TY - JOUR A1 - Rosenwinkel, Swenja A1 - Landgraf, Angela A1 - Schwanghart, Wolfgang A1 - Volkmer, Friedrich A1 - Dzhumabaeva, Atyrgul A1 - Merchel, Silke A1 - Rugel, Georg A1 - Preusser, Frank A1 - Korup, Oliver T1 - Late Pleistocene outburst floods from Issyk Kul, Kyrgyzstan? JF - Earth surface processes and landforms : the journal of the British Geomorphological Research Group KW - outburst flood KW - lake-level changes KW - Issyk Kul KW - Kyrgyzstan KW - cosmogenic nuclides Y1 - 2017 U6 - https://doi.org/10.1002/esp.4109 SN - 0197-9337 SN - 1096-9837 VL - 42 SP - 1535 EP - 1548 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Kröner, A. A1 - Alexeiev, D. V. A1 - Kovach, V. P. A1 - Rojas-Agramonte, Y. A1 - Tretyakov, A. A. A1 - Mikolaichuk, A. V. A1 - Xie, H. A1 - Sobel, Edward T1 - Zircon ages, geochemistry and Nd isotopic systematics for the Palaeoproterozoic 2.3-1.8 Ga Kuilyu Complex, East Kyrgyzstan BT - the oldest continental basement fragment in the Tianshan orogenic belt JF - Journal of Asian earth sciences N2 - Precambrian microcontinents represent key tectonic units in the accretionary collages of the western Central Asian Orogenic Belt (CAOB), and their geological history is reasonably well established since the Mesoproterozoic but remains weakly constrained for older epochs due to a scarcity of exposed Palaeoproterozoic and Archaean rocks. Early Precambrian rocks were previously reported from several metamorphic complexes in the Kyrgyz Tianshan orogenic belt, mainly based on multigrain conventional zircon dating, but the present study only confirmed such rocks at one site, namely in the Kuilyu Complex of eastern Kyrgyzstan. New single grain SHRIMP II zircon ages, geochemical data, and whole-rock Nd isotopic compositions for granitoid gneisses of the Kuilyu Complex elucidate the age, origin and tectonic settings of this oldest continental fragment in the Tianshan. The Kuilyu Complex is part of the basement in the Ishim - Middle Tianshan microcontinent. It consist of a strongly deformed and metamorphosed supracrustal assemblage of paragneisses and schists which are tectonically interlayered with amphibolites, migmatites and granitoid gneisses. Our zircon dating indicates that the Kuilyu Complex contains two suites of Palaeoproterozoic granitoid gneisses with magmatic protolith ages of ca. 2.32-2.33 Ga and 1.85 Ga. Granitoid magmatism at 1.85 Ga was almost immediately followed by amphibolite-facies metamorphism at ca 1.83 Ga, evidenced by growth of metamorphic zircon rims. The older, ca 2.3 Ga granitoid gneisses chemically correspond to calc-alkaline, metaluminous, I-type magnesian quartz diorite and granodiorite. The protolith of the younger, ca. 1.85 Ga granite-gneiss is an alkalic-calcic, metaluminous to peraluminous, ferroan medium-grained porphyric granite with chemical features resembling A-type granites. The 2.3 Ga and 1.85 Ga granitoid gneisses have slightly to distinctly negative initial epsilon(Nd) values of -1.2 and -6.6, and similar depleted mantle Nd model ages of 2.7-2.6 Ga, which imply melting of Neoarchaean continental crust. The zircon age patterns of the Kuilyu Complex resemble those of exposed rocks in the Tarim Craton, where episodes of granitoid magmatism at ca. 2.3-2.4 and 1.85 Ga, followed by amphibolite-facies metamorphism at ca 1.85 Ga, are also recorded. Similarities in the early Precambrian magmatic and metamorphic episodes as well as similar histories during the Neoproterozoic and early Palaeozoic suggest that the Ishim-Middle Tianshan microcontinent was rifted off the Tarim Craton. Similar age patterns also suggest possible tectonic links of the Kuilyu and Tarim continental blocks with the Baidrag Block of central Mongolia. In contrast, substantial differences in age and Precambrian evolution between the Anrakhai block of southern Kazakhstan and the Kuilyu Complex argue against a previous connection and suggest the former to represent an independent continental terrane. Current data show that early Precambrian rocks in the western CAOB outside Tarim only occur at two sites, namely in the Anrakhai Complex of southern Kazakhstan and in the Kuilyu Complex of eastern Kyrgyzstan. (C) 2016 Elsevier Ltd. All rights reserved. KW - Kuilyu Complex KW - Zircon dating KW - Microcontinent KW - CAOB KW - Middle Tianshan KW - Kyrgyzstan Y1 - 2017 U6 - https://doi.org/10.1016/j.jseaes.2016.12.022 SN - 1367-9120 SN - 1878-5786 VL - 135 SP - 122 EP - 135 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Rosenwinkel, Swenja A1 - Korup, Oliver A1 - Landgraf, Angela A1 - Dzhumabaeva, Atyrgul T1 - Limits to lichenometry JF - Quaternary science reviews : the international multidisciplinary research and review journal N2 - Lichenometry is a straightforward and inexpensive method for dating Holocene rock surfaces. The rationale is that the diameter of the largest lichen scales with the age of the originally fresh rock surface that it colonised. The success of the method depends on finding the largest lichen diameters, a suitable lichen-growth model, and a robust calibration curve. Recent critique of the method motivates us to revisit the accuracy and uncertainties of lichenometry. Specifically, we test how well lichenometry is capable of resolving the ages of different lobes of large active rock glaciers in the Kyrgyz Tien Shan. We use a bootstrapped quantile regression to calibrate local growth curves of Xanthoria elegans, Aspicilia tianshanica, and Rhizocarpon geographicum, and report a nonlinear decrease in dating accuracy with increasing lichen diameter. A Bayesian type of an analysis of variance demonstrates that our calibration allows discriminating credibly between rock-glacier lobes of different ages despite the uncertainties tied to sample size and correctly identifying the largest lichen thalli. Our results also show that calibration error grows with lichen size, so that the separability of rock-glacier lobes of different ages decreases, while the tendency to assign coeval ages increases. The abundant young (<200 yr) specimen of fast-growing X elegans are in contrast with the fewer, slow-growing, but older (200-1500 yr) R. geographicum and A. tianshanica, and record either a regional reactivation of lobes in the past 200 years, or simply a censoring effect of lichen mortality during early phases of colonisation. The high variance of lichen sizes captures the activity of rock-glacier lobes, which is difficult to explain by regional climatic cooling or earthquake triggers alone. Therefore, we caution against inferring palaeoclimatic conditions from the topographic position of rock-glacier lobes. We conclude that lichenometry works better as a tool for establishing a relative, rather than an absolute, chronology of rock-glacier lobes in the northern Tien Shan. (C) 2015 Elsevier Ltd. All rights reserved. KW - Lichenometry KW - Rock glacier KW - Absolute age dating KW - Kyrgyzstan KW - Tien Shan Y1 - 2015 U6 - https://doi.org/10.1016/j.quascirev.2015.10.031 SN - 0277-3791 VL - 129 SP - 229 EP - 238 PB - Elsevier CY - Oxford ER -