Contrasting Geology Across The Cradle Brook Thrust Zone: Subaerial vs Marine Precambrian Environments, Caledonia Highlands, New Brunswick

The Cradle Brook fault zone in southern New Brunswick separates highly deformed Precambrlan terranes reflecting radically different geological environments. The zone is comprised of major southward directed thrusts and is interpreted to represent, in part, the boundary between the Central and Eastern volcanic belts of the Caledonia Highlands. The Precambrian rocks north of the fault reflect subaerial and. locally, subaqueous deposition whereas those south of the fault reflect marine deposition. In addition to the differences in Precambrian stratigraphy, extensive areas south of the fault are underlain by felsic and mafic Intrusive bodies of probable late Precambrian age, and by Cambrian rocks that rest unconformably on the stratigraphy of the Eastern Volcanic Belt. Based on a limited number of chemical analyses, the volcanic piles exhibit calc-alkaline and weakly tholelitic affinities south and north of the fault, respectively. The structural and stratigraphic relationships imply that the subaerial rocks are older than the marine rocks and that the latter are probably near the top of the local Precambrian sequence. The abundance of intrusive rocks in the subaqueous sequence substantiate juxtaposition of very different geological regimes. R᳧SUM᳧ Au Nouveau-Brunswick m᳻ridional, la zone de failles de Cradle Brook s᳻pare des laniᳺres pr᳻ambriennes fortement d᳻form᳻es qui temoignent d' environnements g᳻ologiques radicalement diff᳻rents. Cette zone s'organise en chevauchements majeurs de direction sud-est. On croit qu'elle repr᳻sente, en partle, la frontiᳺre entre les ceintures volcaniques centrale et orientale des Monts Caledonia. Au nord de la faille, les roches pr᳻cambriennes relᳺvent essentiellement d'une accumulation subaᳺrienne et, localement, subaquatique, alors qu'au sud de la faille, elles trabissent un d᳻pᴀt marin. On doit ajouter aux diff᳻rences dans la stratigraphie pr᳻cambrienne de vastes ᳻tendues au sud de la faille qui comprennent des appareils intrusifs felsiques et mafiques, probablement tardi-pr᳻camhriens, et des assises cambriennes qui recouvrent en discordance la stratigraphie de la ceinture volcanique orientale. La prise en compte d'un nombre limite d'analyses chimiques r᳻vᳺle les affinites calco-alcalines et falblement tholᳺiitlques des empilements volcaniques sis, respectivement, au sud et au nord de la faille. [Traduit par le journal]