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Deformation of continental crust along a transform boundary, Coast Mountains, British Columbia
Get PDFNew structural, paleomagnetic, and apatite (U-Th)/He results from the continental margin inboard of the Queen Charlotte fault (~54Ā°N) delineate patterns of brittle faulting linked to transform development since ~50 Ma. In the core of the orogen, ~250 km from the transform, north striking, dip-slip brittle faults and vertical axis rotation of large crustal domains occurred after ~50 Ma and before intrusion of mafic dikes at 20 Ma. By 20 Ma, dextral faulting was active in the core of the orogen, but extension had migrated toward the transform, continuing there until <9 Ma. Local tilting in the core of the orogen is associated with glacially driven, post-4 Ma exhumation. Integration with previous results shows that post-50 Ma dextral and normal faulting affected a region ~250 km inboard of the transform and ~300 km along strike. Initially widespread, the zone of active extension narrowed and migrated toward the transform ~25 Ma after initiation of the transform, while dextral faulting continued throughout the region. Differential amounts of post-50 Ma extension created oroclines at the southern and northern boundaries of the deformed region. This region approximately corresponds to continental crust that was highly extended just prior to transform initiation. Variation in Neogene crustal tilts weakens interpretations relying on uniform tilting to explain anomalous paleomagnetic inclinations of mid-Cretaceous plutons. Similarities to the Gulf of California suggest that development of a transform in continental crust is aided by previous crustal extension and that initially widespread extension narrows and moves toward the transform as the margin develops
The Lake Bond deposit: superimposed volcanogenic and synorogenic base and precious metal mineralization in the Robert's Arm Group, central Newfoundland
Get PDFThe Lake Bond deposit is hosted by Lower Ordovician volcanic rocks of the Robert's Arm Group. Detailed penological studies indicate that there are two generations of superimposed alteration and sulphide deposition. The first generation mineralization is pre-kinematic, and is characterized by pyrite and Cu-Zn sulphides associated with pervasive chloritization and locally intense quartz-sericite alteration. The second generation mineralization occurs in syn- to post-kinematic veins, and comprises locally auriferous Cu-Zn-Pb sulphides in a dominantly Ca-Mg-Fe silicate gangue.
First generation mineralization resulted in 5x to 100x enrichments in Cu, Zn, Pb, Au, As, Sb, Cd and Ba, with respect to the probable source basalts. Second generation veins, in contrast, carry 100x to 1000x enrichments in most of these metals (except Sb and Ba), substantial enrichments in Fe and Mn, ?10x enrichment in Ag, and a marked increase in the enrichment of Pb, Au, As and Ag relative to Cu and Zn compared to the first generation mineralization. Sphalerites in second generation veins are enriched in Cd, Mn and Fe relative to first generation sphalerites, parallelling enrichments in the whole rocks. The Ca-Mg-Fe vein silicate assemblage suggests fluid temperatures greater than 200Ā°C and possibly greater than 300Ā°C; abundant calcite in the veins implies that CO2 may have influenced mineralization. Fluid inclusions in second generation sphalerite yield average homogenization temperatures of about 306Ā°C.
The timing of deformation and second generation mineralization in the Lake Bond deposit is constrained to the early Silurian by cross-cutting relationships with dated post-tectonic plutons. Comparisons with other deposits in the Robert's Arm Group and deposits elsewhere in central Newfoundland suggest a two-stage metallogenic model comprising: (1) an early volcanogenic event coeval with the Lower Ordovician host rocks; and (2) early Silurian hydrothermal activity related to shearing and movement on major faults. The latter is tentatively correlated with a widespread lode gold mineralizing event in central Newfoundland. The second generation auriferous mineralization apparently preferentially overprinted early sulphide zones at Lake Bond suggesting an exploration potential for auriferous zones within low-grade volcanogenic sulphide stockworks in the Buchans-Robert's Arm Belt.
RÉSUMÉ
Le gite de Lake Bond est encaissé dans les volcanites du Groupe de Robert's Arm (Ordovicien inférieur). Des études pétrologiques détaillées meltent en évidence deux générations au sein desquelles une altération se superpose au dépôt des sulfures. La minéralisation de première génération est précinématique et se caractérise par de la pyrite et des sulfures de Cu-Zn associés à une chloritisation penétrante ainsi qu'à une altération à quartz et sericite localemenl intense. La minéralisation de seconde génération se développe dans des veines syn- à postcinemauques et comprend des sulfures à Cu-Zn-Pb localement auriferes à l'intérieur d'une gangue silicatée à dominante Ca-Fe-Mg.
