The Piuquencillo fault system: a long-lived, Andean-transverse fault system and its relationship with magmatic and hydrothermal activity

Abstract. Lithospheric-scale fault systems control the large-scale permeability in the Earth's crust and lithospheric mantle, and its proper recognition is fundamental to understand the geometry and distribution of mineral deposits, volcanic and plutonic complexes and geothermal systems. However, their manifestations at the current surface can be very subtle, as in many cases they are oriented oblique to the current continental margin and to the axis of the magmatic arc; be partially obliterated by younger, arc-parallel faults; and also be covered by volcanic and sedimentary deposits, through which the fault might propagate vertically. The Piuquencillo fault system (PFS) is a proposed lithospheric-scale fault system, located in the Main Cordillera of central Chile. Here, we present the results of the first detailed field study of the PFS, based on structural data collected at 82 structural stations distributed across all the western Main Cordillera. The first published U–Pb zircon ages for the La Obra batholith, which is bounded to the south by the PFS but also affected by younger reactivations of it, were obtained. They yielded 20.79 ± 0.13 Ma (granodiorite) and 20.69 ± 0.07 Ma (monzogranite). Statistical analysis of fault-plane data shows that the presence of the PFS is reflected on a strong preferred NW to WNW strike, with variable dip directions, evident from the analysis of the total fault-plane population and also from individual segments of the PFS. In some segments, the presence of major NE- to ENE-striking faults which intersect the PFS is also reflected in the preferred orientation of fault planes. Preferred orientations of hydrothermal veins, breccias and dikes show that both the PFS and some ENE-striking faults were capable of channelling hydrothermal fluids and magma. Kinematic and dynamic analysis of fault-plane data reveals that most of the PFS was reactivated with sinistral ± reverse kinematics during the Neogene, under a strike-slip to transpressive regime with E- to ENE-trending shortening direction (σ1). Detailed kinematic and dynamic analyses were completed for various segments of the PFS and also for the different rock units affected by it. This study supports the concept that the PFS is a lithospheric-scale fault system, which strongly controlled deformation and the flow of magmas and hydrothermal fluids during the Neogene. The PFS forms part of a larger, margin-transverse structure, the Maipo deformation zone, a continental-scale discontinuity which cut across the entire Chilean continental margin and has been active at least since the Jurassic.

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The Piuquencillo Fault System: a long-lived, Andean-transverse fault system and its relationship with magmatic and hydrothermal activity

10.5194/se-2020-142 ◽

2020 ◽

Author(s):

Jose Piquer ◽

Orlando Rivera ◽

Gonzalo Yañez ◽

Nicolas Oyarzun

Keyword(s):

Continental Margin ◽

Large Scale ◽

Fault Plane ◽

Structural Data ◽

Hydrothermal Activity ◽

Hydrothermal Fluids ◽

Fault System ◽

Geothermal Systems ◽

Magmatic Arc ◽

Continental Scale

Abstract. Lithospheric-scale fault systems control the large-scale permeability in the Earth’s crust and lithospheric mantle, and its proper recognition is fundamental to understand the geometry and distribution of mineral deposits, volcanic and plutonic complexes and geothermal systems. However, their manifestations at the current surface can be very subtle, as in many cases they are oriented oblique to the current continental margin and to the axis of the magmatic arc, can be partially obliterated by younger, arc-parallel faults, and can also be covered by volcanic and sedimentary deposits, through which the fault might propagate vertically. The Piuquencillo Fault System (PFS) is a proposed lithospheric-scale fault system, located in the Main Cordillera of Central Chile. Here we present the results of the first detailed field study of the PFS, based on structural data collected at 82 structural stations distributed across all the Western Main Cordillera. The first published U-Pb zircon ages for the La Obra batholith, which is bounded to the south by the PFS but it is also affected by younger reactivations of it, were obtained. They yielded 20.79 ± 0.13 Ma (granodiorite) and 20.69 ± 0.07 (monzogranite). Statistical analysis of fault plane data shows that the presence of the PFS is reflected on a strong preferred NW to WNW strike, with variable dip directions, evident from the analysis of the total fault plane population and also from individual segments of the PFS. In some segments, the presence of major NE to ENE-striking faults which intersect the PFS is also reflected in the preferred orientation of fault planes. Preferred orientations of hydrothermal veins, breccias and dikes show that both the PFS and some ENE-striking faults were capable of channeling hydrothermal fluids and magma. Kinematic and dynamic analysis of fault-plane data reveals that most of the PFS was reactivated with sinistral ± reverse kinematics during the Neogene, under a strike-slip to transpressive regime with E- to ENE-trending shortening direction (σ1). Detailed kinematic and dynamic analyses were completed for various segments of the PFS and also for the different rock units affected by it. This study supports the concept that the PFS is a lithospheric-scale fault system, which strongly controlled deformation and the flow of magmas and hydrothermal fluids during the Neogene. The PFS forms part of a larger, margin-transverse structure, the Maipo Deformation Zone, a continental-scale discontinuity which cut across the entire Chilean continental margin, and which has been active at least since the Jurassic.

