Geochemistry of the northern Cache Creek terrane and implications for accretionary processes in the Canadian Cordillera

2010 ◽  
Vol 47 (1) ◽  
pp. 13-34 ◽  
Author(s):  
Joseph M. English ◽  
Mitchell G. Mihalynuk ◽  
Stephen T. Johnston
Keyword(s):  
Volcanic Rocks ◽  
Minor Component ◽  
Oceanic Lithosphere ◽  
Ocean Basin ◽  
Late Triassic ◽  
Canadian Cordillera ◽  
Basaltic Rocks ◽  
Subducting Plate ◽  
A Minor ◽  
Collisional Orogenesis

The northern Cache Creek terrane in the Canadian Cordillera includes a subduction complex that records the existence of a late Paleozoic – Mesozoic ocean basin and provides an opportunity to assess accretionary processes that involve the transfer of material from a subducting plate to an upper plate. Lithogeochemical data from basaltic rocks indicate that the northern Cache Creek terrane is dominated by two different petrogenetic components: (1) a dominant suite of subalkaline intrusive and extrusive rocks mostly of arc affinity and (2) a volumetrically less significant suite of alkaline volcanic rocks of within-plate affinity. The subalkaline intrusive and extrusive rocks constitute a section of oceanic lithosphere that is interpreted to have occupied a fore-arc position during the Late Triassic and Early Jurassic before it was accreted during collisional orogenesis in the Middle Jurassic. Alkaline volcanic rocks in the northern Cache Creek terrane are stratigraphically associated with carbonate strata that contain Tethyan fauna that are exotic with respect to the rest of North America; together, they are interpreted as remnants of oceanic seamounts and (or) plateaux. The volcanic rocks are a minor component of the carbonate stratigraphy, and it appears that the majority of the volcanic basement was either subducted completely at the convergent margin or underplated at greater depth in the subduction zone. In summary, accretion in the northern Canadian Cordillera occurred principally by the accretion of island arcs and emplacement of fore-arc ophiolites during collisional orogenesis. The transfer of oceanic sediments and the upper portions of oceanic seamounts from the subducting plate to an accretionary margin accounts for only small volumes of growth of the upper plate.

scholarly journals Igneous Rock Associations 21. The Early Permian Panjal Traps of the Western Himalaya

2016 ◽  
Vol 43 (4) ◽  
pp. 251 ◽  
Author(s):  
J. Gregory Shellnutt
Keyword(s):  
Volcanic Rocks ◽  
Crustal Contamination ◽  
Western Himalaya ◽  
Ocean Basin ◽  
Early Permian ◽  
Basaltic Rocks ◽  
Wide Range ◽  
Silicic Volcanic ◽  
Felsic Volcanic ◽  
Sea Floor Spreading

