Neotethys closure history of Anatolia: insights from 40Ar–39Ar geochronology and P–T estimation in high pressure metasedimentary rocks

The multiple high-pressure (HP), low-temperature (LT) metamorphic units of Western and Central Anatolia offer a great opportunity to investigate the subduction- and continental accretion-related evolution of the eastern limb of the long-lived Aegean subduction system. Recent reports of the HP–LT index mineral Fe-Mg-carpholite in three metasedimentary units of the Gondwana-derived Anatolide–Tauride continental block (namely the Afyon Zone, the Ören Unit and the southern Menderes Massif) suggest a more complicated scenario than the single-continental accretion model generally put forward in previous studies. This study presents the first isotopic dates (white mica 40Ar–39Ar geochronology), and where possible are combined with P–T estimates (chlorite thermometry, phengite barometry, multi-equilibrium thermobarometry), on carpholite-bearing rocks from these three HP–LT metasedimentary units. It is shown that, in the Afyon Zone, carpholite-bearing assemblages were retrogressed through greenschist-facies conditions at c. 67–62 Ma. Early retrograde stages in the Ören Unit are dated to 63–59 Ma. In the Kurudere–Nebiler Unit (HP Mesozoic cover of the southern Menderes Massif), HP retrograde stages are dated to c. 45 Ma, and post-collisional cooling to c. 26 Ma. These new results support that the Ören Unit represents the westernmost continuation of the Afyon Zone, whereas the Kurudere–Nebiler Unit correlates with the Cycladic Blueschist Unit of the Aegean Domain. In Western Anatolia, three successive HP–LT metamorphic belts thus formed: the northernmost Tavşanlı Zone (c. 88–82 Ma), the Ören–Afyon Zone (between 70 and 65 Ma), and the Kurudere–Nebiler Unit (c. 52–45 Ma). The southward younging trend of the HP–LT metamorphism from the upper and internal to the deeper and more external structural units, as in the Aegean Domain, points to the persistence of subduction in Western Anatolia between 93–90 and c. 35 Ma. After the accretion of the Menderes–Tauride terrane, in Eocene times, subduction stopped, leading to continental collision and associated Barrovian-type metamorphism. Because, by contrast, the Aegean subduction did remain active due to slab roll-back and trench migration, the eastern limb (below Southwestern Anatolia) of the Hellenic slab was dramatically curved and consequently teared. It therefore is suggested that the possibility for subduction to continue after the accretion of buoyant (e.g. continental) terranes probably depends much on palaeogeography.

Sedimentary evolution and environmental history of Lake Van (Turkey) over the past 600,000 years

The lithostratigraphic framework of Lake Van, eastern Turkey, has been systematically analysed to document the sedimentary evolution and the environmental history of the lake during the past ca 600,000 years. The lithostratigraphy and chemostratigraphy of a 219 m long drill core from Lake Van serves to separate global climate oscillations from local factors caused by tectonic and volcanic activity. An age model was established based on the climatostratigraphic alignment of chemical and lithological signatures, validated by 40Ar/39Ar ages. The drilled sequence consists of ca 76% lacustrine carbonaceous clayey silt, ca 2% fluvial deposits, ca 17% volcaniclastic deposits and 5% gaps. Six lacustrine lithotypes were separated from the fluvial and event deposits, such as volcaniclastics (ca 300 layers) and graded beds (ca 375 layers), and their depositional environments are documented. These lithotypes are: (i) graded beds frequently intercalated with varved clayey silts reflect rising lake-levels during the terminations; (ii) varved clayey silts reflect strong seasonality and an intralake oxic–anoxic boundary, for example, lake-level highstands during interglacials/interstadials; (iii) CaCO3-rich banded sediments are representative of a lowering of the oxic-anoxic boundary, for example, lake-level decreases during glacial inceptions; (iv) CaCO3-poor banded and mottled clayey silts reflect an oxic–anoxic boundary close to the sediment-water interface, for example, lake-level low-stands during glacials/stadials; (v) diatomaceous muds were deposited during the early beginning of the lake as a fresh water system; and (vi) fluvial sands and gravels indicate the initial flooding of the lake basin. The recurrence of lithologies (i) to (iv) follows the past five glacial/interglacial cycles. A 20 m thick disturbed unit reflects an interval of major tectonic activity in Lake Van at ca 414 ka BP.

The history of subaquatic volcanism recorded in the sediments of Lake Kivu

Subaquatic volcanic activity has been ongoing in Lake Kivu since the early Holocene and has a dynamic effect on the biological productivity in the surface water, and the preservation of carbonate in the deep anoxic water. Groundwater discharge into the lake’s deepwater propels the upward advection of the water column that ultimately supplies nutrients to the surface water for biological production. The amount of nutrients supplied from the deepwater can be increased suddenly by (1) a cold meteorological event that drives deep seasonal mixing resulting in increased nutrients from below and oxygen from above, or (2) subaquatic volcanic activity that induces a buoyant hydrothermal plume, which entrains nutrients from the deepwater and results in anoxia or suboxic conditions in the surface water. Previous sedimentological studies in Lake Kivu have hypothesized that regional climatic changes are responsible for sudden changes in the preservation of carbonates in the Main Basin. Here we reveal that sublacustrine volcanic events most likely induce the abrupt changes to the geochemistry in the sediment in Lake Kivu. An unprecedented look into the sediment stratigraphy and geochemistry from high-resolution seismic-reflection, and 15N-isotope analyses was conducted in the Main Basin. The results reveal that buoyant hydrothermal plumes caused by subaquatic volcanic activity are a possible trigger for increased biological productivity and organic matter preservation, and that ongoing hydrothermal activity increases the alkalinity in the deepwater, leading to carbonate preservation. The onset of carbonate preservation since the 1970s that is currently observed in the sediment could indicate that hydrothermal discharge has recently increased in the lake.

How fit turns into misfit and back: institutional transformations of pastoral commons in African floodplains

We enlarge the notion of institutional fit using theoretical approaches from New Institutionalism, including rational choice and strategic action, political ecology and constructivist approaches. These approaches are combined with ecological approaches (system and evolutionary ecology) focusing on feedback loops and change. We offer results drawn from a comparison of fit and misfit cases of institutional change in pastoral commons in four African floodplain contexts (Zambia, Cameroon, Tanzania (two cases). Cases of precolonial fit and misfit in the postcolonial past, as well as a case of institutional fit in the postcolonial phase, highlight important features, specifically, flexible institutions, leadership, and mutual economic benefit under specific relations of bargaining power of actors. We argue that only by combining otherwise conflicting approaches can we come to understand why institutional fit develops into misfit and back again. Key Words: African floodplains; governance; institutional change; institutional fit; New Institutionalism; pastoral commons

From «Pflantz-Gart» to «Stammregister». On the history of knowledge of fruit cultivation in the canton of Bern

Among the efforts for the improvement of agricultural productivity, the cultivation of useful plants is particularly at the center of the Economic Enlightenment. In contrast to fodder and textile plants, cereals and potatoes, fruit trees are not included among its favoured subjects. This may be considered as astonishing in view of the significance that fruit has acquired in the contemporary diet. Be that as it may, efforts to improve fruit cultivation go back to even before the classical period of the Economic Enlightenment. The example of Bern in particular is suited to such an analysis over the Longue durée that covers the time from Daniel Rhagor’s «Pflantz-Gart» (1639) to the «Register of varieties of excellent species of pome fruits for the canton of Bern» (Stammregister, 1865). From the perspective of the history of knowledge, the connections between scholarly knowledge and local experience on the one hand and the changing actors in these knowledge systems on the other hand are of special interest here