The Dog Bay – Liberty Line and its significance for Silurian tectonics of the northern Appalachian orogen1This article is one of a series of papers published in this CJES Special Issue: In honour of Ward Neale on the theme of Appalachian and Grenvillian geology.2Geological Survey of Canada Contribution 20100257.

Douglas N. Reusch; Cees R. van Staal

doi:10.1139/e11-024

The Dog Bay – Liberty Line and its significance for Silurian tectonics of the northern Appalachian orogen1This article is one of a series of papers published in this CJES Special Issue: In honour of Ward Neale on the theme of Appalachian and Grenvillian geology.2Geological Survey of Canada Contribution 20100257.

Canadian Journal of Earth Sciences ◽

10.1139/e11-024 ◽

2012 ◽

Vol 49 (1) ◽

pp. 239-258 ◽

Cited By ~ 4

Author(s):

Douglas N. Reusch ◽

Cees R. van Staal

Keyword(s):

New England ◽

Volcanic Belt ◽

Passive Margin ◽

Special Issue ◽

Marine Strata ◽

Lower Silurian ◽

Slab Breakoff ◽

Minimal Contrast ◽

Back Arc ◽

Extensional Setting

The Dog Bay Line, a Silurian suture key to deciphering Appalachian accretionary history, was first recognized in Newfoundland. It marks where the Ordovician Tetagouch–Exploits ensimatic back-arc basin (TEB), which had opened within the leading peri-Gondwanan Gander terrane, finally closed. Here, we extrapolate this suture into New England, placing it between the Liberty–Orrington–Miramichi inliers (LOM) and the Merrimack–Fredericton trough (MFT). Southeastward, marine strata of the MFT overlie the TEB passive margin, exposed in the Ganderian St. Croix block, and display southeast-vergent structures transected by Acadian cleavage. They structurally underlie southeast-vergent thrusts at the base of the LOM. Northwestward, the LOM, Central Maine – Matapedia trough (CMMT), and Lower Silurian igneous rocks record elements of the upper plate trench–arc system, respectively, a subduction complex, forearc basin, and arc. The CMMT forearc received detritus both from the northwesterly arc region, and also from the Early Silurian-exhumed subduction complex. Minimal contrast in Silurian turbidites near the line may be due to sediment bypassing the subduction complex, and (or) a common provenance when the complex emerged above sea level. Salinic unconformities in the upper plate (arc–trench) reflect episodes of shortening, within an overall extensional setting that resulted in thinned, weakened lithosphere, and also final uplift accompanying latest Silurian slab breakoff. Silurian strata of the Coastal Volcanic Belt document a separate arc system built on Ganderia’s trailing edge, where northwest-directed subduction of a narrow seaway led to latest Silurian collision with buoyant, strong lithosphere of Avalonia’s passive margin, and the onset of Acadian typically dextral-oblique, northwest-vergent deformation.

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Regional Seismic Attribute Analysis and Tectono-Stratigraphy of Offshore South-Western Taranaki Basin, New Zealand

10.26686/wgtn.16998832 ◽

2021 ◽

Author(s):

◽

Jan Robert Baur

Keyword(s):

