The age, chemistry, and tectonic setting of the Middle Proterozoic Moyie sills, Purcell Supergroup, southeastern British Columbia

1989 ◽  
Vol 26 (11) ◽  
pp. 2305-2317 ◽  
Author(s):  
Trygve Höy
Keyword(s):  
British Columbia ◽  
Tectonic Setting ◽  
Coarse Grained ◽  
High Iron ◽  
Basaltic Rocks ◽  
Typical Sequence ◽  
Minimum Age ◽  
Intracratonic Basin ◽  
Chemical Trends ◽  
Middle Proterozoic

Moyie sills comprise an extensive suite of basaltic rocks that have intruded Middle Proterozoic Purcell Supergroup rocks in southeastern British Columbia. The sills are spatially restricted to the Aldridge and Fort Steele formations in the lower part of the Purcell succession and are distinct from a suite of mafic sills higher in the succession. They may constitute up to 30% of a typical sequence but generally decrease in volume upsection as the abundance of thick-bedded A–E turbidites decreases. A number of the sills have textures and contact relationships that suggest they intruded unconsolidated or partly consolidated wet sediments.A U–Pb zircon Middle Proterozoic date of 1445 Ma from a coarse-grained sill is interpreted as being the minimum age of emplacement. Because the sills are penecontemporaneous with Aldridge sedimentation, this date defines the minimum age of deposition of lower and basal middle Aldridge rocks.Two distinct compositions of Moyie sills are recognized. Most are subalkaline, high-iron tholeiitic basalts, whereas others are alkaline basalts. The two different chemical trends are typical of volcanism in an incipient rift environment or in the early stages of continental rifting. This supports a model for deposition of Belt–Purcell rocks in a large, subsiding intracratonic basin formed by Middle Proterozoic rifting.

scholarly journals Heavy minerals in the Wajid Sandstone from Abha-Khamis Mushayt area, southwestern Saudi Arabia: implications on provenance and regional tectonic setting

GeoArabia ◽  
2004 ◽  
Vol 9 (4) ◽  
pp. 77-102 ◽  
Author(s):  
Mahbub Hussain ◽  
Lameed O. Babalola ◽  
Mustafa M. Hariri
Keyword(s):  
Saudi Arabia ◽  
Tectonic Setting ◽  
Principal Component ◽  
Heavy Mineral ◽  
Heavy Minerals ◽  
Coarse Grained ◽  
Distribution Data ◽  
The South ◽  
Quartz Content ◽  
The North

ABSTRACT The Wajid Sandstone (Ordovician-Permian) as exposed along the road-cut sections of the Abha and Khamis Mushayt areas in southwestern Saudi Arabia, is a mediun to coarse-grained, mineralogically mature quartz arenite with an average quartz content of over 95%. Monocrystalline quartz is the dominant framework grain followed by polycrystalline quartz, feldspar and micas. The non-opaque heavy mineral assemblage of the sandstone is dominated by zircon, tourmaline and rutile (ZTR). Additional heavy minerals, constituting a very minor fraction of the heavies, include epidote, hornblende, and kyanite. Statistical analysis showed significant correlations between zircon, tourmaline, rutile, epidote and hornblende. Principal component R-mode varimax factor analysis of the heavy mineral distribution data shows two strong associations: (1) tourmaline, zircon, rutile, and (2) epidote and hornblende suggesting several likely provenances including igneous, recycled sedimentary and metamorphic rocks. However, an abundance of the ZTR minerals favors a recycled sedimentary source over other possibilities. Mineralogical maturity coupled with characteristic heavy mineral associations, consistent north-directed paleoflow evidence, and the tectonic evolutionary history of the region indicate a provenance south of the study area. The most likely provenances of the lower part (Dibsiyah and Khusayyan members) of the Wajid Sandstone are the Neoproterozoic Afif, Abas, Al-Bayda, Al-Mahfid, and Al-Mukalla terranes, and older recycled sediments of the infra-Cambrian Ghabar Group in Yemen to the south. Because Neoproterozic (650-542 Ma) rocks are not widespread in Somalia, Eritrea and Ethiopia, a significant source further to the south is not likely. The dominance of the ultrastable minerals zircon, tourmaline and rutile and apparent absence of metastable, labile minerals in the heavy mineral suite preclude the exposed arc-derived oceanic terrains of the Arabian Shield in the west and north as a significant contributor of the sandstone. An abundance of finer-grained siliciclastic sequences of the same age in the north, is consistent with a northerly transport direction and the existence of a deeper basin (Tabuk Basin?) to the north. The tectonic and depositional model presented in this paper differs from the existing model that envisages sediment transportation and gradual basin filling from west to east during the Paleozoic.

