Lisa Gibson

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Polyorogenic reworking of ore‐controlling shear zones at the South Range of the Sudbury impact structure: A telltale story from in situ U–Pb titanite geochronology

Terra Nova (2018)

Konstantinos Papapavlou James Darling Peter C. Lightfoot Stéphanie Lasalle Lisa Gibson

Abstract The post‐impact orogenic evolution of the world class Ni–Cu– PGE Sudbury mining camp in Ontario remains poorly understood. New temporal constraints from ore‐controlling, epidote–amphibolite facies shear zones in the heavily mineralised Creighton Mine (Sudbury, South Range) illuminate the complex orogenic history of the Sudbury structure. In situ U–Pb dating of shear‐hosted titanite grains by LA ‐ ICP ‐ MS reveals new evidence for shear zone reworking during the Yavapai (ca. 1.77–1.7 Ga), Mazatzalian–Labradorian (1.7–1.6 Ga) and Chieflakian–Pinwarian (1.5–1.4 Ga) accretionary events. The new age data show that the effects of the Penokean orogeny (1.9–1.8 Ga) on the structural architecture of the Sudbury structure have been overestimated. At a regional scale, the new titanite age populations corroborate that the Southern Province of the Canadian Shield documents the same tectonothermal episodes that are recorded along orogenic strike within the accretionary provinces of the Southwestern United States.

Titanite

Geochronology

Orogeny

10.1111/ter.12332

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Citations (13)

Thermo‐mechanical interaction of a large impact melt sheet with adjacent target rock, Sudbury impact structure, Canada

Meteoritics and Planetary Science (2019)

Paul Leon Göllner Torben Wüstemann Lisa Bendschneider Sebastian Reimers Martin Clark

Abstract The 1.85 Ga Sudbury Igneous Complex (SIC) and its thermal aureole are unique on Earth with regard to unraveling the effects of a large impact melt sheet on adjacent target rocks. Notably, the formation of Footwall Breccia, lining the basal SIC, remains controversial and has been attributed to impact, cratering, and postcratering processes. Based on detailed field mapping and microstructural analysis of thermal aureole rocks, we identified three distinct zones characterized by static recrystallization, incipient melting, and crystallization textures. The temperature gradient in the thermal aureole increases toward the SIC and culminates in a zone of partial melting, which correlates spatially with the Footwall Breccia. We therefore conclude that assimilation of target rock into initially superheated impact melt and simultaneous deformation after cratering strongly contributed to breccia formation. Estimated melt fractions of the Footwall Breccia amount to 80 vol% and attest to an extreme loss in mechanical strength and, thus, high mobility of the Breccia during assimilation. Transport of highly mobile Footwall Breccia material into the overlying Sublayer Norite of the SIC and vice versa can be attributed to Raleigh–Taylor instability of both units, long‐term crater modification caused by viscous relaxation of crust underlying the Sudbury impact structure, or both.

Breccia

Impact structure

Migmatite

Shock metamorphism

10.1111/maps.13268

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Citations (6)

Park Volcanics, Murihiku Terrane, New Zealand: Petrology, petrochemistry, and tectonic significance

New Zealand Journal of Geology and Geophysics (1996)

D. S. Coombs Nick Cook Yousuke Kawachi R. D. Johnstone Lisa Gibson

Abstract The Late Triassic to Early Jurassic Park Volcanics Group comprises minor shallow intrusive and extrusive bodies emplaced during mainly marine sedimentation of the Murihiku Terrane, southern New Zealand. Gowan Andesite in western Southland and Glenham Porphyry andesites in eastern Southland are high‐K andesites. Glassy examples have commonly lost K during alteration. Orthoclase contents of Or3.6–3.7 in plagioclase phenocrysts at An50 confirm the high‐K nature of the melts at the time of phenocryst crystallisation. The Gowan andesites have higher Fe/Mg than the Glenham and related differences in minor element chemistry suggesting lower fO 2during fractionation of the parent magma. Pinney Volcanics in western Southland are mostly high‐K trachydacites but, like Glenham Porphyry, include minor rhyolite. Barnicoat Andesite in the Nelson area is medium‐K olivine andesite, marginally tholeiitic in terms of its FeO∗/MgO versus SiO2behaviour, but otherwise is typically calc‐alkaline, as are the Gowan, Glenham, and Pinney. Analyses of pyroxenes (augites, orthopyroxenes, reaction rim and groundmass pigeonites) reveal xenocrysts recording an early stage of magma fractionation, slight iron enrichment in the andesite stage, and lowered Fe/Mg and increased Ca contents in augites of the most felsic rocks. Titanian tschermakite and litanian magnesio‐tschermakite of deep‐seated origin participated in fractionation leading to the Pinney Volcanics, and magnesio‐hornblende, edenite, and biotite crystallised as minor late stage minerals following high‐level emplacement of Gowan Andesite and siliceous Glenham Porphyry members. Low 87Sr/86Sr ratios (c. 0.7034–0.7037), REE and multi‐element distribution patterns, and the mineralogical features collectively suggest fractionation of the andesites from parental basalt originating in an enriched mantle wedge above a subduction zone, with minimal contamination by continental crust. High‐K andesites appear to be unknown in clearly established forearc basins whereas they are characteristic of back‐arc sites. At the time of emplacement of the Park Volcanics, the southern Murihiku sedimentary basin is therefore unlikely to have occupied a forearc setting. The volcanic arc that provided detritus and ash deposits to the basin at that time was probably sited on a strip of largely Proterozoic continental crust detached from the Gondwana mainland by a marginal sea with a subduction zone dipping away from that marginal sea under the volcanic arc, with the Murihiku sedimentary basin towards the rear on the proto‐Pacific side. Drumduan Group, with a low‐temperature, high‐pressure metamorphic overprint, and other largely volcaniclastic terrane fragments in the Median Tectonic Zone of southern New Zealand, may be arc‐front remnants of the same arc system.

Phenocryst

Andesites

Felsic

Hornblende

10.1080/00288306.1996.9514727

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Citations (25)

Structural controls on the localization of the mineralized Copper Cliff embayment and the Copper Cliff Offset dyke, Sudbury Igneous Complex, Canada

Ore Geology Reviews (2021)

Lucie Mathieu Ulrich Riller Lisa Gibson Peter C. Lightfoot

Cliff

Dike

10.1016/j.oregeorev.2021.104071

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Citations (2)