Richard Ketcham

University of Texas at Austin | UT · Jackson School of Geosciences

The Andes of western Argentina record spatiotemporal variations in morphology, basin geometry, and structural style that correspond with changes in crustal inheritance and convergent margin dynamics. Above the modern Pampean flat‐slab subduction segment (27–33°S), retroarc shortening generated a fold‐thrust belt and intraforeland basement uplifts t...

Calibrating human population dispersals across Earth’s surface is fundamental to assessing rates and timing of anthropogenic impacts and distinguishing ecological phenomena influenced by humans from those that were not. Here, we describe the Hartley mammoth locality, which dates to 38,900–36,250 cal BP by AMS 14C analysis of hydroxyproline from bon...

Carbonaceous chondrites (CCs) contain the earliest preserved Solar System material, and objects containing this material are targets of numerous sample return missions. Both laboratory and remote sensing data have shown that this material can be highly porous, but the origin and nature of this porosity is currently not well understood. Because the...

The discovery of He retentivity in magnetite has opened up the use of the magnetite (U-Th)/He method as a thermochronometer to date the exhumation of mafic and ultramafic rocks, and also as a chronometer to date magnetite crystallization during serpentinization. However, published He diffusion data reveal more complex behavior than expected. To res...

The (U-Th)/He dating technique is an essential tool in Earth science research with diverse thermochronologic, geochronologic, and detrital applications. It is now used in a wide range of tectonic, structural, petrological, sedimentary, geomorphic, volcanological, and planetary studies. While in some circumstances the interpretation of (U-Th)/He dat...

The field of (U-Th)/He geochronology and thermochronology has grown enormously over the past ∼25 years. The tool is applicable across much of geologic time, new (U-Th)/He chronometers are under continuous development, and the method is used in a diverse array of studies. Consequently, the technique has a rapidly expanding user base, and new labs ar...

Low-temperature multi-thermochronometry, in which the (U-Th) / He and fission track methods are applied to minerals such as zircon and apatite, is a valuable approach for documenting rock cooling histories and relating them to geological processes. Here we explore the behaviors of two of the most commonly applied low-temperature thermochronometers,...

The Cenozoic North Altyn fault (NAF) is a major splay of the Altyn Tagh fault along the northwestern margin of the Tibetan Plateau, but its role in the development of this plateau margin in response to the India-Eurasia collision is highly debated. Here we investigate fault geometry, kinematics, and shortening magnitude along the westernmost 120 km...

Ore studies using conventional petrographic methods have an intrinsic limitation that spatial (three-dimensional, 3-D) distribution, orientation, shape and mineral associations have to be inferred by 2-D observations and measurements. Further, developing statistically significant data sets is particularly difficult for gold ores, given the fine gra...

Measuring physical properties from rock samples is necessary in geosciences to calibrate models from geophysical surveys. Digital rock physics is one way to estimate these properties. X-ray computed tomography (CT) images can be used to create 3D numerical models of rocks. Numerical simulations on such models are proxies for tests performed in the...

We present a new model for the etching and revelation of confined fission tracks in apatite based on variable along-track etching velocity, vT(x). Insights from step-etching experiments and theoretical energy loss rates of fission fragments suggest two end-member etching structures: constant-core, with a central zone of constant etching rate that t...

The deep structure of continental detachment faults remains debated. Thermo-mechanical models generate detachments that either transect the lithosphere or become distributed shear zones in the mid-lower crust, depending on prescribed thermo-rheological conditions. However, these geometries and prescribed conditions remain little constrained by geol...

The Geology of Colombia book provides an updated background of the geological knowledge of Colombia by integrating the most up–to–date research covering paleontology, biostratigraphy, sedimentary basin analysis, sedimentology, sequence stratigraphy, stratigraphy, geophysics, geochronology, geochemistry, thermochronology, tectonics, structure, volca...

In this chapter, we summarize recent work on the geologic evolution of the northern Andes. Our intention is to present current information so that scientists from other disciplines can differentiate data from interpretations. In this effort, we focus on thermochronological data that provide precise places, dates, and rates. Thermochronological data...

We present a new model for the etching and revelation of confined fission tracks in apatite, based on step etching measurements that demonstrate variable along-track etching velocity, vT(x). We define two end-member model forms: Constant-core, with a central zone of constant etching rate that then falls off toward track tips; and Linear, in which e...

Plain Language Summary Subsurface fluid flow and solute transport are typically described by first‐order or linear rate laws. However, deviations from the first‐order rate laws (or anomalous behavior) are typical and lead to nonlinear flow and non‐Fickian transport phenomena. The shared underlying mechanisms for these “anomalous” flow and transport...

We present the development of thermochronological tools for Andino 3D® software, that integrates Fetkin (Finite Element Temperature Kinematics). These tools allow the user to work on both the structural and the thermochronological model at the same time, providing a user-friendly environment that overcomes the need to work with different programs....

