Quantifying cooling and exhumation patterns in a bivergent metamorphic core complex: the central Menderes Massif, western Turkey

Metamorphic core complexes are commonly associated with an asymmetric exhumation pattern owing to a simple shear mode of extension along the core-bounding extensional detachment fault. In contrast, a symmetric exhumation pattern was proposed for the central Menderes Massif (western Turkey), because it comprises two detachment faults with opposite dip and shear sense, which accommodated N-S extension since the middle Miocene. However, available constraints on the evolution of the central Menderes Massif are mainly based on data from the northern part including the north-dipping Gediz detachment. Exhumation of the southern part along the south-dipping Büyük Menderes detachment was assumed to occur more or less synchronously. New thermochronological and structural data (Wölfler et al., 2017; Nilius et al., 2019) show, however, that extension in the southeastern part of the central Menderes Massif was accommodated along the Büyük Menderes detachment during the middle Miocene and shifted in the Pliocene to the Demirhan detachment, which is situated in the hanging wall of the eastern Büyük Menderes detachment. Together with new zircon and apatite (U-Th)/He and fission track ages from the Gediz detachment, our data set allows constraining temporal and spatial variations in cooling and exhumation patterns in the entire central Menderes Massif. Our new data from the Gediz detachment imply that faulting commenced in the middle Miocene and continuously propagated to the east until the late Pliocene. Exhumation rates in the detachments footwalls were constrained by 1D thermokinematic modelling. The results show that the southern part of the Menderes Massif was exhumed at rates of ~0.5 km/Ma in the middle Miocene and at ~0.4 km/Ma in the Pliocene. In contrast, the western part of the northern central Menderes Massif was exhumed at rates of 0.3-1 km/Ma in the middle to late Miocene; the eastern part shows even higher exhumation rates of ~1.5 km/Ma during the Pliocene. Faster exhumation of the northern central Menderes Massif compared to slower exhumation of the southern part is also expressed in the slip rates derived from cooling ages in the footwalls of the detachments. We obtain the highest slip rate 5.6 km/Ma along the eastern Gediz detachment in the Pliocene, ~2.5 km/Ma along the western Gediz detachment in the middle Miocene, and ~2 km/Ma during the Pliocene along the Demirhan detachment. Consequently, the Gediz detachment is responsible for about twice as much extension and exhumation as the Büyük Menderes and Demirhan detachments

The Schwarzhorn Amphibolite (Eastern Ratikon, Austria): an Early Cambrian intrusion in the Lower Austroalpine basement

The Alpine nappe stack in the Penninic-Austroalpine boundary zone in the Ratikon (Austria) contains a 4x1 km tectonic sliver of meta-diorite, known as the Schwarzhorn Amphibolite. It was deformed and metamorphosed in the amphibolite facies and is unconformably overlain by unmetamorphic Lower Triassic sandstone, indicating pre-Triassic metamorphism. Cataclastic deformation and brecciation of the amphibolite is related to normal faulting and block tilting during Jurassic rifting. Zircon dating of the Schwarzhorn Amphibolite using LA-ICP-MS gave a U-Pb age of 529+9/-8 Ma, interpreted as the crystallization age of the protolith. Geochemical characteristics indicate formation of the magmatic protolith in a supra-subduction zone setting. The Cambrian protolith age identifies the Schwarzhorn Amphibolite as a pre-Variscan element within the Austroalpine basement. Similar calc-alkaline igneous rocks of Late Neoproterozoic to Early Cambrian age are found in the Upper Austroalpine Silvretta Nappe nearby and in several other Variscan basement units of the Alps, interpreted to have formed in a peri-Gondwanan active-margin or island-arc setting

Spatial patterns of erosion and landscape evolution in a bivergent metamorphic core complex revealed by cosmogenic 10Be: The central Menderes Massif (western Turkey)

In extensional provinces with low-angle normal faulting (such as the Aegean region), both tectonic processes and erosion induce landscape change, but their interaction during the evolution of topography and relief accompanying continental extension has rarely been addressed. Here we present local and catchment-wide 10Be erosion rates that document the spatial pattern of erosion in the central Menderes Massif, a metamorphic core complex consisting of two asymmetric mountain ranges (Bozdağ and Aydın) bound by detachment faults and active grabens. Catchment-wide erosion rates on the northern flank of the Bozdağ Range are rather low (40–110 mm/k.y.) but reach values of >300 mm/k.y. on the steep southern escarpment—a pattern that reflects both topography and bedrock lithology. In the Aydın Range, erosion rates are generally higher, with mean erosion rates of ∼190 and ∼260 mm/k.y. on the northern and southern flank, respectively, and more variable along strike. In both ranges, erosion rates of ridge crests derived from amalgamated clasts are 30–90 mm/k.y. The difference between local and catchment-wide erosion rates indicates that topographic relief increases in most parts of the massif in response to ongoing fault-related uplift and concomitant river incision. Our findings document that tectonic processes exert a significant control on landscape evolution during active continental extension and are reflected in both the topographic signature and the spatial pattern of erosion. In the Menderes Massif, rock susceptibility to weathering and erosion is a dominant factor that controls the erosional contribution to rock exhumation, which varies spatially between ∼10% and ∼50%

