Preliminary digital geologic map of the Penokean (early Proterozoic) continental margin in northern Michigan and Wisconsin

1999 ◽  
Author(s):  
W.F. Cannon ◽  
Doug Ottke
Keyword(s):  
Continental Margin ◽  
Early Proterozoic ◽  
Geologic Map ◽  
Northern Michigan

scholarly journals Geochemical features, sources and geodynamic settings of accumulation of the cambrian sedimentary rocks of the Mel’gin trough (Bureya continental massif)

2019 ◽  
Vol 64 (5) ◽  
pp. 503-519
Author(s):  
R. O. Ovchinnikov ◽  
A. A. Sorokin ◽  
V. P. Kovach ◽  
A. B. Kotov
Keyword(s):  
Continental Margin ◽  
Active Continental Margin ◽  
Sedimentary Rocks ◽  
Detrital Zircons ◽  
Igneous Rocks ◽  
Early Cambrian ◽  
Relative Probability ◽  
Early Proterozoic ◽  
Geodynamic Settings ◽  
Probability Plots

The first data about geochemical features of the Cambrian sedimentary rocks of the Mel’gin trough of the Bureya continental Massif, as well as ages of detrital zircons of them are obtained. It is established, that among the detrital zircons from the sandstones of the Chergilen and Allin formations of the Mel’gin trough zircons with Late Riphean (peaks on relative probability plots – 0.78, 0.82, 0.94, 1.04 Ga) and Early Riphean (peaks on relative probability plots – 1.38, 1.45, 1.64 Ga) ages predominate. The single grains have a Middle Riphean, Early Proterozoic and Late Archean ages. We can suppose, that the sources of Late Riphean detrital zircons from sandstones of the Chergilen and Allin formations are igneous rocks of gabbro-granitoids (940–933 Ma) and granite- leucogranites (804–789 Ma) association, identified in the Bureya continental Massif. We can`t assume, what kind of rocks were the source for Middle Riphean and older detrital zircons from the Cambrian sedimentary rocks of the Bureya continental Massif, because in this massif still do not identified complexes older Late Riphean age. The most probable geodynamic conditions of accumulation of the Cambrian deposits of the Mel’gin trough is the conditions of active continental margin, which is corresponding to of Early Cambrian granitoids magmatism.

Striding-Athabasca mylonite zone: implications for the Archean and Early Proterozoic tectonics of the western Canadian Shield

1995 ◽  
Vol 32 (2) ◽  
pp. 178-196 ◽  
Author(s):  
Simon Hanmer ◽  
Michael Williams ◽  
Chris Kopf
Keyword(s):  
Continental Margin ◽  
Canadian Shield ◽  
Magmatic Evolution ◽  
Tectonic Zone ◽  
Early Proterozoic ◽  
Plate Margin ◽  
Mylonite Zone ◽  
Northern Saskatchewan ◽  
Archean Crust ◽  
Rifted Margin

Study of the northern Saskatchewan–District of Mackenzie segment of the Snowbird tectonic zone suggests that fragments of relatively stiff mid-Archean crust, possibly arc related, have controlled the localization, shape, and complex kinematics of the multistage Striding–Athabasca mylonite zone during the Archean, as well as the geometry of the Early Proterozoic rifted margin of the western Churchill continent. By the late Archean, the Striding–Athabasca mylonite zone was located in the interior of the western Churchill continent, well removed from the contemporaneous plate margins. Except for the Alberta segment, the Snowbird tectonic zone was not the site of an Early Proterozoic plate margin. We suggest that the geometry of the Archean–Early Proterozoic boundary in the western Canadian Shield represents a jagged continental margin, composed of a pair of reentrants defined by rifted and transform segments. These segments were inherited from Early Proterozoic breakup and controlled by the Archean structure of the interior of the western Churchill continent. The geometry of this margin appears to have strongly influenced the Early Proterozoic tectono-magmatic evolution of the western Canadian Shield.

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

1989 ◽  
Vol 26 (10) ◽  
pp. 2145-2158 ◽  
Author(s):  
P. K. Sims ◽  
W. R. Van Schmus ◽  
K. J. Schulz ◽  
Z. E. Peterman
Keyword(s):  
Subduction Zone ◽  
Continental Margin ◽  
Volcanic Rocks ◽  
Alkali Feldspar ◽  
Suture Zone ◽  
Island Arcs ◽  
Calc Alkaline ◽  
The South ◽  
Early Proterozoic ◽  
Felsic Volcanic

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.