The Early Permian (290 Ma) Panjal Traps are the largest contiguous outcropping of volcanic rocks associated with the Himalayan Magmatic Province (HMP). The eruptions of HMP-related lava were contemporaneous with the initial break-up of Pangea. The Panjal Traps are primarily basalt but volumetrically minor intermediate and felsic volcanic rocks also occur. The basaltic rocks range in composition from continental tholeiite to ocean-floor basalt and nearly all have experienced, to varying extent, crustal contamination. Uncontaminated basaltic rocks have Sr–Nd isotopes similar to a chondritic source (ISr = 0.7043 to 0.7073; eNd(t) = 0 ± 1), whereas the remaining basaltic rocks have a wide range of Nd (eNd(t) = –6.1 to +4.3) and Sr (ISr = 0.7051 to 0.7185) isotopic values. The calculated primary melt compositions of basalt are picritic and their mantle potential temperatures (TP ≤ 1450°C) are similar to ambient mantle rather than anomalously hot mantle. The silicic volcanic rocks were likely derived by partial melting of the crust whereas the andesitic rocks were derived by mixing between crustal and mantle melts. The Traps erupted within a continental rift setting that developed into a shallow sea. Sustained rifting created a nascent ocean basin that led to sea-floor spreading and the rifting of microcontinents from Gondwana to form the ribbon-like continent Cimmeria and the Neotethys Ocean.RÉSUMÉLes Panjal Traps du début Permien (290 Ma) constituent le plus grand affleurement contigu de roches volcaniques associées à la province magmatique de himalayienne (HMP). Les éruptions de lave de type HMP étaient contemporaines de la rupture initiale de la Pangée. Les Panjal Traps sont essentiellement des basaltes, mais on y trouve aussi des roches volcaniques intermédiaires et felsiques en quantités mineures. La composition de ces roches basaltiques varie de tholéiite continentale à basalte de plancher océanique, et presque toutes ont subi, à des degrés divers, une contamination de matériaux crustaux. Les roches basaltiques non contaminées ont des contenus isotopiques Sr–Nd similaires à une source chondritique (Isr = 0,7043 à 0,7073; eNd (t) = 0 ± 1), alors que les roches basaltiques autres montrent une large gamme de valeurs isotopiques en Nd (eNd (t) = –6,1 à +4,3) et Sr (Isr = de 0,7051 à 0,7185). Les compositions de fusion primaire calculées des basaltes sont picritiques et leurs températures potentielles mantelliques (TP de ≤ 1450°C) sont similaires à la température ambiante du manteau plutôt que celle d’un manteau anormalement chaud. Les roches volcaniques siliciques dérivent probablement de la fusion partielle de la croûte alors que les roches andésitiques proviennent du mélange entre des matériaux de fusion crustaux et mantelliques. Les Traps ont fait irruption dans un contexte de rift continental qui s’est développé dans une mer peu profonde. Un rifting soutenu a créé un début de bassin océanique lequel conduit à une expansion du fond océanique et au rifting de microcontinents tirés du Gondwana pour former le continent rubané de Cimméria et l'océan Néotéthys.

Mesozoic Metallogenesis of Peru: A Reality Check on Geodynamic Models

SEG Discovery ◽  
2021 ◽  
pp. 15-24
Author(s):  
Dave Shatwell
Keyword(s):  
Iron Oxide ◽  
Porphyry Copper ◽  
Oceanic Lithosphere ◽  
Ocean Basin ◽  
Gold Deposits ◽  
Late Triassic ◽  
Peruvian Andes ◽  
Southern Peru ◽  
Porphyry Cu ◽  
Back Arc

Abstract The Andean Cordillera is generally regarded as the product of easterly subduction of oceanic lithosphere below South America since the Late Triassic, but recent syntheses have challenged this paradigm. In one model, W-dipping oceanic subduction pulls the continent west until it collides with a ribbon continent that now forms the coastal region and Western Cordillera of the Peruvian Andes. A second model involves westerly oceanic subduction until 120 to 100 Ma, without the involvement of a ribbon continent, to explain deep, subducted slabs revealed by mantle tomographic images. Both assume that “Andean-style” E-dipping subduction did not exist during the Jurassic and Early Cretaceous. Another model, also involving mantle tomography, assumes that a back-arc basin opened inboard of the trench between 145 and 100 Ma, displacing the E-dipping subduction zone offshore without changing its polarity. This article examines the implications of these hypotheses for southern Peruvian metallogenesis during the Mesozoic, when marginal basins opened and closed and were thrust eastward and then were intruded, between 110 and ~50 Ma, by a linear belt of multiple plutons known as the Coastal Batholith. The earliest mineralization in southern Peru is located on the coast and comprises major iron oxide and minor porphyry copper deposits emplaced between 180 and 110 Ma. This was followed by Cu-rich iron oxide copper-gold deposits and a large Zn-rich volcanogenic massive sulfide (VMS) deposit between 115 and 95 Ma, then minor porphyry Cu deposits at ~80 Ma. A second episode of localized VMS mineralization followed at 70 to 68 Ma, then a group of at least five giant porphyry Cu-Mo deposits in southernmost Peru formed between 62 and 53 Ma. The conventional model of Andean-style subduction, which explains many features of Mesozoic Andean metallogenesis in terms of changing plate vectors and velocities, is a poor fit with mantle tomographic anomalies that are thought to record the paleopositions of ancient trenches. A ribbon-continent model requires some plutons of the Coastal Batholith to have been separated from others by an ocean basin. West-dipping oceanic subduction does not account for Jurassic mineralization and magmatism in southern Peru. A model involving a back-arc basin that opened inboard of the existing trench, forcing E-dipping subduction to retreat offshore between 145 and 100 Ma, seems to best explain the metallogenic and tomographic data.