Glacial Isostatic Adjustment Modelling of the Coast Mountains of British Columbia and Southeastern Alaska

2021 ◽  
Author(s):  
Maximilian Lauch ◽  
Thomas James ◽  
Lucinda Leonard ◽  
Yan Jiang ◽  
Joseph Henton ◽  
...  
Keyword(s):  
British Columbia ◽  
Mass Loss ◽  
Thermal Emission ◽  
Tectonic Setting ◽  
Ice Age ◽  
High Mass ◽  
Cascadia Subduction Zone ◽  
Climate Projections ◽  
Coast Mountains ◽  
Crustal Motion

<p>The Coast Mountains in British Columbia and southeastern Alaska contain around 9040 km<sup>2 </sup>of glaciers and ice fields at present. While these glaciers have followed an overall trend of mass loss since the Little Ice Age (or LIA around 300 years before present), the past decade has seen a significant increase in melting rate that is likely to continue due to the effects of climate change. The region is home to a complex tectonic setting, having proximity to the Queen Charlotte-Fairweather transform plate boundary in the northern region and the Cascadia subduction zone (CSZ) in the southern region, which has an associated active volcanic arc underlying the glaciated area. Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) glacier melt data collected between 2000 and 2019 represent a melt rate that is averaged between periods of relatively low mass loss (2000-2009) and high mass loss (2010-2019). As a preliminary test, this average melt rate was assumed to be constant back to the LIA. A history of gridded ice thicknesses was calculated to create an ice loading model for input to a series of forward modelling calculations to determine the crustal response. Predictions of vertical crustal motion are compared to available Global Navigation Satellite System (GNSS) measurements of uplift rate to constrain Earth rheology. The results using this simplified loading model favour a thin lithosphere (around 20-40 km thick) and asthenospheric viscosities on the order of 10<sup>19</sup> Pa s. These values are significantly lower than those of rheological profiles used in extant global GIA models, but are in general agreement with previous GIA modelling of the forearc region of the CSZ. To improve the glacial history model, the Open Global Glacier Model (OGGM), driven by historic climate data and statistically downscaled climate projections, is being employed to create a more accurate loading model and refine our estimates of Earth rheology and regional crustal motion. The best-fitting models will be employed to separate GIA and tectonic components of crustal motion and to generate improved regional sea-level projections.</p>

Mesozoic – early Cenozoic volcanism, plutonism, and mineralization in southern British Columbia: A plate tectonic synthesis

1977 ◽  
Vol 14 (7) ◽  
pp. 1611-1624 ◽  
Author(s):  
John R. Griffiths
Keyword(s):  
British Columbia ◽  
Subduction Zone ◽  
Subduction Zones ◽  
Tectonic Setting ◽  
Spatial Relationship ◽  
Plate Tectonic ◽  
Time Space ◽  
Cenozoic Volcanism ◽  
Volcanic Belts ◽  
Early Cenozoic

Three time–space profiles have been constructed using geologic data from British Columbia between 49° N and 56° N. They illustrate variations across the Cordillera, (1) in the stratigraphic and tectonic setting of volcanism, (2) in the age and modal type of granitoids, and (3) in the distribution and types of copper and lead deposits related to volcanic and plutonic rocks. These profiles provide the basis for a plate tectonic synthesis of the Mesozoic–Cenozoic geology, illustrated by six true-scale cross sections.The preferred model has, in the Triassic, two eastward-dipping subduction zones, giving rise to the copper-rich Karmutsen and Nicola–Takla volcanics respectively. After collision of the two volcanic belts by the Early Jurassic, a single eastward-dipping subduction zone remained active until the Eocene. Magmas produced by partial melting and fractionation of subducted lithosphere occurred across the western 300 km of the Cordillera, leading to thickening of the crust, and eventually to anatectic melting to generate large batholiths now containing pendants of volcanics. Jurassic and later geologic and metallogenic events across the eastern 500 km of the Cordillera are the results of an increased heat flux through inhomogeneous crust of varying thickness, comprised of relict ocean floor, continental margin sediments, older volcanics, and ancient cratonic basement. This results in patterns of metamorphism, volcanism, and plutonism which have no simple spatial relationship to the subduction zone.