New Zealand ◽

Deep Water ◽

Middle Miocene ◽

Plate Boundary ◽

Water Area ◽

Passive Margin ◽

Extensional Faulting ◽

Deep Water Area ◽

Back Arc ◽

Shelf Margin

<p>This study investigates the nature, origin, and distribution of Cretaceous to Recent sediment fill in the offshore Taranaki Basin, western New Zealand. Seismic attributes and horizon interpretations on 30,000 km of 2D seismic reflection profiles and three 3D seismic surveys (3,000 km²) are used to image depositional systems and reconstruct paleogeography in detail and regionally, across a total area of ~100,000 km² from the basin's present-day inner shelf to deep water. These data are used to infer the influence of crustal tectonics and mantle dynamics on the development of depocentres and depositional pathways. During the Cretaceous to Eocene period the basin evolved from two separate rifts into a single broad passive margin. Extensional faulting ceased before 85 Ma in the present-day deep-water area of the southern New Caledonia Trough, but stretching of the lithosphere was higher (β=1.5-2) than in the proximal basin (β<1.5), where faulting continued into the Paleocene (~60 Ma). The resulting differential thermal subsidence caused northward tilting of the basin and influenced the distribution of sedimentary facies in the proximal basin. Attribute maps delineate the distribution of the basin's main petroleum source and reservoir facies, from a ~20,000 km²-wide, Late Cretaceous coastal plain across the present-day deep-water area, to transgressive shoreline belts and coastal plains in the proximal basin. Rapid subsidence began in the Oligocene and the development of a foredeep wedge through flexural loading of the eastern boundary of Taranaki Basin is tracked through the Middle Miocene. Total shortening within the basin was minor (5-8%) and slip was mostly accommodated on the basin-bounding Taranaki Fault Zone, which detached the basin from much greater Miocene plate boundary deformation further east. The imaging of turbidite facies and channels associated with the rapidly outbuilding shelf margin wedge illustrates the development of large axial drainage systems that transported sediment over hundreds of kilometres from the shelf to the deep-water basin since the Middle Miocene. Since the latest Miocene, south-eastern Taranaki Basin evolved from a compressional foreland to an extensional (proto-back-arc) basin. This structural evolution is characterised by: 1) cessation of intra-basinal thrusting by 7-5 Ma, 2) up to 700 m of rapid (>1000 m/my) tectonic subsidence in 100-200 km-wide, sub-circular depocentres between 6-4 Ma (without significant upper-crustal faulting), and 3) extensional faulting since 3.5-3 Ma. The rapid subsidence in the east caused the drastic modification of shelf margin geometry and sediment dispersal directions. Time and space scales of this subsidence point to lithospheric or asthenospheric mantle modification, which may be a characteristic process during back-arc basin development. Unusual downward vertical crustal movements of >1 km, as inferred from seismic facies, paleobathymetry and tectonic subsidence analysis, have created the present-day Deepwater Taranaki Basin physiography, but are not adequately explained by simple rift models. It is proposed that the distal basin, and perhaps even the more proximal Taranaki Paleogene passive margin, were substantially modified by mantle processes related to the initiation of subduction on the fledgling Australia-Pacific plate boundary north of New Zealand in the Eocene.</p>

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An overview of thriving through transformation

International Journal of Rural Law and Policy ◽

10.5130/ijrlp.i2.2017.5525 ◽

2017 ◽

Author(s):

Boyd Dirk Blackwell

Keyword(s):

New England ◽

New South ◽

Human Existence ◽

Special Issue ◽

Competing Interests ◽

Biennial Conference ◽

South Wales ◽

Trade Offs ◽

Multiple Dimensions ◽

The University

The articles published in this special issue come from the blind peer review and refinement of papers presented to the biennial conference of the Australia New Zealand Society for Ecological Economics (ANZSEE) held at the University of New England (UNE) in Armidale, New South Wales (NSW), Australia on 19-23 October 2015. All papers jointly contribute to helping transform the human existence toward one that is socially, culturally, environmentally, ecologically, economically and politically sustainable. Transforming our human existence to meet these multiple dimensions of ‘true’ sustainability is a difficult task, balancing potentially competing interests and, inevitably, involving trade-offs between these dimensions.

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Passive-margin magmatism caused by enhanced slab-pull forces in central Tibet

Geology ◽

10.1130/g47957.1 ◽

2020 ◽

Author(s):

Wei Dan ◽

Qiang Wang ◽

William M. White ◽

Xian-Hua Li ◽

Xiu-Zheng Zhang ◽

...

