Structural Control of Thermal Fluid Circulation and Geochemistry in a Flat-Slab Subduction Zone, Peru

Hot spring geochemistry from the Peruvian Andes provide insight on how faults, or fractures in the Earth\u27s crust, are capable of influencing fluid circulation. Faults can either promote or inhibit fluid flow and the goal of this study is test the role of a major fault, such as the Cordillera Blanca detachment, as a channel for transporting deep fluids to the surface. Hot springs are abundant in the Cordillera Blanca and Huayhuash ranges in Peru, and several springs issue along the Cordillera Blanca detachment, making this region an ideal setting for our study. To test the role of the Cordillera Blanca detachment, hot springs were sampled along the trace of the fault (Group 1), the western edge of the Cordillera Blanca (Group 2), the eastern side of the Cordillera Blanca (Group 3), and in the Cordillera Huayhuash (Group 4). Water and dissolved gas samples were collected from a total of 25 springs and then analyzed for an array of geochemical parameters. Distinct fluid chemistries from Groups 1 and 2 suggest that the Cordillera Blanca detachment and adjacent minor faults to the west intersect at depth and provide a preferential flow path for deep fluid circulation. Understanding the influence of faults on fluid flow is essential for many disciplines (e.g. oil exploration, hydrology), and this work demonstrates that fluid geochemistry is an excellent tool for assessing the role of faults on fluid distribution

Structural Controls on Crustal Fluid Circulation and Hot Spring Geochemistry Above a Flat‐Slab Subduction Zone, Peru

Hot spring geochemistry from the Cordillera Blanca and Cordillera Huayhuash, Peru, reveal the influence of crustal‐scale structures on geothermal fluid circulation in an amagmatic region located above a flat‐slab subduction zone. To test the influence of contrasting modes of faulting in these regions, springs were targeted along the Cordillera Blanca detachment fault, within its hanging wall, in the footwall of the detachment, and in the Cordillera Huayhuash. Hot springs along the Cordillera Blanca detachment fault zone are associated with recent extension and normal faulting, and those in its footwall and the Cordillera Huayhuash are located in the Marañon fold and thrust belt where compressional structures dominate. Springs along and in the hanging wall of the Cordillera Blanca detachment fault yield brackish‐saline, alkaline‐chloride waters, with oxygen, hydrogen, carbon, and chlorine stable isotope values that suggest mixing between meteoric groundwater and saline brine affected by high water‐rock interaction. Geothermometry reservoir temperature estimates (RTEs) of 91–226°C indicate maximum flow path depths of 8.7 or 11 km, depending on geothermal gradient, associated with the Cordillera Blanca detachment fault. In contrast, springs in the footwall and in the Cordillera Huayhuash exhibit a wide range of water types with an isotopic affinity to meteoric water, suggesting a greater influence from shallow groundwater and less water‐rock interaction. For these springs, RTEs of 40–98°C correspond to much shallower circulation (1.6–4 km). Results indicate that the Cordillera Blanca detachment system accommodates significantly deeper circulation of crustal fluids compared to other regional compressional structures

Rol de la erosión y de la isostasia en la construcción de la topografía en contexto de tectónica activa: contribuciones a partir de datos de termocronologia de baja temperatura y de modelos de evolución del relieve (Cordillera Blanca, Andes Peruanos)

