Petrogenesis of the Neoarchean (2.7 Ga) Poularies intrusion: Geochemical evolution of a shallow syn-volcanic granitoid complex from the Abitibi granite-greenstone belt, Québec

Abstract

The Poularies igneous complex is a Neoarchean (2728 Ma) intrusion composed of diorite, quartz diorite, hornblende tonalite, and biotite tonalite. It is was emplaced into the shallow crust of the Abitibi granite-greenstone belt during volcanic cycle 1 (2730–2725 Ma) and is contemporaneous with the eruption of mafic (Stoughton-Roquemaure Group) and silicic volcanic rocks (Hunter Mine Group). The petrogenetic relationship between the silicic rocks of the Poularies igneous complex is not constrained. In this study we test the petrological association between the different rock types of the Poularies complex using fractional crystallization modeling. Hydrous (H₂O = 3 wt%) fractional crystallization modeling using a ‘primitive’ intermediate starting composition demonstrates that all rock types of the Poularies complex can be generated from a common parental magma in the upper crust (1 kbar) under mildly oxidizing conditions (ΔFMQ = 0). Moreover, it is demonstrated that the parental magma of the Poularies complex was likely derived by partial melting of mafic rocks from the Abitibi granite-greenstone belt. We conclude that the Poularies complex is representative of a magma chamber that generated the silicic lavas of the spatially associated Hunter Mine Group in a rifting or tensional plate stress environment. Our model may be applicable to other shallow syn-volcanic plutons of the Abitibi granite-greenstone belt.