Keyword(s):

Passive Margin ◽

Lower Plate ◽

Isotopic Signatures ◽

Ridge Subduction ◽

Slab Rollback ◽

Element Enrichment ◽

Central Tibet ◽

Back Arc ◽

Ocean Ridge ◽

Qiangtang Terrane

We report on a ca. 239 Ma mafic dike swarm intruded in the Southern Qiangtang terrane, central Tibet, that was generated on the passive continental margin of a subducting lower plate. The dikes are tholeiitic basalts and exhibit light rare earth element enrichment, modest negative anomalies in Nb and Ta, and enriched isotopic signatures. The dikes are coeval with a back-arc basin formed in the upper plate as a result of the rollback of the Paleo-Tethys oceanic slab. Thus, after ocean-ridge subduction, enhanced slab-pull forces related to slab rollback on one side of the ocean induced extension and magmatism in the passive margin on the opposite side. We argue that enhanced slab-pull forces are a previously unrecognized mechanism for the generation of lower-plate passive-margin magmatism.

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Geochemistry of Sainte-Marguerite volcanic rocks: implications for the evolution of Silurian–Devonian volcanism in the Gaspé Peninsula

Canadian Journal of Earth Sciences ◽

10.1139/e07-012 ◽

2008 ◽

Vol 45 (1) ◽

pp. 15-29 ◽

Cited By ~ 1

Author(s):

Alan D’hulst ◽

Georges Beaudoin ◽

Michel Malo ◽

Marc Constantin ◽

Pierre Pilote

Keyword(s):

Lower Devonian ◽

Volcanic Rocks ◽

Magma Source ◽

Volcanic Arc ◽

Lower Silurian ◽

Trace Element Signature ◽

Arc Setting ◽

Back Arc ◽

Gaspe Peninsula ◽

Gaspé Peninsula

The Lower Devonian Sainte-Marguerite volcanic rocks are part of a Silurian–Devonian volcanic sequence deposited between the Taconian and Acadian orogenies in the Gaspé Peninsula, Quebec, Canada. The Sainte-Marguerite unit includes basaltic and dacitic lava flows with calc-alkaline and volcanic-arc affinities. Such affinities are also recorded by the trace-element signature in Lower Silurian and most Lower Devonian volcanic units of the Gaspé Peninsula. However, most of the other Silurian–Devonian volcanic rocks occurring in the Gaspé Peninsula have been previously interpreted to have erupted in an intracontinental setting. A back-arc setting for the Gaspé Peninsula between the Taconian and Acadian orogenies could account for these subduction volcanic-arc signatures, though a metasomatized lithospheric mantle magma source, unrelated to subduction, cannot be excluded. Lower Silurian and Lower Devonian volcanic rocks in the central part of the Gaspé Peninsula show an arc affinity, whereas Upper Silurian and Lower to Middle Devonian volcanic rocks, located in the south and north of the Gaspé Peninsula, respectively, show a within-plate affinity. The Lower Devonian Archibald Settlement and Boutet volcanic rocks of the southern and northern Gaspé Peninsula, respectively, show a trend toward a within-plate affinity. This suggests that within-plate volcanism migrated from south to north through time in an evolving back-arc environment and that the subduction signature of Lower Silurian and Lower Devonian rocks results from a source that melted only under the central part of the Gaspé Peninsula.

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The ophiolites of the Tibetan Geotraverses, Lhasa to Golmud (1985) and Lhasa to Kathmandu (1986)

Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences ◽

10.1098/rsta.1988.0127 ◽

1988 ◽

Vol 327 (1594) ◽

pp. 215-238 ◽

Cited By ~ 107

Keyword(s):

