Softening the Lower Crust: Modes of Syn-Transport Transposition Around and Adjacent to a Deep Crustal Granulite Nappe, Parry Sound Domain, Grenville Province, Ontario, Canada

The Parry Sound domain is a granulite nappe-stack transported cratonward during reactivation of the ductile lower and middle crust in the late convergence of the Mesoproterozoic Grenville orogeny. Field observations suggest the following with respect to the ductile sheath: (1) Formation of a carapace of transposed amphibolite facies gneiss derived from and enveloping the western extremity of the Parry Sound domain and separating it from high-strain gneiss of adjacent allochthons. This ductile sheath formed dynamically around the moving granulite nappe through the development of systems of progressively linked shear zones. (2) Transposition initiated by hydration (amphibolization) of granulite facies gneiss by introduction of fluid along cracks accompanying pegmatite emplacement. Shear zones nucleated along pegmatite margins and subsequently linked and rotated. The source of the pegmatites was most likely subjacent migmatitic and pegmatite-rich units or units over which Parry Sound domain was transported. Comparison of gneisses of the ductile sheath with high-strain layered gneiss of adjacent allochthons show the mode of transposition of penetratively layered gneiss depended on whether or not the gneiss protoliths were amphibolite or granulite facies tectonites before initiation of transposition, resulting in, e.g., folding before shearing, no folding before shearing, respectively. Meter-scale truncation along high-strain gradients at the margins of both types of transposition-related shear zones observed within and marginal to Parry Sound domain mimic features at kilometer scales, implying that apparent truncation by transposition originating in a manner similar to the ductile sheath may be a common feature of deep crustal ductile reworking. Citation: Culshaw, N., C. Gerbi, and J. Marsh (2010), Softening the lower crust: Modes of syn-transport transposition around and adjacent to a deep crustal granulite nappe, Parry Sound domain, Grenville Province, Ontario, Canada, Tectonics, 29, TC5013, doi:10.1029/2009TC002537

Depositional and tectonic setting of the Paleoproterozoic Lower Aillik Group, Makkovik Province, Canada: evolution of a passive margin-foredeep sequence based on petrochemistry and U-Pb (TIMS and LAM-ICP-MS) geochronology

26 page(s

Coeval migmatites and granulites, Muskoka domain, southwestern Grenville Province, Ontario

We present new field observations and petrologic and geochronological data from the Muskoka domain in the southwestern Grenville Province of Ontario in an attempt to constrain the relationship between amphibolite-facies and granulite-facies gneisses in areas of transitional metamorphic grade, and to examine their implication for tectonometamorphic models for the Grenville Province of Ontario. The predominant medium-grained amphibolite-facies migmatitic orthogneisses of the Muskoka domain contain several generations of leucosome, some of which are related to southeast-directed extensional structures. The amphibolite-facies granitoid gneisses contain numerous mafic enclaves with granulite-facies assemblages recrystallized from anhydrous precursors during Grenvillian metamorphism. Other associated granulites are characterized by their patchy occurrence and gradational contacts, similar to the charnockites in southern India. Patchy granulites, leucocratic vein networks in mafic enclaves, and crosscutting leucocratic granulite veins are interpreted to have formed as a result of local differences in reaction sequences and (or) fluid compositions. The U�Pb zircon lower intercept age of the patchy granulites overlaps with the previously determined range of 1080�1060 Ma for high-grade metamorphism in the Muskoka domain, while zircon and titanite from a crosscutting granulite vein crystallized at about 1065�1045 Ma, supporting a Grenvillian age for granulite formation. Peak metamorphic conditions of 750�850°C and 10�11.5 kbar (1 kbar = 100 MPa) were determined from the mafic enclaves, whereas the more felsic migmatites reequilibrated at somewhat lower temperatures. The high temperatures caused extensive migmatization and facilitated rheological weakening of the Muskoka domain 10�25 million years after the start of the Ottawan orogeny in the Central Gneiss Belt

Culshaw et al, dataset for BDR paper

Spreadsheet containing raw data and statistical analyses for Figures 1, 4, 5, 6 and 8

Ramp-Flat Geometry within the Central Kapuskasing Uplift? Evidence from Potential Field Modeling Results

Potential field data constrained by seismic reflection, seismic refraction, geologic, and physical-properties data have been used to study the deep crustal structure of the central Kapuskasing uplift. The Val Rita block is interpreted as a thrust sheet of granulites detached at mid-crustal depths and uplifted along a ramp producing an arched, double granulite layer. A thin thrust sheet of southward-thickening granulites best describes the Groundhog River bloc, whereas simple thrusting along a ramp characterizes the Chapleau block. From this interpretation, a sequential evolution of the Kapuskasing uplift is proposed

Developing skills via work placements in accounting: Student and employer views

This paper evaluates the development of skills during a work placement year within a Scottish accounting degree. It discusses the history of placements within higher education, the advantages and disadvantages of placements from student and employer perspectives, and work placement as a vehicle for developing personal transferable skills. Students and employers involved in work placements agreed that they were effective in developing a range of skills. Their views were then compared with those of students at a similar university without a placement degree. Degrees including a work placement were found to be a useful complement to more traditionally structured degrees