Iapetan Oceans: An analog of Tethys?

Geology ◽  
2020 ◽  
Vol 48 (9) ◽  
pp. 929-933 ◽  
Author(s):  
B. Robert ◽  
M. Domeier ◽  
J. Jakob
Keyword(s):  
Second Phase ◽  
Continental Margins ◽  
Deep Time ◽  
Zircon Age ◽  
Continental Extension ◽  
Iapetus Ocean ◽  
Mid Ocean Ridge ◽  
Tethys Ocean ◽  
Late Neoproterozoic ◽  
Ocean Ridge

Abstract The Iapetus Ocean opened during the breakup of Rodinia by the separation of the major continental blocks of Laurentia (LA), Baltica, and Amazonia (AM). Relics of protracted continental extension to rifting from 750 to 530 Ma are observed along those continental margins, including two distinct phases of rifting: (1) at 750–680 Ma, and (2) at 615–550 Ma. Conventionally, the second phase is thought to have led to the opening of the Iapetus, while the first phase marked a failed rifting attempt. We challenge this concept on the basis of a new review of the geological observations from those margins and propose the successive opening of two “Iapetan” ocean basins. First, a “Paleo-Iapetus” opened between LA and AM at ca. 700 Ma, followed by the opening of the “Neo-Iapetus” at 600 Ma, which led to the final disaggregation of the supercontinent Rodinia. This scenario better explains the absence of the second rifting phase in western AM, as well as an otherwise enigmatic late Neoproterozoic detrital zircon age fraction in Phanerozoic sediments along that margin. We further propose that the opening of the Neo-Iapetus led to the detachment of small terranes from LA and their drift toward AM, following subduction of the Paleo-Iapetus mid-ocean ridge and the arrival of a mantle plume around 615 Ma. This could be a direct, deep-time analog of the opening of the Neo-Tethys Ocean in the late Paleozoic.

A diachronous opening of the Iapetus Ocean in the Neoproterozoic

2020 ◽  
Author(s):  
Boris Robert ◽  
Mathew Domeier ◽  
Johannes Jakob
Keyword(s):  
Paleomagnetic Data ◽  
Time Interval ◽  
Second Phase ◽  
Continental Margins ◽  
Zircon Age ◽  
Continental Extension ◽  
Rifted Margins ◽  
Iapetus Ocean ◽  
Accreted Terranes ◽  
Late Neoproterozoic

<p><span>The late Neoproterozoic is a time interval of dramatic changes affecting the biosphere, the cryosphere and the lithosphere, including the final disaggregation of the supercontinent Rodinia and the formation of Gondwana. The Iapetus Ocean opened during the breakup of Rodinia, i.e. resulting from the separation of the three major continental blocks: Laurentia, Baltica and Amazonia. Protracted continental extension to rifting from 750 to 530 Ma is observed along the involved continental margins and may indicate several ocean openings in addition to the Iapetus Ocean. Breakup timing is still much debated in the literature, as it remains unclear how to best interpret the fragmentary geological record along the rifted margins, and because only few reliable paleomagnetic data are available for this period of time. Three distinct times for the breakup are proposed for Laurentia and Amazonia: at (1) 750-700 Ma, (2) 615-570 Ma and (3) 550-530 Ma. Various terranes are also involved in the opening of the Iapetus Ocean and may have drifted along with or independently of Amazonia.</span></p><p><span>In this study, we reviewed the geological observations of each of the involved margins and the available paleomagnetic data from 750 to 520 Ma to test these scenarios. Paleomagnetic data from Laurentia and Amazonia-West Africa constrain the breakup age to occur before 575 Ma, discarding the possibility of a late Ediacaran/Early Cambrian opening. Geological observations, better preserved in Laurentia and Baltica, indicate two main phases of (attempted) continental rifting, from 750 to 680 Ma and from 615 to 550 Ma. The second phase is usually interpreted as leading to the breakup of Laurentia, Amazonia and Baltica, as in scenarios (2) and (3). Nevertheless, it cannot easily explain (i) the absence of the Central Iapetus Magmatic Province in West Amazonia, (ii) the dynamics of accreted terranes now observed in South America and (iii) the distinct late Neoproterozoic detrital zircon age population in Phanerozoic sediments along West Amazonia (which are moreover absent in East Laurentia). These observations are better explained by a model wherein Laurentia and Amazonia broke apart during the first rifting phase around 750-680 Ma. In this scenario, the second phase of rifting (615-550 Ma) leads, in the west, to drifting of small terranes southward and toward Amazonia, and in the east, to the final breakup between Laurentia and Baltica.</span></p>

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.

