Growth and demise of an Archean carbonate platform, Steep Rock Lake, Ontario, Canada

1999 ◽  
Vol 36 (4) ◽  
pp. 565-584 ◽  
Author(s):  
Timothy M Kusky ◽  
Peter J Hudleston
Keyword(s):  
Carbonate Platform ◽  
Volcanic Rocks ◽  
Evolutionary Model ◽  
Biological Processes ◽  
Metasedimentary Rocks ◽  
Carbonate Sedimentation ◽  
Volcaniclastic Rocks ◽  
The Witch ◽  
Flexural Bulge ◽  
Rock Lake

The Steep Rock Group of northwest Ontario's Wabigoon subprovince is one of the world's thickest Archean carbonate platform successions. It was deposited unconformably over a 3001-2928 Ma gneissic terrane, and contains a remarkable group of biogenic and oolitic limestones, dolostones, micrites, and karst breccias capped by a thick paleosol developed between and over karst towers. The presence of aragonite fans, herringbone calcite, and rare gypsum molds suggests that the carbonate platform experienced at least local anaerobic and hypersaline depositional conditions. This sequence shows that a combination of chemical and biological processes was able to build a carbonate platform 500 m thick by 3 billion years ago. The carbonate platform is structurally overlain by a mixture of complexly deformed rocks of the Dismal Ashrock forming a mélange with blocks of ultramafic volcaniclastic rocks, mafic volcanics, carbonate, tonalite, lenses of Fe-ore rock, and metasedimentary rocks, in a shaly, serpentinitic, and fragmental ultramafic volcaniclastic matrix. The mélange shows evidence of polyphase deformation, with early high-strain fabrics formed at amphibolite facies, and later superimposed brittle fabrics related to the final emplacement of the mélange over the carbonate platform. An amphibolite- through greenschist-grade shear zone marks the upper contact of the mélange with overlying mafic volcanic and tuffaceous rocks of the ca. 2932 Ma Witch Bay allochthon, interpreted as a primitive island arc sequence. We suggest an evolutionary model for the area that begins with rifting of an arc sequence (Marmion Complex of the Wabigoon arc) that initiated subsidence and sedimentation on the Steep Rock platform and its correlatives that extend for a restored strike length exceeding 1000 km. Shallow water carbonate sedimentation continued until the platform was uplifted on the flanks of a flexural bulge related to the approach of the Witch Bay allochthon, representing collision of the rifted arc margin of the Wabigoon subprovince with the Witch Bay arc. Mélange of the Dismal Ashrock was formed as off-axis volcanic rocks were accreted to the base of the Witch Bay allochthon prior to its collision with the Steep Rock platform.

scholarly journals From Ordovician nascent to early Permian mature arc in the southern Altaids: Insights from the Kalatage inlier in the Eastern Tianshan, NW China

Geosphere ◽  
2021 ◽  
Author(s):  
Qigui Mao ◽  
Jingbin Wang ◽  
Wenjiao Xiao ◽  
Brian F. Windley ◽  
Karel Schulmann ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Evolutionary Model ◽  
Early Permian ◽  
Calc Alkaline ◽  
Eastern Tianshan ◽  
Central Asian ◽  
Intrusive Rocks ◽  
Volcaniclastic Rocks ◽  
Felsic Volcanic ◽  
Potassium Enrichment

