Geochemistry of amphibolite-facies volcanics and gabbros of the Storen Nappe in extensions west and southwest of Trondheim, western gneiss region, Norway: A key to correlations and paleotectonic settings

Hollocher, Kurt; Robinson, Peter; Walsh, Emily O.; Roberts, David L.

doi:10.2475/04.2012.01

Cited by 137 publications

(61 citation statements)

References 122 publications

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“…• The Ordovician back-arc basin formation in Mid Norway is linked to changing subduction polarity in the Iapetus Ocean following Early Ordovician ophiolite obduction and gave rise to the gross distribution of land areas and uplift centres (Torsvik, 1996;Grenne & Roberts, 1998;Hollocher et al, 2012;Hollocher et al, 2016). The short-term tectonics and proximity to a volcanic arc were important features in the staging of sediments in near-shore and shelfal areas and their sudden release and transport to the receptor basin.…”

Section: Discussionmentioning

confidence: 99%

“…These magmato-sedimentary associations constitute a part of the Upper Allochthon of Caledonide tectonostratigraphy. These are interpreted to represent the exotic oceanic terranes of the Iapetus Ocean deriving from far outside the Baltoscandian margin of Baltica, Laurentia, or even an intervening microcontinent Stephens & Gee, 1989;Roberts et al, 2002;Lippard, & Roberts, 2010;Hollocher et al, 2012;Nilsson & Roberts, 2014). Although well known for their paleontology, the Ordovician basinal successions in this part of Norway have received comparatively little attention with regard to their sedimentology and overall development, with a few exceptions (Siedlecka, 1967;Roberts, 1972;Buller & Johnsen, 1982).…”

Section: Introductionmentioning

confidence: 99%

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Turbidite and conglomerate successions in an Ordovician back-arc basin, Mid-Norwegian Caledonides: a result of long-term staging followed by catastrophic release of sediments

Henriksen¹,

Roberts²,

Pedersen³

2018

NJG

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The Ordovician metasedimentary rocks in the Caledonian nappes in Mid Norway were deposited in a back-arc setting, following ophiolite obduction, uplift and erosion, related to continental uplift and changing directions of subduction during this period. Deep-water conditions were established in the basin and this accommodated a thick succession of variously coarse-grained, conglomeratic and argillaceous sediments. The conglomerates typically display the well-rounded clast material of variable igneous, volcanic, sedimentary and carbonate origin and alternate between being clast-supported and matrix-supported with interbedded sandstone beds. The rounded clasts suggest significant reworking and long-term storage of sediments in the source area before transport into the deeper part of the basin. The basal surface of conglomerates always shows an erosive contact with underlying shales or coarsening-upward sandstone successions. The basal surfaces probably represent sedimentary fairways, where several conglomerate units separated by erosional contacts are stacked on top of each other. The conglomerate successions likely result from episodic release of large quantities of sediments. Between each burst of release, sediments accumulated in alluvial fans, fan deltas and fluvial delta systems along the basin shoreline and carbonate reefs established on the outer shelf. Laterally accreting channel sandstone beds were probably important in setting up sedimentary fairways for the succeeding conglomerates. In the inferred deepest part of the basin, smaller channellised features and thin-bedded turbidites seem to dominate. Channel features and hummocky cross-stratification in shelf to upper slope sandstone beds are alternatively interpreted to result from unidirectional flows and constitute an integral part of the turbidite system. By including all the observed facies within the turbidite system we invoke a depositional model which does not require a eustacy-driven sequence-stratigraphic model for explanation. We rather suggest a tectonic model involving an elevated source area, either volcanic or continental, where erosional products are stored and reworked in the alluvial accommodation zone. These sediments are built up to a threshold level and flushed to the sea by a sudden availability of large amounts of water. The actual cause of this sudden availability of water remains uncertain, but the consequent mixture of water and sediments resulted in a super-concentrated high-energy density current. Turbidite and conglomerate successions in an Ordovician back-arc basin, Mid-Norwegian Caledonides: a result of long-term staging followed by catastrophic release of sediments IntroductionThe Caledonides of central Norway are especially well known for their fragmented ophiolite assemblages and, in some areas, the overlying, richly fossiliferous, Ordovician to inferred Early Silurian, low-grade metasedimentary rocks (Bergström, 1979(Bergström, , 1997Bruton & Bockelie, 1980;Ryan et al., 1980;Neuman & Bruton, 1989;Neuman et al., 1997). The...

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Turbidite and conglomerate successions in an Ordovician back-arc basin, Mid-Norwegian Caledonides: a result of long-term staging followed by catastrophic release of sediments

Henriksen¹,

Roberts²,

Pedersen³

2018

NJG

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“…Much less abundant are andesitic, dacitic, and rhyolitic volcanic rocks, and thin marbles. Coarse-grained metamorphosed gabbroic rocks, from which our samples were collected, occur as a laterally extensive unit 16 to 33 m thick in the Moldefjord synform (Robinson, 1995;Hollocher et al, 2012), and as incompletely mapped bodies at Litleneset and elsewhere. We selected gabbroic rocks with apparent cumulate protoliths for petrographic work because they lacked chlorite.…”

