Geodynamic models of terrane accretion: Testing the fate of island arcs, oceanic plateaus, and continental fragments in subduction zones

Establishing the paleogeographic origin of most of the terranes within the Cordillera remains an ellusive goal; despite more than 10 years of multidisciplinary research, the home port of any major terrane has not been identified unequivocally. Even most continental fragments that show affinities to North America cannot be repositioned confidently along the Cordilleran margin, and some continental fragments (e.g. Chulita) probably are not North American in origin. Cordilleran oceanic terranes, including island arcs, seamounts, off-ridge islands, and scraps of ocean basins, are especially difficult to reposition because Panthalassa has been destroyed. Faunal studies with emphasis on palaeobiogeographic affinities are the most useful, particularly when coupled with analyses of faunal diversity and endemism. Such studies suggest that some terranes previously thought to have formed near the Cordillerran margin were situated thousands of kilometres to the west, and were separated from the continent by broad ocean basins, rather than by a narrow marginal sea.

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4D stress signals in the upper plate record subduction nucleation and lateral propagation

10.5194/egusphere-egu21-6388 ◽

2021 ◽

Author(s):

Brandon Shuck ◽

Sean Gulick ◽

Harm Van Avendonk ◽

Michael Gurnis ◽

Rupert Sutherland ◽

...

Keyword(s):

Subduction Zones ◽

Time Lag ◽

Plate Boundary ◽

Subduction Initiation ◽

The North ◽

Stress Signal ◽

Show Evidence ◽

Stress Signals ◽

Geologic Record ◽

Geodynamic Models

<div> <p><strong>Subduction zones are fundamental to Earth&#8217;s plate tectonic history yet details of how they initiate remain enigmatic. Geodynamic models suggest that early stages of subduction depend on whether underthrusting is driven by horizontal or vertical forces. If horizontal forces dominate, the upper plate experiences compression and uplift followed by extension and subsidence, whereas vertically-forced subduction involves only extension. Geologic evidence from the Izu-Bonin-Mariana forearc supports a ~1 Myr rapid transition, whereas observations from Oman indicate a >8 Myr time lag between initial underthrusting and the onset of upper plate extension. We present seismic images of the incipient Puysegur subduction zone south of New Zealand. Our data show evidence for a stress signal (compression followed by extension) that spread from north to south as the trench initiated and propagated along the plate boundary. Both the magnitude and duration of the compressional phase diminish from ~8 Myrs long in the north to ~5 Myrs in the south. This timing indicates that the transition to self-sustaining subduction is more rapid when an adjacent downgoing slab contributes a driving force that aids subduction initiation. We therefore argue for a new framework in which horizontal forces dominate at sites of subduction nucleation and vertical forces gradually strengthen during later propagation as the developing plate boundary weakens and the slab-pull force intensifies. Our findings corroborate evidence for ancient horizontally-forced subduction initiation events and suggest that the geologic record may be biased, since vertically-forced scenarios of subduction propagation are more likely to be preserved than destructive subduction nucleation events. </strong></p> </div>

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Evolution and dynamics of subduction zones from 4-D geodynamic models

Geochimica et Cosmochimica Acta ◽

10.1016/j.gca.2006.06.1134 ◽

2006 ◽

Vol 70 (18) ◽

pp. A612

Author(s):

D.R. Stegman ◽

J. Freeman ◽

W.P. Schellart ◽

L.N. Moresi ◽

D. may

Keyword(s):

Subduction Zones ◽

Geodynamic Models

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Future accreted terranes: a compilation of island arcs, oceanic plateaus, submarine ridges, seamounts, and continental fragments

Solid Earth Discussions ◽

10.5194/sed-6-1451-2014 ◽

2014 ◽

Vol 6 (2) ◽

pp. 1451-1521 ◽

Cited By ~ 1

Author(s):

J. L. Tetreault ◽

S. J. H. Buiter

Keyword(s):

