Neogene Uplift and Magmatism of Anatolia: Insights from Drainage Analysis and Basaltic Geochemistry

It is generally agreed that mantle dynamics have played a significant role in generating and maintaining the elevated topography of Anatolia during Neogene times. However, there is much debate about the relative importance of subduction zone and asthenospheric processes. Key issues concern onset and cause of regional uplift, thickness of the lithospheric plate, and the presence or absence of temperature and/or compositional anomalies within the convecting mantle. Here, we tackle these interlinked issues by analyzing and modeling two disparate suites of observations. First, a drainage inventory of 1,844 longitudinal river profiles is assembled. This geomorphic database is inverted to calculate the variation of Neogene regional uplift through time and space by minimizing the misfit between observed and calculated river profiles subject to independent calibration. Our results suggest that regional uplift commenced in the east at 20 Ma and propagated westward. Secondly, we have assembled a database of geochemical analyses of basaltic rocks. Two different approaches have been used to quantitatively model this database with a view to determining the depth and degree of asthenospheric melting across Anatolia. Our results suggest that melting occurs at depths as shallow as 60 km in the presence of mantle potential temperatures as high as 1400°C. There is evidence that potential temperatures are higher in the east, consistent with the pattern of sub-plate shear wave velocity anomalies. Our combined results are consistent with isostatic and admittance analyses and suggest that elevated asthenospheric temperatures beneath thinned Anatolian lithosphere have played a first order role in generating and maintaining regional dynamic topography and basaltic magmatism

The Thickness of the Mantle Lithosphere and Collision-Related Volcanism in the Lesser Caucasus

The Lesser Caucasus mountains sit on a transition within the Arabia–Eurasia collision zone between very thin lithosphere (<100 km) to the west, under Eastern Anatolia, and a very thick lithospheric root (up to 200 km) in the east, under western Iran. A transect of volcanic highlands running from NW to SE in the Lesser Caucasus allows us to look at the effects of lithosphere thickness variations on the geochemistry of volcanic rocks in this continental collision zone. Volcanic rocks from across the region show a wide compositional range from basanites to rhyolites, and have arc-like geochemical characteristics, typified by ubiquitous negative Nb–Ta anomalies. Magmatic rocks from the SE, where the lithosphere is thought to be thicker, are more enriched in incompatible trace elements, especially the light rare earth elements, Sr and P. They also have more radiogenic ⁸⁷Sr/⁸⁶Sr, and less radiogenic ¹⁴³Nd/¹⁴⁴Nd. Across the region, there is no correlation between SiO₂ content and Sr–Nd isotope ratios, revealing a lack of crustal contamination. Instead, ‘spiky’ mid-ocean ridge basalt normalized trace element patterns are the result of derivation from a subduction-modified mantle source, which probably inherited its subduction component from subduction of the Tethys Ocean prior to the onset of continent–continent collision in the late Miocene. In addition to the more isotopically enriched mantle source, modelling of non-modal batch melting suggests lower degrees of melting and the involvement of garnet as a residual phase in the SE. Melt thermobarometry calculations based on bulk-rock major elements confirm that melting in the SE must occur at greater depths in the mantle. Temperatures of melting below 1200°C, along with the subduction-modified source, suggest that melting occurred within the lithosphere. It is proposed that in the northern Lesser Caucasus this melting occurs close to the base of the very thin lithosphere (at a depth of ∼45 km) as a result of small-scale delamination. A striking similarity between the conditions of melting in NW Iran and the southern Lesser Caucasus (two regions between which the difference in lithosphere thickness is ∼100 km) suggests a common mechanism of melt generation in the mid-lithosphere (∼75 km). The southern Lesser Caucasus magmas result from mixing between partial melts of deep lithosphere (∼120 km in the south) and mid-lithosphere sources to give a composition intermediate between magmas from the northern Lesser Caucasus and NW Iran. The mid-lithosphere magma source has a distinct composition compared with the base of the lithosphere, which is argued to be the result of the increased retention of metasomatic components in phases such as apatite and amphibole, which are stabilized by lower temperatures prior to magma generation

