AFTER THEIR ACCRETION TO THE LAURENTIAN MARGIN, ROCKS IN WESTERN CONNECTICUT STAYED DEEP AND HOT FOR 60 MILLION YEARS

The Scottish Caledonides have grown by the accretion of terranes generated somewhere along the Laurentian margin. By the time these terranes had been emplaced along the Scottish sector, they were structurally truncated then reassembled to form an incomplete collage of indirectly related tectonic elements of a destructive margin. The basement to some of these tectonic elements and the basement blocks belonging to the previously accreted Precambrian are of uncertain provenance and a source in the Pan-African craton is possible. As terranes migrate along the orogen they generate in the fault zones and on their periphery a reservoir of mature sediment. This mature sediment is produced because of the recycling produced during the generation and destruction of sedimentary basins developing during terrane translation. At each period of recycling the mature sediments are mixed with less mature sediments yielded from local uplifts generated by the new basin formation. If a large part of the orogen suffers orthogonal closure, giant river systems may form and disperse sediment across terranes. This is likely to have happened during the Devonian-Carboniferous of parts of N. Europe.

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Geochemical and Sr–Nd isotopic constraints on the mantle source of Neoproterozoic mafic dikes of the rifted eastern Laurentian margin, north-central Appalachians, USA

Lithos ◽

10.1016/j.lithos.2014.11.011 ◽

2015 ◽

Vol 212-215 ◽

pp. 202-213 ◽

Cited By ~ 15

Author(s):

Richard A. Volkert ◽

Mark D. Feigenson ◽

Sara Mana ◽

Louise Bolge

Keyword(s):

Mantle Source ◽

North Central ◽

Central Appalachians ◽

Laurentian Margin ◽

Isotopic Constraints

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A seismic-based cross-section of the Grenville Orogen in southern Ontario and western Quebec

Canadian Journal of Earth Sciences ◽

10.1139/e99-094 ◽

2000 ◽

Vol 37 (2-3) ◽

pp. 183-192 ◽

Cited By ~ 61

Author(s):

D J White ◽

D A Forsyth ◽

I Asudeh ◽

S D Carr ◽

H Wu ◽

...

Keyword(s):

Cross Section ◽

Seismic Refraction ◽

Shear Zones ◽

Tectonic Zone ◽

Grenville Province ◽

Crustal Layer ◽

Seismic Reflection Data ◽

Velocity Models ◽

Laurentian Margin ◽

Structural Boundary

A schematic crustal cross-section is presented for the southwestern Grenville Province based on reprocessed Lithoprobe near-vertical incidence seismic reflection data and compiled seismic refraction - wide-angle velocity models interpreted with geological constraints. The schematic crustal architecture of the southwest Grenville Province from southeast to northwest comprises allochthonous crustal elements (Frontenac-Adirondack Belt and Composite Arc Belt) that were assembled prior to ca. 1160 Ma, and then deformed and transported northwest over reworked rocks of pre-Grenvillian Laurentia and the Laurentian margin primarily between 1120 and 980 Ma. Reworked pre-Grenvillian Laurentia and Laurentian margin rocks are interpreted to extend at least 350 km southeast of the Grenville Front beneath all of the Composite Arc Belt. Three major structural boundary zones (the Grenville Front and adjacent Grenville Front Tectonic Zone, the Central Metasedimentary Belt boundary thrust zone, and the Elzevir-Frontenac boundary zone) have been identified across the region of the cross-section based on their prominent geophysical signatures comprising broad zones of southeast-dipping reflections and shallowing of mid-crustal velocity contours by 12-15 km. The structural boundary zones accommodated southeast over northwest crustal stacking at successively earlier times during orogeny (ca. 1010-980 Ma, 1080-1060 Ma, and 1170-1160 Ma, respectively). These shear zones root within an interpreted gently southeast-dipping regional décollement at a depth of 25-30 km corresponding to the top of a high-velocity lower crustal layer.