A Laurentian margin subduction perspective: Geodynamic constraints from phase equilibria modeling of barroisite greenstones, northern USA Appalachians

2020 ◽  
Vol 132 (11-12) ◽  
pp. 2587-2605
Author(s):  
I.W. Honsberger ◽  
J. Laird ◽  
J.E. Johnson
Keyword(s):  
Phase Equilibria ◽  
Continental Margin ◽  
Volcanic Rocks ◽  
Oceanic Lithosphere ◽  
Ocean Basin ◽  
Iapetus Ocean ◽  
Continental Arc ◽  
Slab Tear ◽  
Shallow Subduction ◽  
Laurentian Margin

Abstract Phase equilibria modeling of sodic-calcic amphibole-epidote assemblages in greenstones in the northern Appalachians, USA, is compatible with relatively shallow subduction of the early Paleozoic Laurentian margin along the Laurentia-Gondwana suture zone during closure of a portion of the Iapetus Ocean basin. Pseudosection and isopleth calculations demonstrate that peak metamorphic conditions ranged between 0.65 GPa, 480 °C and 0.85 GPa, 495 °C down-dip along the subducted Laurentian continental margin between ∼20 km and ∼30 km depth. Quantitative petrological data are explained in the context of an Early Ordovician geodynamic model involving shallow subduction of relatively young, warm, and buoyant Laurentian margin continental-oceanic lithosphere and Iapetus Ocean crust beneath a relatively warm and wet peri-Gondwanan continental arc. A relatively warm subduction zone setting may have contributed to the formation of a thin, ductile metasedimentary rock-rich channel between the down-going Laurentian slab and the overriding continental arc. This accretionary channel accommodated metamorphism and tectonization of continental margin sediments and mafic volcanic rocks (greenstones) of the Laurentian margin and provided a pathway for exhumation of serpentinite slivers and rare eclogite blocks. Restricted asthenospheric flow in the forearc mantle wedge provides one explanation for the lack of ophiolites and absence of a well-preserved ultra-high-pressure terrane in central and northern Vermont. Exhumation of the subducted portion of the Laurentian margin may have been temperature triggered due to increased asthenospheric flow following a slab tear at relatively shallow depths.

Nd, Sr, and Pb isotopic evidence for contrasting origins of late Paleozoic volcanic rocks from the Slide Mountain and Cache Creek terranes, south-central British Columbia

1995 ◽  
Vol 32 (4) ◽  
pp. 447-459 ◽  
Author(s):  
Alan D. Smith ◽  
Richard StJ. Lambert
Keyword(s):  
Volcanic Rocks ◽  
Trace Element Composition ◽  
Ocean Basin ◽  
Late Triassic ◽  
Late Paleozoic ◽  
Spreading Ridge ◽  
South Pacific Ocean ◽  
South Central ◽  
Pb Isotopic Composition ◽  
Back Arc

The Slide Mountain and Cache Creek terranes are two prominent oceanic sutures in the Canadian Cordillera. Petrological and isotopic variations between volcanic rocks in these terranes support earlier interpretations from stratigraphic evidence that the Slide Mountain terrane represents the remnant of a late Paleozoic basin situated marginal to western North America, whereas the Cache Creek terrane represents a remnant of a much larger, open-ocean basin. Slide Mountain terrane volcanic rocks, represented by Late Pennsylvanian basalts of the Fennell Formation, resemble normal mid-oceanic ridge basalts but possess an unusual kaersutite- or augite-dominated mineralogy. Their εNd(300 Ma) values of +7.7 to +10.2 are among the highest observed for Paleozoic basalts. The hydrous mineralogy can be reconciled with eruption on a spreading ridge in either a back-arc or marginal basin setting. The latter is preferred from Pb isotope compositions (206Pb/204Pb = 17.7–18.5, 207Pb/204Pb = 15.51–15.61, 208Pb/204Pb = 37.2–38.8), which suggest exchange with high Th/U continental-derived sediment during hydrothermal alteration. Volcanic rocks, probably middle Mississippian, in the Bonaparte subterrane of the Cache Creek terrane include picrites and basalts belonging to a within-plate tholeiite suite. The intraplate suite broadly resembles Hawaiian basalts in major and trace element composition. However, moderate positive εNd values (εNd(340 Ma) +4.2 to +5.6) and a transition toward DUPAL signatures in Pb isotopic composition (206Pb/204Pb = 18.1–19.1, 207Pb/204Pb = 15.54–15.61, 208Pb/204Pb = 37.8–38.6) are features more similar to volcanic rocks from modern South Pacific ocean islands. Basaltic andesite and andesitic tuffs, also found in the Bonaparte subterrane, are tentatively correlated with Late Triassic to Early Jurassic low-K tholeiitic volcanic rocks of the Nicola Group on the Quesnel terrane.