Tectonic evolution at an early proterozoic continental margin: The Svecokarelides of eastern Finland

1984 ◽  
Vol 1 (3-5) ◽  
pp. 359-386 ◽  
Author(s):  
A.F. Park ◽  
D.R. Bowes ◽  
N.M. Halden ◽  
T.J. Koistinen
Keyword(s):  
Continental Margin ◽  
Tectonic Evolution ◽  
Early Proterozoic ◽  
Eastern Finland

A Discussion on the evolution of the Precambrian crust - Evolution of an early Proterozoic continental margin: the Coronation geosyncline and associated aulacogens of the northwestern Canadian shield

1973 ◽  
Vol 273 (1235) ◽  
pp. 547-581 ◽  
Keyword(s):  
Continental Shelf ◽  
Continental Margin ◽  
Regional Metamorphism ◽  
Sedimentary Rocks ◽  
Fault System ◽  
Shelf Edge ◽  
The West ◽  
Western Margin ◽  
Early Proterozoic ◽  
Continental Rise

The Coronation geosyncline developed in the early Proterozoic along the western margin of a continental platform (the Slave Province) of Archaean rocks older than 2300 Ma, and culminated between 1725 and 1855 Ma ago with the emplacement of a pair of batholiths (the Bear Province). The evolution of the geosyncline has a strong family resemblance to Phanerozoic geosynclines believed to delineate ancient continental margins and have been controlled by global plate interactions. Such geosynclines are unknown in Archaean orogenic belts, from which it is inferred that creation of the first large rigid continental platforms marked the end of the Archaean and the beginnings of actualistic plate tectonics. The geosyncline began with deposition of a westward-facing continental shelf, consisting of a lower formation dominated by orthoquartzite, derived from the platform, and an upper cyclic stromatolitic dolomite formation. West of the shelf edge, the dolomite passes abruptly into a much thinner mudstone sequence with dolomite debris-flows, and the orthoquartzite into a thick laminated silt and mudstone sequence with quartzite turbidites. The oldest rocks west of the shelf edge, an area interpreted to have been a continental rise, are pillow basalts and volcanic breccias, extruded above a basement of unknown character. The principal turning point in the evolution of the geosyncline came with the foundering of the continental shelf. It is draped by a thin laminated pyritic black mudstone sequence, overlain by a westward-thickening clastic wedge resulting from intrusion and erosion of the batholiths to the west. The clastic wedge begins with a thick sequence of coarse greywacke turbidites that passes eastward into concretionary mudstone on the platform. The mudstone grades upward into laminated shaly limestone with minor greywacke turbidites, overlain in turn by cross-bedded red lithic sandstone. The supracrustal rocks of the geosyncline have been compressed and tectonically transported toward the platform. Adjacent to the batholithic belt, the continental rise and clastic wedge sequences are penetratively deformed and recrystallized by regional low-pressure metamorphism. To the east, the unmetamorphosed continental shelf and clastic wedge sequences have been flexurally folded and overthrust above a basal detachment surface. East of the thrust zone, relatively thin rocks on the platform are nearly flat-lying except around large anticlinal basement uplifts. Unusual features of the platform are its two aulacogens - long-lived deeply subsiding fault troughs that extend at high angles from the geosyncline far into the interior of the platform. During every phase in the evolution of the geosyncline, the aulacogens received much thicker sedimentary sequences, commonly with the addition of basaltic volcanics, than adjacent parts of the platform. Although equal in thickness to the geosyncline, the aulacogens were never subjected to the batholithic intrusions, regional metamorphism or low-angle overthrusting characteristic of the geosyncline. The Athapuscow aulacogen, in the region of Great Slave Lake, is interpreted as having been an incipient rift, located over a crustal arch, during the continental shelf stage of the geosyncline, but sagged to become a crustal downwarp during the clastic wedge stage, ultimately with sufficient transverse compression to produce broad folds. Finally, the aulacogen became part of a regional transcurrent fault system, along which thick fanglomerates accumulated in local troughs. The batholithic belt consists of two batholiths, eroded to different depths, separated by the northtrending 350 km long Wopmay River fault. The Hepburn batholith, east of the fault, is a composite intrusion of mesozonal granodiorite plutons. The foliated and migmatitic borders of the plutons are normally concordant with wall rock sheaths of sillimanitic paragneiss. Along the eastern margin of the batholith, metamorphosed rocks of the continental rise sequence dip gently to the west beneath the batholithic rocks. Belts of intensely deformed and metamorphosed supracrustal rocks within the batholithic terrain include sequences of pillow basalt, pelites and granite-pebble conglomerate, perhaps the lower part of the continental rise deposited during the initial rifting of the continental margin. The Great Bear batholith, west of the fault, consists of discordant epizonal plutons, mostly adamellite, that intrude broadly folded but regionally unmetamorphosed sequences of welded rhyodacitic ash-flow tuff, trachybasalt and derived sedimentary rocks. The volcanic rocks, intruded by dense dyke swarms radiating from the plutons and by felsite plugs, are interpreted to be comagmatic with the plutons. Mapping is as yet insufficient to establish, speculations aside, the possible relations of the two batholiths to arc-trench systems. Furthermore, the western margin of the batholithic belt, a region of critical importance, is covered by a veneer of younger Proterozoic and Paleozoic sedimentary rocks. Until fossil arc-trench systems are outlined, the contention that the Coronation Geosyncline involved global plate interactions is based on indirect evidence - the analogous evolution of the geosyncline east of the batholithic belt with Phanerozoic geosynclines in which fossil arc-trench systems have been found.

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