Stratigraphy and age of the Cappadocia ignimbrites, Turkey: reconciling field constraints with paleontologic, radiochronologic, geochemical and paleomagnetic data

The stratigraphy and age of the Neogene Cappadocia ignimbrites (Central Turkey) have been inferred in previous studies from fieldwork and K–Ar age determinations. The resulting stratigraphic schemes, however, differed from each other, suggesting that further studies were required to produce a reliable succession. In this paper, we examine the chronostratigraphy of mammalian remains recovered in the continental sediments interbedded with the Cappadocia ignimbrites. Using recent advances in mammalian chronostratigraphy, we evaluate selected taxa and faunal associations to place new and independent constraints on the ignimbrite ages. The biostratigraphically bracketed ages concur with some published radiometric dates, but they disagree with others, principally at localities where major stratigraphic discrepancies have arisen in the literature. In order to reconcile these apparent inconsistencies, we combine, at selected sites, our field observations with the biostratigraphic and radiometric age limits, and we compare these with the available geochemical and magnetic data. This allows us to present revised age estimates, and a revised stratigraphy which includes the correlation of the local Sofular deposits with the large-volume Gördeles ignimbrite. The issues faced in this study apply to other ignimbrite provinces in the world. For instance, ignimbrite eruption frequency in Cappadocia is higher than the resolution of many published K–Ar ages. Furthermore, different K–Ar ages have led to the description of individual and distinct ignimbrites that fieldwork and geochemical data allow to merge into a single ignimbrite. Argon loss from pumice samples leading to radiometric “rejuvenation” provides a likely explanation for most stratigraphic discrepancies. Cappadocia is the only documented ignimbrite field in which the chronostratigraphy of vertebrate remains provides better constraints on some ignimbrite ages than scattered K–Ar dates. We further argue that K–Ar dates from the Cappadocia area are too imprecise to establish a reliable magnetostratigraphic scheme for the ignimbrite succession, with the exception of the not, vert, similar2.8 Ma Valibaba Tepe ignimbrite

Petrology of the 2006-2007 tephras from Ubinas volcano, southern Peru

[ESP] El volcán Ubinas (16º 22 'S, 70º 54' O) se encuentra en el rango volcánico cuaternario en el sur de Perú, ~ 60 km al este de la ciudad de Arequipa (Fig. 1). Ubinas es históricamente el volcán más activo en el sur del Perú con 24 eventos volcánicos (VEI 1-3) registrados desde 1550 AD (Hantke y Parodi, 1966; Simkin y Siebert 1994; Rivera et al. 1998). Estos eventos son episodios de desgasificación en gran parte intensos, con algunas caídas de cenizas y bloqueos balísticos (<10.106m3) producidos por actividad explosiva vulcaniana y freatomagmática (Thouret et al. 2005; Rivera et al. 1998). Los eventos causaron daños a los cultivos y al ganado y afectaron a aproximadamente 3,500 personas que viven en seis aldeas a 12 km del volcán (Fig. 1). La actividad explosiva más reciente comenzó el 27 de marzo de 2006 y duró dos años con eventos eruptivos intermitentes, mientras que la desgasificación aún continúa. Según las características de la actividad y los productos en erupción, el episodio eruptivo ha progresado en cuatro etapas: 1) actividad freática y freatomagmática inicial (del 27 de marzo al 19 de abril de 2006), incluidas las columnas de alta erupción que dispersaron la caída de cenizas a una distancia de hasta 7 km del cumbre; 2) las explosiones vulcanianas (~ 20 de abril al 11 de junio de 2006) formaron columnas de 3 a 4 km de altura que expulsaron bloques de hasta 40 cm de diámetro a distancias de 2 km del respiradero (Fig. 2). La lava fresca llegó al fondo del respiradero el 20 de abril; 3) fuerte desgasificación intercalada con al menos 12 eventos que produjeron columnas de 2 a 3 km de altura entre mediados de junio de 2006 y abril de 2007, dispersando cenizas hasta 40 km del respiradero; 4) la desgasificación suave produce un penacho permanente de 200 a 800 m de altura y ocasionalmente cenizas ligeras alrededor de la cumbre (mayo de 2007 hasta el presente). Las columnas de babosas duraderas y de corta duración, explosiones tipo cañón, pequeñas cantidades de material juvenil y la composición andesítica de las bombas de corteza de pan indican un estilo de comportamiento vulcaniano en Ubinas. El comportamiento es similar a la primera fase de la erupción del Nevado Sabancaya en 1990-1998 (Gerbe y Thouret, 2004) o al comportamiento de Sakurajima, Japón desde 1955 (Morrisey y Mastin, 2000), y a Ngauruhoe, Nueva Zelanda en 1974 -1975 (Hobden et al. 2002). Las características petrográficas y geoquímicas de los bloques juveniles y las escoria erupcionadas durante la actividad explosiva 2006-2007 permiten la descripción del magma recién erupcionado y, por lo tanto, conducen a una mejor comprensión del origen de la erupción

