Middle Carnian Arc-Type Basalts from the Lycian Nappes, Southwestern Anatolia: Early Late Triassic Subduction in the Northern Branch of Neotethys


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SAYIT K., GÖNCÜOĞLU M. C. , TEKİN U. K.

JOURNAL OF GEOLOGY, cilt.123, sa.6, ss.561-579, 2015 (SCI İndekslerine Giren Dergi) identifier identifier

  • Yayın Türü: Makale / Tam Makale
  • Cilt numarası: 123 Konu: 6
  • Basım Tarihi: 2015
  • Doi Numarası: 10.1086/683664
  • Dergi Adı: JOURNAL OF GEOLOGY
  • Sayfa Sayıları: ss.561-579

Özet

The Turunc Unit, which represents one of the tectonic slices within the Lycian Nappes in southwestern Anatolia, preserves the remnants derived from the northern branch of Neotethys. The unit includes basalts intercalated with pelagic limestones of middle Carnian age (early Late Triassic) based on the characteristic radiolarian assemblage of the Tetraporobrachia haeckeli Zone. The Turunc lavas reflect trace element signatures resembling those from subduction zones, displaying selective enrichment of Th and light rare earth elements over high-field strength elements and heavy rare earth elements. Considering the overall geochemical characteristics of the Turunc basalts and given that they are found to be associated with no continent-derived detritus, the Turunc lavas appear to represent fragments of a Late Triassic island arc formed on the Neotethyan oceanic lithosphere. This result is of particular importance, since it reflects the oldest subduction age obtained from the entire Neotethyan realm to date. It may further indicate that the Neotethyan oceanic lithosphere had already been formed by the early Late Triassic, thus suggesting a pre-early Late Triassic oceanization of the northern branch of Neotethys. On the basis of this, we also suggest that the initial rifting leading to the opening of the northern branch of Neotethys should have taken place during the Middle Triassic or earlier.

The Mersin Mélange is a tectonostratigraphic unit within the allochthonous Mersin Ophiolitic Complex in the Taurides, southern Turkey. This chaotic structure consists of blocks and tectonic slices of diverse origins and ages set in a clasticmatrix of Upper Cretaceous age. In this study,we examine two blocks at two different sections characterized by basaltic lava flows alternating with radiolarian-bearing pelagic sediments. The radiolarian assemblage extracted fromthemudstone–chert alternation overlying the lavas yields an upper Anisian age (Middle Triassic). The immobile element geochemistry suggests that the lava flows are predominantly characterized by sub-alkaline basalts. All lavas display pronounced negative Nb anomalies largely coupled with normal midocean basalt (N MORB)-like high field strength element (HFSE) patterns. On the basis of geochemical modelling, the basalts appear to have dominantly derived from spinel–peridotite and pre-depleted spinel-peridotite sources, while some enriched compositions can be explained by contribution of garnet-facies melts from enriched domains. The overall geochemical characteristics suggest generation of these Middle Triassic lavas at an intra-oceanic back-arc basinwithin the northern branch of Neotethys. This finding is of significant importance, since these rocks may represent the presence of the oldest subduction zone found thus far from the Neotethyan branches. This, in turn, suggests that the rupturing of the Gondwanan lithosphere responsible for the opening of the northern branch of Neotethys should have occurred during the Lower Triassic or earlier.