The Schwarzhorn Amphibolite (Eastern Rätikon, Austria): an Early Cambrian intrusion in the Lower Austroalpine basement

The Alpine nappe stack in the Penninic-Austroalpine boundary zone in the Rätikon (Austria) contains a 4×1 km tectonic sliver of meta-diorite, known as the Schwarzhorn Amphibolite. It was deformed and metamorphosed in the amphibolite facies and is unconformably overlain by unmetamorphic Lower Triassic sandstone, indicating pre-Triassic metamorphism. Cataclastic deformation and brecciation of the amphibolite is related to normal faulting and block tilting during Jurassic rifting. Zircon dating of the Schwarzhorn Amphibolite using LA-ICP-MS gave a U-Pb age of 529+9/-8 Ma, interpreted as the crystallization age of the protolith. Geochemical characteristics indicate formation of the magmatic protolith in a supra-subduction zone setting. The Cambrian protolith age identifies the Schwarzhorn Amphibolite as a pre-Variscan element within the Austroalpine basement. Similar calc-alkaline igneous rocks of Late Neoproterozoic to Early Cambrian age are found in the Upper Austroalpine Silvretta Nappe nearby and in several other Variscan basement units of the Alps, interpreted to have formed in a peri-Gondwanan active-margin or island-arc setting

Spatial patterns of erosion and landscape evolution in a bivergent metamorphic core complex revealed by cosmogenic Be-10: The central Menderes Massif [western Turkey]

In extensional provinces with low-angle normal faulting (such as the Aegean region), both tectonic processes and erosion induce landscape change, but their interaction during the evolution of topography and relief accompanying continental extension has rarely been addressed. Here we present local and catchment-wide Be-10 erosion rates that document the spatial pattern of erosion in the central Menderes Massif, a metamorphic core complex consisting of two asymmetric mountain ranges (Bozdag and Aydin) bound by detachment faults and active grabens. Catchment-wide erosion rates on the northern flank of the Bozdag Range are rather low (40-110 mm/k.y.) but reach values of >300 mm/k.y. on the steep southern escarpment-a pattern that reflects both topography and bedrock lithology. In the Aydin Range, erosion rates are generally higher, with mean erosion rates of similar to 190 and similar to 260 mm/k.y. on the northern and southern flank, respectively, and more variable along strike. In both ranges, erosion rates of ridge crests derived from amalgamated clasts are 30-90 mm/k.y. The difference between local and catchment-wide erosion rates indicates that topographic relief increases in most parts of the massif in response to ongoing fault-related uplift and concomitant river incision. Our findings document that tectonic processes exert a significant control on landscape evolution during active continental extension and are reflected in both the topographic signature and the spatial pattern of erosion. In the Menderes Massif, rock susceptibility to weathering and erosion is a dominant factor that controls the erosional contribution to rock exhumation, which varies spatially between similar to 10% and similar to 50%

Exhumation history of the Aydin range and the role of the Buyuk Menderes detachment system during bivergent extension of the central Menderes Massif, western Turkey

The central Menderes Massif (western Turkey) is a prominent example of symmetrical exhumation of a core complex. It comprises the Bozdag and Aydin ranges, which represent the footwalls of the north-dipping Gediz detachment and the south-dipping Buyuk Menderes detachment, respectively. In contrast to the Gediz detachment, the role of the Buyuk Menderes detachment during Late Cenozoic extension and exhumation of the central Menderes Massif is less well resolved. Here, we present results from structural and geological mapping as well as new fission-track and (U-Th)/He data to show that two low-angle normal faults contributed to the exhumation of the Aydin range. Our data indicate that the sustained activity of the Buyuk Menderes detachment since the early Miocene is followed by the onset of faulting along the previously unrecognized Demirhan detachment, which is situated in the hanging wall of the Buyuk Menderes detachment, in the latest Miocene/Pliocene. Thermokinematic modelling of cooling ages from the footwalls of the Buyuk Menderes and Demirhan detachments yielded exhumation rates of c. 0.5 and c. 0.4 km Ma(-1), respectively. Apatite fission track ages from the Demirhan detachment indicate a slip rate of c. 2 km Ma(-1) during the Pliocene. High-angle normal faulting along the modern Buyuk Menderes graben commenced in the Quaternary

