Cambrian-Eocene pre-rift, pulsed rift, passive margin and emplacement processes along the northern margin of the Southern Neotethys: evidence from the Antalya Complex in the Alanya Window (S Turkey)

Sedimentary rocks in the Alanya Window document pulsed Permian-Triassic rifting in a proximal basin setting, adjacent to the Tauride continental unit (Geyik Dağ). Late Cambrian-Early Ordovician clastic sediments accumulated along the north margin of Gondwana on a variable shallow-marine shelf. Above an unconformity related to rift-shoulder uplift, Late Permian facies document shallow-marine to evaporitic environments during regional tectonic subsidence (first main rift pulse). Above a second unconformity (both extension and sea-level controlled), Early Triassic carbonates and mudrocks accumulated on an unstable, gently subsiding shelf. Mudrocks, sandstones and lithoclastic debris-flows, derived from the underlying succession, accumulated during the Middle Triassic (Anisian-early Ladinian), implying strong tectonic subsidence and flank uplift (second main rift pulse). Radiolarian mudstones accumulated during late Middle Triassic-early Late Triassic in a well-oxidised, organically productive, but relatively quiescent, deep-water basin above the carbonate compensation depth (CCD). Thick (100s m) lithoclastic sandstone turbidites (commonly plant-rich) and localised debris-flows accumulated during the Late Triassic (Carnian), together with detached blocks of underlying lithologies (third main rift pulse, with regional uplift). Alkaline basaltic sills were intruded locally. Final continental break-up to create the Southern Neotethys took place regionally during the Late Triassic (Carnian). Latest Triassic-Late Cretaceous deposition records passive margin subsidence. Variable low-grade metamorphism and two-stage tectonic emplacement (southwards(?) then northwards) took place during latest Cretaceous and Eocene, respectively. The tectonic-sedimentary development of the Antalya Complex provides insights into rift/continental break-up processes that differ from the recently well-documented Alpine-North Atlantic region.Publisher PDFPeer reviewe

Thermal evolution of an ancient subduction interface revealed by Lu–Hf garnet geochronology, Halilbagi Complex (Anatolia)

The thermal structure of subduction zones exerts a major influence on deep-seated mechanical and chemical processes controlling arc magmatism, seismicity, and global element cycles. Accretionary complexes exposed inland may comprise tectonic blocks with contrasting pressure–temperature (P–T) histories, making it possible to investigate the dynamics and thermal evolution of former subduction interfaces. With this aim, we present new Lu–Hf geochronological results for mafic rocks of the Halilbagi Complex (Anatolia) that evolved along different thermal gradients. Samples include a lawsonite–epidote blueschist, a lawsonite–epidote eclogite, and an epidote eclogite (all with counter-clockwise P–T paths), a prograde lawsonite blueschist with a “hairpin”-type P–T path, and a garnet amphibolite from the overlying sub-ophiolitic metamorphic sole. Equilibrium phase diagrams suggest that the garnet amphibolite formed at ~0.6–0.7 GPa and 800–850 °C, whereas the prograde lawsonite blueschist records burial from 2.1 GPa and 420 °C to 2.6 GPa and 520 °C. Well-defined Lu–Hf isochrons were obtained for the epidote eclogite (92.38 ± 0.22 Ma) and the lawsonite–epidote blueschist (90.19 ± 0.54 Ma), suggesting rapid garnet growth. The lawsonite–epidote eclogite (87.30 ± 0.39 Ma) and the prograde lawsonite blueschist (ca. 86 Ma) are younger, whereas the garnet amphibolite (104.5 ± 3.5 Ma) is older. Our data reveal a consistent trend of progressively decreasing geothermal gradient from granulite-facies conditions at ~104 Ma to the epidote-eclogite facies around 92 Ma, and the lawsonite blueschist–facies between 90 and 86 Ma. Three Lu–Hf garnet dates (between 92 and 87 Ma) weighted toward the growth of post-peak rims (as indicated by Lu distribution in garnet) suggest that the HP/LT rocks were exhumed continuously and not episodically. We infer that HP/LT metamorphic rocks within the Halilbagi Complex were subjected to continuous return flow, with “warm” rocks being exhumed during the tectonic burial of “cold” ones. Our results, combined with regional geological constraints, allow us to speculate that subduction started at a transform fault near a mid-oceanic spreading centre. Following its formation, this ancient subduction interface evolved thermally over more than 15 Myr, most likely as a result of heat dissipation rather than crustal underplating

Epidote - lawsonite coexistence in blueschist-facies block from the Tavsanli Zone - Turkey: petrological implications