The Kalatage inlier in the Dananhu-Haerlik arc is one of the most important arcs in the Eastern Tianshan, southern Altaids (or Central Asian orogenic belt). Based on outcrop maps and core logs, we report 16 new U-Pb dates in order to reconstruct the stratigraphic framework of the Dananhu-Haerlik arc. The new U-Pb ages reveal that the volcanic and intrusive rocks formed in the interval from the Ordovician to early Permian (445–299 Ma), with the oldest diorite dike at 445 ± 3 Ma and the youngest rhyolite at 299 ± 2 Ma. These results constrain the ages of the oldest basaltic and volcaniclastic rocks of the Ordovician Huangchaopo Group, which were intruded by granite- granodiorite-diorite plutons in the Late Ordovician to middle Silurian (445–426 Ma). The second oldest components are intermediate volcanic and volcaniclastic rocks of the early Silurian Hongliuxia Formation (S1h), which lies unconformably on the Huangchaopo Group and is unconformably overlain by Early Devonian volcanic rocks (416 Ma). From the mid- to late Silurian (S2-3), all the rocks were exhumed, eroded, and overlain by polymictic pyroclastic deposits. Following subaerial to shallow subaqueous burial at 416–300 Ma by intermediate to felsic volcanic and volcaniclastics rocks, the succession was intruded by diorites, granodiorites, and granites (390–314 Ma). The arc volcanic and intrusive rocks are characterized by potassium enrichment, when they evolved from mafic to felsic and from tholeiitic via transitional and calc-alkaline to final high-K calc- alkaline compositions with relatively low initial Sr values, (87Sr/86Sr)i = 0.70391–0.70567, and positive εNd(t) values, +4.1 to +9.2. These new data suggest that the Dananhu-Haerlik arc is a long-lived arc that consequently requires a new evolutionary model. It began as a nascent (immature) intra-oceanic arc in the Ordovician to early Silurian, and it evolved into a mature island arc in the middle Silurian to early Permian. The results suggest that the construction of a juvenile-to-mature arc, in combination with its lateral attachment to an incoming arc or continent, was an important crustal growth mechanism in the southern Altaids.

The Peninsular Ranges Batholith: an insight into the evolution of the Cordilleran batholiths of southwestern North America

1988 ◽  
Vol 79 (2-3) ◽  
pp. 105-121 ◽  
Author(s):  
L. T. Silver ◽  
B. W. Chappell
Keyword(s):  
Baja California ◽  
Volcanic Rocks ◽  
Oceanic Lithosphere ◽  
Radiometric Dating ◽  
Island Arcs ◽  
Magmatic Arc ◽  
Metasedimentary Rocks ◽  
Basaltic Composition ◽  
Peninsular Ranges ◽  
General Aspects

ABSTRACTThe Peninsular Ranges Batholith of southern and Baja California is the largest segment of a Cretaceous magmatic arc that was once continuous from northern California to southern Baja California. In this batholith, the emplacement of igneous rocks took place during a single sequence of magmatic activity, unlike many of the other components of the Cordilleran batholiths which formed during successive separate magmatic episodes. Detailed radiometric dating has shown that it is a composite of two batholiths. A western batholith, which was more heterogeneous in composition, formed as a static magmatic arc between 140 and 105 Ma and was intrusive in part into related volcanic rocks. The eastern batholith formed as a laterally transgressing arc which moved away from those older rocks between 105 and 80 Ma, intruding metasedimentary rocks. Rocks of the batholith range from undersaturated gabbros through to felsic granites, but tonalite is the most abundant rock throughout. Perhaps better than elsewhere in the Cordillera, the batholith shows beautifully developed asymmetries in chemical and isotopic properties. The main gradients in chemical composition from W to E are found among the trace elements, with Ba, Sr, Nb and the light rare earth elements increasing by more than a factor of two, and P, Rb, Pb, Th, Zn and Ga showing smaller increases. Mg and the transition metals decrease strongly towards the E, with Sc, V and Cu falling to less than half of their value in the most westerly rocks. Oxygen becomes very systematically more enriched in18O from W to E and the Sr, Nd and Pb isotopic systems change progressively from mantle values in the W to a more evolved character on the eastern side of the batholith. In detail the petrogenesis of the Peninsular Ranges Batholith is not completely understood, but many general aspects of the origin are clear. The exposed rocks, particularly in the western batholith, closely resemble those of present day island arcs, although the most typical and average tonalitic composition is distinctly more felsic than the mean quartz diorite or mafic andesite composition of arcs. Chemical and isotopic properties of the western part of the batholith indicate that it formed as the root of a primitive island arc on oceanic lithosphere at a convergent plate margin. Further E, the plutonic rocks appear to have been derived by partial melting from deeper sources of broadly basaltic composition at subcrustal levels. The compositional systematics of the batholith do not reflect a simple mixing of various end-members but are a reflection of the differing character of the source regions laterally and vertically away from the pre-Cretaceous continental margin.