2011 ◽  
Vol 48 (2) ◽  
pp. 161-185 ◽  
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.

scholarly journals The Ocean – Continent Transition Zones Along the Appalachian – Caledonian Margin of Laurentia: Examples of Large-Scale Hyperextension During the Opening of the Iapetus Ocean

2014 ◽  
Vol 41 (2) ◽  
pp. 165 ◽  
Author(s):  
David M. Chew ◽  
Cees R. Van Staal
Keyword(s):  
Large Scale ◽  
Continental Margins ◽  
Transition Zones ◽  
Iapetus Ocean ◽  
Fold And Thrust Belt ◽  
Appalachian Orogen ◽  
Late Neoproterozoic ◽  
Laurentian Margin ◽  
Orogenic Belts ◽  
Detailed Nature

A combination of deep seismic imaging and drilling has demonstrated that the ocean-continent transition (OCT) of present-day, magma-poor, rifted continental margins is a zone of hyperextension characterized by extreme thinning of the continental crust that exhumed the lowermost crust and/or serpentinized continental mantle onto the seafloor. The OCT on present-day margins is difficult to sample, and so much of our knowledge on the detailed nature of OCT sequences comes from obducted, magma-poor OCT ophiolites such as those preserved in the upper portions of the Alpine fold-and-thrust belt. Allochthonous, lens-shaped bodies of ultramafic rock are common in many other ancient orogenic belts, such as the Caledonian – Appalachian orogen, yet their origin and tectonic significance remains uncertain. We summarize the occurrences of potential ancient OCTs within this orogen, commencing with Laurentian margin sequences where an OCT has previously been inferred (the Dalradian Supergroup of Scotland and Ireland and the Birchy Complex of Newfoundland). We then speculate on the origin of isolated occurrences of Alpine-type peridotite within Laurentian margin sequences in Quebec – Vermont and Virginia – North Carolina, focusing on rift-related units of Late Neoproterozoic age (so as to eliminate a Taconic ophiolite origin). A combination of poor exposure and pervasive Taconic deformation means that origin and emplacement of many ultramafic bodies in the Appalachians will remain uncertain. Nevertheless, the common occurrence of OCT-like rocks along the whole length of the Appalachian – Caledonian margin of Laurentia suggests that the opening of the Iapetus Ocean may have been accompanied by hyperextension and the formation of magma-poor margins along many segments.SOMMAIREDes travaux d’imagerie sismique et des forages profonds ont montré que la transition océan-continent (OCT) de marges continentales de divergence pauvre en magma exposée de nos jours, correspond à une zone d’hyper-étirement tectonique caractérisée par un amincissement extrême de la croûte continentale, qui a exhumé sur le fond marin, jusqu’à la tranche la plus profonde de la croûte continentale, voire du manteau continental serpentinisé.  Parce qu’on peut difficilement échantillonner l’OCT sur les marges actuelles, une grande partie de notre compréhension des détails de la nature de l’OCT provient d’ophiolites pauvres en magma d’une OCT obduite, comme celles préservées dans les portions supérieures de la bande plissée alpine.  Des masses lenticulaires de roches ultramafiques allochtones sont communes dans de nombreuses autres bandes orogéniques anciennes, comme l’orogène Calédonienne-Appalaches, mais leur origine et signification tectonique reste incertaine.  Nous présentons un sommaire des occurrences d’OCT potentielles anciennes de cet orogène, en commençant par des séquences de la marge laurentienne, où la présence d’OCT a déjà été déduites (le Supergroupe Dalradien d’Écosse et d'Irlande, et le complexe de Birchy de Terre-Neuve).  Nous spéculons ensuite sur l'origine de cas isolés de péridotite de type alpin dans des séquences de marge des Laurentides du Québec-Vermont et de la Virginie-Caroline du Nord, en nous concentrant sur les unités de rift d'âge néoprotérozoïque tardif (pour éviter les ophiolites du Taconique).  La conjonction d’affleurements de piètre qualité et de la déformation taconique omniprésente, signifie que l'origine et la mise en place de nombreuses masses ultramafiques dans les Appalaches demeureront incertaines.  Néanmoins, la présence fréquente de roches de type OCT tout le long de la marge Calédonnienne-Appalaches de Laurentia suggère que l'ouverture de l'océan Iapetus peut avoir été accompagnée d’hyper-étirement et de la formation de marges pauvres en magma le long de nombreux segments.

scholarly journals Evidence of Late Ediacaran Hyperextension of the Laurentian Iapetan Margin in the Birchy Complex, Baie Verte Peninsula, Northwest Newfoundland: Implications for the Opening of Iapetus, Formation of Peri-Laurentian Microcontinents and Taconic – Grampian Orogenesis

2013 ◽  
Vol 40 (2) ◽  
pp. 94 ◽  
Author(s):  
Cees R. Van Staal ◽  
Dave M. Chew ◽  
Alexandre Zagorevski ◽  
Vicki McNicoll ◽  
James Hibbard ◽  
...  
Keyword(s):  
Hanging Wall ◽  
Ultramafic Rocks ◽  
Nous Proposons ◽  
Mafic Rocks ◽  
Metasedimentary Rocks ◽  
Iapetus Ocean ◽  
Icp Ms ◽  
Mid Ocean Ridge ◽  
Continental Lithospheric Mantle ◽  
Ocean Ridge