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Structural evolution of a crustal-scale seismogenic fault in a magmatic arc: The Bolfin Fault Zone (Atacama Fault System)

10.5194/egusphere-egu21-3093 ◽

2021 ◽

Author(s):

Simone Masoch ◽

Rodrigo Gomila ◽

Michele Fondriest ◽

Erik Jensen ◽

Tom Mitchell ◽

...

Keyword(s):

Fault Zone ◽

Large Scale ◽

Damage Zone ◽

Structural Evolution ◽

Crystalline Basement ◽

Fault System ◽

Fault Mechanics ◽

Seismogenic Fault ◽

Magmatic Arc ◽

Atacama Fault System

The nucleation and evolution of major crustal-scale seismogenic faults in the crystalline basement as well as the process of strain localization represent a long-standing, but poorly understood, issue in structural geology and fault mechanics. Here, we addressed the spatio-temporal evolution of the Bolfin Fault Zone (BFZ), a >40-km-long exhumed seismogenic splay fault of the 1000-km-long strike-slip Atacama Fault System. The BFZ has a sinuous fault trace across the Mesozoic magmatic arc of the Coastal Cordillera (Northern Chile). Seismic faulting occurred at 5-7 km depth and &#8804; 270 &#176;C in a fluid-rich environment as recorded by extensive propylitic alteration and epidote-chlorite veining. The ancient (125-118 Ma) seismicity is attested by the widespread occurrence of pseudotachylytes both in the fault core and in the damage zone. Field geological surveys indicate nucleation of the BFZ on precursory geometrical anisotropies represented by magmatic foliation of plutons (northern and central segments) and andesitic dyke swarms (southern segment) within the heterogeneous crystalline basement. Faulting exploited the segments of precursory anisotropies that were favorably oriented with respect to the long-term stress field associated with the oblique ancient subduction. The large-scale sinuous geometry of the BFZ may result from linkage of these anisotropy-pinned segments during fault growth. This evolution may provide a model to explain the complex fault pattern of the crustal-scale Atacama Fault System.

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Exhumed vs active geothermal systems: faults controlling ore deposits in Las Minas area as a key for the deep exploration in the Los Humeros geothermal field (Mexico)

10.5194/egusphere-egu2020-3918 ◽

2020 ◽

Author(s):

Domenico Liotta ◽

Alessandro Agostini ◽

Eivind Bastesen ◽

Caterina Bianco ◽

Chiara Boschi ◽

...

Keyword(s):

