Late Cretaceous alkaline magmas of the Eastern Pontides Orogenic Belt (NE Turkey): A review with new geological, geochemical and geochronological data

The Eastern Pontides Orogenic Belt (EPOB) in northeastern Turkey is a continental arc that is part of the Himalayan-Alpine orogeny. Late Cretaceous magmatism in this belt is dominated by high-K calc-alkaline, shoshonitic, and alkaline rocks that occur over an area of -600 km (E-W) and -200 km (N-S). We present new geochemical data (whole rock major and trace element analyses, mineral compositions, U-Pb zircon and titanite ages, zircon trace element data, and Sr-Nd-Pb isotopic analyses) for 153 samples, with compiled data for an additional 265 samples. Magmatism is diachronous across the arc. In the north, Cycle-I (92-84 Ma) commenced with tholeiitic and calc-alkaline basalts and andesites, and continued with felsic extrusive rocks. Cycle-II (84-70 Ma) includes mainly intermediate and felsic extrusive rocks. Over time, the low-K granitoids progressively give way to calc-alkaline granitoids in the north. In the south, Cycle-I (84-78 Ma) includes high-K trachyandesites, trachytes and felsic extrusive rocks. Cycle-II (78-65 Ma) comprises leucitites, trachybasalts, and other K-rich rocks. Shoshonitic granitoids in the south show ages between 80 and 65 Ma. Clinopyroxene compositions in trachyandesites and leucitites indicate initial crystallization at -38 km depth and 1120 degrees C. Amphibole joins the phase assemblage at -8 km depth and T < 950 degrees C. All samples have LILE and LREE enrichments and negative Nb, Ta, and Ti, and positive Pb anomalies, consistent with their subduction-related origin. Isotopic data indicate mixing between magmas from heterogeneous, enriched subcontinental mantle sources and those from a range of crustal sources. Mantle-derived and crustally-derived magmas are clearly separated by (Gd/Yb)N. Chemical zoning of the EPOB, from tholeiitic and calc-alkaline rocks to high-K calc-alkaline, shoshonitic, and alkaline rocks, from north to south, and the timing of magmatism younging southward, are consistent with a model of southward subduction in the Late Cretaceous. (c) 2021 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

Automated summary

The research on the Eastern Pontides Orogenic Belt in northeastern Turkey reveals a complex continental arc system with multi-stage Late Cretaceous magmatism showing different characteristics in terms of rock types and geochemical features, indicating a significant geological differentiation.