calc‐alkaline in character. They are also subalkaline with molar ratios of Al2O3/(Na2O + K2O) from 0.74 to 1.00 and are metaluminous. Most samples are diopside‐normative (0.36–8.64), with Na2O > K2O. Chondrite normalized rare earth element (REE) patterns show various degrees of light REE (LREE) enrichment, with LaN = 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.