La minéralisation de première génération engendra un enrichissement de 5 à 100 fois en Cu, Zn, Pb, Au, As, Sb, Cd et Ba par rapport aux basaltes dont elle est probablement issue. En revanche, les veines de seconde génération présentent un enrichissement de 100 à 1000 fois pour la plupart de ces métaux (hormis Sb et Ba), un enrichissement substantiel en Fe et Mn, un enrichissement supérieur à 10 fois en Ag, ainsi qu'un accroissement marque de l'enrichissement en Pb, Au, As et Ag au regard de Cu et Zn par rapport à la minéralisation de première génération. En comparaison des blendes de première génération, les blendes localised dans les veines de second génération sont enrichies en Cd, Mn, Fe d 'une façon comparable à lāenrichissement de laroche to tale. L'assemblage silicaté à Ca-Fe-Mg des veines suggére une température des fluides supérieure à 200Ā°C et peut-être dépassant les 300Ā°C; l'abondance de calcite dans ces veines suggére une influence du CO2 sur la minéralisation. Les inclusions fluides dans la blende de seconde génération livrent des températures moyennes d'homogénéisation autour de 306Ā°C.
Le recoupement par des plutons post-cinématiques dont l'âge est connu permet de cantonner la déformation et la minéralisation de seconde génération dans le gite de Lake Bond au début du Silurien. Une comparaison avec les autres gites présents dans le Groupe de Robert's Arm ainsi qu'avec des gites situés en d'autres points du centre de Terre-Neuve suggére un modèle métallogénique en deux étapes qui sont: (1) un épisode volcanogène précoce contemporain des roches éncaissantes ordoviciermes inférieures et (2) un hydrothermalisme eosilurien en liaison avec un cisaillement et un déplacement le long de failles majeures. On conele provisoirement cet hydrothermalisme avec un épisode repandu de minéralisation filonienne en or dans le centre de Terre-Neuve. Il semble qu'à Lake Bond, la minéralisation aurifere de seconde génération se soit supérposée aux zones de sulfures précoces, ce qui suggére un potentiel d'exploration pour les zones auriferes au sein des stockwerks de sulfures volcanogènes à faible teneur dans la ceinture de Buchans-Robert's Arm.
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Brief of Appellee, Magma Mining Co.: Thirteenth Annual Pace National Environmental Moot Court Competition
Get PDFAnchored multi-phasic osteochondral construct
Get PDFDisclosed are osteochondral constructs that can be utilized to encourage both bone and articular cartilage tissue repair in synovial joints. Disclosed constructs are composites including a hydrogel portion for implant in a cartilage defect site and an adjacent portion for implant in a bone defect site. The portion to be implanted in a bone defect site can include a polymeric/ceramic composite material. Disclosed constructs also include a polymeric anchor that can secure the construct at the desired site. Disclosed constructs can also include capillary channeled fibers within the bone portion of the construct that can provide improved nutrient flow to and waste flow from cells growing and developing on and in the construct
An experimental and computational investigation of a translating throat single expansion-ramp nozzle
Get PDFA translating throat single expansion-ramp nozzle (SERN) concept was designed to improve the off-design performance of a SERN with a large, fixed expansion ratio. The concept of translating the nozzle throat provides the SERN with a variable expansion ratio. An experimental and computational study was conducted to predict and verify the internal performance of this concept. Three nozzles with expansion ratios designed for low, intermediate, and high Mach number operating conditions were tested in the Jet-Exit Test Facility at the NASA Langley Research Center. Each nozzle was tested with a concave and a convex geometric expansion ramp surface design. Internal nozzle performance, paint-oil flow and focusing Schlieren flow visualization were obtained for nozzle pressure ratios (NPR's) up to 13. The Navier-Stokes code, PAB3D, with a k-epsilon turbulence model was utilized to verify experimental results at selected NPRs and to predict the performance at conditions unattainable in the test facility. Two-dimensional simulations were computed with near static free-stream conditions and at nozzle pressure ratios of 5, 9, and 13 for the concave ramp, low Mach number configuration and at the design NPR of 102 for the concave ramp, high Mach number configuration. Remarkable similarities between predicted and experimental flow characteristics, as well as performance quantities, were obtained
Clostridium difficile infection in the United States: A national study assessing preventive practices used and perceptions of practice evidence
Get PDFWe surveyed 571 US hospitals about practices used to prevent Clostridium difficile infection (CDI). Most hospitals reported regularly using key CDI prevention practices, and perceived their strength of evidence as high. The largest discrepancy between regular use and perceived evidence strength occurred with antimicrobial stewardship programs.Infect. Control Hosp. Epidemiol. 2015;36(8):969ā971</jats:p
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