The Birchy Complex of the Baie Verte Peninsula, northwestern Newfoundland, comprises an assemblage of mafic schist, ultramafic rocks, and metasedimentary rocks that are structurally sandwiched between overlying ca. 490 Ma ophiolite massifs of the Baie Verte oceanic tract and underlying metasedimentary rocks of the Fleur de Lys Supergroup of the Appalachian Humber margin. Birchy Complex gabbro yielded a Late Ediacaran U–Pb zircon ID–TIMS age of 558.3 ± 0.7 Ma, whereas gabbro and an intermediate tuffaceous schist yielded LA–ICPMS concordia zircon ages of 564 ± 7.5 Ma and 556 ± 4 Ma, respectively. These ages overlap the last phase of rift-related magmatism observed along the Humber margin of the northern Appalachians (565–550 Ma). The associated ultramafic rocks were exhumed by the Late Ediacaran and shed detritus into the interleaved sedimentary rocks. Psammite in the overlying Flat Point Formation yielded a detrital zircon population typical of the Laurentian Humber margin in the northern Appalachians. Age relationships and characteristics of the Birchy Complex and adjacent Rattling Brook Group suggest that the ultramafic rocks represent slices of continental lithospheric mantle exhumed onto the seafloor shortly before or coeval with magmatic accretion of mid-ocean ridge basalt-like mafic rocks. Hence, they represent the remnants of an ocean – continent transition zone formed during hyperextension of the Humber margin prior to establishment of a mid-ocean ridge farther outboard in the Iapetus Ocean. We propose that microcontinents such as Dashwoods and the Rattling Brook Group formed as a hanging wall block and an extensional crustal allochthon, respectively, analogous to the isolation of the Briançonnais block during the opening of the Alpine Ligurian–Piemonte and Valais oceanic seaways.SOMMAIRELe complexe de Birchy de la péninsule de Baie Verte, dans le nord-ouest de Terre-Neuve, est constitué d’un assemblage de schistes mafiques, de roches ultramafiques et de métasédiments qui sont coincés entre des massifs ophiolitiques d’ascendance océanique de la Baie Verte au-dessus, et des métasédiments du Supergroupe de Fleur de Lys de la marge de Humber des Appalaches en-dessous. Le complexe de gabbro de Birchy a donné une datation U-Pb sur zircon ID-TIMS correspondant à la fin de l’Édiacarien, soit 558,3 ± 0,7 Ma, alors qu’un gabbro et un schiste tufacé intermédiaire montrent une datation LA-ICP-MS Concordia sur zircon de 564 ± 7,5 Ma et 556 ± 4 Ma, respectivement. Ces datations chevauchent la dernière phase de magmatisme de rift observée le long de la marge Humber des Appalaches du Nord (565-550 Ma). Les roches ultramafiques associées ont été exhumées vers la fin de l’Édiacarien et leurs débris ont été imbriqués dans des roches sédimentaires. Les psammites de la Formation de Flat Point susjacente ont donné une population de zircons détritiques typique de la marge laurentienne de Humber des Appalaches du Nord. Les relations chronologiques et les caractéristiques du complexe de Birchy et du groupe de Rattling Brook adjacent, permettent de penser que ces roches ultramafiques pourraient être des écailles de manteau lithosphérique continental qui auraient été exhumées sur le plancher océanique peu avant ou en même temps que l’accrétion magmatique de roches mafiques basaltiques de type dorsale médio-océanique. Par conséquent, elles seraient des vestiges d’une zone de transition océan-continent formée au cours de l’hyper-extension de la marge de Humber avant l’apparition d’une dorsale médio-océanique plus loin au large dans l’océan Iapétus. Nous proposons que des microcontinents comme de Dashwoods et du groupe de Rattling Brook ont constitués respectivement un bloc de toit et un allochtone crustal d’extension, de la même manière que le bloc Briançonnais a été isolé lors de l’ouverture des bras océaniques alpins de Ligurie-Piémont et de Valais.

