Opposing shear senses in a subdetachment mylonite zone: Implications for core complex mechanics

[1] Global studies of metamorphic core complexes and low‐angle detachment faults have highlighted a fundamental problem: Since detachments excise crustal section, the relationship between the mylonitic rocks in their footwalls and the brittle deformation in their hanging walls is commonly unclear. Mylonites could either reflect ductile deformation related to exhumation along the detachment fault, or they could be a more general feature of the extending middle crust that has been “captured ” by the detachment. In the first case we would expect the kinematics of the mylonite zone to mirror the sense of movement on the detachment; in the second case both the direction and sense of shear in the mylonites could be different. The northern Snake Range décollement (NSRD) is a classic Basin and Range detachment fault with a well‐documented top‐east of displacement. We present structural, paleo-magnetic, geochronological, and geothermometric evidence to suggest that the mylonite zone below the NSRD locally experienced phases of both east ‐ and west‐directed shear, inconsistent with movement along a single detachment fault. We therefore propose that the footwall mylonites represent a predetachment dis-continuity in the middle crust that separated localized deformation above from distributed crustal flow below (localized‐distributed transition (LDT)). The mylonites were subsequently captured by a moderately dipping brittle detachment that soled down to the middle crust and exhumed them around a rolling hinge into a subhorizontal orientation at the surface, produc-ing the present‐day NSRD. In this interpretation the brittle hanging wall represents a series of rotated upper crustal normal faults, whereas the mylonitic footwall represents one or more exhumed middl

Kinematics and Vorticity in Kangmar Dome, Southern Tibet: Testing Midcrustal Channel-flow Models for the Himalaya

Kinematic, kinematic vorticity (Wm), and deformation temperature analyses were completed to test the hypothesis that midcrustal rocks exposed in the core of the Kangmar gneiss dome, southern Tibet record ductile deformation patterns of a “frozen” segment of a southward flowing midcrustal channel. Microscopic and mesoscopic kinematic indicators exhibit a downward transition from a subequal mix of top-north and top-south shear in garnet zone rocks to dominantly top-north shear in staurolite/kyanite zone and deeper rocks. Kinematic vorticity values indicate an increase in pure shear component with depth from ∼48% pure shear in chloritoid zone rocks through ∼62% in garnet zone to staurolite/kyanite zone rocks to ∼68% pure shear in an orthogneiss, the deepest exposed rocks. Deformation temperatures inferred from grain-scale microstructures and quartz lattice preferred orientations increase from ∼300°C–400°C in chloritoid zone rocks to ≥600°C in the deepest exposed rocks. These temperatures are equivalent to temperatures derived from garnet-biotite thermobarometry, indicating that Wm was recorded during peak metamorphism. This ductile deformation zone was cut by the brittle southern Tibetan detachment system (STDS) that juxtaposed metasedimentary rocks upon the orthogneiss. On the basis of these relations, midcrustal rocks in the core of Kangmar Dome record: (1) general shear (vertical thinning and N–S horizontal extension) with a component of top-north shear during peak metamorphism within a ductile shear zone corresponding to the northern and deeper portion of the STDS, (2) an increase in pure shear with structural depth, a consequence of an increase in lithostatic load, and (3) displacement of the high-temperature shear zone by the brittle STDS. Our data are compatible with the deformation patterns predicted for the top part of a southward flowing midcrustal channel

Seismic anisotropy as a constraint on composition in the lower crust

Our current interpretation of the composition of the middle and lower crust comes mainly from seismic observations, yet it remains a challenge to link seismic observations directly to composition. This is because isotropic seismic properties are similar across a range of compositions. Taking anisotropy into account allows for further refinement of our interpretation of composition provided that anisotropy is characterized for candidate rock types. This study uses electron backscatter diffraction (EBSD) measurements of crystallographic preferred orientation of minerals to calculate seismic anisotropy in samples of the Pelona-Orocopia-Rand (POR) schist from the Mojave region of southern California. The goals of this work are to characterize the seismic anisotropy of the POR schist and its relationship to observed lower crustal anisotropy in the region, and to refine predictions of lower crustal composition based on seismic anisotropy

Rapid Microwave Preparation of Thermoelectric TiNiSn and TiCoSb Half-Heusler Compounds

The 18-electron ternary intermetallic systems TiNiSn and TiCoSb are promising for applications as high-temperature thermoelectrics and comprise earth-abundant, and relatively nontoxic elements. Heusler and half-Heusler compounds are usually prepared by conventional solid state methods involving arc-melting and annealing at high temperatures for an extended period of time. Here, we report an energy-saving preparation route using a domestic microwave oven, reducing the reaction time significantly from more than a week to one minute. A microwave susceptor material rapidly heats the elemental starting materials inside an evacuated quartz tube resulting in near single phase compounds. The initial preparation is followed by a densification step involving hot-pressing, which reduces the amount of secondary phases, as verified by synchrotron X-ray diffraction, leading to the desired half-Heusler compounds, demonstrating that hot-pressing should be treated as part of the preparative process. For TiNiSn, high thermoelectric power factors of 2 mW/mK^2 at temperatures in the 700 to 800 K range, and zT values of around 0.4 are found, with the microwave-prepared sample displaying somewhat superior properties to conventionally prepared half-Heuslers due to lower thermal conductivity. The TiCoSb sample shows a lower thermoelectric figure of merit when prepared using microwave methods because of a metallic second phase