The eruptive chronology of the Yucamane-Calientes compound volcano: a potentially active edifice of the Central Andes (Southern Peru)

We have reconstructed the eruptive chronology of the Yucamane–Calientes compound volcano in southern Peru based on extensive fieldwork and a large dataset of geochronological (40K–40Ar, 40Ar–39Ar, U-Pb and 14C) and geochemical (major and trace element) analyses. This compound volcano is composed of two edifices that have experienced discontinuous volcanic activity from the Middle Pleistocene to the Holocene. The Calientes volcano has been constructed in four successive stages: Calientes I is composed of andesitic lava flows that were dated at ~500 ka. Then, the Callazas ignimbrite (Calientes II stage) was emplaced (~160-190 ka), followed by the main cone-building stage (Calientes III), which was dated at ~125 ka. Finally, the Holocene Caliente domes were emplaced and represent the last eruptive products of this edifice. The Yucamane volcano has been constructed in three stages: Yucamane I stage consists of a sequence of andesitic lava flows exposed at the base of the volcano with an age older than 37-40 ka. Yucamane II stage (~36-24 ka) comprises a thick sequence of block-and-ash deposits that represents a dome-growth episode that predates the younger Yucamane cone (Yucamane III stage) since 20-25 ka. During the Holocene, the Yucamane had shown vulcanian to sub-Plinian activity resulting in the emplacement of tephra fallout and pyroclastic density current deposits. The last sub-Plinian eruption occurred ca. 3085 ± 35 aBP and emitted a pumice fall deposit associated with a pumice flow deposit. Most samples from the Calientes volcano are andesites and dacites (60.1-67.7 wt.% SiO2), while rocks of the Yucamane volcano correspond to basic andesites to dacites (53.4-66.9 wt.% SiO2). These rocks show a mineral assemblage of plagioclase, amphibole, biotite, ortho- and clino-pyroxene, olivine, and Fe-Ti oxides. All of the analyzed samples belong to a high-K, calc-alkaline series. Calientes volcano erupted mostly andesitic magmas and is punctuated by rare eruptions involving silica-rich magmas. In contrast, Yucamane volcano displays a different pattern, characterized by a gradual decrease of silica content through post-glacial time, from moderate (VEI <=2) vulcanian events comprising basic andesitic magmas to the large (VEI 3) sub-Plinian eruption of ~3 ka, involving andesitic magma. On the basis of this recurrent low-to-moderate explosive activity, Yucamane must be considered as an active and potentially threatening volcano, which may affect the province of Candarave with about 12 000 inhabitants

Rol de la contaminación crustal en el magmatismo de los Andes del sur peruano: ejemplo del volcán Misti

El volcán Misti (16º17’ S; 71º24’ O) es uno de los siete volcanes activos situados en la cadena volcánica Plio-Cuaternaria del sur peruano, perteneciente a la ZVC (Zona Volcánica Central) de los Andes. Este volcán se encuentra localizado a 17 km del centro de la ciudad de Arequipa (Fig. 1), la segunda ciudad en términos de población del Perú, con aproximadamente 1 millón de habitantes. Numerosos autores han estudiado la estratigrafía del volcán Misti, cuya actividad se inició hace ~833 ka (e.g. Thouret et al., 2001). Thouret et al. (2001) han dividido la evolución de este volcán en cuatro etapas: "Misti 1" (833 - 112 ka), "Misti 2" (112 - 40 ka), "Misti 3" (38 - 14 ka) y "Misti 4" (<11 ka). En este trabajo, nos hemos focalizado en los mecanismos de génesis y evolución de magmas ocurridos durante los últimos 112 ka, ya que durante este tiempo, el Misti ha presentado variados tipos de dinamismos eruptivos: erupciones explosivas (plinianas, freatomagmáticas, vulcanianas), erupciones efusivas y episodios de construcción y destrucción de domos, así como fenómenos de inestabilidad de flanco que han generado al menos dos depósitos de avalancha de escombros