Magnetite is a ubiquitous oxide in ultramafic and mafic rocks, which is present in a large range of geological and tectonic settings. In the case of high-pressure ultramafic rocks, exhumation timing is commonly constrained by geochronometers in nearby lithologies. The development of the magnetite (U-Th-Sm)/He method (MgHe) has opened new perspectiv...

Interpretation of apatite fission-track length data rests on the assumptions that etching fully reveals latent tracks, and that laboratory annealing of induced tracks constitutes a good proxy for geological annealing of spontaneous tracks. Recent work using improved step-etching procedures questions both of these assumptions. Step etching experimen...

The retrieval of accurate thermal histories recorded by the (U-Th)/He system relies on empirical estimates of diffusion kinetics from natural minerals, although the difficulty in obtaining samples with homogeneous gas concentrations (required for accurate diffusivities) has limited the collection of such datasets. Whole-grain analyses are relativel...

The failure hazard rock burst is very dangerous as it can occur very suddenly and violent-ly. Due to the fact, that tunnel and mining projects are in deeper areas than ever, the im-portance of investigating this hazard is more relevant than ever. The Graz University of Technology and the University of Salzburg are investigating rock burst with diff...

The southern Central Andes recorded retroarc shortening, basin evolution, and magmatic arc migration during Neogene changes in subduction. At 31–33°S, above the modern flat‐slab segment, spatial and temporal linkages between thin‐ and thick‐skinned foreland shortening, basement‐involved exhumation of the main Cordillera, and lower‐crustal hinterlan...

We summarize recent work regarding the geologic evolution of the northern Andes. Our intention is to present current information so that scientists from other disciplines can differentiate data from interpretations. In this effort, we focus on thermochronological data that provide precise places, dates, and rates. Thermochronological data provide c...

In this study, we utilize high-resolution X-ray computed tomography (XCT) to track the progress of a leaching process within a pore network. Dissolution and leaching are difficult processes to observe with combined temporal and spatial context, particularly when dissolving material within a non-reactive pore network, and XCT is a uniquely suited te...

The quantification of He and Ne diffusion behavior in crystals rich in U and Th such as zircon is key for the interpretation of (U-Th)/⁴He and (U-Th)/²¹Ne thermochronometric ages. Multiple parameters such as chemical substitution, channel obstruction and damage can modify the diffusivity compared to a pristine structure. To investigate the impact o...

Previous inter-laboratory experiments on confined fission-track length measurements in apatite have consistently reported variation substantially in excess of statistical expectation. There are two primary causes for this variation: (1) differences in laboratory procedures and instrumentation, and (2) personal differences in perception and assessme...

(U–Th) ∕ He thermochronometry relies on the accurate and precise quantification of individual grain volume and surface area, which are used to calculate mass, alpha ejection (FT) correction, equivalent sphere radius (ESR), and ultimately isotope concentrations and age. The vast majority of studies use 2-D or 3-D microscope dimension measurements an...

Non-invasive 3D Crystallography of Geological Media in the Laboratory - Volume 25 Supplement - Matthew Andrew, Hrishikesh Bale, Nicolas Gueninchault, Jun Sun, Romy Hanna, Jessica Maisano, Richard Ketcham, Matthew Pankhurst, Mike Zolensky

This chapter reviews the evolving state of knowledge concerning fission-track (FT) annealing, primarily in apatite and zircon, based on theory, experiments, and geological observations. Multiple insights into track structure, formation, and evolution arise from transmission electron microscopy, small-angle X-ray scattering, atomic force microscopy,...

The Pliocene hominin fossil ‘Lucy’ (A.L. 288-1, Australopithecus afarensis) was discovered in the Afar region of Ethiopia in 1974 and dates to 3.18 million years in age. In Kappelman et al.,¹ we presented the results of a detailed investigation of the skeleton that for the first time identified and described unusual bone-into-bone compressive fract...

(U-Th)/He thermochronometry relies on accurate and precise quantification of individual grain volume and surface area, which are used to calculate mass, alpha ejection (FT) correction, isotope concentrations, equivalent sphere radius (ESR), and ultimately age. The vast majority of studies use 2D or 3D microscope dimension measurements and an ideali...

In this study, we provide new data to understand the groundwater flow patterns in the Llanos Basin and their impact on oil biodegradation and the geothermal regimes as well as how the structural styles and anthropogenic activities impact these patterns. Previous studies suggest an active flow of groundwater and variable salinities whose spatial pat...

Geophysical Research AbstractsVol. 21, EGU2019-17048, 2019EGU General Assembly 2019© Author(s) 2019.A method and work flow for quantifying Rock Burst in 4DRobert Marschallinger (1), Peter Hofmann (1), Fritz Zobl (1), Richard Ketcham (2), Dave Edey (2), LukasGottsbacher (3), Angelika Klammer (3), and Wulf Schubert (3)(1) Department of Geoinformatics...

We present a method for measuring small, discrete features near the resolution limit of X-ray computed tomography (CT) data volumes with the aim of providing consistent answers across instruments and data resolutions. The appearances of small features are impacted by the partial volume effect and blurring due to the data point-spread function, and...

