Assembly, configuration, and break-up history of Rodinia: A synthesis

Tectonic processes associated with supercontinent cycles result in a variety of basin types, and the isotopic dating of detrital minerals within sedimentary sequences assists palaeogeographical reconstructions. Basins located along the Laurentia–Baltica margin prior to assembly of Rodinia at 1.2–1.0 Ga are dominated by zircon detritus derived from contemporaneous magmatic arcs. Basins formed during assembly are also dominated by zircon detritus with ages similar to that of sediment accumulation, reflecting syn-collisional magmatism and rapid exhumation of the developing Grenville–Sveconorwegian orogen. Post-collision intracratonic basins lack input from syn-depositional magmatism, and are dominated by significantly older detritus derived from the mountain range as well as its foreland. Basins formed during late Neoproterozoic to Cambrian breakup of Rodinia are divisible into two types. Those within the Caledonides lie on the Grenville–Sveconorwegian foreland and incorporate Archaean and Palaeoproterozoic detritus derived from the cratonic interior and Mesoproterozoic detritus derived from the eroded remnants of the orogen. In the Appalachian orogen, such basins are dominated by Mesoproterozoic detritus with older detritus forming only a minor component, suggesting restricted input from the cratonic interior as a result of either the Grenville orogen still forming a drainage divide or the formation of rift shoulders.

Sedimentary basin and detrital zircon record along East Laurentia and Baltica during assembly and breakup of Rodinia

Tracing the 850-Ma continental flood basalts from a piece of subducted continental crust in the North Qaidam UHPM belt, NW China

Detrital zircons in siliciclastic units of the Dalradian Supergroup yield U–Pb ages ranging from 3.2 to 0.5 Ga. Detrital zircons from the sub-Grampian Group basement and the Grampian Group are predominantly of Palaeoproterozoic and Mesoproterozoic ages with Archaean grains absent or rare. In contrast, the overlying Appin, Argyll and Southern Highland groups contain a significant contribution of Archaean detrital zircon grains, some of which locally preserve evidence for late Palaeoproterozoic overgrowths dated at c . 1.8 Ga. In addition, on concordia plots Archaean grains are slightly discordant with a lower intercept at c . 1.8 Ga suggesting they were affected by a tectonothermal event at this time. Late Palaeoproterozoic and Mesoproterozoic grains also show evidence for overprinting by a tectonothermal event around 1.0–0.9 Ga. These tectonothermal events occurred in the source region before accumulation of the siliciclastic detritus. The analysed samples contained no definitive evidence for having been affected by a late Neoproterozoic (Knoydartian) event or of containing detritus derived from a source showing evidence for this event. The overall age range of detritus, combined with sparse palaeocurrent data, is consistent with derivation from the Laurentian foreland, especially the Labrador–Greenland region. Archaean detritus overlaps with that of Archaean cratons, notably the Superior, whereas Palaeoproterozoic detritus corresponds to the timing of suturing of Archaean cratons by a series of orogenic belts (Ketilidian–Makkovik, New Quebec, Nagssugtoqidian, Torngat belts). Mesoproterozoic detritus is consistent with derivation from the Grenville Orogen. The presence of a series of detrital age peaks in the late Palaeoproterozoic and early Mesoproterozoic (1.8–1.5 Ga), the paucity of mid-Mesoproterozoic detritus (1.4–1.2 Ga), and evidence for a tectonothermal event between 1.0 and 0.9 Ga is typical of the geological history of the Labrador–Greenland region of Laurentia.

Source of the Dalradian Supergroup constrained by U-Pb dating of detrital zircon and implications for the East Laurentian margin

Thirty-seven granitoids from Scotland have been dated using the sensitive high-resolution ion microprobe zircon method. Granitoids were intruded during: (1) crustal stretching at c . 600 Ma after Rodinia broke up (A-types); (2) the Grampian event of crustal thickening when the Midland Valley Arc terrane collided with Laurentia at c . 470 Ma (S-types); (3) erosion and decompression of the over-thickened Laurentian margin at c . 455 Ma (S-types); (4) subduction of Iapetus Ocean lithosphere under Laurentia starting at 430 Ma (I-types); (5) roll-back beginning at 420 Ma (I-types); (6) bilateral slab break-off and lithospheric delamination at 410 Ma (I- and S-type granites) when Baltica hard-docked against the Northern Highland terrane and Avalonia soft-docked against the Grampian Highland terrane. Far-field Acadian events at 390 Ma were recorded by I-type granites intruded along active sinistrally transpressive faults. I-types formed in lower crustal hot zones above subduction zones, whereas S-types formed in lower crustal hot zones above lithospheric windows through which hot asthenosphere had risen.

Geochronology and geodynamics of Scottish granitoids from the late Neoproterozoic break-up of Rodinia to Palaeozoic collision

The Hebridean shield, the northwest foreland of the Caledonian Orogen of Scotland, is a small fragment of Laurentia detached during the Cenozoic opening of the North Atlantic Ocean and is now part of Europe. The shield was at the tip of a major promontory of the ancestral core of North America, between the Newfoundland (Appalachian) and Greenland (Caledonian) margins. Its history is important to understanding late Precambrian and early Paleozoic global paleogeography and tectonics. Isotopic ages and structural complexities in the Moine and Dalradian Supergroups of the Caledonian Orogen have been interpreted as reflecting Neoproterozoic orogenic episodes overprinted by early Paleozoic deformation and metamorphism. A critical body of rock in the Scottish Highlands, the West Highland Granite Gneiss, has been viewed as a synorogenic intrusion into Moine metasedimentary rocks, and its ∼870‐Ma U‐Pb zircon age as dating a Riphean “Knoydartian” orogeny. However, field evidence shows that the granitic pro...

https://www.jstor.org/stable/10.1086/319974

N. J. Soper

Papers

Neoproterozoic Extension on the Scottish Promontory of Laurentia: Paleogeographic and Tectonic Implications