Shear Zones ◽

Crustal Thickness ◽

Ocean Floor ◽

Seismic Velocities ◽

Island Arcs ◽

Crustal Layer ◽

Oceanic Plateaus ◽

Geographical Regions ◽

Accreted Terranes ◽

Crustal Density

Abstract. Allochthonous accreted terranes are exotic geologic units that originated from anomalous crustal regions on a subducting oceanic plate and were transferred to the overriding plate during subduction by accretionary processes. The geographical regions that eventually become accreted allochthonous terranes include island arcs, oceanic plateaus, submarine ridges, seamounts, continental fragments, and microcontinents. These future allochthonous terranes (FATs) contribute to continental crustal growth, subduction dynamics, and crustal recycling in the mantle. We present a review of modern FATs and their accreted counterparts based on available geological, seismic, and gravity studies and discuss their crustal structure, geological origin, and bulk crustal density. Island arcs have an average crustal thickness of 26 km, average bulk crustal density of 2.79 g cm−3, and have 3 distinct crustal units overlying a crust-mantle transition zone. Oceanic plateaus and submarine ridges have an average crustal thickness of 21 km and average bulk crustal density of 2.84 g cm−3. Continental fragments presently on the ocean floor have an average crustal thickness of 25 km and bulk crustal density of 2.81 g cm−3. Accreted allochthonous terranes can be compared to these crustal compilations to better understand which units of crust are accreted or subducted. In general, most accreted terranes are thin crustal units sheared off of FATs and added onto the accretionary prism, with thicknesses on the order of hundreds of meters to a few kilometers. In addition many island arcs, oceanic plateaus, and submarine ridges were sheared off in the subduction interface and underplated onto the overlying continent. And other times we find evidence of collision leaving behind accreted terranes 25 to 40 km thick. We posit that rheologically weak crustal layers or shear zones that were formed when the FATs were produced can be activated as detachments during subduction, allowing parts of the FAT crust to accrete and others to accrete. In many modern FATs on the ocean floor, a sub-crustal layer of high seismic velocities, interpreted as ultramafic material, could serve as a detachment or delaminate during subduction.

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DIVERSITY OF ISLAND ARCS: JAPAN, PHILIPPINES, NORTHERN MOLUCCAS

The APPEA Journal ◽

10.1071/aj72004 ◽

1973 ◽

Vol 13 (1) ◽

pp. 19

Author(s):

Richard W. Murphy

Keyword(s):

Late Cretaceous ◽

Subduction Zones ◽

The Philippines ◽

Island Arc ◽

Late Oligocene ◽

Island Arcs ◽

Isostatic Gravity ◽

Formed Part ◽

Northeast Asian ◽

Surface Geology

Modern bathymetric, geophysical, and volcanic studies have revealed a remarkably consistent principal profile for island arcs of the Western Pacific. Examination of surface geology, however, suggests great diversity in the geological development of island arcs. Three island arc complexes show the diversity well: Japan, the Philippines, and the Northern Moluccas.Although Japan appears to have been an island arc in roughly its present configuration only since Early Miocene time, the surface geology indicates that Japan has formed part of the continental margin of Asia at least since Permian and probably Devonian time. Subduction polarity, as displayed in paired metamorphic belts; juxtaposition of continental rise prisms with contemporaneous oceanic suites; and overall tectonic fabric strongly supports belief in the existence of the Pacific Ocean since the Devonian. Hokkaido is a reversed island arc segment which together with Sakhalin is probably a relatively recent addition to the northeast Asian continental perimeter.The Philippines were formed by the Late Oligocene coalescence of at least four island arc-subduction zone complexes into a single archipelagic basin which has remained more or less coherent throughout Neogene time. Although the oldest Philippine fossils are Permian, the island arcs probably did not start to form until Late Cretaceous time. Neogene volcanism, intrusion and sedimentation are thought to be creating a new small continent out of materials that were originally entirely oceanic.Island arc systems flanking the Molucca Sea were born in Late Cretaceous time and now appear to be in a stage of coalescence similar to that of the Philippines in Late Oligocene time. The convergence of two west-dipping and one east-dipping Benioff zones, the existence of a very large negative isostatic gravity anomaly, the outcrop of fossil subduction zones and the existence of short topographic trench segments indicate an active, youthful region of crustal construction.