High Temperature ◽

Ore Deposits ◽

Hydrothermal Fluids ◽

Fault System ◽

Magmatic Fluid ◽

Geothermal System ◽

Central Mexico ◽

Geothermal Systems ◽

Fluid Circulation ◽

Rock Interaction

The investigation of the deep geothermal systems is a challenging task in active geothermal systems. In order to decrease the mining risk, the study of the analogue exhumed systems sheds light on the relationships between fluid circulation and geological structures through the analyses of faults and ore deposits distributions. In the Las Minas area (Central Mexico), ore deposits are quite diffuse at the boundary between crystalline and sedimentary rocks and in fault zones. This is a consequence of the interaction between cooling of Miocene felsic magmas, hydrothermal fluids and coeval fault activity. We investigated the role of the faults in channeling the hydrothermal fluids by fieldwork and analysis of fractures at outcrops. The field mapping was carried out at 1:10000 scale (60 km2). When possible, kinematic data on recent fault planes influencing the permeability and geothermal fluid paths were collected. This includes information on the main structural trends and the orientation of the intermediate kinematic axis.The evolution and origin of the hydrothermal fluids circulating in the exhumed geothermal system of Las Minas area (Central Mexico) were investigated by i) structural and minero-petrographic studies and, ii) fluid inclusion and isotope analyses carried out on skarn and hydrothermal alteration minerals.Two families of faults have been recognized, NNW-SSE and SW-NE oriented, respectively. The SW-NE trending faults often controlled the emplacement of dykes, indicating that the magmatic fluid was channeled and driven by the faults induced permeability. Their activity is at least encompassed between Miocene and Quaternary. The kinematic relation between these two fault systems could be explained in a extensional framework, assuming that the NNW-SSE fault system acted as transfer faults. Fluid inclusions recorded the circulation of: 1) high-temperature (up to 650&#176;C), high-salinity (up to 60 wt.% NaCl equiv.) fluid of magmatic origin; 2) high-temperature (470-650&#176;C) aqueous-carbonic fluid produced during fluid-rock interaction with carbonate basement rocks and 3) relatively low-salinity (up to 2 wt.% NaCl equiv.) fluid of meteoric origin. A general evolution from high- to low-temperature fluid circulation characterized the geothermal system.

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Analog Downscaling of Seasonal Rainfall Forecasts in the Murray Darling Basin

Monthly Weather Review ◽

10.1175/mwr-d-12-00098.1 ◽

2013 ◽

Vol 141 (3) ◽

pp. 1099-1117 ◽

Cited By ~ 18

Author(s):

Andrew Charles ◽

Bertrand Timbal ◽

Elodie Fernandez ◽

Harry Hendon

Keyword(s):

General Circulation ◽

Large Scale ◽

Seasonal Prediction ◽

General Circulation Models ◽

Meridional Wind ◽

Seasonal Forecasts ◽

Local Climate ◽

Continental Scale ◽

Predictive Skill ◽

Murray Darling Basin

Abstract Seasonal predictions based on coupled atmosphere–ocean general circulation models (GCMs) provide useful predictions of large-scale circulation but lack the conditioning on topography required for locally relevant prediction. In this study a statistical downscaling model based on meteorological analogs was applied to continental-scale GCM-based seasonal forecasts and high quality historical site observations to generate a set of downscaled precipitation hindcasts at 160 sites in the South Murray Darling Basin region of Australia. Large-scale fields from the Predictive Ocean–Atmosphere Model for Australia (POAMA) 1.5b GCM-based seasonal prediction system are used for analog selection. Correlation analysis indicates modest levels of predictability in the target region for the selected predictor fields. A single best-match analog was found using model sea level pressure, meridional wind, and rainfall fields, with the procedure applied to 3-month-long reforecasts, initialized on the first day of each month from 1980 to 2006, for each model day of 10 ensemble members. Assessment of the total accumulated rainfall and number of rainy days in the 3-month reforecasts shows that the downscaling procedure corrects the local climate variability with no mean effect on predictive skill, resulting in a smaller magnitude error. The amount of total rainfall and number of rain days in the downscaled output is significantly improved over the direct GCM output as measured by the difference in median and tercile thresholds between station observations and downscaled rainfall. Confidence in the downscaled output is enhanced by strong consistency between the large-scale mean of the downscaled and direct GCM precipitation.

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Delineation of catchment zones of geothermal systems in large-scale rifted settings

Journal of Geophysical Research Atmospheres ◽

10.1029/2012jb009515 ◽

2012 ◽

Vol 117 (B10) ◽

Cited By ~ 9

Author(s):

D. E. Dempsey ◽

S. F. Simmons ◽

R. A. Archer ◽

J. V. Rowland

Keyword(s):

Large Scale ◽

Geothermal Systems

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Microearthquake seismicity and tectonics of Coastal Northern California

Bulletin of the Seismological Society of America ◽

10.1785/bssa0600051669 ◽

1970 ◽

Vol 60 (5) ◽

pp. 1669-1699 ◽

Cited By ~ 7

Author(s):

Leonardo Seeber ◽

Muawia Barazangi ◽

Ali Nowroozi

Keyword(s):

