Carboniferous high-potassium I-type granitoid magmatism in the Eastern Pontides: The Gümüşhane pluton (NE Turkey)

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• 作者：Gü ; ltekin Topuz ; Rainer Altherr ; Wolfgang Siebel ; Winfried H. Schwarz ; Thomas Zack ; Altuğ ; Hasö ; zbek ; Mathias Barth ; Muharrem Satı ; r ; Cü ; neyt Ş ; en
• 关键词：High-K granite ; Sr– ; Nd isotopy ; Ar– ; Ar dating ; U– ; Pb zircon dating ; Variscan orogeny ; Eastern Pontides Turkey
• 刊名：Lithos
• 出版年：2010
• 出版时间：April 2010
• 年：2010
• 卷：116
• 期：1-2
• 页码：92-110
• 全文大小：2437 K

文摘

The Gümüşhane pluton, a high-K calc-alkaline I-type granodiorite/granite complex, forms an important component of the pre-Liassic basement of the Eastern Pontides (NE Turkey). In its eastern part, the pluton shows a compositional zonation ranging from biotite–hornblende granodiorite in the NW through biotite–hornblende granite to leucogranite/granophyre in the SE. Numerous mafic microgranular enclaves (up to  40 cm in diameter) suggest the former presence of globules of mafic melt during crystallization. Emplacement of the pluton occurred during the latest Early Carboniferous, as shown by the 320 ± 4 Ma ⁴⁰Ar–³⁹Ar biotite/hornblende and 324 ± 6 Ma LA-ICP-MS U–Pb zircon ages. In Harker diagrams, samples of the different rock types exhibit well-defined data trends. With increasing SiO₂, the abundances of TiO₂, Al₂O₃, Fe₂O₃^tot, MnO, MgO, CaO, P₂O₅ and Sc decrease, but those of K₂O and Rb increase. However, the variations of Sr, Ba, (La/Yb)_cn, Sr/Y and ∑ REEs vs. SiO₂ form distinctive groupings, which cannot be explained by a simple fractional crystallization. Chondrite-normalized (cn) REE patterns of granodiorite/granite samples show concave-upward shapes with (La/Yb)_cn ranging from 5.2 to 12.4 and Eu/Eu* from 0.84 to 0.47, while there is almost no fractionation of the middle REE relative to the heavy REE. In primitive mantle-normalized element concentration diagrams, all rocks display marked negative anomalies in Ba, Nb/Ta, Sr, P and Ti, but positive anomalies in K and Pb. These geochemical features imply a fractionating mineral assemblage of clinopyroxene, amphibole and plagioclase without significant involvement of garnet. The granophyres are, on the other hand, characterized by higher K₂O/Na₂O and Rb/Sr ratios, lower (La/Yb)_cn ratios (1.3 to 4.8) and more pronounced negative anomalies in Ba, Nb/Ta, Sr, Eu, P and Ti. Initial ε_Nd values range from − 3.78 to − 5.30 and Nd model ages from 1.38 to 163 Ga. The magmas of the granite/granodiorite portion were probably generated by partial melting of high-potassic amphibolitic rocks, and those of the granophyres by a relatively felsic micaceous crustal source. The Gümüşhane pluton was emplaced at the wake of the low-pressure–high-temperature metamorphism, and is regarded as a late phase of Hercynian orogeny in the Eastern Pontides.