Discovery of a large resurgent caldera at Incahuasi, southern Ayacucho Province, Peru

The Central Volcanic Zone (CVZ) of the Andes is well known for its intense silicic volcanism, with emplacement of large-volume plinian fall deposits and ignimbrites in Cenozoic to Quaternary times (de Silva and Francis, 1991). The CVZ hosts a number of silicic calderas (super-volcanoes) that are preserved in nowadays topography or have been inferred from volcanological studies (e.g. calderas concealed beneath younger stratovolcanoes). While source calderas of several CVZ ignimbrites have been identified, many others are still unknown because they experienced later volcanism, fluviatile and glacial erosion, as well as tectonic dismantling. This is the case in Southern Peru where successions of voluminous ignimbrites with unknown sources are exposed in 2–3.5 km-deep canyons of Ica, Ayacucho, Arequipa, and Moquegua provinces (Sébrier and Soler, 1991; Thouret et al., 2007; 2016; Schildgen et al., 2009; de La Rupelle, 2013). In this note we describe for the first time a large resurgent caldera in Southern Ayacucho province, where geothermal and epithermal economic potentials might exist

Estudio preliminar acerca de la geología, petrografía y geoquímica del volcán Sara Sara (Ayacucho) en el sur del Perú

The Sara Sara volcano (5505 masl.) is a composite volcano located south of the department of Ayacucho in Perú. This volcano is characterized by a series of eruptions of magnitude between 3 and 5. According to the stratigraphy and location of the Sara Sara erupted deposits, (1) the first eruptive episode termed "Sara Sara I" was effusive with lava flows, (2) the period "Sara Sara II" was dominated by an explosive activity resulting in pumice and ash-rich pyroclastic-flow deposits, followed by (3) growth and collapse of summit domes. Later, the period "Sara Sara III" was dominated by fallout deposits, products of Plinian and sub-Plinian eruptions. (4) The most recent effusive eruptive period termed "Sara Sara IV" produced relatively youthful lava flows. The rocks show a mineralogical ensemble of plagioclase, quartz, biotite, amphibole, oxides and volcanic glass. The composition of lavas ranges from dacites (65.1-69.9 wt.% SiO2) to rhyolites (70.1-73.6 wt.% SiO2). Los diagramas de elementos traza no presentan cambios significativos entre las diferentes etapas evolutivas del volcán Sara Sara

The Incahuasi resurgent caldera (Ayacucho Province, Peru), a site of high-magnitude explosive eruptions in Miocene times

In this work we document a large Miocene resurgent caldera located south of the Ayacucho province (area between the cities of Coracora, Jaqui and Pauza), where geothermal-epithermal economic potentials might exist, and this is the first resurgent caldera ever reported in the Peruvian territory. Geological studies combined with geochronological and remote sensing analyses allowed us to recognize a flat and depressed area at Laguna de Parinacochas (3278 m asl), a 10 x 8 km-large salar (salt lake) encircled by hills and elevations peaking at about 3600 m asl. On the north-western side of the salt lake, the crest consists of weathered whitish-yellowish ignimbrite deposits, with local sliding structures towards the lake. The eastern side of Laguna de Parinacochas exhibits a series of normal faults at the north-western base of Sara Sara volcano, with subsidence towards Laguna de Parinacochas depression. In our interpretation these morpho-structural features around the lake are expressions of the southern part of a wider caldera complex. Siliciclastic and finely stratified lacustrine sedimentary sequences, in which major ca 9 Ma-old Plinian tephra fall deposits are interbedded, are exposed in the area and support the existence of an intra-caldera paleo-lake. Altered zones with kaolin and silicified patches, fluid circulations, hot springs, bubbling, and sulfur smells are reported within and on the edge of a vast 25 x 35 km-wide structure that we call the Incahuasi caldera system. The caldera is likely polygenic and the last collapse event occurred during the eruption of the approx. 300 cubic km, 9 Ma-old rhyolitic Caraveli ignimbrite, which flowed 100 km west to the Pacific seashore. In addition, a combination of structural elements reveals that the 16 x 18 km-wide and about 1 km-high volcanic complex located north of Laguna de Parinacochas has been upheaved partly by tectonic processes, and also by volcanic resurgence, as evidenced by a typical apical graben associated with intense alteration features. The lavas that cap the resurgent dome are dated at ca 6.6 Ma and seemingly mark the end of the activity at the Incahuasi caldera system. Younger volcanism in the area includes formation of the Sara Sara edifice, a quaternary volcano that grew near, but outside of the Incahuasi caldera complex. Sara Sara erupted essentially rhyo-dacitic products, notably during repeated powerful Plinian events of Pleistocene age. This suggests the presence of a potentially still active silicic reservoir at some depth beneath the area

