Brian Bagley

Titanium concentration in quartz as a record of multiple deformation mechanisms in an extensional shear zone

Results of high precision analysis of Ti concentration ([Ti]) in quartz representing different recrystallization microstructures in a suite of progressively deformed quartzite mylonites show the effect of recrystallization on distribution of Ti in quartz. Petrographic observations and ion microprobe analysis reveals three texturally and geochemically distinct quartz microstructures in mylonites: (1) cores of recrystallized quartz ribbons preserve the highest [Ti] and are interpreted to have recrystallized via grain boundary migration recrystallization, (2) recrystallized rims and grain margins preserve a lower and more variable [Ti] and are interpreted to reflect the combined influence of subgrain rotation and bulging recrystallization, and (3) neocrystallized quartz precipitated in dilatancy sites has low (∼1 ppm) [Ti], reflecting the Ti content of the syndeformational fluid. Muscovite in nonmylonitic quartzite (at the base of the sampling traverse) is compositionally zoned, whereas muscovite in mylonitic quartzite shows a progressive decreasing in zoning in higher strain samples. Three-dimensional phase distribution mapping using X-ray computed tomography analysis of rock hand samples reveals that Ti-bearing accessory phases are less abundant and more dispersed in higher strained mylonites compared to nonmylonitic quartzite. This study demonstrates the influence of dynamic recrystallization on Ti substitution in quartz and evaluates the Ti buffering capacity of aqueous fluids (meteoric versus metamorphic/magmatic) as well as the distribution and reactivity of Ti-bearing accessory phases in a deforming quartzite. Results of this study suggest that Ti-in-quartz thermobarometry of deformed quartz is a sensitive technique for resolving the multistage history of quartz deformation and recrystallization in crustal shear zones.

Precocity in a tiny titanosaur from the Cretaceous of Madagascar

Tiny giant Titanosaurs were the largest land vertebrates to have evolved, but even they had to start small. Curry Rogers et al. describe a baby Rapetosaurus only 35 cm at the hip at death. Histological and limb analysis suggest that this tiny giant had a much greater range of movement than it would have had as an adult. Furthermore, the work confirms hypotheses that these largest of dinosaurs were precocial, being able to move independently immediately after birth. This pattern differs from that seen in many contemporary dinosaur groups, such as theropods and ornithischians, for which increasing evidence suggests that parental care was important. Science, this issue p. 450 Tiny giant suggests that largest dinosaurs were precocial at birth. Sauropod dinosaurs exhibit the largest ontogenetic size range among terrestrial vertebrates, but a dearth of very young individuals has hindered understanding of the beginning of their growth trajectory. A new specimen of Rapetosaurus krausei sheds light on early life in the smallest stage of one of the largest dinosaurs. Bones record rapid growth rates and hatching lines, indicating that this individual weighed ~3.4 kilograms at hatching. Just several weeks later, when it likely succumbed to starvation in a drought-stressed ecosystem, it had reached a mass of ~40 kilograms and was ~35 centimeters tall at the hip. Unexpectedly, Rapetosaurus limb bones grew isometrically throughout their development. Cortical remodeling, limb isometry, and thin calcified hypertrophic metaphyseal cartilages indicate an active, precocial growth strategy.

Permeability, porosity, and mineral surface area changes in basalt cores induced by reactive transport of CO2‐rich brine

Four reactive flow-through laboratory experiments (two each at 0.1 mL/min and 0.01 mL/min flow rates) at 150°C and 150 bar (15 MPa) are conducted on intact basalt cores to assess changes in porosity, permeability, and surface area caused by CO2-rich fluid-rock interaction. Permeability decreases slightly during the lower flow rate experiments and increases during the higher flow rate experiments. At the higher flow rate, core permeability increases by more than one order of magnitude in one experiment and less than a factor of two in the other due to differences in preexisting flow path structure. X-ray computed tomography (XRCT) scans of pre- and post-experiment cores identify both mineral dissolution and secondary mineralization, with a net decrease in XRCT porosity of ∼0.7%–0.8% for the larger pores in all four cores. (Ultra) small-angle neutron scattering ((U)SANS) data sets indicate an increase in both (U)SANS porosity and specific surface area (SSA) over the ∼1 nm to 10 µm scale range in post-experiment basalt samples, with differences due to flow rate and reaction time. Net porosity increases from summing porosity changes from XRCT and (U)SANS analyses are consistent with core mass decreases. (U)SANS data suggest an overall preservation of the pore structure with no change in mineral surface roughness from reaction, and the pore structure is unique in comparison to previously published basalt analyses. Together, these data sets illustrate changes in physical parameters that arise due to fluid-basalt interaction in relatively low pH environments with elevated CO2 concentration, with significant implications for flow, transport, and reaction through geologic formations.