Geochemistry and origin of Mesoproterozoic metavolcanic rocks from Fisher Massif, Prince Charles Mountains, East Antarctica

1996 ◽  
Vol 8 (1) ◽  
pp. 85-104 ◽  
Author(s):  
E. V. Mikhalsky ◽  
J. W. Sheraton ◽  
A. A. Laiba ◽  
B. V. Beliatsky
Keyword(s):  
Tectonic Setting ◽  
Active Continental Margin ◽  
Volcanic Rocks ◽  
Granulite Facies ◽  
Island Arc ◽  
Crustal Component ◽  
Basaltic Rocks ◽  
Metavolcanic Rocks ◽  
High K ◽  
Low K

Fisher Massif consists of Mesoproterozoic (c. 1300 Ma) lower amphibolite-facies metavolcanic rocks and associated metasediments, intruded by a variety of subvolcanic and plutonic bodies (gabbro to granite). It differs in both composition and metamorphic grade from the rest of the northern Prince Charles Mountains, which were metamorphosed to granulite facies about 1000 m.y. ago. The metavolcanic rocks consist mainly of basalt, but basaltic andesite, andesite, and more felsic rocks (dacite, rhyodacite, and rhyolite) are also common. Most of the basaltic rocks have compositions similar to low-K island arc tholeiites, but some are relatively Nb-rich and more akin to P-MORB. Intermediate to felsic medium to high-K volcanic rocks, which appear to postdate the basaltic succession, have calc-alkaline affinities and probably include a significant crustal component. On the present data, an active continental margin with associated island arc was the most likely tectonic setting for generation of the Fisher Massif volcanic rocks.

Petrology, age, and tectonic setting of the rapakivi-bearing Margaree pluton, Cape Breton Island, Canada: evidence for a Late Devonian posttectonic cryptic silicic-mafic magma chamber

2020 ◽  
Vol 57 (9) ◽  
pp. 1011-1029
Author(s):  
Gabriel Sombini dos Santos ◽  
Sandra M. Barr ◽  
Chris E. White ◽  
Deanne van Rooyen
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Magma Chamber ◽  
Magma Mixing ◽  
Tectonic Setting ◽  
Mafic Magma ◽  
Coarse Grained ◽  
Late Devonian ◽  
Cape Breton Island ◽  
Cape Breton

The Margaree pluton extends for >40 km along the axis of the Ganderian Aspy terrane of northern Cape Breton Island, Nova Scotia. The pluton consists mainly of coarse-grained megacrystic syenogranite, intruded by small bodies of medium-grained equigranular syenogranite and microgranite porphyry, all locally displaying rapakivi texture. The three rock types have similar U–Pb (zircon) ages of 363 ± 1.6, 364.8 ± 1.6, and 365.5 ± 3.3 Ma, respectively, consistent with field and petrological evidence that they are coeval and comagmatic. The rare earth elements display parallel trends characterized by enrichment in the light rare earth elements, flat heavy rare earth elements, moderate negative Eu anomalies, and, in some cases, positive Ce anomalies. The megacrystic and rapakivi textures are attributed to thermal perturbation in the magma chamber caused by the mixing of mafic and felsic magma, even though direct evidence of the mafic magma is mainly lacking at the current level of exposure. Magma evolution was controlled by fractionation of quartz, K-feldspar, and Na-rich plagioclase in molar proportions of 0.75:0.12:0.13. The chemical and isotopic (Sm–Nd) signature of the Margaree pluton is consistent with the melting of preexisting continental crust that was enriched in heat-producing elements, likely assisted by intrusion of mantle-derived mafic magma during Late Devonian regional extension. The proposed model involving magma mixing at shallow crustal levels in a cryptic silicic-mafic magma chamber during post-Acadian extension is consistent with models for other, better exposed occurrences of rapakivi granite in the northern Appalachian orogen.

Polyphase tectonothermal events recorded in metamorphic basement rocks from the northern Altyn Tagh, southeastern Tarim Craton

2020 ◽  
Author(s):  
Zhongmei Wang ◽  
Chunming Han ◽  
Wenjiao Xiao ◽  
Patrick Asamoah Sakyi
Keyword(s):  
Tectonic Setting ◽  
Volcanic Rocks ◽  
Mineral Chemistry ◽  
Metasedimentary Rocks ◽  
Exposed Rock ◽  
Altyn Tagh ◽  
Argillaceous Rocks ◽  
Southeastern Margin ◽  
Minimum Age ◽  
Tarim Craton