scholarly journals Geochemistry of volcanic and plutonic rocks from the Nahlin ophiolite with implications for a Permo–Triassic arc in the Cache Creek terrane, northwestern British Columbia

2017 ◽  
Vol 54 (12) ◽  
pp. 1214-1227 ◽  
Author(s):  
Siobhan McGoldrick ◽  
Alex Zagorevski ◽  
Dante Canil
Keyword(s):  
British Columbia ◽  
Volcanic Rocks ◽  
Minor Component ◽  
Volcaniclastic Rocks ◽  
Fractional Melting ◽  
Ultramafic Cumulates ◽  
A Minor ◽  
Lower Crustal ◽  
Island Basalt ◽  
Mantle Section

In northwestern British Columbia, the Permian Nahlin ophiolite in the northern Cache Creek terrane comprises spinel harzburgite tectonite with minor lherzolite, lower crustal mafic and ultramafic cumulates, gabbroic rocks including dikes intruding mantle harzburgite, and basaltic volcanic and volcaniclastic rocks. New lithogeochemical data from the Menatatuline Range area confirm that plutonic and volcanic rocks of the ophiolite are tholeiitic and arc related, while only a minor component of volcanic rocks are alkaline intraplate basalts. Tholeiitic basalts of the Nahlin ophiolite represent the products of 2%–20% fractional melting, and their complementary residue may be peridotite from the ophiolite mantle section. Correlative tholeiitic volcanic sections can be found elsewhere in the northern Cache Creek terrane, and they may be linked to a regionally extensive (∼200 km) intraoceanic arc. The arc tholeiite geochemistry of the plutonic and volcanic rocks, and the highly depleted nature of the mantle residues, imply that the Nahlin ophiolite formed in a supra-subduction zone environment. The Nahlin ophiolite therefore occupied the upper plate during intraoceanic collision prior to emplacement of the Cache Creek terrane. The volumetrically minor ocean island basalt type volcanic rocks in the northern Cache Creek terrane are associated with carbonate successions bearing Tethyan fauna. These sequences are likely fragments of oceanic plateaux and their carbonate atolls sliced off of the subducting plate and are unrelated to the Nahlin ophiolite-arc system.

Geochemical, Sr–Nd–Pb and zircon U–Pb–Hf isotopic constraints on the Late Carboniferous back-arc basin basalts from the Chengjisihanshan Formation in West Junggar, NW China

2020 ◽  
Vol 157 (11) ◽  
pp. 1781-1799
Author(s):  
Qian Zhi ◽  
Yongjun Li ◽  
Fenghao Duan ◽  
Lili Tong ◽  
Jun Chen ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Oceanic Lithosphere ◽  
Late Carboniferous ◽  
Geochemical Data ◽  
Upper Carboniferous ◽  
Basaltic Rocks ◽  
Central Asian ◽  
West Junggar ◽  
Back Arc ◽  
T Values