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Computing LPO for Geodynamic Models in ASPECT

10.5194/egusphere-egu2020-12579 ◽

2020 ◽

Author(s):

Magali Billen ◽

Menno Fraters

Keyword(s):

Water Content ◽

Flow Pattern ◽

Subduction Zones ◽

Seismic Anisotropy ◽

Flow Patterns ◽

Mantle Flow ◽

Lattice Preferred Orientation ◽

Axis Alignment ◽

Geodynamic Models ◽

Initial Results

<p>When modeling subduction processes, the results are usually constrained by looking at the geological surface expressions, geochemistry and geophysical observations such as tomography and seismic anisotropy. Of these observations, seismic anisotropy is the only type of observation that can potentially be directly linked to the spatial flow pattern in the mantle. Seismic anisotropy in the mantle is due to lattice-preferred orientation (LPO) of olivine minerals. In subduction environments, which can have complex and changing flow patterns, it is not expected that the LPO necessarily aligns with the flow pattern. This is partly due to the fact that it takes time to realign the LPO and partly because the olivine fast axis alignment depends on the water content and the magnitude of stress. To overcome this problem, the LPO must be computed for realistic and end member subduction zones in order to be able to relate seismic anisotropy to mantle flow and thereby slab dynamics.</p><p>There are many ways to compute LPO. For this study we have used DREX (Kaminski et al., 2004), because the underlying method is accurate and fast enough for use in geodynamic models. To achieve a good and native integration with ASPECT (Kronbichler et al., 2012; Heister et al., 2017; Bangerth et al,. 2019), we have rewritten DREX in CPP as a plugin for ASPECT. In this presentation we will show how it was implemented and what the limitations and possibilities are. Furthermore, we will show initial results from 3D subduction models to study the link between seismic anisotropy and mantle flow.</p>

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Igneous and Tectonic Events in Northeastern Cape Breton Island, Nova Scotia

Canadian Journal of Earth Sciences ◽

10.1139/e72-110 ◽

1972 ◽

Vol 9 (10) ◽

pp. 1262-1277 ◽

Cited By ~ 10

Author(s):

Robert A. Wiebe

Keyword(s):

Subduction Zones ◽

Coarse Grained ◽

Island Arcs ◽

Cape Breton Island ◽

Cape Breton ◽

Igneous Activity ◽

Northern Cape ◽

History Of ◽

George River ◽

Metamorphic Unit

The geology of northern Cape Breton Island is characterized by two structurally and compositionally distinct metamorphic units and an extended history of igneous activity ranging in age from Precambrian to Devonian. The older metamorphic unit (George River Group(?)) is composed of metamorphosed psammitic and semipelitic rocks with some distinctive quartzite and coarse-grained marble layers. It was deformed and probably metamorphosed, prior to emplacement of Precambrian diorites. A younger metamorphic unit (Fourchu Group(?)) consists mostly of metamorphosed intermediate to acidic volcanic and volcaniclastic rocks and rests with angular unconformity on the George River Group (?) and the diorites. Shallow-level plutonic activity was contemporaneous with the Fourchu Group(?). Younger leucocratic granodiorites (410 m.y.) were emplaced at a depth of about 15 km and require deposition of a thick surficial sequence during the early Paleozoic (between 560 and 410 m.y.). Mississippian sedimentary rocks rest unconformably on all of the older rocks.Igneous rocks of the Precambrian are dominantly andesitic and are similar to present-day suites in island arcs associated with subduction zones. Their composition requires that they be generated in the mantle. The average compositions of igneous rocks emplaced from late Precambrian to Devonian time become more granitic and probably reflect increasing generation of magma from crustal sources.

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3D geodynamic models for the development of opposing continental subduction zones: The Hindu Kush–Pamir example

Earth and Planetary Science Letters ◽

10.1016/j.epsl.2017.10.005 ◽

2017 ◽

Vol 480 ◽

pp. 133-146 ◽

Cited By ~ 15

Author(s):

Jie Liao ◽

Taras Gerya ◽

Marcel Thielmann ◽

A. Alexander G. Webb ◽

Sofia-Katerina Kufner ◽

...

Keyword(s):

Subduction Zones ◽

Continental Subduction ◽

Hindu Kush ◽

Geodynamic Models

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