The Neoproterozoic Franklin large igneous province on Victoria Island, Canada, is characterized by continental fl ood basalts and a sill-dominated feeder system. Field relationships indicate that fault-guided transfer zones allowed magma to jump up-section to form higher-level intrusions. Where sills connect to dikes and magmas moved upsection , roof and wall rocks are characterized by wide and intense contact-metamorphic haloes , consistent with throughfl ow of magma. The geometric constraints suggest that conduits may have opened episodically and then closed when magma pressure waned. The episodic nature of conduit opening events can explain the pulsed ascent of crystal slurries, and may also play a role in the deposition of Ni-sulfi des.

The Southern Feeder Dike Complex is part of the Franklin Large Igneous Province (LIP), exposed in the Minto Inlier of Victoria Island in the Canadian Arctic. Previous field and geochemical studies on the Franklin LIP considered its igneous rocks to be prospective for Fe-Ni-Cu mineralization. The Southern Feeder Dike Complex comprises a series of NW-SE-trending gabbroic intrusions and sedimentary hosts. Field and textural relationships show that the Complex intrusions were emplaced contemporaneously with Neoproterozoic normal faulting. Faulted contact zones correspond to prominent first derivative magnetic lineaments. Gabbroic dikes have intrusive contacts against brecciated country rock, and diabasic microxenoliths in basaltic matrices indicate multiple intrusive/brecciation events. Intrusive breccias are commonly overprinted by hydrothermal greenschist facies assemblages, with calcite + pyrite veins filling open spaces between breccia fragments. Late dikes emplaced into these heterogeneous breccias contain disseminated globular and net-textured sulfides suggesting that sulfide immiscibility was triggered on a local scale by assimilation of local wall rock. This inference is supported by elevated δ 34 S values of sulfides in these dikes, consistent with assimilation of country rocks. Wall-rock assimilation would have been facilitated by fault-related brecciation and cataclasis, which would expose extensive xenolith surface areas to fresh magma. Gossanous and meter-scale semimassive sulfide showings associated with dikes and sills located upsection from the Southern Feeder Dike Complex suggest that immiscible sulfide liquids may have been flushed downstream (or upsection) during replenishment of composite dike systems. Fault-mediated melt ascent along northwest-southeast faults has been documented elsewhere in the Minto Inlier, providing equivalent opportunities for wall-rock assimilation and consequent triggering of sulfide immiscibility and sulfide melt redistribution.The evidence preserved in the Complex confirms the Fe-Ni-Cu potential of the Franklin LIP and informs current models of ore deposit formation in conduit-type magmatic plumbing systems.

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This contribution addresses contact metamorphism and fluid flow in calcareous rocks of the Neoproterozoic Shaler Supergroup on Victoria Island, Arctic Canada. These processes occurred due to intrusion of gabbroic sills and dykes at c. 720 Ma during the Franklin magmatic event, which was associated with the break‐up of Rodinia. The intrusive sheets (sills and dykes) are a few metres to ∼50 m thick. Metasedimentary rocks were examined in three locations with very good exposures of vertical dykes feeding horizontal sills, the Northern Feeder Dyke (NFD) complex, the Southern Feeder Dyke (SFD) complex and the Uhuk Massif. In the NFD and SFD complexes, protoliths were limestones and dolostones with minor silicates, and at the Uhuk Massif, the protoliths were silty dolostones. At the time of magma emplacement, these locations were at depths of 1–4 km. The widths of contact aureoles are only several decametres wide, commensurate with thicknesses of the dykes and sills. Splays of tremolite mark incipient metamorphism. Highest grade rocks in the NFD and SFD complexes contain the prograde assemblage diopside + phlogopite whereas at Uhuk they contain the assemblage vesuvianite + garnet + diopside. The assemblages are successfully modelled with T–X(CO2)fluid pseudosections that suggest achievement of CO2‐rich fluid compositions due to early decarbonation reactions, followed by influx of aqueous fluids after peak metamorphism. Rapid heating of host rocks and short near‐peak temperature intervals are demonstrated by the prevalent morphology of diopside as radial splays of acicular crystals that appear to pseudomorph tremolite and by incomplete recrystallization of calcite in marbles. Calcsilicates in the roof of one sill at Uhuk experienced metasomatic influx of Fe that is evidenced by nearly pure andradite rims on grossular garnet. Vesuvianite, which overgrew the grossular portions of garnet, also contains ferric iron. Vesuvianite was partially consumed during retrograde growth of serpentine and andradite. The occurrence of serpentine in high‐grade portions of aureoles is consistent with eventual levelling‐off of temperatures between 350 and 400 °C, an inference that is supported by modelled conductive heat transfer from the cooling magma sheets. Focused fluid flow near intrusion‐wall rock contacts is demonstrated by narrow zones of anomalously low δ13C and δ18O values of carbonate minerals. Although the up to 5‰ decrease of both δ13C and δ18O values from sedimentary values is much smaller than is typical for calcsilicate aureoles around large plutons, it is greater than what could have been achieved by decarbonation alone. The decrease in δ13C is attributed to fluid‐mediated exchange with organic low‐13C carbon that is dispersed through the unmetamorphosed rocks and the decrease in δ18O is attributed to fluid‐mediated isotopic exchange with the gabbroic intrusive sheets. This study shows that when gabbroic sills and dykes intrude a sedimentary basin, (i) contact aureoles are likely to be narrow, only on the scale of ...

NTS 87-G/9 (Nalluryaq) and the southernmost part of NTS 87-G/16 are mostly underlain by Neoproterozoic Shaler Supergroup sedimentary rocks, with limestone and dolostone of the Boot Inlet and Jago Bay formations, quartz arenite of the Fort Collinson Formation, and gypsum evaporite of the Minto Inlet Formation. The latter locally form quarryable alabaster deposits as a result of contact metamorphism. Sedimentary rocks are injected by basaltic sills and dykes of Franklin age (ca. 720 Ma) that can be divided into older, more olivine-rich Type 1 intrusions and younger diabasic to feldspar-porphyritic Type 2 intrusions. Fe-oxide exoskarns are developed in the hangingwall panels of some synmagmatic normal faults. Strata are either flat-lying, or dip gently to the north or south to either side of the Walker Bay Anticline. Steeper bedding orientations occur near faults as a result of structural entrainment. A regional-scale basal unconformity separates Paleozoic clastic and carbonate rocks in the north from underlying Proterozoic rocks to the south, but the contact is often faulted, and isolated domains of Paleozoic rocks are preserved within graben. North-northwest-trending syn-magmatic (Proterozoic) and east-northeast-trending (Phanerozoic) normal faults are ubiquitous, breaking up the outcrop pattern into a series of polygonal blocks.