Section: Sample Set and Analytical Methodsmentioning

confidence: 99%

“…Abund ant descriptive petrographic work has been done on mafic rocks in the Upper Allochthon (e.g., Grenne & Roberts, 1980;Roberts, 1982;Heim et al, 1987;Furnes et al, 1988;Bjerkgård & Bjørlykke, 1994;Hollocher et al, 2012). In general, the mafic rocks are described as greenstones, greenschists, and amphibolites.…”

Section: Metamorphism In the Central Caledonide Upper Allochthonmentioning

confidence: 99%

“…In the recent literature, most detailed petrographic work and P-T (pressure-temperature) calculations have been on eclogite and ultramafic rocks, which occur in deeply subducted parts of the Lower and Middle allochthons Hollocher et al (2012). The cross-hatched parts of the Støren Nappe show the Lower and Upper Hovin groups and related units.…”

Section: Metamorphism In the Central Caledonide Upper Allochthonmentioning

confidence: 99%

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Metamorphosed cumulate gabbros from the Støren Group of the Upper Allochthon, northern Western Gneiss Region, Norway: petrology and metamorphic record

Hollocher¹,

Robinson²,

Kennedy³

et al. 2015

NJG

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The Støren Group of the Upper Allochthon, in the Scandinavian Caledonides, contains Late Cambrian to Early Ordovician ophiolitic fragments that developed in a tholeiitic oceanic suprasubduction zone setting. These were obducted onto an epicontinental margin (Gula Complex) in the Early Ordovician, and metamorphosed in most areas to greenschist facies. Later, these rocks were thrust onto Baltica as part of the Upper Allochthon during the Silurian-Devonian Scandian Orogeny. Cumulate gabbros in the Støren Group contain the prograde metamorphic assemblage amphibole-plagioclase-diopside-epidote. They have complex textures that include early metamorphic mineral cores and inclusions, later rims, and late vein assemblages. The textures and mineral compositions in nine samples were interpreted iteratively with Perple_X thermodynamic modeling, to reveal three sequential P-T conditions: ~350°C and ~6 kbars for early prograde mineral cores and inclusions, ~530°C and ~6 kbars for peak prograde conditions, and ~425°C and ~3 kbars for an early retrograde vein assemblage. Additionally, minor but ubiquitous, discontinuous Fe 3+ -rich rims on epidote suggest the rocks underwent isothermal decompression immediately after peak prograde conditions, crossing increasingly Fe-rich epidote isopleths predicted by models. We interpret a single-episode, clockwise P-T path representing an Early Devonian phase of Scandian metamorphism. In the study area, prograde metamorphism produced these assemblages only in rocks close to the contact between the Upper and Middle allochthons, which is interpreted as a late-Scandian detachment fault (Agdenes detachment). Prograde Scandian metamorphism of this part of the Upper Allochthon was a form of contact metamorphism, occurring as the detachment fault juxtaposed cool Upper Allochthon rocks against the hotter, exhuming Middle Allochthon.

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Age and structure of the Shyok suture in the Ladakh region of northwestern India: Implications for slip on the Karakoram fault system

et al. 2015

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A precise age for the collision of the Kohistan-Ladakh block with Eurasia along the Shyok suture zone (SSZ) is one key to understanding the accretionary history of Tibet and the tectonics of Eurasia during the India-Eurasia collision. Knowing the age of the SSZ also allows the suture to be used as a piercing line for calculating total offset along the Karakoram Fault, which effectively represents the SE border of the Tibetan Plateau and has played a major role in plateau evolution. We present a combined structural, geochemical, and geochronologic study of the SSZ as it is exposed in the Nubra region of India to test two competing hypotheses: that the SSZ is of Late Cretaceous or, alternatively, of Eocene age. Coarse-continental strata of the Saltoro Molasse, mapped in this area, contain detrital zircon populations suggestive of derivation from Eurasia despite the fact that the molasse itself is deposited unconformably onto Kohistan-Ladakh rocks, indicating that the molasse is postcollisional. The youngest population of detrital zircons in these rocks (approximately 92 Ma) and a U/Pb zircon date for a dike that cuts basal molasse outcrops (approximately 85 Ma) imply that deposition of the succession began in the Late Cretaceous. This establishes a minimum age for the SSZ and rules out the possibility of an Eocene collision between Kohistan-Ladakh and Eurasia. Our results support correlation of the SSZ with the Bangong suture zone in Tibet, which implies a total offset across the Karakoram Fault of approximately 130-190 km.

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Geochemistry of amphibolite-facies volcanics and gabbros of the Storen Nappe in extensions west and southwest of Trondheim, western gneiss region, Norway: A key to correlations and paleotectonic settings

Cited by 137 publications

References 122 publications

Turbidite and conglomerate successions in an Ordovician back-arc basin, Mid-Norwegian Caledonides: a result of long-term staging followed by catastrophic release of sediments

Turbidite and conglomerate successions in an Ordovician back-arc basin, Mid-Norwegian Caledonides: a result of long-term staging followed by catastrophic release of sediments

Metamorphosed cumulate gabbros from the Støren Group of the Upper Allochthon, northern Western Gneiss Region, Norway: petrology and metamorphic record

Age and structure of the Shyok suture in the Ladakh region of northwestern India: Implications for slip on the Karakoram fault system

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