El levantamiento y la exhumación de la Cordillera Blanca están vinculados a la falla normal de la Cordillera Blanca (CBNF), esta estructura tectónica regional delimita y da forma al flanco occidental del batolito de la Cordillera Blanca. Dos modelos han sido propuestos anteriormente para explicar la presencia de esta falla normal activa en un contexto en compresión (Dalmayrac and Molnar, 1981; McNulty and Farber, 2002), pero hoy, la falla normal de la Cordillera Blanca y la exhumación asociada de la Cordillera Blanca permanecen como procesos geológicos poco conocidos. Estudios recientes (e.g. Margirier et al., 2016) sugieren un aumento en las tasas de exhumación durante el Cuaternario en la Cordillera Blanca y relacionan este aumento con un cambio en el clima y/o proceso erosivo dominante (erosión glacial vs. erosión fluvial). La intrusión de Cordillera Blanca se ha erosionado significativamente desde su emplazamiento hace 12-5 Myr. Recientemente se ha demostrado que el efecto de la erosión de rocas más densas, como el batolito Cordillera Blanca, puede contribuir a un aumento en el rebote isostático impulsado por la erosión y la tasa de elevación (Braun et al., 2014). Sin embargo, faltan responder preguntas sobre si la erosión y la isostasia son responsables del aumento reciente de la tasa de elevación en la Cordillera Blanca, y como esto influye a lo largo de la falla normal de la Cordillera Blanca. Aquí abordamos el efecto de la erosión y de la isostasia sobre el levantamiento y la exhumación de la Cordillera Blanca utilizando un modelo numérico de evolución del paisaje (FastScape). Realizamos varias inversiones de la topografía actual, de la exhumación total (deducida de la barometría de anfíboles) y datos termocronológicos (trazas de fisión de apatita y (U-Th-Sm)/He) para obtener los mejores valores de ajuste de la tasa de elevación, el espesor elástico de la litosfera, la erosionabilidad del batolito y de la roca caja que alberga el batolito, y el gradiente geotérmico. Nuestros resultados muestran que la contribución de la erosión y del rebote flexural asociada es de ~20% de la tasa de elevación actual en la Cordillera Blanca. Sugerimos que la erosión de la intrusión densa de la Cordillera Blanca desde 3 Ma también puede contribuir al aumento de la tasa de exhumación cuaternaria en esta área. Finalmente, comparamos con nuestros resultados los dos modelos propuestos antiguamente para la formación de la falla normal de Cordillera Blanca

The Cordillera Blanca fault system as structural control of the Jurassic-Cretaceous basin in central-northern Peru

Many works related to the Cordillera Blanca fault system exist (e.g. Bonnot, 1984; McNulty and Farber, 2002). These studies were mainly in the central part of the Cordillera Blanca fault, between northern Yungay and southern Recuay, without taking account the northern outcrops in the Pallasca zone and to the south the Cajatambo zone. The present study presents a new interpretation of the Cordillera Blanca fault system, based on stratigraphic and structural observations of the Jurassic-Cretaceous Chicama-Goyllarisquizga basin in centralnorthern Peru between Pallasca-Huaraz-Cajatambo, which form part the Cordillera Blanca fault system (CBFS)

Climate trends and glacier retreat in the Cordillera Blanca, Peru, revisited

The total glacial area of the Cordillera Blanca, Peru, has shrunk by more than 30% in the period of 1930 to the present with a marked glacier retreat also in the recent decades. The aim of this paper is to assess local air temperature and precipitation changes in the Cordillera Blanca and to discuss how these variables could have affected the observed glacier retreat between the 1980s and present. A unique data set from a large number of stations in the region of the Cordillera Blanca shows that after a strong air temperature rise of about 0.31 °C per decade between 1969 and 1998, a slowdown in the warming to about 0.13 °C per decade occurred for the 30 years from 1983 to 2012. Additionally, based on data from a long-term meteorological station, it was found that the freezing line altitude during precipitation days has probably not increased significantly in the last 30 years. We documented a cooling trend for maximum daily air temperatures and an increase in precipitation of about 60 mm/decade since the early 1980s. The strong increase in precipitation in the last 30 years probably did not balance the increase of temperature before the 1980s. It is suggested that recent changes in temperature and precipitation alone may not explain the glacial recession within the thirty years from the early 1980s to 2012. Glaciers in the Cordillera Blanca may be still reacting to the positive air temperature rise before 1980. Especially small and low-lying glaciers are characterised by a serious imbalance and may disappear in the near future

Multiple ways of understanding Peru's changing climate

Published versio

Cordillera blanca : glaciares en la historia

La plus vaste couverture glaciaire de l'entre-tropiques n'apparaît comme un objet d'études que très tard, à la fin du 19ème siècle et, surtout grâce aux expéditions austro-allemandes, à partir des années 1930-1940. Le développement de l'alpinisme et un grand nombre de catastrophes meurtrières associées à la dynamique de ces glaciers (rupture de lacs de barrage morainique, avalanches) ont attiré l'attention sur eux et suscité des recherches glaciologiques. En 1980, ils comptent parmi les mieux surveillés des glaciers tropicaux, d'abord grâce à un programme d'étude développé par les Péruviens eux-mêmes. A un moment où le réchauffement global fait craindre un recul très important de la glaciation dans la zone tropicale, les glaciers de la Cordillère Blanche deviennent d'excellents indicateurs de l'évolution climatique en cours et la ressource en eau qui leur est associée constitue à la fois un sujet d'étude et un enjeu économique de haute importance. (Résumé d'auteur