Axial‐type olivine crystallographic preferred orientations: The effect of strain geometry on mantle texture

The effect of finite strain geometry on crystallographic preferred orientation (CPO) is poorly constrained in the upper mantle. Specifically, the relationship between shape preferred orientation (SPO) and CPO in the mantle rocks remains unclear. We analyzed a suite of 40 spinel peridotite xenoliths from Marie Byrd Land, west Antarctica. X-ray computed tomography allows for quantification of spinel SPO, which ranges from prolate to oblate shape. Electron backscatter diffraction analysis reveals a range of olivine CPO patterns, including A-type, axial-[010], axial-[100], and B-type patterns. Until now, these CPO types were associated with different deformation conditions, deformation mechanisms, or strain magnitudes. Microstructures and deformation mechanism maps suggest that deformation in all studied xenoliths is dominated by dislocation-accommodated grain boundary sliding. For the range of temperatures (779–1198 oC), extraction depths (39–72 km), differential stresses (2–60 MPa), and water content (up to 500 H/106Si) of the xenolith suite, variations in olivine CPO do not correlate with changes in deformation conditions. Here we establish for the first time in naturally deformed mantle rocks that finite strain geometry controls the development of axial-type olivine CPOs; axial-[010] and axial-[100] CPOs form in relation to oblate and prolate fabric ellipsoids, respectively. Girdling of olivine crystal axes results from intracrystalline slip with activation of multiple slip systems, and grain boundary sliding. Our results demonstrate that mantle deformation may deviate from simple shear. Olivine texture in field studies and seismic anisotropy in geophysical investigations can provide critical constraints for the 3D strain in the upper mantle.

Pushing the record of trematode parasitism of bivalves upstream and back to the Cretaceous

The Judith River Formation of Montana, USA, renowned for its preservation of Late Cretaceous dinosaurs, now yields the oldest-known evidence of trematode parasitism of bivalves. Highly distinctive igloo-shaped traces found on shells of the freshwater bivalve Sphaerium are virtually identical to igloo-shaped traces known from living marine bivalves infected by metacercaria larvae of gymnophallid trematodes (flatworms). This unique record of paleoparasitism provides key insights into the evolution of an important parasite group, reveals the inner workings of cryptic ecological associations, and enriches our understanding of ancient food webs. Our discovery extends the record of trematode–bivalve interaction back to the Late Cretaceous (ca. 76 Ma), and indicates that this parasite–host relationship was established in freshwater ecosystems much earlier than previously surmised. The complex multi-host lifecycles of modern trematodes and the general stability of parasite–host associations suggest that sphaeriid bivalves in the Judith River record likely served as the second intermediate host. Potential candidates for the definitive host range from molluscivorous fish to birds and non-avian predatory dinosaurs. With the history of trematode–bivalve interaction pushed back to the Late Cretaceous, patterns in trematode infection can now be interrogated across major episodes of global change, including the Cretaceous-Paleogene mass extinction and the Paleocene-Eocene thermal maximum.

Ectopic Bone as a Nidus for Calcium Oxalate Urocystolithiasis in a Cat

A 7‐year‐old female spayed domestic shorthair cat was referred to the urology service for nonsurgical urocystolith removal. A urolith was attached to the urothelium by ectopic bone. Interventional removal without surgery was successful. Follow‐up evaluation 3 years after urolith removal revealed recurrent uroliths, bladder wall mineralization, and marked renal mineralization. This case illustrates the metaplastic potential of the urothelium and that ectopic bone should be included among the pathological factors that promote lithogenesis.

PHYSICAL AND CHEMICAL CHANGES FROM BASALT-CO2-RICH FLUID INTERACTION DURING FLOW-THROUGH EXPERIMENTS AT 150°C AND 150 BAR

To further our understanding of the relationship between environmental change and hominin evolution, at an important archeological and paleontological locality, XRD bulk analysis was completed on 1,183 core samples from a drilling core collected in West Turkana, Kenya. The core itself covers about 1.354 -1.85 Ma. Most minerals present are detrital feldspars, mica, and quartz. The authigenic minerals present are mostly carbonates, zeolites, and sulfur bearing minerals such as gypsum and pyrite. The few metal oxides present may be derived from paleosols in the core. This particular study is focused almost entirely on the data gathered from the XRD analysis of clay samples. We analyzed 70 samples from the submicron fraction for clay mineralogy. Both oriented and randomly oriented analyses were completed in order to characterize the clay minerals present.

Applications of MicroCT in Earth Sciences

Case study 1: Changes in permeability and pore-scale geometries from in-situ microCT In-situ microCT experiments will document changes in permeability and pore-scale geometries of serpentinized olivine-rich samples. These experiments are designed to explore interactions of chemical and physical processes of feedback by fluid and mineral components as fluids flow through confined core samples. 3D reconstructions of pore and solid geometries (Fig. 1) of ongoing experiments will link chemical reactions, pore geometries, and resultant permeability fields.