Nd isotopic characteristics of metamorphic and plutonic rocks of the Coast Mountains near Prince Rupert, British Columbia

1998 ◽  
Vol 35 (5) ◽  
pp. 556-561 ◽  
Author(s):  
P J Patchett ◽  
G E Gehrels ◽  
C E Isachsen
Keyword(s):  
British Columbia ◽  
Volcanic Rocks ◽  
Metamorphic Rocks ◽  
Published Data ◽  
Isotopic Data ◽  
Crustal Component ◽  
Coast Mountains ◽  
Crustal Rocks ◽  
Metasedimentary Rocks ◽  
Plutonic Rocks

Nd isotopic data are presented for a suite of metamorphic and plutonic rocks from a traverse across the Coast Mountains between Terrace and Prince Rupert, British Columbia, and for three contrasting batholiths in the Omineca Belt of southern Yukon. A presumed metamorphic equivalent of Jurassic volcanic rocks of the Stikine terrane gives epsilon Nd = +6, and a number of other metaigneous and metasedimentary rocks in the core of the Coast Mountains give epsilon Nd values from +3 to +7. A single metasedimentary rock approximately 3 km east of the Work Channel shear zone gives a epsilon Nd value of -9. Coast Belt plutons in the traverse yield epsilon Nd from -1 to +2. The Omineca Belt plutons give epsilon Nd from -10 to -17. All results are consistent with published data in demonstrating that (i) juvenile origins for both igneous and metamorphic rocks are common in the Coast Belt; (ii) representatives of a continental-margin sedimentary sequence with Precambrian crustal Nd are tectonically interleaved in the Coast Mountains; (iii) Coast Mountains plutons can be interpreted as derived from a blend of metamorphic rocks like those seen at the surface, or as arc-type melts contaminated with the older crustal component; and (iv) Omineca Belt plutons are dominated by remelted Precambrian crustal rocks.

scholarly journals Mise En Évidence De Nouvelles Structures Géologiques Dans La Région De Brobo (Centre De La Côte d’Ivoire). Aide À La Compréhension De La Tectonique Du Paléoprotérozoïque Du Craton Ouest Africain

2018 ◽  
Vol 14 (18) ◽  
pp. 305
Author(s):  
Daï Bi Seydou Mathurin ◽  
Ouattara Gbele ◽  
Koffi Gnammytchet Barthélémy ◽  
Gnanzou Allou ◽  
Coulibaly Inza
Keyword(s):  
Cote D'ivoire ◽  
Field Data ◽  
Côte D’Ivoire ◽  
Volcanic Rocks ◽  
Shear Zones ◽  
Cote D’Ivoire ◽  
Metasedimentary Rocks ◽  
Large Structures ◽  
Côte D'ivoire ◽  
Ductile Shear Zones

The lithological and structural observations of the region of Brobo (Central Côte d'Ivoire) indicate a succession of metasedimentary rocks (micaschists with cordierite, silstones, graphitic sediments, sandstones with amphibole-garnet, etc.) intermixed with volcanic rocks (rhyolite, dacite, andesite, basalt and the volcanoclastics). The whole is intruded by granites with one or two micas, sometimes porphyries, granodiorites, gabbros, and granite gneisses. Interpretations of Landsat ETM+ , RadarSat-1 and SRTM remote sensing imageries, as well as field data, revealed several lineament directions which, after field control, correspond to major faults and shear zones. These large structures show the N-S, NE-SW, NNE-SSW, E-W, NWSE, and NNW-SSE orientations. The field data also made it possible to describe several structures and to propose a preliminary geodynamic model for the setting and structuring of the formations of this region. This model suggests that the geodynamic took place in three stages: distension with a deformation of basement formations generating a gneissocity (D1), as well as deposits of sediments in the basins; followed by a NW-SE to E-W convergence generating a cleavage in the volcanogenic series (D2). This phase of deformation continues while creating, locally, a strain slip cleavage or a transposed schistosity. The third cleavage affects the volcanogenic series (fractures cleavages, D3) and ends in large corridors of ductile shear zones and associated faults.

scholarly journals Gold-hosting supracrustal rocks on Storø, southern West Greenland: lithologies and geological environment