High Frequency ◽

Fault Plane ◽

San Andreas Fault ◽

High Gain ◽

Strike Slip ◽

Fault System ◽

Northern California ◽

Fault Plane Solutions ◽

Sharp Bend ◽

San Andreas

Abstract This paper demonstrates that high-gain, high-frequency portable seismographs operated for short intervals can provide unique data on the details of the current tectonic activity in a very small area. Five high-frequency, high-gain seismographs were operated at 25 sites along the coast of northern California during the summer of 1968. Eighty per cent of 160 microearthquakes located in the Cape Mendocino area occurred at depths between 15 and 35 km in a well-defined, horizontal seismic layer. These depths are significantly greater than those reported for other areas along the San Andreas fault system in California. Many of the earthquakes of the Cape Mendocino area occurred in sequences that have approximately the same magnitude versus length of faulting characteristics as other California earthquakes. Consistent first-motion directions are recorded from microearthquakes located within suitably chosen subdivisions of the active area. Composite fault plane solutions indicate that right-lateral movement prevails on strike-slip faults that radiate from Cape Mendocino northwest toward the Gorda basin. This is evidence that the Gorda basin is undergoing internal deformation. Inland, east of Cape Mendocino, a significant component of thrust faulting prevails for all the composite fault plane solutions. Thrusting is predominant in the fault plane solution of the June 26 1968 earthquake located along the Gorda escarpement. In general, the pattern of slip is consistent with a north-south crustal shortening. The Gorda escarpment, the Mattole River Valley, and the 1906 fault break northwest of Shelter Cove define a sharp bend that forms a possible connection between the Mendocino escarpment and the San Andreas fault. The distribution of hypocenters, relative travel times of P waves, and focal mechanisms strongly indicate that the above three features are surface expressions of an important structural boundary. The sharp bend in this boundary, which is concave toward the southwest, would tend to lock the dextral slip along the San Andreas fault and thus cause the regional north-south compression observed at Cape Mendocino. The above conclusions support the hypothesis that dextral strike-slip motion along the San Andreas fault is currently being taken up by slip along the Mendocino escarpment as well as by slip along northwest trending faults in the Gorda basin.

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The Ceres, South Africa, earthquake of September 29, 1969

Bulletin of the Seismological Society of America ◽

10.1785/bssa0610040851 ◽

1971 ◽

Vol 61 (4) ◽

pp. 851-859 ◽

Cited By ~ 2

Author(s):

R. W. E. Green ◽

S. Bloch

Keyword(s):

South Africa ◽

Fault Plane ◽

Large Earthquake ◽

Aftershock Sequence ◽

Fault System ◽

Vertical Fault ◽

Seismic Recording ◽

The Republic ◽

Aftershock Region ◽

Considerable Damage

abstract Aftershocks following the Ceres earthquake of September 29, 1969, (Magnitude 6.3) were monitored using a number of portable seismic recording stations. Earthquakes of this magnitude are rare in South Africa. The event occurred in a relatively densely-populated part of the Republic, and resulted in nine deaths and considerable damage. Accurate locations of some 125 aftershocks delineate a linear, almost vertical fault plane. The volume of the aftershock region is 3 × 9 × 20 km3 with the depth of the aftershocks varying from surface to 9 km. Aftershocks following the September event had almost ceased when another large earthquake (Magnitude 5.7) occurred on April 14, 1970. Following this event, the frequency and magnitude of aftershocks increased, and they were located on a limited portion of the same fault system delineated by the September 29th aftershocks. Previously-mapped faults do not correlate simply with the fault zone indicated by the aftershock sequence.

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Global scale hydrological modelling at 100 m, 1 h resolution, in Python

10.5194/egusphere-egu21-7154 ◽

2021 ◽

Author(s):

Kor de Jong ◽

Marc van Kreveld ◽

Debabrata Panja ◽

Oliver Schmitz ◽

Derek Karssenberg

Keyword(s):

