TY - JOUR A1 - Schneider, K. P. A1 - Hoffmann, J. E. A1 - Münker, C. A1 - Patyniak, Magda A1 - Sprung, P. A1 - Roerdink, D. A1 - Garbe-Schönberg, D. A1 - Kröner, A. T1 - Petrogenetic evolution of metabasalts and metakomatiites of the lower Onverwacht Group, Barberton Greenstone Belt (South Africa) JF - Chemical geology : official journal of the European Association for Geochemistry N2 - A well-preserved sequence, by Archean standards, of mantle-derived metabasalts and metakomatiites forms large parts of the lower Onverwacht Group of the Barberton Greenstone Belt (South Africa). To elucidate the origin of mafic and ultramafic rocks from this 3.55 to 3.45 Ga sequence, we present a comprehensive geochemical dataset including major and trace elements as well as Lu-Hf and Sm-Nd isotope compositions for a variety of metavolcanic rocks. These include metabasalts of the amphibolite-facies Sandspruit and Theespruit Formations as well as metabasalts and metakomatiites of the lower greenschist-facies Komati Formation. Based on their incompatible trace element patterns, the basalts of the Sandspruit and Theespruit Formations can be subdivided into a light rare earth element (LREE) depleted group, a LREE-undepleted group, and a LREE-enriched group. Positive epsilon Hf-(t) and epsilon Nd-(t) values of ca. +3 to +4 and 0 to +2, respectively, together with depletions in Th and La-CN/Yb-CN indicate derivation of the LREE-depleted basalts from a depleted mantle source. However, chondritic epsilon Hf-(t) and epsilon Nd-(t) values combined with positive Th and La-CN/Yb-CN of the LREE-enriched samples indicate a contribution from older granitoid crust in the petrogenesis of these samples. Trace element patterns of komatiites and basalts of the Komati Formation are generally flat relative to primitive mantle with slight depletions in heavy rare earth elements and Th and overall positive epsilon Hf-(t) of + 2.5 +/- 3.5 (2 s.d.) and epsilon Nd-(t) of + 0.5 +/- 2.2 (2 s. d.). The coherence in trace element characteristics suggests a common magmatic origin for basalts and komatiites. This study reveals that the two lavas were derived from the same mantle plume, i. e. komatiites were formed by high degrees of melting of a depleted mantle source containing residual garnet and the basalts were formed by moderate degrees of partial melting in shallower regions of the mantle. Based on the current dataset, combined with published data, we propose a geodynamic model for the oldest units of the Barberton Greenstone Belt that describes the development from a submerged continental setting (for the Sandspruit and Theespruit Formations) to a submarine plateau setting (for the Komati Formation) as a consequence of continental rifting. KW - Paleoarchean KW - Assimilation-fractional crystallization KW - Mantle source KW - Ancient Gneiss Complex Y1 - 2019 U6 - https://doi.org/10.1016/j.chemgeo.2019.02.020 SN - 0009-2541 SN - 1872-6836 VL - 511 SP - 152 EP - 177 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Perez-Lopez, Raul A1 - Martin-Velazquez, Saul A1 - Sanchez-Moral, Sergio A1 - Patyniak, Magda A1 - Lopez-Gutierrez, Jose A1 - Cuezva, Soledad A1 - Lario, J. A1 - Silva, P. G. A1 - Rodriguez-Pascua, M. A. A1 - Giner-Robles, J. L. T1 - New insights on speleoseismology: The geothermal gradient and heat flow values in caves for the study of active faults JF - Quaternary international : the journal of the International Union for Quaternary Research N2 - Normally in paleoseismology, the study of the tectonic slip-rate is performed in trenches on the fault scarp, or by the estimation of fault movements from the geomorphic features. In this work, we have carried out a paleoseismic analysis of the Benis Fault, located in southeast Spain, combined with a geothermal analysis inside a deep cave related to the fault (-350 m). Thus, we have estimated the last earthquake magnitude and time of occurrence from evidence of ceiling collapse and displaced carbonate blocks inside a cave, which