Crustal source of the Late Cretaceous Satansarı monzonite stock (central Anatolia – Turkey) and its significance for the Alpine geodynamic evolution

Abstract

The Late Cretaceous granitic rocks within central Anatolia (Turkey) not only date and show the magmatic aspects of the Alpine realm, but also give clues about its geodynamic character. Among them, the Satansarı monzonite stock (SMS), part of the Terlemez pluton (Aksaray), characterizing the inception of an extensional tectonic regime in central Anatolia, has a subalkaline, metaluminous and magnesian geochemical nature with depletion in Ba, Nb, P and Ti, and with enrichment of Th, U, K and Pb relative to primitive mantle. The SMS has LREE enriched patterns ([La/Yb]N=18.45–21.21) with moderately negative Eu-anomalies ([Eu/Eu*]N=0.65–0.73). The geochemical data infer a crustal source with an inherited subduction-related component, and fractionation of plagioclase and amphibole. A crustal signature for the SMS is also inferred from high 87Sr/86Sr(t) ratios (0.70826–0.70917), and low ɛNd(t) values (−6.9 to −7.6).Zircon crystals from the SMS typically have magmatic rims overgrowing inherited cores that are reworked, resorbed and overgrown. Completely new zircon crystals grown in a single magmatic episode have also been identified. Laser ablation ICP-MS U–Pb zircon analyses yield a mean 206Pb/238U age of 74.4±0.6Ma (2σ) for the intrusion of the SMS. Rare discordant analyses range from the Devonian to the Proterozoic (i.e., 207Pb/206Pb ages between 364Ma and 1263Ma). In situ zircon Hf isotope analyses reveal low 176Lu/177Hf ratios and negative ɛHf(t) values, which is consistent with a predominantly crustal source of the SMS.We suggest that the water-rich magmas were generated in a hot zone within the crust produced by residual melts from basalt crystallization and partial melts of pre-existing metamorphic and igneous rocks within the lower crust of central Anatolia. The SMS likely formed by episodic injections of these hybrid monzonite melts by adiabatic ascent to shallow crust where they crystallized. This interpretation may be useful in interpreting the involvement of crustal sources for other monzonitic rocks in central Anatolia and granitic magmatism in other similar tectonic environments.