The impact of immediate breast reconstruction on the time to delivery of adjuvant therapy: the iBRA-2 study

Background: Immediate breast reconstruction (IBR) is routinely offered to improve quality-of-life for women requiring mastectomy, but there are concerns that more complex surgery may delay adjuvant oncological treatments and compromise long-term outcomes. High-quality evidence is lacking. The iBRA-2 study aimed to investigate the impact of IBR on time to adjuvant therapy. Methods: Consecutive women undergoing mastectomy ± IBR for breast cancer July–December, 2016 were included. Patient demographics, operative, oncological and complication data were collected. Time from last definitive cancer surgery to first adjuvant treatment for patients undergoing mastectomy ± IBR were compared and risk factors associated with delays explored. Results: A total of 2540 patients were recruited from 76 centres; 1008 (39.7%) underwent IBR (implant-only [n = 675, 26.6%]; pedicled flaps [n = 105,4.1%] and free-flaps [n = 228, 8.9%]). Complications requiring re-admission or re-operation were significantly more common in patients undergoing IBR than those receiving mastectomy. Adjuvant chemotherapy or radiotherapy was required by 1235 (48.6%) patients. No clinically significant differences were seen in time to adjuvant therapy between patient groups but major complications irrespective of surgery received were significantly associated with treatment delays. Conclusions: IBR does not result in clinically significant delays to adjuvant therapy, but post-operative complications are associated with treatment delays. Strategies to minimise complications, including careful patient selection, are required to improve outcomes for patients

Breast cancer management pathways during the COVID-19 pandemic: outcomes from the UK ‘Alert Level 4’ phase of the B-MaP-C study

Abstract: Background: The B-MaP-C study aimed to determine alterations to breast cancer (BC) management during the peak transmission period of the UK COVID-19 pandemic and the potential impact of these treatment decisions. Methods: This was a national cohort study of patients with early BC undergoing multidisciplinary team (MDT)-guided treatment recommendations during the pandemic, designated ‘standard’ or ‘COVID-altered’, in the preoperative, operative and post-operative setting. Findings: Of 3776 patients (from 64 UK units) in the study, 2246 (59%) had ‘COVID-altered’ management. ‘Bridging’ endocrine therapy was used (n = 951) where theatre capacity was reduced. There was increasing access to COVID-19 low-risk theatres during the study period (59%). In line with national guidance, immediate breast reconstruction was avoided (n = 299). Where adjuvant chemotherapy was omitted (n = 81), the median benefit was only 3% (IQR 2–9%) using ‘NHS Predict’. There was the rapid adoption of new evidence-based hypofractionated radiotherapy (n = 781, from 46 units). Only 14 patients (1%) tested positive for SARS-CoV-2 during their treatment journey. Conclusions: The majority of ‘COVID-altered’ management decisions were largely in line with pre-COVID evidence-based guidelines, implying that breast cancer survival outcomes are unlikely to be negatively impacted by the pandemic. However, in this study, the potential impact of delays to BC presentation or diagnosis remains unknown

The development of high temperature scanning electron microscopy and electron backscatter diffraction with application to the study of phase transformations

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Middle Crustal Ductile Deformation Patterns in Southern Tibet: Insights from Vorticity Studies in Mabja Dome

Kinematic, kinematic vorticity (Wm), and deformation-temperature analyses were performed to test the hypothesis that mid-crustal rocks exposed in Mabja Dome, southern Tibet, were penetratively deformed within a southward-flowing mid-crustal channel during the late Eocene/early Oligocene to early Miocene. Outcrop and thin-section kinematic indicators show a downward transition from mixed top-N and top-S shear in chloritoid- and garnet-zone rocks, through dominantly top-S shear in garnet- and kyanite-zone rocks, to solely top-S shear in staurolite-zone and deeper rocks. Along mineral elongation lineation-parallel transects, Wm in schists and orthogneisses decreases with structural depth from ∼0.80 (∼40% pure shear) to ∼0.55 (∼63% pure shear). Deformation temperature increases from ∼450 °C in the chloritoid-zone to \u3e700 °C in the sillimanite-zone, coincident with peak metamorphic temperatures, indicating that Wm was recorded during peak metamorphism. These mid-crustal rocks thus exhibit deformational patterns characterized by: (1) locally opposing shear sense suggesting bulk pure shear at moderate structural depths; (2) a broad top-S shear zone above the Main Central Thrust; and (3) increasing pure shear with structural depth, suggesting an increase in lithostatic load. Our results from mid-crustal rocks exposed in the core of Mabja Dome yield patterns of ductile deformation in southern Tibet that define non-ideal channel flow