Detecting fault zone characteristics and paleovalley incision using electrical resistivity: Loma Blanca Fault, New Mexico

Geophysics ◽  
2021 ◽  
Vol 86 (3) ◽  
pp. B209-B221
Author(s):  
Heather Barnes ◽  
Johnny R. Hinojosa ◽  
Glenn A. Spinelli ◽  
Peter S. Mozley ◽  
Daniel Koning ◽  
...  
Keyword(s):  
Electrical Resistivity ◽  
Fault Zone ◽  
Water Table ◽  
Unsaturated Zone ◽  
Late Quaternary ◽  
Rio Grande ◽  
Rio Grande Rift ◽  
High Resistivity ◽  
Low Resistivity ◽  
Sand And Gravel

We have combined electrical resistivity tomography (ERT), geologic information from boreholes and outcrops, and hydrogeologic data to investigate field-scale fault-zone cementation of the Loma Blanca Fault in the Rio Grande Rift. We have collected electrical resistivity data from 16 transects and geologic samples from 29 boreholes (completed as groundwater wells to 30 m depth) across and around the fault. The 2D ERT profiles, whose interpretations are constrained by geologic data, indicate (1) a high resistivity zone in cemented portions of the fault below the water table and (2) in the unsaturated zone, a low-resistivity feature along the cemented portions of the fault. The high-resistivity zone below the water table is consistent with a 10% reduction in porosity due to the fault zone cementation. With the same porosity in the unsaturated zone, the low-resistivity feature in the cemented fault zone is consistent with saturation >0.7, in contrast to saturation 0.2–0.7 for sediment outside of the cemented fault zone. In addition, subsurface samples and ERT profiles delineate a buttress unconformity (i.e., steeply dipping erosional contact) corresponding to a paleovalley margin. This unconformity truncates the cemented fault zone and separates Pliocene axial-fluvial sand (deposited by an ancestral Rio Grande) from late Quaternary sand and gravel (deposited by the Rio Salado, a Rio Grande tributary). The cemented fault zone in the southern portion of the study area is a hydrogeologic barrier; north of the buttress unconformity, where the cemented fault zone has been removed by erosion, the fault is not a hydrogeologic barrier. The integration of geologic, geophysical, and hydrogeologic observations is key to developing our understanding of this complex system, and it allows us to demonstrate the utility of ERT in detecting subsurface fault-zone cementation.

scholarly journals Chronology of terraces in the Rio Grande rift, Socorro basin, New Mexico: Implications for terrace formation

Geosphere ◽  
2020 ◽  
Vol 16 (6) ◽  
pp. 1457-1478
Author(s):  
Brad D. Sion ◽  
Fred M. Phillips ◽  
Gary J. Axen ◽  
J. Bruce J. Harrison ◽  
David W. Love ◽  
...  
Keyword(s):  
New Mexico ◽  
Late Quaternary ◽  
Rio Grande ◽  
New Age ◽  
Alluvial Fan ◽  
Rio Grande Rift ◽  
Arid Environments ◽  
Alluvial Deposits ◽  
Continental Scale ◽  
Geomorphic Surfaces

Abstract The Rio Grande rift hosts a remarkable record of Quaternary river incision preserved in an alluvial terrace sequence that has been studied for more than a century. However, our understanding of Rio Grande incision history in central New Mexico since the end of basin filling ca. 0.78 Ma remains hampered by poor age control. Robust correlations among Rio Grande terrace sequences in central and southern New Mexico are lacking, making it difficult to address important process-related questions about terrace formation in continental-scale river systems. We present new age controls using a combination of 40Ar/39Ar, 36Cl surface-exposure, and 14C dating techniques from alluvial deposits in the central New Mexico Socorro area to document the late Quaternary incision history of the Rio Grande. These new age controls (1) provide constraints to establish a firm foundation for Socorro basin terrace stratigraphy, (2) allow terrace correlations within the rift basin, and (3) enable testing of alternative models of terrace formation. We identified and mapped a high geomorphic surface interpreted to represent the end of basin filling in the Socorro area and five distinct, post–Santa Fe Group (ca. 0.78 Ma) alloformations and associated geomorphic surfaces using photogrammetric methods, soil characterization, and stratigraphic descriptions. Terrace deposits exhibit tread heights up to 70 m above the valley floor and are 5 to >30 m thick. Their fills generally have pebble-to-cobble bases overlain by fine-to-pebbly sand and local thin silt and clay tops. Alluvial-fan terraces and associated geomorphic surfaces grade to former valley levels defined by axial terrace treads. Carbon-14 ages from detrital charcoal above and below a buried tributary terrace tread show that the most recent aggradation event persisted until ca. 3 ka during the transition from glacial to modern climate conditions. Drill-log data show widespread valley fill ∼30 m thick that began aggrading after glacial retreat in northern New Mexico and southern Colorado (ca. 14 ka). Aggradation during this transition was likely due to hillslope destabilization, increased sediment yield, decreased runoff, and reduced stream competence. Chlorine-36 ages imply similar controls on earlier terraces that have surface ages of ca. 27–29, 64–70, and 135 ka, and suggest net incision during glacial expansions when increased runoff favored down-cutting and bedload mobilization. Our terrace chronology supports existing climate-response models of arid environments and links tributary responses to the axial Rio Grande system throughout the central Rio Grande rift. The terrace chronology also reflects a transition from modest (60 m/m.y.) to rapid (300 m/m.y.) incision between 610 and 135 ka, similar to patterns observed throughout the Rio Grande rift and the western United States in general.

scholarly journals GEOELECTRIC PROSPECTION OF COPPER OCCURRENCE IN FOLDING LAYERS IN THE SUL-RIOGRANDENSE SHIELD (BRAZIL)