Large Scale ◽

Model Building ◽

Flow Direction ◽

Building Blocks ◽

Global Scale ◽

Data Availability ◽

Hydrological Models ◽

Continental Scale ◽

Modelling Framework ◽

Scale Models

Data availability at global scale is increasing exponentially. Although considerable challenges remain regarding the identification of model structure and parameters of continental scale hydrological models, we will soon reach the situation that global scale models could be defined at very high resolutions close to 100 m or less. One of the key challenges is how to make simulations of these ultra-high resolution models tractable ([1]).Our research contributes by the development of a model building framework that is specifically designed to distribute calculations over multiple cluster nodes. This framework enables domain experts like hydrologists to develop their own large scale models, using a scripting language like Python, without the need to acquire the skills to develop low-level computer code for parallel and distributed computing.We present the design and implementation of this software framework and illustrate its use with a prototype 100 m, 1 h continental scale hydrological model. Our modelling framework ensures that any model built with it is parallelized. This is made possible by providing the model builder with a set of building blocks of models, which are coded in such a manner that parallelization of calculations occurs within and across these building blocks, for any combination of building blocks. There is thus full flexibility on the side of the modeller, without losing performance.This breakthrough is made possible by applying a novel approach to the implementation of the model building framework, called asynchronous many-tasks, provided by the HPX C++ software library ([3]). The code in the model building framework expresses spatial operations as large collections of interdependent tasks that can be executed efficiently on individual laptops as well as computer clusters ([2]). Our framework currently includes the most essential operations for building large scale hydrological models, including those for simulating transport of material through a flow direction network. By combining these operations, we rebuilt an existing 100 m, 1 h resolution model, thus far used for simulations of small catchments, requiring limited coding as we only had to replace the computational back end of the existing model. Runs at continental scale on a computer cluster show acceptable strong and weak scaling providing a strong indication that global simulations at this resolution will soon be possible, technically speaking.Future work will focus on extending the set of modelling operations and adding scalable I/O, after which existing models that are currently limited in their ability to use the computational resources available to them can be ported to this new environment.More information about our modelling framework is at https://lue.computationalgeography.org.References[1] M. Bierkens. Global hydrology 2015: State, trends, and directions. Water Resources Research, 51(7):4923&#8211;4947, 2015. [2] K. de Jong, et al. An environmental modelling framework based on asynchronous many-tasks: scalability and usability. Submitted. [3] H. Kaiser, et al. HPX - The C++ standard library for parallelism and concurrency. Journal of Open Source Software, 5(53):2352, 2020.

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Aftershocks of the February 21, 1973 Point Mugu, California earthquake

Bulletin of the Seismological Society of America ◽

10.1785/bssa0660061931 ◽

1976 ◽

Vol 66 (6) ◽

pp. 1931-1952

Author(s):

Donald J. Stierman ◽

William L. Ellsworth

Keyword(s):

Fault Zone ◽

Main Shock ◽

Fault Plane ◽

Body Wave ◽

P Wave ◽

Fault System ◽

Wave Radiation ◽

Fault Plane Solutions ◽

Complex Deformation ◽

Transverse Ranges

abstract The ML 6.0 Point Mugu, California earthquake of February 21, 1973 and its aftershocks occurred within the complex fault system that bounds the southern front of the Transverse Ranges province of southern California. P-wave fault plane solutions for 51 events include reverse, strike slip and normal faulting mechanisms, indicating complex deformation within the 10-km broad fault zone. Hypocenters of 141 aftershocks fail to delineate any single fault plane clearly associated with the main shock rupture. Most aftershocks cluster in a region 5 km in diameter centered 5 km from the main shock hypocenter and well beyond the extent of fault rupture estimated from analysis of body-wave radiation. Strain release within the imbricate fault zone was controlled by slip on preexisting planes of weakness under the influence of a NE-SW compressive stress.

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The reproducing earthquakes of the Galapagos Islands

Bulletin of the Seismological Society of America ◽

10.1785/bssa0700051759 ◽

1980 ◽

Vol 70 (5) ◽

pp. 1759-1770

Author(s):

Kris Kaufman ◽

L. J. Burdick

Keyword(s):

Large Scale ◽

Fault Plane ◽

Seismic Energy ◽

Galapagos Islands ◽

The Body ◽

Galápagos Islands ◽

Plane Solution ◽

Extensional Faulting ◽

Strain Release ◽

Wave Trains

abstract The largest swarm of earthquakes of the last few decades accompanied the collapse of the Fernandina caldera in the Galapagos Islands in June of 1968. Many of the events were relatively large. (The largest 21 had moments ranging from 6 ×1024 to 12 ×1024 dyne-cm.) They produced teleseismic WWSSN records that were spectacularly consistent from event to event. The entire wave trains of the signals were nearly identical on any given component at any given station. This indicates that the mode of strain release in the region was unusually stable and coherent. The body waveforms of the events have been modeled with synthetic seismograms. The best fault plane solution was found to be: strike = 335°, dip = 47°, and rake = 247°. The depths of all the larger shocks were close to 14 km. Previous work had suggested that the seismic energy was radiated by the collapsing caldera block at a depth of about 1 km. The new results indicate that large scale extensional faulting at depth was an important part of the multifaceted event during which the caldera collapsed.

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