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Trace element and Pb isotopic constraints on the provenance of the Rosroe and Derryveeny formations, South Mayo, Ireland

Transactions of the Royal Society of Edinburgh Earth Sciences ◽

10.1017/s0263593300000353 ◽

2002 ◽

Vol 93 (2) ◽

pp. 101-110 ◽

Cited By ~ 3

Author(s):

Peter D. Clift ◽

Amy E. Draut ◽

Robyn Hannigan ◽

Graham Layne ◽

Jerzy Blusztajn

Keyword(s):

Trace Element ◽

Limited Range ◽

Ion Microprobe ◽

Pb Isotope ◽

Metamorphic Belt ◽

Volcanic Arc ◽

Trace Element Chemistry ◽

Lower Ordovician ◽

Western Ireland ◽

Laurentian Margin

The Rosroe Formation comprises a series of Lower Ordovician (Llanvirn) conglomerates and sandstones, that lies on the southern limb of the South Mayo Trough, within the Iapetus Suture Zone of western Ireland. Trace element chemistry of granite boulders within the formation indicates a continental, rather than a volcanic arc character that can be correlated to latest Precambrian granites within the Dalradian Metamorphic Block, part of the deformed Laurentian margin. A minority of the clasts may correlate with syn-collisional granites, similar to, but older than, the Oughterard Granite of Connemara. Pb isotope compositions of K-feldspar grains within the sandstones, measured by both ion microprobe and conventional mass spectrometry, show a clear Laurentian affinity, albeit with greater source variability in the sand grains compared to a limited range in the proximal boulders. Palaeo-current indicators demonstrate dominant derivation from the NE, with a significant axial E–W flow. We propose that the Rosroe Formation records unroofing of a rapidly exhuming Dalradian metamorphic belt in North Mayo, following extensional collapse of the Grampian Orogen starting at ˜468 Ma, with minor input from a southerly arc source. The lack of metamorphic input from the S until deposition of the Derryeeny Conglomerate argues that the Connemara terrane was not positioned S of South Mayo Trough through strike-slip faulting until after the end of Rosroe sedimentation (460–443 Ma).

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Stratigraphy and lithogeochemistry of the Goldenville horizon and associated rocks, Baie Verte Peninsula, Newfoundland

10.4095/328990 ◽

2021 ◽

Author(s):

C Mueller ◽

S J Piercey ◽

M G Babechuk ◽

D Copeland

Keyword(s):

Gold Mineralization ◽

Iron Formation ◽

Fine Grained ◽

Hydrothermal Sediment ◽

Post Archean Australian Shale ◽

Oxygenated Water ◽

Volcaniclastic Rocks ◽

Laurentian Margin ◽

Mn Oxides ◽

Hydrothermal Venting

The Goldenville horizon in the Baie Verte Peninsula is an important stratigraphic horizon that hosts primary (Cambrian to Ordovician) exhalative magnetite and pyrite and was a chemical trap for younger (Silurian to Devonian) orogenic gold mineralization. The horizon is overlain by basaltic flows and volcaniclastic rocks, is intercalated with variably coloured argillites and cherts, and underlain by mafic volcaniclastic rocks; the entire stratigraphy is cut by younger fine-grained mafic dykes and coarser gabbro. Lithogeochemical signatures of the Goldenville horizon allow it to be divided into high-Fe iron formation (HIF; &gt;50% Fe2O3), low-Fe iron formation (LIF; 15-50% Fe2O3), and argillite with iron minerals (AIF; &lt;15% Fe2O3). These variably Fe-rich rocks have Fe-Ti-Mn-Al systematics consistent with element derivation from varying mineral contributions from hydrothermal venting and ambient detrital sedimentation. Post-Archean Australian Shale (PAAS)-normalized rare earth element (REE) signatures for the HIF samples have negative Ce anomalies and patterns similar to modern hydrothermal sediment deposited under oxygenated ocean conditions. The PAAS-normalized REE signatures of LIF samples have positive Ce anomalies, similar to hydrothermal sediment deposited under anoxic to sub-oxic conditions. The paradoxical Ce behaviour is potentially explained by the Mn geochemistry of the LIF samples. The LIF have elevated MnO contents (2.0-7.5 weight %), suggesting that Mn from hydrothermal fluids was oxidized in an oxygenated water column during hydrothermal venting, Mn-oxides then scavenged Ce from seawater, and these Mn-oxides were subsequently deposited in the hydrothermal sediment. The Mn-rich LIF samples with positive Ce anomalies are intercalated with HIF with negative Ce anomalies, both regionally and on a metre scale within drill holes. Thus, the LIF positive Ce anomaly signature may record extended and particle-specific scavenging rather than sub-oxic/redox-stratified marine conditions. Collectively, results suggest that the Cambro-Ordovician Taconic seaway along the Laurentian margin may have been completely or near-completely oxygenated at the time of Goldenville horizon deposition.

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