High-resolution X-ray texture goniometry

High-resolution X-ray texture goniometry (HRXTG) significantly improves peak/background ratios and allows for the determination of crystallographic preferred fabrics of small regions (2) in heterogeneously deformed rocks. The basic instrument is a commercially available automated single-crystal X-ray diffractometer equipped with a Mo source. A stage for transmission mode was constructed that is driven by the original motors, so the unit is fully computer controlled. Absorption corrections are calculated, which removes the need for generally difficult to obtain empirical corrections. This, combined with equipment optimization, enables us to use small irradiated volumes of rocks with variable compositions. The advantage of HRXTG in heterogeneously deformed rocks is demonstrated in a cleaved mudstone. Analysis of 2 areas in a 2 cm bed showing a gradation from micaceous sandstone to slate reveals that fabric intensity of both mica and chlorite increases significantly (dM from 0.64 to 1.03 and from 0.45 to 0.78, respectively), without appreciable change in the oblate shape (kM) of the fabric. Thus, HRXTG can record a strain state at the mm-scale of heterogeneously deformed rocks.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31487/1/0000409.pd

Contradictions of slate formation resolved?

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62973/1/392348a0.pd

Preferred orientation development of phyllosilicates in diagenetic to greenschist facies environments, and related geological processes.

Phyllosilicates are the principal components of phyllosilicate-rich diagenetic to low-grade metamorphic rocks such as mudstones, shales, and slates, and are among the most common rock types on the Earth's surface. Understanding how the chemical composition, structure and textures of phyllosilicates in those rocks evolved under different geological conditions provides critical information about many geological processes in the upper crust. Advances in electron microbeam technology have made it possible to study fine-grained phyllosilicates in detail. However, a piece of critical information, the dimensional and crystallographic preferred orientation of phyllosilicates, is not easily obtained. This dissertation was designed to develop a method and systematically examine preferred orientation development of phyllosilicates in environments from diagenetic to low metamorphic grades, using a combination of transmission X-ray texture goniometry and electron microscopy. Samples from various environments and geologic settings were studied. The results of these studies show that (1) in a burial environment, the preferred orientation development of phyllosilicates is largely affected by the mineralogical transformation from smectite to illite (S-I); this supports the proposal that coalescence of illite packets during the S-I transition provides the hydraulic seal for the generation of basin overpressure. (2) In the presence of tectonic stress, cleavages form as the result of reorientation of phyllosilicates in a new orientation. In the reorientation process, larger detrital grains (tens of $\rm\mu m)$ change orientation by mechanical processes, whereas fine-grained authigenic grains (tens of nm) change orientation primarily by chemical processes (dissolution and neocrystallization). (3) Mechanical processes are favored at low metamorphic grade and low strain, whereas chemical processes are favored in relatively high-grade and high-strain environments. This suggests that the dominant cleavage-forming mechanism is a function of the combined effects of thermal and strain energy in rocks. The contribution of either source to the total energy of the system is complementary and fully interchangeable. (4) After deformation stopped, preferred orientation of phyllosilicates continues to improve with metamorphic grade by extending cleavage-parallel phyllosilicate grains along the (001) planes at the expense of phyllosilicate grains in less favorable orientations, by dissolution and neocrystallization.Ph.D.Earth SciencesGeologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/130992/2/9825249.pd

Mitochondrial diseases in Hong Kong: prevalence, clinical characteristics and genetic landscape

Abstract Objective To determine the prevalence of mitochondrial diseases (MD) in Hong Kong (HK) and to evaluate the clinical characteristics and genetic landscape of MD patients in the region. Methods This study retrospectively reviewed the phenotypic and molecular characteristics of MD patients from participating public hospitals in HK between January 1985 to October 2020. Molecularly and/or enzymatically confirmed MD cases of any age were recruited via the Clinical Analysis and Reporting System (CDARS) using relevant keywords and/or International Classification of Disease (ICD) codes under the HK Hospital Authority or through the personal recollection of treating clinicians among the investigators. Results A total of 119 MD patients were recruited and analyzed in the study. The point prevalence of MD in HK was 1.02 in 100,000 people (95% confidence interval 0.81–1.28 in 100,000). 110 patients had molecularly proven MD and the other nine were diagnosed by OXPHOS enzymology analysis or mitochondrial DNA depletion analysis with unknown molecular basis. Pathogenic variants in the mitochondrial genome (72 patients) were more prevalent than those in the nuclear genome (38 patients) in our cohort. The most commonly involved organ system at disease onset was the neurological system, in which developmental delay, seizures or epilepsy, and stroke-like episodes were the most frequently reported presentations. The mortality rate in our cohort was 37%. Conclusion This study is a territory-wide overview of the clinical and genetic characteristics of MD patients in a Chinese population, providing the first available prevalence rate of MD in Hong Kong. The findings of this study aim to facilitate future in-depth evaluation of MD and lay the foundation to establish a local MD registry