Subduction Zone ◽

Oceanic Lithosphere ◽

Island Arc ◽

Passive Margin ◽

Jinsha River ◽

Geochemical Composition ◽

The North ◽

Kunlun Mountains ◽

Slow Spreading ◽

Back Arc

Ophiolite belts are found in Tibet along the Zangbo, Banggong and Jinsha River Sutures and in the Anyemaqen mountains, the eastern extension of the Kunlun mountains. Where studied, the Zangbo Suture ophiolites are characterized by: apparently thin crustal sequences (3-3.5 k m ); an abundance of sills and dykes throughout the crustal and uppermost mantle sequences; common intraoceanic melanges and unconformities; and an N-MORB petrological and geochemical composition. The ophiolites probably formed within the main neo-Tethyan ocean and the unusual features may be due to proximity to ridge-transform intersections, rather than to genesis at very slow -spreading ridges as the current consensus suggests. The Banggong Suture ophiolites have a supra-subduction zone petrological and geochemical composition — although at least one locality in the Ado Massif shows MORB characteristics. However, it is also apparent that the dykes and lavas show a regional chemical zonation, from boninites and primitive island arc tholeiites in the south of the ophiolite belt, through normal island arc tholeiites in the central belt to island arc tholeiites transitional to N-MORB in the north. The ophiolites could represent fragments of a fore-arc, island arc, back-arc complex developed above a Jurassic, northward-dipping subduction zone and emplaced in several stages during convergence of the Lhasa and Qiangtang terranes. The ophiolites of the Jinsha River Suture have a N-MORB composition where analysed, but more information is needed for a proper characterization. The Anyemaqen ophiolites, where studied, have a within-plate tholeiite composition and may have originated at a passive margin: it is not, however, certain whether true oceanic lithosphere, as opposed to strongly attenuated continental lithosphere, existed in this region.

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Geochronology and geochemistry of Precambrian gneisses, metabasites, and pegmatite from the Tobacco Root Mountains, northwestern Wyoming craton, MontanaThis article is one of a series of papers published in this Special Issue on the theme of Geochronology in honour of Tom Krogh.T.E. Krogh deceased April 2008.

Canadian Journal of Earth Sciences ◽

10.1139/e10-095 ◽

2011 ◽

Vol 48 (2) ◽

pp. 161-185 ◽

Cited By ~ 10

Author(s):

Thomas E. Krogh ◽

Sandra L. Kamo ◽

Thomas B. Hanley ◽

David F. Hess ◽

Peter S. Dahl ◽

...

Keyword(s):

Special Issue ◽

Zircon Age ◽

Mafic Rocks ◽

Wyoming Craton ◽

Fault Block ◽

Mid Ocean Ridge ◽

Tonalitic Gneiss ◽

Back Arc ◽

Ocean Ridge ◽

Tobacco Root Mountains

The Middle Mountain Metamorphic Domain of the Montana Metasedimentary Terrane, northwestern Wyoming Craton, within the northwestern Tobacco Root Mountains, mainly comprises migmatized tonalitic gneiss interlayered with amphibolitic (hornblende) gneiss, both of which are cut by metamorphosed mafic rocks. Together, these gneisses are defined as Middle Mountain Gneiss. Archean tonalitic gneiss from west of, and amphibolitic gneiss from east of, the Bismark Fault give, from chemically and air-abraded zircon grains, U–Pb ID–TIMS ages of 3325.5 ± 1.7 and 3340 Ma, respectively. These results reflect primary magmatic ages and show that the Middle Mountain Gneiss extends into the northern area of the Central Fault Block, between the Bismark and Mammoth faults. Older crustal processes in the tonalitic gneiss are evidenced by inherited grains, the oldest of which is >3460 Ma. A metabasite hosted in tonalitic gneiss in the Bismark Fault selvage zone yields a zircon age of 2468 Ma, which is interpreted as the time of metamorphism. This date and other ca. 2470 Ma dates known in the region reflect a series of thermotectonic events designated here as the Beaverhead – Tobacco Root Orogeny. Geochemical evidence in the Central Fault Block metabasites suggests that their >2470 Ma precursors evolved in a back-arc – arc-rift setting, whereas their equivalents west of the Bismark Fault were largely mid-ocean ridge basalt-related tholeiites and east of the Central Fault Block were back-arc tholeiites showing some continental affinity. The metabasite was metamorphosed, deformed, and intruded by pegmatite at 1756 Ma during the Big Sky Orogeny. This orogenic event also produced new zircon growth in Archean tonalitic gneiss. Monazite with an age of 75 Ma, found at one location, reflects nearby intrusion of the Cretaceous Tobacco Root Batholith.

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