Role of mantle and lower continental crust in the genesis of Eocene post-collisional granitoids: Insights from the Topuk pluton (NW Turkey)

Işıl Nur Güraslan*, Şafak Altunkaynak

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

12 Citations (Scopus)

Abstract

We present here new mineral chemistry and major trace element and Sr-Nd-Pb-O isotope data as well as detailed field and petrographic studies of the Topuk Pluton (TP; ca. 48 Ma) and its hypabyssal counterparts. We aim to constrain the granitic magma genesis and emplacement and magmatic processes within the framework of post-collisional evolution of NW Anatolia. The TP is a shallow level intrusion (1.5–2.1 kbar, 680–760 °C, and 4.5–6.3 km depth) which is characterized by a dominant granodiorite composition and presents holocrystalline porphyritic texture. The pluton includes mafic microgranular enclaves (MMEs) of diorite/quartz diorite composition. During its emplacement, the pluton developed radial and ring fractures around itself, and aplite, porphyry dykes, and stocks were emplaced coeval with the pluton along these ring and radial fractures. The TP shows metaluminous and calc-alkaline I-type characteristics. Normal-mid ocean ridge basalt-normalized trace element patterns show that the samples are enriched in large-ion lithophile elements and light rare earth elements but depleted in Nb, Ti, and Ta elements. Granodiorite, MMEs, and hypabyssal rocks present similar initial 87Sr/86Sr and 143Nd/144Nd isotopic values, which lie in the ranges 0.705860–0.706247 and 0.512455–0.512584, respectively. The 206Pb/204Pb, 207Pb/204Pb, 208Pb/206Pb, and 207Pb/206Pb ratios are 18.831–19.046, 15.673–15.748, 2.0621–2.0725, and 0.82816–0.83321 values, respectively, while the δ18O isotope values range from 9.6 to 10.7. These similar Sr-Nd-Pb-O isotopic features of MMEs and host granodiorites indicate a common igneous precursor as the magma source. We infer that the magma-forming TP originated from enriched mantle type II (EMII) with contribution from the lower crust. The results of numerical modelling indicate that this lower crustal input ranges from 5 to 20%. The Eocene melt generation was most probably caused by the upwelling asthenosphere due to the break-off of Neo-Tethys slab in NW Anatolia.

Original languageEnglish
Pages (from-to)365-384
Number of pages20
JournalJournal of Asian Earth Sciences
Volume179
DOIs
Publication statusPublished - 1 Aug 2019

Bibliographical note

Publisher Copyright:
© 2019 Elsevier Ltd

Funding

This study is a part of Işıl Nur Güraslan’s master’s thesis, and is funded by the The Scientific and Technological Research Council of Turkey (TÜBİTAK-ÇAYDAG Project No: 117Y151 ). Special thanks to Alp Ünal for his help on field studies and assistance on writing, and Ömer Kamacı for bringing helpful insights to the article. We are grateful for the constructive and insightful comments from Orhan Karslı and Chao Wang, their comments improved the content and organization of the paper significantly.

FundersFunder number
TÜBİTAK-ÇAYDAG
Türkiye Bilimsel ve Teknolojik Araştirma Kurumu117Y151

    Keywords

    • Eocene
    • Granite genesis
    • NW anatolia
    • Sr-Nd-Pb-O isotope
    • Topuk pluton

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