Late Cenozoic cooling history of the central Menderes Massif: Timing of the Buyuk Menderes detachment and the relative contribution of normal faulting and erosion to rock exhumation

Based on new thermochronological data and Be-10-derived erosion rates from the southern part of the central Menderes Massif (Aydin block) in western Turkey, we provide new insights into the tectonic evolution and landscape development of an area that undergoes active continental extension. Fission-track and (U-Th)/He data reveal that the footwall of the Buyuk Menderes detachment experienced two episodes of enhanced cooling and exhumation. Assuming an elevated geothermal gradient of similar to 50 degrees C/km, the first phase occurred with an average rate of similar to 0.90 km/Myr in the middle Miocene and the second one in the latest Miocene and Pliocene with a rate of similar to 0.43 km/Myr. The exhumation rates between these two phases were lower and range from similar to 0.14 to similar to 0.24 km/Myr, depending on the distance to the detachment. Cosmogenic nuclide-based erosion rates for catchments in the Aydin block range from similar to 0.1 to similar to 0.4 km/Myr. The similarity of the erosion rates on both sides of the Aydin block (northern and southern flank) indicate that a rather symmetric erosion pattern has prevailed during the Holocene. If these millennial erosion rates are representative on a million-year timescale they indicate that, apart from normal faulting, erosion in the hanging wall of the Buyuk Menderes detachment fault did also contribute to the exhumation of the metamorphic rocks. (C) 2017 Elsevier B.V. All rights reserved

Spatial patterns of erosion and landscape evolution in a bivergent metamorphic core complex revealed by cosmogenic 10Be: The central Menderes Massif (western Turkey)

In extensional provinces with low-angle normal faulting (such as the Aegean region), both tectonic processes and erosion induce landscape change, but their interaction during the evolution of topography and relief accompanying continental extension has rarely been addressed. Here we present local and catchment-wide 10Be erosion rates that document the spatial pattern of erosion in the central Menderes Massif, a metamorphic core complex consisting of two asymmetric mountain ranges (Bozdağ and Aydın) bound by detachment faults and active grabens. Catchment-wide erosion rates on the northern flank of the Bozdağ Range are rather low (40–110 mm/k.y.) but reach values of >300 mm/k.y. on the steep southern escarpment—a pattern that reflects both topography and bedrock lithology. In the Aydın Range, erosion rates are generally higher, with mean erosion rates of ∼190 and ∼260 mm/k.y. on the northern and southern flank, respectively, and more variable along strike. In both ranges, erosion rates of ridge crests derived from amalgamated clasts are 30–90 mm/k.y. The difference between local and catchment-wide erosion rates indicates that topographic relief increases in most parts of the massif in response to ongoing fault-related uplift and concomitant river incision. Our findings document that tectonic processes exert a significant control on landscape evolution during active continental extension and are reflected in both the topographic signature and the spatial pattern of erosion. In the Menderes Massif, rock susceptibility to weathering and erosion is a dominant factor that controls the erosional contribution to rock exhumation, which varies spatially between ∼10% and ∼50%

Detachment faulting in a bivergent core complex constrained by fault gouge dating and low-temperature thermochronology

The central Menderes Massif in western Turkey is a bivergent metamorphic core complex characterised by two detachment faults that operated with opposite sense of shear. Here, we present K-Ar ages and hydrogen isotope data for fault gouge as well as fission track and (U-Th)/He ages for apatite and zircon from bedrock samples to constrain the timing of detachment faulting. Comparison of the K-Ar ages and low-temperature thermochronologic ages indicates brittle faulting at temperatures between similar to 240 and similar to 70 degrees C. At the western termination of the Gediz detachment, K-Ar ages between similar to 12 and similar to 5 Ma suggest rather continuous faulting since the mid-Miocene; a Pliocene phase of rapid slip is mainly recorded in the eastern part of this detachment. In contrast, K-Ar ages from the Buyuk Menderes detachment cluster at 22-16 and 9-3 Ma and provide evidence for two phases of faulting, which is in accordance with new and published low-temperature thermochronologic data. Hydrogen isotope ratios of -76 to -115 parts per thousand indicate infiltration of meteoric water during detachment faulting and gouge formation. The youngest K-Ar ages and cooling histories for hanging and footwall rocks imply that the activity of both detachments ended similar to 3 Ma ago when the currently active grabens were established