2007 ◽  
Vol 13 ◽  
pp. 41-44 ◽  
Author(s):  
Christian Knudsen ◽  
Jeroen A.M. Van Gool ◽  
Claus Østergaard ◽  
Julie A. Hollis ◽  
Matilde Rink-Jørgensen ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
West Greenland ◽  
Metasedimentary Rocks ◽  
Quartz Veins ◽  
Rock Types ◽  
Minimum Age ◽  
Arc Setting ◽  
Basic Volcanic ◽  
Back Arc ◽  
Different Sources

A gold prospect on central Storø in the Nuuk region of southern West Greenland is hosted by a sequence of intensely deformed, amphibolite facies supracrustal rocks of late Mesoto Neoarchaean age. The prospect is at present being explored by the Greenlandic mining company NunaMinerals A/S. Amphibolites likely to be derived from basaltic volcanic rocks dominate, and ultrabasic to intermediate rocks are also interpreted to be derived from volcanic rocks. The sequence also contains metasedimentary rocks including quartzites and cordierite-, sillimanite-, garnet- and biotite-bearing aluminous gneisses. The metasediments contain detrital zircon from different sources indicating a maximum age of the mineralisation of c. 2.8 Ga. The original deposition of the various rock types is believed to have taken place in a back-arc setting. Gold is mainly hosted in garnet- and biotite-rich zones in amphibolites often associated with quartz veins. Gold has been found within garnets indicating that the mineralisation is pre-metamorphic, which points to a minimum age of the mineralisation of c. 2.6 Ga. The geochemistry of the goldbearing zones indicates that the initial gold mineralisation is tied to fluid-induced sericitisation of a basic volcanic protolith. The hosting rocks and the mineralisation are affected by several generations of folding.

Origin of the Tulameen ultramafic-gabbro complex, southern British Columbia

1969 ◽  
Vol 6 (3) ◽  
pp. 399-425 ◽  
Author(s):  
D. C. Findlay
Keyword(s):  
British Columbia ◽  
Internal Structure ◽  
Fractional Crystallization ◽  
Volcanic Rocks ◽  
Age Determination ◽  
Upper Triassic ◽  
Ultramafic Rocks ◽  
Metasedimentary Rocks ◽  
Gabbroic Intrusion

The Tulameen Complex is a composite ultramafic-gabbroic intrusion that outcrops over 22 sq. mi. (57 km2) in the Southern Cordillera of British Columbia. The complex intruded Upper Triassic metavolcanic and metasedimentary rocks of the Nicola Group, and on the basis of geologic relations and a K–Ar age determination (186 m.y.) is tentatively dated as Late Triassic.The principal ultramafic units — dunite, olivine clinopyroxenite, and hornblende clinopyroxenite — form an elongate, non-stratiform body whose irregular internal structure is best explained by deformation contemporaneous with crystallization of the rocks. The derivation of the ultramafic rocks is attributed to fractional crystallization of an ultrabasic magma. The gabbroic mass, which consists of syenogabbro and syenodiorite, partly borders and partly overlies the ultramafic body and was apparently intruded by it.The ultramafic and gabbroic parts of the complex probably formed from separate intrusions of different magmas, but the two suites have sufficient mineralogical and chemical features in common to indicate an ultimate petrogenic affinity of the magmas. Comparison of the Tulameen rocks with nearby intrusions of the same general age, in particular the Copper Mountain stock, suggests that they are members of a regional suite of alkalic intrusions. The possibility is also raised that these intrusions may be comagmatic with the Nicola volcanic rocks.

