Frozen subduction in Canada's Northwest Territories: Lithoprobe deep lithospheric reflection profiling of the western Canadian Shield

Cook, Frederick A.; Velden, Arie J. van der; Hall, Kevin; Робертс, Б.

doi:10.1029/1998tc900016

Cited by 263 publications

(288 citation statements)

References 62 publications

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“…Differences in station spacing are accounted for by a variable horizontal stretching proportional to the station separation (Figure 3b). This approach allows comparison of the profiles with timemigrated reflection data of Cook et al [1999] through a simple scaling between the direct P-to-S conversion time and the 2-way vertical P reflection time as described in more detail in section 7.…”

Section: Methodsmentioning

confidence: 99%

“…It comprised a series of geophysical and geological experiments that led to several important discoveries. In particular, an active-source, seismic reflection experiment in the Wopmay orogen revealed the presence of several clearly defined and laterally coherent mantle reflectors [Cook et al, 1998[Cook et al, , 1999. The most prominent among them is an eastward dipping layer in the lithospheric mantle merging with the crust at the suture of Fort Simpson and Hottah terranes, and extending eastward beneath the Great Bear magmatic arc where it reaches a depth of $100 km (see Figure 1b for geographic location).…”

Section: Introductionmentioning

confidence: 99%

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The teleseismic signature of fossil subduction: Northwestern Canada

Mercier¹,

Bostock²,

Audet³

et al. 2008

J. Geophys. Res.

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broadband, three-component seismometers were deployed along the MacKenzie-Liard Highway in Canada's Northwest Territories as part of the joint Lithoprobe-IRIS Canada Northwest Experiment (CANOE). These stations traverse a paleo-Proterozoic suture and subduction zone that has been previously documented to mantle depths using seismic reflection profiling. Teleseismic receiver functions computed from $250 earthquakes clearly reveal the response of the ancient subduction zone. On the radial component, the suture is evident as a direct conversion from the Moho, the depth of which increases from $30 km to $50 km over a horizontal distance of $70 km before its signature disappears. The structure is still better defined on the transverse component where the Moho appears as the upper boundary of a 10 km thick layer of anisotropy that can be traced from 30 km to at least 90 km depth. The seismic response of this layer is characterized by a frequency dependence that can be modeled by upper and lower boundaries that are discontinuous in material properties and their gradients, respectively. Anisotropy can be characterized by a ±5% variation in shear velocity and hexagonal symmetry with a fast axis that plunges at an oblique angle to the subduction plane. The identification of this structure provides an unambiguous connection between fossil subduction and fine-scale, anisotropic mantle layering. Previous documentation of similar layering below the adjacent Slave province and from a range of Precambrian terranes across the globe provides strong support for the thesis that early cratonic blocks were stabilized through processes of shallow subduction.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The teleseismic signature of fossil subduction: Northwestern Canada

Mercier¹,

Bostock²,

Audet³

et al. 2008

J. Geophys. Res.

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show abstract

“…In NW Canada (SNOR-CLE transect), for instance, a delaminated crustal structure has been found by tracing the continuity of the reflective layers in the lower crust and the uppermost mantle. The delamination was considered to be generated by collision tectonics of several continental blocks during the early-Proterozoic ages (e.g., Cook et al, 1999;Eaton et al, 1999). As such, the reflection image of a terrain is a result of the various tectonic processes experienced during continental evolution.…”

Section: Introductionmentioning

confidence: 99%

Origins of the lower crustal reflectivity in the Lützow-Holm Complex, Enderby Land, East Antarctica

Kanao

Ishikawa

2014

Earth Planet Sp

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The combination of rock velocities with a seismic signature has been used as a clue to understanding the structure and evolution of the continental lithosphere. The lower crustal reflectivity beneath part of the Pan-African orogeny, the Lützow-Holm Complex (LHC), Western Enderby Land, East Antarctica, has been imaged on single-fold seismic reflection profiles using active seismic studies on the continental ice sheet. The set of velocity layers at middle to lower crustal depths were obtained by modeling the later phases of teleseismic receiver functions observed at Syowa Station (39• E, 69• S), in the LHC. The later phases around 10-16 s from P onset in radial components are explained by assuming a layered lower crustal model with velocity changes of 0.3 km/s in shear waves for 0.5-1.0 km thick layers. The origin of lower crustal reflectivity is discussed in terms of high-pressure laboratory measurements on metamorphic rocks from Western Enderby Land. Lower crustal velocities of 6.9 km/s derived by seismic refraction surveys can be explained by a major composition of mafic pyroxene granulite, as occurs in the Archean Napier Complex. A tectonic model involving collision between the paleo East and West Gondwana blocks during the last stage of Pan-African orogeny is presented to explain the high velocities and reflectivity in the lower crust underlying the LHC. The Napier Complex is considered to have descended eastward under part of the Pan-African belt (LHC), generating a higher-pressure mafic granulite composition. The reflectivity of the lower crust of the LHC may have been enhanced subsequently by extensional stress during the breakup process.

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“…There have been numerous articles written on the subject and academics will continue to fill journal pages with arguments on the subject. Suffice it to say that the results of the Canadian LITHOPROBE project have provided convincing arguments for subduction related processes and images of potential fossil subduction systems potentially as old as 3600 Ma (Cook et al, 1998), but certainly well and truly active by about 3000 Ma (Kimura et al, 1993). Figure 4 shows a seismic reflection image which has been interpreted as a fossil subduction zone.…”

Section: Subduction Zones In the Early Earthmentioning

confidence: 99%

Subduction fluxes through geologic time

Ludden

2009

Applied Geochemistry

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Much of my research career has been spent working both on modern oceanic volcanic systems and at the same time looking at their Archaean counterparts. Many authors have attempted to make inferences on early Earth models based on modern processes which can be increasingly well constrained. In this short review I show how we are beginning to understand and quantify inputs to modern subduction systems and I pose some questions as to how these processes may have affected Earth's evolution in its distant past.Geochemical models have convincingly demonstrated that sediment and altered oceanic crust must be recycled into the mantle through subduction zones. These 'subduction factories' use these components, along with molten mantle, to create arc magmas. The 'residue' from this process is recycled into the mantle and has a modified chemical and mineralogical composition. The altered oceanic crust input function in the current plate tectonic cycle seems to be relatively constant in composition, but the chemical compositions of the sediment fluxes into subduction zones vary widely and control many of the end-member compositions of arc magmas. They must also control the compositions of fluids and gases derived from these magmas and ultimately ore-deposition and atmospheric fluxes associated with arc volcanoes.There is relatively strong evidence for subduction processes for at least the past 3.5 Ma and some would argue that exogenic components have been recycled into the mantle since at least ~4.3 Ma. How might the subduction fluxes have changed through time, and how might they have influenced crust, ocean and atmospheric compositions?Can different ore regimes in temporal and spatial distribution on Earth be related to the change in inputs and residues from the subduction factory through time?

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Frozen subduction in Canada's Northwest Territories: Lithoprobe deep lithospheric reflection profiling of the western Canadian Shield

Cited by 263 publications

References 62 publications

The teleseismic signature of fossil subduction: Northwestern Canada

The teleseismic signature of fossil subduction: Northwestern Canada

Origins of the lower crustal reflectivity in the Lützow-Holm Complex, Enderby Land, East Antarctica

Subduction fluxes through geologic time

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