<p>  Paleoproterozoic is a pivotal time for understanding the geochronological framework of the Tarim Craton. Located on the southeastern margin of the Tarim Craton, the northern Altyn Tagh is the main exposed region for Paleoproterozoic magmatic-metamorphic rocks. These rocks are diverse, diachronous and modified by multiple magmatic and/or metamorphic events. In this study, we performed systematic analyses on the amphibolite, felsic gneisses, and metasedimentary rocks in the Aketashitage area, southeastern Tarim Craton, including petrography, mineral chemistry, and whole-rock geochemistry, as well as in-situ zircon U-Pb ages and Hf isotopes, to examine the Paleoproterozoic magmatic-metamorphic events in the northern Altyn Tagh. Geochemically, the amphibolite and felsic gneisses in the Aketashitage area seemingly represent the typical bimodal associations of mafic and acidic volcanic rocks. In addition, the felsic gneisses are characterized by high Sr and low Y contents, with high Sr/Y and La<sub>N</sub>/Yb<sub>N</sub> ratios, and indistinctive Eu anomalies, closely resembling high-SiO<sub>2</sub> adakites derived from subducted basaltic slab-melt. The palimpsest textures and geochemical features of the Aketashitage metasedimentary rocks suggest that their protoliths are argillaceous rocks. The amphibolite has a metamorphic age of 1.96 Ga, and the felsic gneisses yield crystallization ages of 2.54-2.52 Ga. For the metasedimentary rocks, the major age peaks of 2.72 Ga, 2.05 Ga and 1.97 Ga are consistent with the magmatic and/or metamorphic events in the study area. The minimum age peak suggests that the depositional age is no earlier than 1.97 Ga. The geochemical and geochronological evidences documented by the exposed rock associations in the Aketashitage area suggest a subduction-related tectonic setting in the Paleoproterozoic. Our new data combined with the previous studies indicate that the Paleoproterozoic magmatism and metamorphism in the northern Altyn Tagh area are nearly synchronous, and both are likely related to oceanic subduction.</p>

Minimum age of deglaciation of upper Elk Valley, British Columbia

1981 ◽  
Vol 18 (10) ◽  
pp. 1635-1636 ◽  
Author(s):  
Angus Ferguson ◽  
Gerald Osborn
Keyword(s):  
British Columbia ◽  
Minimum Age

Bog sediments at an elevation of 1582 m in the upper Elk Valley of British Columbia were dated at three horizons. The lowermost of these, radiocarbon dated at 13 430 ± 450 years BP, provides a minimum age for deglaciation of Elk Valley. This date is probably also a minimum for the Canmore advance in the Bow Valley, Alberta, and suggests that the Canmore was not related to deposition of the Bighill Creek Formation at Cochrane. Pollen samples from the bog indicate a shrub–herb pioneer assemblage following deglaciation of that portion of the valley.

Very coarse-grained beaches as a response to generalized sea level drops in a complex active tectonic setting: Pleistocene marine terraces at the Cadiz coast, SW Spain

2016 ◽  
Vol 382 ◽  
pp. 92-110 ◽  
Author(s):  
Laura González-Acebrón ◽  
Ramón Mas ◽  
José Arribas ◽  
Jose Manuel Gutiérrez-Mas ◽  
Carlos Pérez-Garrido
Keyword(s):  
Sea Level ◽  
Tectonic Setting ◽  
Coarse Grained ◽  
Sw Spain ◽  
Marine Terraces ◽  
Active Tectonic

Devonian Plutonism in South-Central British Columbia

1975 ◽  
Vol 12 (10) ◽  
pp. 1760-1769 ◽  
Author(s):  
Andrew V. Okulitch ◽  
R. K. Wanless ◽  
W. D. Loveridge
Keyword(s):  
British Columbia ◽  
Middle Devonian ◽  
Metamorphic Complex ◽  
Western Margin ◽  
South Central ◽  
Minimum Age ◽  
History Of ◽  
Shuswap Metamorphic Complex

An apparently tabular body of granitoid gneiss, 3 to 5 km wide and more than 70 km long, that lies along the western margin of the Shuswap Metamorphic Complex between Shuswap and Admas Lakes, shows intrusive relationships with Palaeozoic and older rocks and has yielded zircons whose minimum age is 372 Ma. This intrusion, together with other granitoid plutons in the area that appear to be related to it, provide evidence of widespread plutonism during Middle Devonian time near the western edge of the Paleozoic Cordillera geosyncline and necessitate significant revisions in the interpretation of the crustal history of this region.

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