Inversion of magnetic and frequency-domain electromagnetic data for investigating lithologies associated with gold mineralization in the Canadian Malartic area, Québec, Canada

2020 ◽  
pp. 1-20
Author(s):  
Mehrdad Darijani ◽  
Colin G. Farquharson
Keyword(s):  
Frequency Domain ◽  
Gold Mineralization ◽  
Volcanic Rocks ◽  
Tetrahedral Mesh ◽  
Iron Formation ◽  
Magnetic Data ◽  
Low Grade ◽  
Metasedimentary Rocks ◽  
Magnetic Inversion ◽  
Northern Edge

Canadian Malartic is an Archean low-grade bulk tonnage native gold deposit. The deposit is mostly located in altered clastic metasedimentary rocks, mafic–ultramafic dykes, and monzodioritic porphyry intrusions. Airborne magnetic and frequency-domain electromagnetic (EM) data were inverted to reconstruct the geological units associated with the mineralization, especially the intrusive masses. The 3-D inversion of magnetic data, which used a tetrahedral mesh to a depth of 2.4 km, shows that mafic volcanic rocks and iron formation rocks extend to depth in the area, more so than diabase dykes. The magnetic inversion also shows that the diorite and monzodiorite rocks of the Lac Fournière A pluton are dipping toward the south on its northern edge at the contact with the metasedimentary rocks. The 1-D inversion of the frequency-domain EM data, for both electrical conductivity and magnetic susceptibility, is able to reconstruct geological structures to a depth of approximately 100 m, providing more details and information about these features. The intrusive masses such as diabase dykes, diorite and monzodiorite rocks, and mafic volcanic rocks are reconstructed as electrically conductive structures in the inversion results. The metasedimentary rocks are resistive, and the overburden is conductive in most of the area. The geophysical data and inversion results suggest the presence of some features (such as diabase dykes and monzodiorite rocks) that are not yet present on some parts of the geology map. A comparison of the EM-derived susceptibility and the magnetic-derived susceptibility over the iron formations can reveal the effect of remanent magnetization.

scholarly journals Petrogenesis and depositional environment of paleozoic Sedili and Pengerang Volcaniclastics in East Johor Basin, Peninsular Malaysia

2019 ◽  
Vol 76 ◽  
pp. 04009
Author(s):  
Sugeng Sapto Surjono ◽  
Mohd. Shafeea Leman ◽  
Che Aziz Ali ◽  
Kamal Roslan Mohamed ◽  
Fathan Hanifi Mada M
Keyword(s):  
Depositional Environment ◽  
Active Continental Margin ◽  
Volcanic Rocks ◽  
Peninsular Malaysia ◽  
Calc Alkaline ◽  
Great Abundance ◽  
Volcaniclastic Rocks ◽  
Geochemical Analyses ◽  
Depositional Setting ◽  
Magma Series

Volcaniclastic rocks in East Johor Basin are found in a relatively great abundance comprising Sedili and Pengerang Formations excluding the metamorphics, siliciclastics, and granites. Since the volcaniclastic rocks are found in a different formation, this study aims to find out the characteristics of each rock. Geology, petrography, and geochemical analyses were elaborated to reveal the petrogenesis and depositional environment in the studied area on the basis of fieldwork data and 24 samples collected from outcrops. The Sedili and Pengerang Formations are dominated by acidic rocks of rhyolite, rhyodacite, ignimbrite, and lava classifiied into calc-alkaline magma series which indicates a subduction-related product. Moreover, those acidic rocks are grouped into active continental margin. Eventhough volcanic rocks in Sedili and Pengerang Formations exhibit similar characteristics, they are different in several major contents. Therefore, it is inferred that both Sedili and Pengerang Formations were deposited in different phase. Coincidentally, depositional environment of both formations is also distinct. Sedili Formation were deposited in the subaerial to shallow marine, meanwhile, Pengerang Formation is interpreted to be deposited in deeper depositional setting.

Tectonic setting and regional correlation of Ordovician–Silurian rocks of the Aspy terrane, Cape Breton Island, Nova Scotia

1991 ◽  
Vol 28 (11) ◽  
pp. 1769-1779 ◽  
Author(s):  
Sandra M. Barr ◽  
Rebecca A. Jamieson
Keyword(s):  
Tectonic Setting ◽  
Volcanic Rocks ◽  
Volcanic Arc ◽  
Cape Breton Island ◽  
Metasedimentary Rocks ◽  
Tectonic History ◽  
Cape Breton ◽  
Metavolcanic Rocks ◽  
High Grade Metamorphism ◽  
Arc Setting

