Reconstruction and evolution of Archean intracaldera facies: the Rouyn-Pelletier Caldera Complex, Abitibi greenstone belt, Canada.

Lyndsay Moore1, Réal Daigneault1, Hannah M Aird2, Neil Banerjee3 and Wulf U Mueller1, (1)Centre d'études sur les Ressources minérales (CERM), Département des sciences appliquées, UQAC, Chicoutimi, QC, Canada, (2)University of Puget Sound, Geology, Tacoma, WA, United States, (3)Western University, Department of Earth Sciences, London (Ontario), ON, Canada

Contact First Author: Lyndsay Moore; lyndsay.moore@uqac.ca

Previously Published Material: This presentation is a summary of a paper that is currently under revision by the Canadian Journal of Earth Sciences.

Abstract ID#: 36599

 

English Abstract:
The internal architecture of modern subaqueous volcanic edifices is rarely exposed and when visible, is difficult to access. Vertically-dipping Archean strata allow for the study of synvolcanic structures and the internal organization of subaqueous volcanic complexes. The Abitibi greenstone belt in Canada, and specifically the Blake River Group, hosts numerous subaqueous volcanic centres including the Blake River megacaldera complex (BRMCC). Within the BRMCC are three previously identified caldera complexes: the host Misema Caldera and the nested and overlapping New Senator and Noranda Calderas. Of particular interest is the southern sector of the New Senator Caldera (SNSC) and its close association with the 54 Mt Horne Au-rich volcanogenic massive sulfide (VMS) deposit.

Detailed mapping of volcanic and intrusive facies, along with site-specific geochemical and geochronological analysis at selected outcrop localities throughout the SNSC show that the stratigraphy of the sector is composed of mostly subaqueous effusive mafic volcanic sequences with intermittent felsic events. With the use of available structural data and the geometry of synvolcanic faults and dykes, volcanic and intrusive facies are grouped into facies assemblages. These facies assemblages compose a volcanic complex known as the Rouyn-Pelletier Caldera Complex. This study predominantly focuses on the Basal and Central Intracaldera Facies Assemblages (BIFA and CIFA respsectively) but also characterizes the other facies assemblages and places the Horne deposit within the context of the complex.

Facies of the BIFA represent the terminal stages of seamount construction and compose the first caldera floor. Following emplacement of those facies, a trapdoor collapse event occurred, allowing for the emplacement of the ponded lavas in the western CIFA. Piecemeal-type faulting follows this event and permits the extrusion and intrusion of facies of the eastern CIFA; forming yet another caldera floor. The caldera complex continues to build and shallows and a shift to more explosive activity occurs. This shift is interpreted to be one of the final phases of activity and is represented by the volcanic facies of the Horne deposit.

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