Iodine staining combined with X-ray computed tomography (CT) has become a core approach in anatomy, offering three-dimensional and essentially non-destructive imaging of soft tissues. Although there have been rapid advances in methodologies and techniques, the mechanisms underlying diffusible iodine contrast-enhanced CT are not yet fully understood...

New thermochronometric data provide evidence for an along-strike diachronous building of the Andes in north-central Chile (28.5–32°S). Geochronological (U-Pb zircon) and thermochronological (apatite fission track and (U-Th)/He) analyses of rock units were obtained in west-to-east transects across the western topographic front. Thermal models indica...

We report a new interlaboratory exercise to evaluate the reproducibility of apatite fission-track (AFT) and (U-Th)/He (AHe) data and thermal history analysis. Twelve laboratory groups participated, analyzing apatite separates from two previously studied localities. Ten groups returned AFT data from 13 analysts, five groups returned AHe data, one co...

A long running debate in human evolution concerns the degree to which early hominins combined arboreal behaviors with terrestrial bipedalism. The argument in favor of obligate terrestrial bipedalism considers the arboreal-linked traits such as curved phalanges to be retained primitive features inherited from an arboreal ancestor that had no adaptiv...

We use X-ray computed tomography (XCT) to examine the 3D morphology and spatial relationship of fine-grained rims (FGRs) of Type I chondrules in the CM carbonaceous chondrite Murchison to investigate the formation setting (nebular vs. parent body) of the FGRs. We quantify the sizes, shapes, and orientations of the chondrules and FGRs and develop a...

The ROCKBURST project researches the influence of micromechanical and micro-structural characteristics and their individual effect on rock failure. In this project, we use Ob-ject based image analysis (OBIA) for knowledge-based, automated mineral classification and rock texture analysis from petrographic micrographs. Our work flow closely mimicks a...

A regional, balanced cross section is presented for the thin-skinned Tajik fold-andthrust belt, constrained by new structural and stratigraphic data, industrial well-log data, flexural modeling, and existing geologic and geophysical mapping. A sequential restoration of the section was calibrated with 15 new apatite (U-Th)/He ages and 7 new apatite...

X-ray computed tomography (XCT) is a powerful 3D imaging technique that has been used to investigate meteorites, mission-returned samples, and other planetary materials of all scales from dust particles to large rocks. With this technique, a 3D volume representing the X-ray attenuation (which is sensitive to composition and density) of the material...

Please cite this article in press as:Chirchir, H., et al., Does trabecular bone structure within the metacarpal heads of primates vary with hand posture? C. R. Palevol (2016), http://dx. a b s t r a c t Reconstructing function from hominin fossils is complicated by disagreements over how to interpret primitively inherited, ape-like morphology. This...

While there is broad agreement that early hominins practiced some form of terrestrial bipedality, there is also evidence that arboreal behavior remained a part of the locomotor repertoire in some taxa, and that bipedal locomotion may not have been identical to that of modern humans. It has been difficult to evaluate such evidence, however, because...

Relative humeral diaphyseal strength and forearm muscle size. Regression of the residuals of humeral diaphyseal strength (polar section modulus) on humeral head superoinferior breadth against the residuals of maximum forearm muscle area on humeral head superoinferior breadth in modern 17-year-old human growth study participants (see S1 Text). (TIF)

CT scan parameters for A.L. 288–1. (XLSX)

Hip Joint Loading and Gait Energetics in Modern Humans and Early Hominins. (DOCX)

Effects of pelvic and proximal femoral morphology on hip joint reaction force and femoral shaft bending. Predicted abductor (M) and hip joint reaction (J) forces, and femoral diaphyseal bending moments during the stance phase of gait in a) modern humans, b) hypothetical early Homo, and c) A.L. 288–1. Force triangles in b) and c) show predicted vect...

Relative deviations of fossil specimens from modern humans and chimpanzees. (XLSX)

Femoral biomechanical neck length and total length' in fossil specimens. (XLSX)

Diaphyseal Strength/Articular Size as a Proxy for Relative Muscular Strength. (DOCX)

Reduced major axis statistics and comparisons between samples. (XLSX)

Muscle Strength in Chimpanzees. (DOCX)

Bilateral asymmetry in A.L. 288–1 right and left humeri. (XLSX)

The Pliocene fossil 'Lucy' (Australopithecus afarensis) was discovered in the Afar region of Ethiopia in 1974 and is among the oldest and most complete fossil hominin skeletons discovered. Here we propose, on the basis of close study of her skeleton, that her cause of death was a vertical deceleration event or impact following a fall from considera...

Surface uplift of the Garzón Massif in the northern Andes formed a critical orographic barrier (2500–3000 m elevation) that generated a deep rain shadow and strongly influenced the evolution of the largest river systems draining northern South America. This basement massif and its corresponding foreland basement high define the headwaters and drain...

Diffusible iodine-based contrast-enhanced computed tomography presents a comparatively new tool kit for imaging fine-scale three-dimensional phenotypes that is rapidly becoming standard anatomical practice. However, relatively few studies have attempted to look at subtle differences in staining protocols or attempted to model tissue reactions to ga...