Interlayered mafic and felsic metavolcanic rocks and metasedimentary rocks of Ordovician to Silurian age are characteristic of the Aspy terrane of northwestern Cape Breton Island. These rocks were affected by medium- to high-grade metamorphism and were intruded by synkinematic granitoid orthogneisses during Late Silurian to Early Devonian times. They were intruded by posttectonic Devonian granitic plutons and experienced rapid Devonian decompression and cooling. The chemical characteristics of the mafic metavolcanic rocks indicate that they are tholeiites formed in a volcanic-arc setting. The volcanic rocks of the Aspy terrane differ from many other Silurian and Silurian–Devonian successions in Atlantic Canada, which have chemical and stratigraphic characteristics of volcanic rocks formed in extensional within-plate settings, and are somewhat younger than the Aspy terrane sequences. Aspy terrane units are most similar to Ordovician–Silurian volcanic and metamorphic units in southwestern Newfoundland, including the La Poile Group and the Port aux Basques gneiss. Together with other occurrences of Late Ordovician to Early Silurian volcanic-arc units, they indicate that subduction-related compressional tectonics continued into the Silurian in parts of the northern Appalachian Orogen. The complex Late Silurian – Devonian tectonic history of the Aspy terrane may reflect collision with the southeastern edge of a Grenvillian crustal promentory.

Rb–Sr geochronology and metamorphic history of Proterozoic to early Archean rocks north of the Cape Smith Fold Belt, Quebec

1987 ◽  
Vol 24 (4) ◽  
pp. 813-825 ◽  
Author(s):  
Ronald Doig
Keyword(s):  
Volcanic Rocks ◽  
Granitic Rocks ◽  
Iron Formation ◽  
Fold Belt ◽  
Metasedimentary Rocks ◽  
Metamorphic History ◽  
The North ◽  
Basement Rocks ◽  
History Of ◽  
Wide Zone

The Churchill Province north of the Proterozoic Cape Smith volcanic fold belt of Quebec may be divided into two parts. The first is a broad antiform of migmatitic gneisses (Deception gneisses) extending north from the fold belt ~50 km to Sugluk Inlet. The second is a 20 km wide zone of high-grade metasedimentary rocks northwest of Sugluk Inlet. The Deception gneisses yield Rb–Sr isochron ages of 2600–2900 Ma and initial ratios of 0.701–0.703, showing that they are Archean basement to the Cape Smith Belt. The evidence that the basement rocks have been isoclinally refolded in the Proterozoic is clear at the contact with the fold belt. However, the gneisses also contain ubiquitous synclinal keels of metasiltstone with minor metapelite and marble that give isochron ages less than 2150 Ma. These ages, combined with low initial ratios of 0.7036, show that they are not part of the basement, as the average 87Sr/86Sr ratio for the basement rocks was about 0.718 at that time.The rocks west of Sugluk Inlet consist mainly of quartzo-feldspathic sediments, quartzites, para-amphibolites, marbles, and some pelite and iron formation. In contrast to the Proterozoic sediments in the Deception gneisses, these rocks yield dates of 3000–3200 Ma, with high initial ratios of 0.707–0.714. These initial ratios point to an age (or a provenance) much greater than that of the Archean Deception gneisses. The rocks of the Sugluk terrain are intruded by highly deformed sills of granitic rocks with ages of about 1830 Ma, demonstrating again the extent and severity of the Proterozoic overprint. The eastern margin of this possibly early Archean Sugluk block is a discontinuity in age, lithology, and geophysical character that could be a suture between two Archean cratons. It is not known if such a suturing event is of Archean age, or if it is related to the deformation of the Cape Smith Fold Belt.Models of evolution incorporating both the Cape Smith Belt and the Archean rocks to the north need to account for the internal structure of the fold belt, the continental affinity of many of the volcanic rocks, the continuity of basement around the eastern end of the belt, and the increase in metamorphism through the northern part of the belt into a broad area to the north. The Cape Smith volcanic rocks may have been extruded along a continental rift, parallel to a continental margin at Sugluk. Continental collison at Sugluk would have thrust the older and higher grade Sugluk rocks over the Deception gneisses, produced the broad Deception antiform, and displaced the Cape Smith rocks to the south in a series of north-dipping thrust slices.

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