Historia eruptiva del complejo volcánico Ampato-Sabancaya (Arequipa)

El Complejo Volcánico Ampato-Sabancaya (CVAS) está localizado a 60 km al NO de la ciudad de Arequipa (71° 49’ – 71° 54’ W; 15° 46’ – 15° 52’ S), (Fig. 1) y fue construido durante el Pleistoceno sobre los remanentes de un complejo volcánico más antiguo, el Hualca Hualca (6025 msnm.), ubicado entre el CVAS y el profundo valle del río Colca (al norte). El Sabancaya (5967 msnm.) constituye la parte joven y activa del complejo volcánico, juntamente con el estratovolcán Ampato (6280 msnm.), cuya cima está ubicada a 4 km al SW del cráter activo del Sabancaya. El Sabancaya, constituye uno de los siete volcanes activos (Siebert et al., 2010) del arco peruano, cuyo último episodio eruptivo ocurrió entre 1988 y 1997 (Gerbe y Thouret, 2004). A pesar de que algunos estudios han sido realizados sobre este volcán, y en particular sobre la tefrocronología holocénica (Juvigné et al., 2008), a la fecha no existe un estudio integral sobre su historia eruptiva. El volcán Ampato está constituido por un estratovolcán de base, antiguo y erosionado, cubierto por un estratocono alargado de sur a norte, en cuya cima se distinguen tres centros de emisión que muestran secuencias lávicas discordantes entre ellas. Por su parte, el volcán Nevado Sabancaya está constituido de dos conos superpuestos: al sur un domo y al norte un cono de lava cubierto por cenizas, al medio del cual se encuentra el cráter activo, de 300 m de profundidad, de donde continuamente emanan emisiones fumarólicas. El presente estudio es parte de un proyecto de investigación llevado a cabo entre la Dirección de Geología Ambiental y Riesgo del INGEMMET y el Instituto de Investigación para el Desarrollo de Francia (IRD). Los objetivos de este proyecto son la reconstrucción de la historia eruptiva de este complejo volcánico (este trabajo), el estudio de la evolución petrológica de los magmas de este centro eruptivo (Rivera et al., 2012) y la evaluación de los peligros volcánicos (Mariño et al., 2012)

The ArT\'eMiS wide-field submillimeter camera: preliminary on-sky performances at 350 microns

ArTeMiS is a wide-field submillimeter camera operating at three wavelengths simultaneously (200, 350 and 450 microns). A preliminary version of the instrument equipped with the 350 microns focal plane, has been successfully installed and tested on APEX telescope in Chile during the 2013 and 2014 austral winters. This instrument is developed by CEA (Saclay and Grenoble, France), IAS (France) and University of Manchester (UK) in collaboration with ESO. We introduce the mechanical and optical design, as well as the cryogenics and electronics of the ArTeMiS camera. ArTeMiS detectors are similar to the ones developed for the Herschel PACS photometer but they are adapted to the high optical load encountered at APEX site. Ultimately, ArTeMiS will contain 4 sub-arrays at 200 microns and 2x8 sub-arrays at 350 and 450 microns. We show preliminary lab measurements like the responsivity of the instrument to hot and cold loads illumination and NEP calculation. Details on the on-sky commissioning runs made in 2013 and 2014 at APEX are shown. We used planets (Mars, Saturn, Uranus) to determine the flat-field and to get the flux calibration. A pointing model was established in the first days of the runs. The average relative pointing accuracy is 3 arcsec. The beam at 350 microns has been estimated to be 8.5 arcsec, which is in good agreement with the beam of the 12 m APEX dish. Several observing modes have been tested, like On-The-Fly for beam-maps or large maps, spirals or raster of spirals for compact sources. With this preliminary version of ArTeMiS, we concluded that the mapping speed is already more than 5 times better than the previous 350 microns instrument at APEX. The median NEFD at 350 microns is 600 mJy.s1/2, with best values at 300 mJy.s1/2. The complete instrument with 5760 pixels and optimized settings will be installed during the first half of 2015.Comment: 11 pages, 11 figures. Presented at SPIE Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy VII, June 24, 2014. To be published in Proceedings of SPIE Volume 915