Metamorphic evolution of an epidote-lawsonite blueschist sample characterized by the coexistence of lawsonite and epidote from Sivrihisar area (Taysanli Zone) was studied herein in terms of petrology and mineral equilibria. Based on the textural evidence and phase composition, 2 prograde stages, defined by assemblage-I and -II and 1 retrograde stage were recognized. Assemblage-I indicates epidote-blueschist facies conditions (12 +/- 1 kbar / 485 +/- 10 degrees C). Assemblage-II is characterized by the coexistence of epidote and lawsonite (17 +/- 1 kbar / 515 +/- 10 degrees C) corresponding to the interface of lawsonite blueschist and epidote blueschist facies. Phase diagram calculations and mineral compositions revealed that along this interface, an equilibrium field with lawsonite and epidote is stable. This closed-equilibrium field is controlled by high aH(2)O and an elevated Fe3+/Al ratio of minerals. Pressure-temperature (P-T) estimates and textural observations indicated a counter-clockwise path during the subduction and exhumation history. The preservation of lawsonite and epidote during the retrograde stage pointed to the fact that the path followed the stability field of lawsonite and epidote during exhumation

Multi-Stage P-T-t Evolution of Precambrian Aged Rocks in Anamur (Alanya Massif, Mersin) Region

The Anamur region in the eastern part of the Alanya Massif is defined by high temperature metamorphism. Metamorphic rocks (Sariagac unit), under the conditions of the upper amphibolite facies which are interrupted by basic and acidic meta-magmatics in the region, constitute the para-autochtonous basis. Kapidag nappe, has undergone metamorphism the Barrow-type medium-pressure metamorphism in the greenschist facies is overlain by the tectonic contact of the Sariagac unit with the ductile conditions. The Kapidag nappe, which forms a regular and thick sequence, begins with a probable infra-cambrian aged assemblage in the base consisting of dolomite, marble, muscovite-quartz schist and chlorite schist alternation. This assemblage is overlain by low-grade metamorphics of Tauride units consist of quartzite, meta-carbonate and schists derived from Hudai, Caltepe and Seydisehir formations in Cambro-Ordovician aged. All these metamorphic units are unconformably overlain by conglomerates belonging to Late Eocene-Oligocene Anamur Formation and then Hadim nappe thrusted over to all units

First occurrence of Fe-Mg-carpholite documenting a high-pressure metamorphism in metasediments of the Lycian Nappes, SW Turkey

In the basal thrust sheets of the Lycian nappes fresh Fe-Mg-carpholite documents low-grade. high-pressure (HP) metamorphism. Here we describe the first occurrences of this HP indicator mineral in Turkey, its regional distribution and geodynamic consequences. Carpholite and its breakdown products, such as chloritiod and pyrophyllite, occur in the Lycian nappes s.s. Relics of Fe-Mg-carpholite were also found in klippen of Lycian nappe material located on top of the Menderes crystalline massif. The distribution of the Fe-Mg-carpholite and its relies traces an extensive area of HP metamorphism in the sediments of a passive continental margin

Pressure-temperature evolution of lawsonite eclogite in Sivriihisar; Tavsanli Zone-Turkey

The Cretaceous blueschist belt, Tavsanli Zone, representing the subducted and exhumed northern continental margin of the Anatolide-Tauride platform is exposed in Western Anatolia. The Sivihisar area east of Tavsanli is made Lip of tectonic units consisting of i) metaclastics and conformably overlying massive marbles (coherent blueschist unit), ii) blueschist-eclogite unit, iii) marble-calcschist intercalation and iv) metaperidotite slab. The metaclastics are composed of jadeite-lawsonite-glaucophane and jadeite-glaucophane-chloritoid schists, phengite phyllitei, and calcschists with glaucophane-lawsonite metabasite layers. The blueschist-eclogite unit representing strongly sheared, deeply buried and imbricated tectonic slices of accreted uppermost levels of the oceanic crust with minor metamorphosed serpentinite bodies consists of lawsonite-bearing eclogitic metabasites (approximately 90% of the field), lawsonite eclogites, metagabbros, serpentinites., pelagic marbles, omphacite-glaucophane-lawsonite metapelites and metacherts. The mineral assemblage of the lawsonite eclogite (garnet+omphacite >70%) is omphacite, garnet, lawsonite, glaucophane, phengite and rutile. Lawsonite eclogite lenses are enclosed by garnet-lawsonite blueschist envelopes. Textural evidence from lawsonite eclogites and country rocks reveals that they did not leave the stability field of lawsonite during subduction and exhumation. The widespread preservation of lawsonite in eclogitic metabasites and eclogites can be attributed to rapid subduction and subsequent exhumation in a low geothermal gradient of the oceanic crust material without experiencing a thermal relaxation. Peak P-Tconditions of lawsonite eclogites are estimated at 24 +/- 1 kbar and 460 +/- 25 degrees C. These P-T conditions indicate a remarkably low geotherm of 6.2 degrees C/km corresponding to a burial depth of 74 km. (C) 2007 Elsevier B.V. All rights reserved