Tectono-stratigraphic evolution of the Early Proterozoic Wisconsin magmatic terranes of the Penokean Orogen

Abstract

The Early Proterozoic Penokean Orogen developed along the southern margin of the Archean Superior craton. The orogen consists of a northern deformed continental margin prism overlying an Archean basement and a southern assemblage of oceanic arcs, the Wisconsin magmatic terranes. The south-dipping Niagara fault (suture) zone separates the south-facing continental margin from the accreted arc terranes. The suture zone contains a dismembered ophiolite.The Wisconsin magmatic terranes consist of two terranes that are distinguished on the basis of lithology and structure. The northern Pembine-Wausau terrane contains a major succession of tholeiitic and calc-alkaline volcanic rocks deposited in the interval 1860-1889 Ma and a more restricted succession of calc-alkaline volcanic rocks deposited about 1835-1845 Ma. Granitoid rocks ranging in age from about 1870 to 1760 Ma intrude the volcanic rocks. The older succession was generated as island arcs and (or) closed back-arc basins above the south-dipping subduction zone (Niagara fault zone), whereas the younger one developed as island arcs above a north-dipping subduction zone, the Eau Pleine shear zone. The northward subduction followed deformation related to arc-continent collision at the Niagara suture at about 1860 Ma. The southern Marshfield terrane contains remnants of mafic to felsic volcanic rocks about 1860 Ma that were deposited on Archean gneiss basement, foliated tonalite to granite bodies ranging in age from about 1890 to 1870 Ma, and younger undated granite plutons. Following amalgamation of the two arc terranes along the Eau Pleine suture at about 1840 Ma, intraplate magmatism (1835 Ma) produced rhyolite and anorogenic alkali-feldspar granite that straddled the internal suture.L'orogtne du PCnokten d'lge prottrozoique prtcoce s'est CdifiC le long de la marge sud du craton Suptrieur de I'Archten. L'orogtne inclut, dans sa partie nord, un prisme de marge continentale dtformt qui repose sur un socle archten, et dans le sud un assemblage d'arcs ocCaniques, les terranes magmatiques de Wisconsin. La zone de failles Niagara (suture) inclinCes vers le sud stpare la face sud de la marge continentale d'avec les terranes d'arcs accrttts. La zone de suture renferme une ophiolite dCmembrte.Les terranes magmatiques de Wisconsin sont form& de deux terranes qui diffirent par leurs lithologies et leurs structures. Le terrane de Pembine-Wausau du nord est composC principalement d'une succession de roches volcaniques tholttitiques et calco-alcalines dkposk durant l'intervalle 1860 -1889 Ma et d'une succession d'ttendue plus restreinte des roches volcaniques calco-alcalines dCposte aux environs de 1835-1845 Ma. Des roches granitoides d'lges qui varient de 1870 B 1760 Ma recoupent les roches volcaniques. La succession la plus vieille a crCC les arcs insulaires et (ou) les bassins d'arrikrearc fermts sus-jacents B la zone de subduction plongeant vers le sud (zone de failles Niagara), tandis que la plus jeune succession a formt des arcs insulaires B l'aplomb de la zone de subducti...

Geochemistry of Paleoproterozoic Gunflint Formation carbonate: Implications for hydrosphere-atmosphere evolution

“…This supports the idea that the conglomeratic layer was formed by the 1850±1 Ma Sudbury impact event. Given that Penokean and Trans-Hudson volcanism occurred throughout the 1860 to 1832 Ma interval (Sims et al, 1989;Gordon et al, 1990), it is plausible that surface volcanic ash was locally present at the time of the impact and was caught-up in the base-surge cloud, thereby providing a source for the zircons now found in the matrix of the conglomeratic layer. If so, the volcanic ash was some 4-8 Ma older than the impact event .…”

Differentiation and emplacement of the Worthington Offset Dike of the Sudbury impact structure, Ontario

“…This has led to the development of mesoscopic planar and linear metamorphic mineral fabrics in these rocks, which are generally attributed to the Paleoproterozoic Penokean orogeny (e.g., Sims et al 1989). In the Sudbury area, the intensity and metamorphic grade of these fabrics decrease generally towards the north.…”

Evolution of Palaeoproterozoic mafic intrusions located within the thermal aureole of the Sudbury Igneous Complex, Canada: Isotopic, geochronological and geochemical evidence

“…Lastly, the extensive metamorphism of the Drury has not affected the adjacent SIC, and must be assumed to reflect earlier, Penokean metamorphism. The approximately syn-SIC-aged Penokean Orogeny is not manifested by magmatic activity anywhere in Ontario (e.g., van Breemen and Davidson, 1988;Prevec, 1995), unlike further to the southwest (e.g., Sims et al, 1989), so it is considered to be equally unlikely that the Drury Twp represents the sole manifestation of Penokean melting, locally. Therefore, a total magmatic origin for the Drury Twp intrusion is considered to be extremely unlikely.…”