2018 ◽  
Vol 36 (3) ◽  
pp. 1
Author(s):  
Shaiely Fernandes Santos ◽  
Cesar Augusto Moreira ◽  
Fernanda Teles Gomes Rosa ◽  
Karolliny Borssatto ◽  
Marly Aparecida Silva
Keyword(s):  
Electrical Resistivity ◽  
Geophysical Methods ◽  
High Resistivity ◽  
Electrical Tomography ◽  
Mineral Research ◽  
2D Inversion ◽  
Copper Sulfides ◽  
Low Resistivity ◽  
Quartz Veins ◽  
Probable Presence

ABSTRACTSulfide prospecting with the geophysical methods, such as electrical resistivity and induced polarization, are promising due to the contrast of electrical resistivity and chargeability, where deposits with disseminated sulfides or filoneans are characterized by low resistivity and high polarizability. This work carried out a study of geophysical prospecting by means of tomographic acquisition in mineral copper occurrence, in the region of Caçapava do Sul. Three acquisition lines were performed by means of electrical tomography technique using a Dipole-dipole arrangement, with a length of 400 m and a spacing of 5 m between the electrodes, arranged in perpendicular layout to the structure of the area, represented by a large synclinal where research galleries with carbonates and copper sulfides were recognized in the ridge. The 2D inversion models and 3D multilevel maps indicate central and lateral regions with high resistivity and chargeability with indication of probable presence of copper sulfide, possibly housed in quartz veins. Peripheral zones with moderate resistivity and chargeability infer possible areas with presence of argilization, zones with high chargeability and low resistivity are likely to be zones of sulfation and possible silicification zones with high resistivity and low chargeability, observed in the vicinity of the probable mineralized zones.Keywords: Chargeability, Mineral Research, Resistivity, Sulfide, 3D Multilevel modeling.RESUMO A prospecção de sulfetos por meio de métodos geofísicos de eletrorresistividade e polarização induzida são altamente efetivos devido ao contraste de resistividade elétrica e cargabilidade, uma vez que os depósitos com sulfetos disseminados ou filoneanos são cvaracterizados por baixa resistividade e alta polarizabilidade. Esse trabalho realizou aquisição de tomografia elétricas em ocorrência mineral de cobre, na região de Caçapava do Sul (RS). Foram realizadas 3 linhas de tomografia elétrica em arranjo dipolo-dipolo, com 400 m de comprimento e 5 m de espaçamento entre eletrodos, dispostas de forma perpendicular à crista de um anticlinal, onde no passado foram reconhenhecidos carbonatos e sulfetos de cobre, em galerias de exploração mineral. Os modelos de inversão 2D e mapas de multiníveis 3D indicam regiões centrais e laterais com alta resistividade e alta cargabilidade com provável zona de sulfetos alojados em veios de quartzo. Zonas periféricas com moderada resistividade e cargabilidade sugerem a presença de argilização; zonas com alta cargabilidade e baixa resistividade são prováveis zonas de sulfetação e altos valores de resistividade e baixos de cargabilidade indicam zonas de silicificação.Palavras-chave: Cargabilidade, Pesquisa Mineral, Resistividade Elétrica, Sulfeto, Modelamento Multinível 3D.

scholarly journals Pore resistivity variation by Resistivity imaging technique in sedimentary part of main Gadilam river basin, Cuddalore District, Tamil Nadu, India

2021 ◽  
Vol 13 (1) ◽  
pp. 268-277
Author(s):  
R. Ravi ◽  
S. Aravindan ◽  
C. Ramachandran ◽  
Sanjay Kumar Balabantaray ◽  
B. Selvaraj ◽  
...  
Keyword(s):  
Electrical Resistivity ◽  
River Basin ◽  
Tamil Nadu ◽  
Saline Water ◽  
Groundwater Potential ◽  
High Resistivity ◽  
Clay Layer ◽  
Clayey Sand ◽  
Low Resistivity ◽  
Matching Techniques

Electrical resistivity is the only property of physics which give information of subsurface moisture content in the formation, Hence geophysical electrical resistivity survey was carried out to investigate the nature of shallow subsurface formations and geological contact in the main Gadilam river basin of Cuddalore District in Tamil Nadu. Twenty-seven vertical electrical soundings (VES) were conducted by Schlumberger configuration in the basin. Data is interpreted by curve matching techniques using IPI2 WIN software, layer parameters like apparent resistivity (?a) and thickness (h) interpretation were exported to Geographic Information System (GIS). Interpretation distinguishes three major geoelectric layers like topsoil, sandy clay layer, clayey sand layer along the contact zone in the basin. Interpreted VES sounding curves are mostly four-layer cases of QH, H, HA and KH type. Investigation demarcates lithology of subsurface and hydrogeological set up by employing maximum possible electrode sounding to infer saline water and freshwater occurrence based on resistivity signals. Zone of groundwater potential map was prepared with the combination of resistivity (?= ?1+ ?2+ ?3+ ?4) and corresponding thickness (T= T1+T2+T3+T4). High resistivity value of >200 ? m and low resistivity value of <10 ? m show the occurrence of alkaline and saline water within the formation aquifers as a result of possible rock water interaction and saline water dissolution. Four-layer resistivity cases from the matched curve (namely KH, AH, QA, and KA type) show the resistivity distribution/variation. It separates the freshwater depth wish from 1 to 140 ? m in fluvial sediments. Flood basin, sandstone and clay layer with low resistivity value of 3.16 - 7.5 ? m indicates contact with saline and freshwater aquifer. The Iso – resistivity map delineates saline water and freshwater zones with in the fourth layer cases in the same locations to indicate the irrational way of abstracting groundwater, resulting in saltwater ingress.

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