AbstractWest Junggar in the southwestern Central Asian Orogenic Belt is a critical area for the study of the Junggar oceanic basin and may also reveal tectonic evolutionary events before the final closure of the Palaeo-Asian Ocean. The sedimentary formations and paragenetic associations of the Upper Carboniferous Chengjisihanshan Formation in southern West Junggar jointly reveal a back-arc basin setting with zircon U–Pb ages of 313–310 Ma for the basaltic rocks. Geochemically, the basaltic rocks are tholeiitic with low SiO2 (47.76–52.06 wt %) and K2O (0.05–0.74 wt %) but high MgO (6.55–7.68 wt %) contents and Mg no. (52.9–58.9) values. They display slightly flat rare earth element patterns with weak positive Eu anomalies, and show enrichments in large ion lithophile elements relative to high field strength elements with negative Nb and Ta anomalies, exhibiting both N-MORB-like and arc-like signatures, similar to the back-arc basin basalt from the Mariana Trough. The high positive zircon εHf(t) and bulk εNd(t) values as well as high initial Pb isotopes, together with relatively high Sm/Yb and slightly low Th/Ta ratios imply a depleted spinel lherzolitic mantle source metasomatized by slab-derived fluids. The field and geochemical data jointly suggest that the volcanic rocks within the Chengjisihanshan Formation were formed in an intra-oceanic back-arc basin above the northwestward subduction of the Junggar oceanic lithosphere in southern West Junggar. The confirmation of the Late Carboniferous back-arc basin basalts, together with other geological observations, indicate that an arc-basin evolutionary system still existed in southern West Junggar at c. 310 Ma, and the Junggar Ocean closed after Late Carboniferous time.

Geology and geochemistry of the volcanic rocks of the Pioneer Formation, Bridge River area, southwestern British Columbia (Canada)

1994 ◽  
Vol 131 (2) ◽  
pp. 243-253 ◽  
Author(s):  
J. Dostal ◽  
B. N. Church
Keyword(s):  
British Columbia ◽  
Volcanic Rocks ◽  
Accretionary Prism ◽  
Oceanic Lithosphere ◽  
Source Rocks ◽  
Late Triassic ◽  
Stability Field ◽  
The North ◽  
Mantle Diapir ◽  
North American Craton

AbstractThe Pioneer Formation of southwestern British Columbia (Canada) is composed predominantly of middle to late Triassic pillow basalts. These rocks are an integral part of the Cadwallader and the Bridge River terranes that were delaminated from the oceanic lithosphere and stacked against the continental margin of the North American craton by middle Jurassic time. The basalts are underlain and locally intercalated with ribbon cherts and argillites that range in age from Mississippian to Triassic. The Triassic basalts are conformably overlain by clastic sediments containing late Carnian–Norian conodont fauna. The tholeiitic basalts have enriched and depleted REE patterns, and have been emplaced in an oceanic environment. The compositional variations of the basalts are attributed to dynamic partial melting of source rocks that are believed to have been part of the rising mantle diapir. According to our model, after initial melting in the garnet stability field, the mantle diapir rose up to the spinel stability field where it underwent subsequent melting. The reconstructed stratigraphy of the Bridge River area may be interpreted in terms of an oceanic plate moving over a mantle plume and into a trench where offscraping preserved tectonic lenses of the subducting plate in an accretionary prism.

Protonation effects on dynamic flux properties of aqueous metal complexes

2009 ◽  
Vol 74 (10) ◽  
pp. 1543-1557 ◽  
Author(s):  
Herman P. Van Leeuwen ◽  
Raewyn M. Town
Keyword(s):  
Complex Formation ◽  
Metal Ion ◽  
Good Description ◽  
Minor Component ◽  
Outer Sphere ◽  
Metal Species ◽  
Central Metal ◽  
Inner Sphere ◽  
A Minor ◽  
Protonated Ligand

The degree of (de)protonation of aqueous metal species has significant consequences for the kinetics of complex formation/dissociation. All protonated forms of both the ligand and the hydrated central metal ion contribute to the rate of complex formation to an extent weighted by the pertaining outer-sphere stabilities. Likewise, the lifetime of the uncomplexed metal is determined by all the various protonated ligand species. Therefore, the interfacial reaction layer thickness, μ, and the ensuing kinetic flux, Jkin, are more involved than in the conventional case. All inner-sphere complexes contribute to the overall rate of dissociation, as weighted by their respective rate constants for dissociation, kd. The presence of inner-sphere deprotonated H2O, or of outer-sphere protonated ligand, generally has a great impact on kd of the inner-sphere complex. Consequently, the overall flux can be dominated by a species that is a minor component of the bulk speciation. The concepts are shown to provide a good description of experimental stripping chronopotentiometric data for several protonated metal–ligand systems.

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