The analysis of geomorphological pronunciation of neotectonics on Cordillera Blanca faults

Práce se zabývá analýzou geomorfologických projevů neotektonické aktivity podél úpatního zlomu jihoamerického pohoří Cordillera Blanca. Obsahuje základní fyzickogeografickou charakteristiku pohoří s důrazem na geologii, geomorfologii a teoretický koncept týkající se tvarů na zlomových svazích a neotektonické aktivity. V praktické části práce je mapováno vybrané území pohoří pomocí snímků aplikace Google Earth na základě něhož, jsou analyzovány a inventarizovány tvary související s aktivními tektonickými procesy pohoří Cordillera Blanca. Dále jsou z digitálního modelu terénu vytvořeny a analyzovány podélné profily vodních toků, které protékají napříč zlomovou oblastí. Analyzována je i bloková stavba pohoří. Klíčová slova Cordillera Blanca, geomorfologie, morfometrie, neotektonika, PeruThe study deals with analysis of of geomorphological pronunciation of neotectonics along the based on fault slope in the South American Cordillera Blanca range. It contains research about physical-geographycal characteristic of the mountain range with the focus on geology, geomorphology and the theoretical concept of forms on fault slopes and neotectonic acitivity. In the practical part of the thesis, the selected area of the mountain range was mapped using Google Earth imagery. On the base of created map the forms associated with the active tectonic uplift of the Cordillera Blanca were analyzed and invented. Then the longitudinal profiles of rivers that flow across the fault zone were created and analyzed from the digital terrain model. The block structure of the mountain range was analyzed too. Keywords Cordillera Blanca, geomorphology, morphometry, neotectonics, PeruKatedra fyzické geografie a geoekologieDepartment of Physical Geography and GeoecologyFaculty of SciencePřírodovědecká fakult

Geología económica del yacimiento de oro de Tumpa (Nueva California)

The Tumpa gold deposit, operated by Cia. Minera Nueva California, located on the western flank of the Cordillera Blanca; It is a vein located between the intensely argilized granodiorite of the Cordillera Blanca batholith and a silicified andesitic dam. The mineralizing flow in its upper part was horizontal with a higher concentration of gold. The vein and dike were cut into 3 parts according to their direction by 2 similar faults to the vein and dike, of dip contrary to these structures; they have intense oxidation.El yacimiento de oro de Tumpa, que opera Cia. Minera Nueva California, ubicado en el flanco occidental de la Cordillera Blanca; es una veta emplazada entre la granodiorita intensamente argilizada del batolito de la Cordillera Blanca y un dique andesítico silicificado. El flujo mineralizante en su parte superior fue horizontal con mayor concentración de oro. La veta y el dique fueron cortados en 3 partes según su rumbo por 2 fallas de rumbo similar a la veta y al dique, de buzamiento contrario a estas estructuras; tienen una intensa oxidación

Dust Deposits from Anthropogenic Sources on the Snowpack of the Glaciers in the Cordillera Blanca, Peru

The tropical glaciers in the Cordillera Blanca are currently experiencing rapid melting due to climate change and increased human activity. To understand better whether anthropogenic airborne particulates, such as dust or black carbon, are having an effect on the retreat of the glaciers, snow samples from five separate mountains located throughout the range were collected, melted and then filtered through 25 mm quartz filters (Pallflex Tissuquartz, 0.7 µm pore size). The filters were analyzed for dust concentrations and for percentage of organic carbons. By comparing the spatial variability of the dust concentration throughout the range, the percentage of carbon in the snowpack, and present-day dust concentrations to that of the paleo-dust concentrations from the entire Holocene and into the Late Glacial Stage derived from ice-cores on Huascaran Sur, this study shows that glaciers on the west side and southern end of the Cordillera Blanca are indeed being affected by albedo-reducing anthropogenic dust