is developed across the fault. The magnitude was obtained from the application of the empirical relationship of the fault parameters and coseismic vertical displacement, yielding a value ranging between M 5.9 and M 6.5. Moreover, we dated this paleoearthquake by the paleontological record of a "Lynx pardinus spelaea", with an age of 65 +/- 18 ka BP. Additionally, we have measured the thermal profile of the Benis Cave (-350 m of depth), from single rock point temperature measurements during 2 years. The temperature profile shows three different parts inside the cave, the shallow heterogeneous thermal zone till 50 m depth; the homogeneous thermal zone 150 m till with constant temperature and the hetero-thermal deep zone, deeper than 150 m and till the deepest zone (350 m). Furthermore, we have estimated the Vertical Geothermal Gradient, 1.85 degrees C/100 m for the deepest zone (-150; -290 m). The temperature increases with depth, showing a reverse thermal profile in comparison with normal gradients in deep caves. Finally, we have calculated the heat flux of 0.46 mWm(2). (C) 2016 Elsevier Ltd and INQUA. All rights reserved. KW - Speleoseismology KW - Active fault KW - Cave KW - Slip-rate KW - Heat flux Y1 - 2017 U6 - https://doi.org/10.1016/j.quaint.2016.11.026 SN - 1040-6182 SN - 1873-4553 VL - 451 SP - 165 EP - 175 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Patyniak, Magda A1 - Landgraf, Angela A1 - Dzhumabaeva, Atyrgul A1 - Abdrakhmatov, Kanatbek E. A1 - Rosenwinkel, Swenja A1 - Korup, Oliver A1 - Preusser, Frank A1 - Fohlmeister, Jens Bernd A1 - Arrowsmith, J. Ramon A1 - Strecker, Manfred T1 - Paleoseismic Record of Three Holocene Earthquakes Rupturing the Issyk-Ata Fault near Bishkek, North Kyrgyzstan JF - Bulletin of the Seismological Society of America N2 - The northern edge of the western central Tien Shan range is bounded by the Issyk-Ata fault situated south of Bishkek, the capital of Kyrgyzstan. Contraction in this thick-skinned orogen occurs with low-strain accumulation and long earthquake recurrence intervals. In the nineteenth to twentieth centuries, a sequence of large earthquakes with magnitudes between 6.9 and 8 affected the northern Tien Shan but left nearly the entire extent of the Issyk-Ata fault unruptured. Here, the only known historic earthquake ruptured in A.D. 1885 (M6.9) along the western end of the Issyk-Ata fault. Because earthquakes in low-strain regions often tend to cluster in time and may promote failure along nearby structures, the earthquake history of the northern Tien Shan represents an exceptional structural setting for studying fault behavior affected by an intraplate earthquake sequence. We present a paleoseismological study from one site (Belek) along the Issyk-Ata fault located east of the A.D. 1885 epicentral area. Our analysis combines a range of tools, including photogrammetry, differential Global Positioning System, 3D visualization, and age modeling with different dating methods (infrared stimulated luminescence, radiocarbon, U-series) to improve the reliability of an event chronology for the trench stratigraphy and fault geometry. We were able to distinguish three different surfacerupturing paleoearthquakes; these affected the area before 10.5 +/- 1.1 cal ka B.P., at similar to 5.6 +/- 1.0 cal ka B.P., and at similar to 630 +/- 100 cal B.P., respectively. Associated paleomagnitudes for the last two earthquakes range between M6.7 and 7.4, with a cumulative slip rate of 0.7 +/- 0.32 mm/yr. We did not find evidence for the A.D. 1885 event at Belek. Our study yielded two main overall results: first, it extends the regional historic and paleoseismic record; second, the documented rupture events along the Issyk-Ata fault suggest that this fault was not affected in its entirety; instead, these events indicate segmented rupture behavior. Y1 - 2017 U6 - https://doi.org/10.1785/0120170083 SN - 0037-1106 SN - 1943-3573 VL - 107 SP - 2721 EP - 2737 PB - Seismological Society of America CY - Albany ER -