Dynamics of the amphibian chytrid fungus (Batrachochytrium dendrobatidis) in isolated patches of lowland rainforest

Over the past 20 years, amphibian declines caused by Batrachochytrium dendrobatidis (Bd) have prompted a significant amount of research into the amphibian-chytrid host-parasite relationship. The complexities of the relationship have limited our ability to understand the pathogen, particularly as differences are observed in the impacts of Bd among different amphibian species, and the variation in the impact of the pathogen along an elevation gradient.\ud \ud The significant declines of amphibians at high elevations (400+ m asl) in the Wet Tropics bioregion of north eastern Australia has focused research on endemic species, and the environmental conditions they experience. There is, however, little research on tropical lowland areas. Within tropical lowlands rainforest of the Wet Tropics bioregion, Bd-susceptible amphibians continue to thrive, and although Bd is present in the tropical lowlands, it has not been as devastating to amphibian populations.\ud \ud Much of the lowland tropical rainforest of the Wet Tropics is contiguous with higher elevation areas, providing the potential for Bd at higher elevations to influence lowland populations as infected hosts and Bd zoospores move downstream. However, not all areas of lowland rainforest are contiguous with the uplands. There are isolated rainforest patches, with no connection to high-elevation streams, where Bd is present and experiences a different set of environmental conditions to much of the rest of the Wet Tropics. It is within these lowland areas, which are not contiguous with highland rainforest streams, that I conducted my research. The aims of my study were to investigate the ecology of the common mist frog (Litoria rheocola), and determine the influence of Bd in this system. This was done by a) investigating seasonal variation in the behaviour of uninfected L. rheocola, b) examining behavioural differences between Bd infected and uninfected L. rheocola, and c) investigating the potential reservoir hosts of the amphibian chytrid fungus Bd of various amphibian and non-amphibian species.\ud \ud The common mist frog, L. rheocola, has similar ecological requirements to Bd; both share the need of moisture and relatively cool conditions. I examined seasonal changes in the thermal microenvironment, behaviour, movement, microhabitat selection and body temperatures of uninfected L. rheocola, using harmonic radar tracking. Warm environmental temperatures in my study area limit the suitability of the tropical lowlands for Bd to winter. Movements and microhabitat use of L. rheocola were similar year-round. My results suggested that increases in body temperatures due to seasonal increases in environmental temperatures may protect lowland populations from decline due to Bd.\ud \ud During the winter, a large proportion of L. rheocola in my study area became infected. Comparing the behaviours of infected and uninfected individuals in winter suggested that uninfected individuals maintained higher body temperatures, perched further from the stream, and used microhabitats that minimized the probability of becoming infected. The behaviour of individuals during periods of high infection risk can reduce their probability of infection.\ud \ud In my study areas, prevalence of Bd dropped to zero in L. rheocola in the summer. The range of amphibians that naturally become infected by Bd is large, but Bd has not been recorded in all amphibians, including species common within the distributional range of Bd. By swabbing all the frogs in my study area, I detected Bd in northern dwarf treefrogs (Litoria bicolor) and Australian wood frogs (Hylarana daemeli), in which Bd had not previously been detected. I also detected Bd on a range of stream-associated invertebrates. If Bd can persist on flying invertebrates, it provides a potential method for the spread and dispersal of Bd, an aspect of the pathogen's ecology that remains unknown. Stream-associated invertebrates provide a potential vector that could have aided in the spread of Bd within and between regions and countries.\ud \ud The tropical lowlands of the Wet Tropics provide a refuge for many species of Bd-susceptible amphibians. Their persistence may permit the evolution of increased immunity, allowing recolonisation of upland areas. My study of lowland populations has provided an increased understanding of the dynamics allowing persistence of these frogs

Distributional records, natural history notes, and conservation of some poorly known birds from southwestern Ecuador and northwestern Peru

Volume: 113Start Page: 108End Page: 11