Zeolite Fades Metamorphism of the Late Cretaceous Nanaimo Group, Vancouver Island and Gulf Islands, British Columbia

Stewart, Richard J.; Page, R.J.

doi:10.1139/e74-024

Cited by 10 publications

(6 citation statements)

References 5 publications

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“…Any northward coast‐wise transport of all three units occurred during oblique subduction (Coutts et al., 2020; Matthews et al., 2017). At ∼52 Ma (Figure 11b), the Metchosin Basalt was erupted as part of an oceanic plateau (U‐Pb zircon age of 52 ± 2 Ma; Massey, 1986), while the LRC was underthrust and deformed as an accretionary complex during subduction of the Kula/Resurrection and Farallon plates, and the Nanaimo Group was shallowly buried (Stewart & Page, 1974). The Kula/Resurrection‐Farallon ridge (and slab window) was subducted ahead of the Metchosin Basalt.…”

Section: Discussionmentioning

confidence: 99%

Structural and Metamorphic History of the Leech River Shear Zone, Vancouver Island, British Columbia

et al. 2022

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Subduction zone dynamics are strongly influenced by the mechanical properties of subduction interface shear zones (Behr et al., 2022). However, the relevant properties of subduction interfaces, such as their widths, rock types, and internal structure, cannot be determined via geophysical observation. Instead, field-and microscale observations of exhumed shear zones that were active during subduction are needed to fill this knowledge gap. Subduction dynamics and thermal gradients evolve as they mature (e.g., Holt & Condit, 2021), and subduction zones can encompass a broad range of environments (Chelle-Michou et al., 2022), for example, when influenced by atypical subduction geometries like ridge subduction (e.g., Brown, 1998;DeLong et al., 1979;Sakaguchi, 1996). A more complete inventory capturing the variability of subduction interfaces is therefore needed to better understand their behavior.The Canadian Cordillera potentially exposes numerous subduction-related structures as it was assembled through a series of accretionary orogenies. One candidate structure is the Leech River Fault (Figure 1), a terrane-bounding fault located on southern Vancouver Island in British Columbia that juxtaposes mafic volcanic and igneous rocks of the Metchosin Igneous Complex (MIC) to the south with the predominantly metapelitic Leech River Complex (LRC). For clarity, we will term this structure the "Leech River Shear Zone" (LRSZ) to differentiate it from the recently active "Leech River Fault," which is locally coincident (

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Section: Discussionmentioning

confidence: 99%

Structural and Metamorphic History of the Leech River Shear Zone, Vancouver Island, British Columbia

et al. 2022

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“…Recently discovered fossils indicate that the Nanaimo locally ranges down into the Coniacian or Turonian (P. Ward, oral communication, 1985). Stewart and Page (1974) show that zeo lite metamorphic assemblages are widespread in the Nanaimo Group.…”

Section: Ha Ro Terrane: Up Per Triassic and Ju Ra-creta Ceous Volcanimentioning

confidence: 89%

The Late Cretaceous San Juan thrust system, San Juan Islands, Washington

Brandon

Cowan²,

Vance³

1988

Geological Society of America Special Papers

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The San Juan Islands expose a thick and regionally extensive sequence of Late Cretaceous thrust faults and nappes, referred to as the San Juan thrust system. This thrust system, which straddles the southeastern edge of the Wrangellia terrane of Van couver Island, contains important information on the accretionary history of Wrangellia and other, related, far-traveled terranes. Nappes of the thrust system contain a diverse group of rocks ranging from early Paleozoic to middle Cretaceous in age. Based on contrasts in stratigraphy, metamorphism, and geochemistry, we identify five terranes within, and peripheral to, the thrust system. These terranes were widely separated from each other, and also from Wrangellia, until the Late Jurassic: (1) the Haro terrane, an Upper Triassic arc-volcanic sequence; (2) the Turtleback terrane, a Paleozoic arc plutonic and volcanic unit; (3) the Deadman Bay terrane, a Permian to Lower Jurassic oceanic-island sequence containing Tethyan-fusulinid timestones; (4) the Garrison ter rane, a Permo-Triassic, high-pressure metamorphic unit; and (5) the Decatur terrane, a Middle to Upper Jurassic ophiolite and superimposed arc-volcanic sequence. Thick Jura-Cretaceous clastic units are linked to these older San Juan terranes and to Wran gellia, either as directly overlapping units or by the presence of clastic material derived from the terranes. The voluminous amount of clastic material in these Jura-Cretaceous units requires a large, subaerially exposed source region. We infer that this source region was a continent-like landmass, presumably part of continental America (North or Central?). Late Cretaceous thrusting juxtaposed these older terranes and disrupted the Jura Cretaceous clastic units. Very low-temperature high-pressure metamorphic assem blages, including lawsonite and aragonite, were developed during this event, and formed as a direct result of thrust-related burial to depths of about 20 km. Stratigraphic evi dence indicates that structural burial, metamorphism, and subsequent uplift back to the surface all occurred during a very short time interval, between 100 and 84 Ma, with average vertical transport rates of about 2 km/m.y. The Upper Cretaceous Nanaimo Group, a syn-orogenic basin to the north of the San Juan system, contains cobbles of metamorphosed rocks from the San Juan nappes, and therefore records the erosional unroofing of the thrust system. We envision the San Juan system to be a short-lived collision-like orogen, rather than a long-lived subduction complex. This conclusion is based primarily on the diver sity of rock units involved and the punctuated nature of the deformation. What remains unclear is the cause of this orogenic deformation. The clastic-rich Jura-Cretaceous units imply that Wrangellia and the older San Juan terranes were adjacent to or part of the American continent by latest Jurassic time. Moreover, there is no evidence for the arrival and collision of an exotic terrane during the Cretaceous. As a result, the San Juan system is considered to be the produc...

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“…Wrangellia and the overlying Nanaimo Group strata were deformed in the Cenozoic Cowichan fold and thrust belt that formed in response to Eocene accretion of the Crescent terrane (Eddy et al., 2017; England & Calon, 1991). The minerals laumontite and heulandite, identified in the uppermost ∼2,500 m of the stratigraphic succession indicate that only zeolite‐grade burial metamorphism affected rocks of the basin (England, 1990; Stewart & Page, 1974). Apatite fission track and vitrinite reflectance data suggest peak temperatures of <215°C were reached by some parts of the basin and underlying basement during the Eocene (England et al., 1997).…”

Section: Geological Backgroundmentioning

confidence: 99%

Improved Provenance Constraints for Nanaimo Group Sediments, British Columbia, Canada, Through Zircon LA‐ICP‐MS Depth‐Profiling

et al. 2022

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Zeolite Fades Metamorphism of the Late Cretaceous Nanaimo Group, Vancouver Island and Gulf Islands, British Columbia

Cited by 10 publications

References 5 publications

Structural and Metamorphic History of the Leech River Shear Zone, Vancouver Island, British Columbia

Structural and Metamorphic History of the Leech River Shear Zone, Vancouver Island, British Columbia

The Late Cretaceous San Juan thrust system, San Juan Islands, Washington

Improved Provenance Constraints for Nanaimo Group Sediments, British Columbia, Canada, Through Zircon LA‐ICP‐MS Depth‐Profiling

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