Fractionation and contamination of Maquereau Group lavas, southern Gaspé, Québec Appalachians

Abstract

Most Maquereau Group lavas are tholeiitic basalts that exhibit an Fe-Ti-enrichment trend. The tholeiites are divisible into incompatible-element-enriched and depleted types. Enriched tholeiites have chondrite-normalized La/Yb > 1 and higher incompatible element contents than do depleted, normal mid-ocean ridge basalt-like tholeiites. Subordinate transitional-alkaline basalts are even more enriched in TiO 2 , P 2 O 5 , Nb, and light rare-earth elements (REE). Intrasuite geochemical variations are consistent with coupled fractional crystallization and assimilation of Grenvillean continental crust or sediments derived therefrom. Assimilation leads to the development of characteristic enrichment in Ba, Th, Zr, and light REE. Intersuite variations cannot be accounted for through crystal fractionation or crustal contamination, and must reflect either source-mantle heterogeneity or mantle melting processes. Most major-and trace-element paleotectonic discriminants do not favor an arc-related environment for these lavas. An intracontinental rift or an incipient spreading ridge environment are most consistent with the geochemical data and field relationships.

Clinopyroxene trace element compositions of cumulate mafic rocks and basalts from the Hercynian Moroccan Central Meseta: Petrogenetic implications

“…Bédard and Wilson, 1997;Cottin et al, 1998). Moreover, most of the clinopyroxene major element data are in good agreement with the clinopyroxene compositions from anorogenic igneous provinces (Fig.…”

A lost arc-back-arc terrane of the Dunnage oceanic tract recorded in clasts from the Garin Formation and McCrea mélange in the Gaspé Appalachians of Québec

“…3): the McCrea mélange, and the forearc turbidites of the Arsenault Formation. The Maquereau-Mictaw inlier is a tectonic collage made up of Cambrian rift-related basalt, arkose, and slate of the Maquereau Group (Humber zone; Bédard and Wilson, 1997) juxtaposed against Dunnage zone rocks of the Rivière Port-Daniel mélange and the Mictaw Group (De Broucker, 1987). The Lower Ordovician McCrea and Rivière Port-Daniel mélanges are made up of tectonic slices and mappable blocks of serpentinite, listwaenite, granitic rocks, and basalt, and clasts of granitic gneiss, serpentinite, red slate, and calcareous siltstone embedded in a matrix of black shale and pebbly mudstone (De Broucker, 1987;Malo et al, 1992b (Malo and Bourque, 1993) are correlative and consist of turbiditic sandstones, shales, and minor tuffs.…”

“…Basaltic rocks of the mafi c-intermediate suite do not correlate with lavas of the Maquereau Group (Bédard and Wilson, 1997), and there is little resemblance with gabbros of the Pabos Suite (Figs. 7A and 16A), or with older (480-473 Ma) ophiolitic rocks of the Annieopsquotch accretionary tract (Lissenberg et al, 2005a;Zagorevski et al, 2006).…”