4. Subduction of oceanic lithosphere

2015 ◽  
pp. 53-76
Author(s):  
Peter Molnar
Keyword(s):  
Oceanic Lithosphere ◽  
Great Depth ◽  
Continental Margins ◽  
Island Arcs ◽  
The Andes ◽  
Mid Ocean Ridge ◽  
Subducting Plate ◽  
Ocean Ridge ◽  
Large Earthquakes ◽  
Adjacent Rock

‘Subduction of oceanic lithosphere’ begins with the notion that for the Earth not to expand, the sum total of new lithosphere made at a spreading centre (or mid-ocean ridge) must be matched by the removal, by subduction, of an equal amount of lithosphere elsewhere. The subduction process is asymmetric: one plate will slide beneath the other at island arcs and continental margins like the Andes of South America. Before it plunges beneath the island arc, the subducting plate of lithosphere bends down gently to cause a deep-sea trench. The subducting plate slides beneath the region between the trench and volcanoes, commonly in large earthquakes, and plunges to great depth, pulled down by gravity acting on the dense slab of subducted lithosphere. Water carried to depth by the subducting plate lowers the melting temperature of the adjacent rock and enables volcanoes to form.

Bay of Islands and Little Port complexes, revisited: age, geochemical and isotopic evidence confirm suprasubduction-zone origin

1991 ◽  
Vol 28 (10) ◽  
pp. 1635-1652 ◽  
Author(s):  
G. A. Jenner ◽  
G. R. Dunning ◽  
J. Malpas ◽  
M. Brown ◽  
T. Brace
Keyword(s):  
Transform Fault ◽  
Isotopic Data ◽  
Isotopic Study ◽  
Zircon Age ◽  
Suprasubduction Zone ◽  
Mid Ocean Ridge ◽  
Appalachian Orogen ◽  
Ocean Ridge ◽  
Source Materials ◽  
Oceanic Domain

The Bay of Islands Complex of the Humber Arm allochthon, west Newfoundland, contains the best-exposed ophiolite in the Appalachian Orogen. Associated structural slices, the Little Port and Skinner Cove complexes, also contain rocks formed in an oceanic domain, although their relationship to the Bay of Islands Complex remains controversial.To constrain the origin of the complexes and obtain a better understanding of the geology of the Humber Arm allochthon, we have undertaken an integrated geochronological, geochemical, and isotopic study. A U/Pb zircon age of [Formula: see text] Ma for the Little Port Complex and a zircon and baddeleyite age of 484 ± 5 Ma for the Bay of Islands Complex have been obtained. Geochemical and isotopic data on trondhjemitic rocks from the two complexes indicate that petrogenetic models for these rocks must account for fundamental differences in source materials and mineralogy during differentiation. The Little Port Complex trondhjemites are characterized by initial εNd of −1 to +1, whereas those in the Bay of Islands have εNd of +6.5. Geochemical signatures in mafic and felsic volcanics of the complexes are diverse, and show a complete gradation between arc and non-arc.The Bay of Islands and Little Port complexes are not related by any form of a major mid-ocean-ridge – transform-fault model. An alternative model to explain the relationships between the two complexes interprets the Little Port as arc-related and the Bay of Islands as a suprasubduction-zone ophiolite.

Age and origin of the Boil Mountain ophiolite and Chain Lakes massif, Maine: implications for the Penobscottian orogeny

1997 ◽  
Vol 34 (5) ◽  
pp. 646-654 ◽  
Author(s):  
T. M. Kusky ◽  
J. S. Chow ◽  
S. A. Bowring
Keyword(s):  
North America ◽  
Late Ordovician ◽  
Ophiolite Complex ◽  
Middle Ordovician ◽  
Iapetus Ocean ◽  
Lower Ordovician ◽  
Mid Ocean Ridge ◽  
Back Arc ◽  
Ocean Ridge ◽  
Age Constraints

The Boil Mountain ophiolite complex of west-central Maine is widely interpreted to mark the Lower Ordovician Penobscottian suture between the Dunnage, Chain Lakes, and Gander terranes. The ophiolite consists of two distinct volcanic groups, including a lower island-arc tholeiite sequence and an upper mid-ocean-ridge basalt sequence. A new Middle Ordovician 477 ± 1 Ma U–Pb age on a tonalite sill that intrudes the lower volcanic–gabbroic sequence is younger than other ca. 500 Ma age constraints for the ophiolite and represents a maximum age for the ophiolite prior to final emplacement over gneissic rocks of the Chain Lakes massif. A comparison of ages and paleogeography of the Boil Mountain ophiolite with ophiolitic sequences in Quebec and Newfoundland indicates that the Taconian and Penobscottian orogenies and ophiolite obduction occurred simultaneously, although on different margins of the Iapetus Ocean. The Taconian ophiolite sequences were obducted onto the Appalachian margin of Laurentia during its collision with the Notre Dame – Bronson Hill belt in the Middle Ordovician, whereas the Boil Mountain ophiolite was obducted onto the Gander margin of Gondwana during its collision with the Exploits subzone – Penobscot arc of the Dunnage terrane in the Lower – Middle Ordovician. We suggest that the lower volcanic–gabbroic sequence of the Boil Mountain ophiolite represents the fore-arc ophiolitic basement to the Penobscot arc. Middle Ordovician rifting of the Penobscottian orogenic collage on the Gander margin formed a new volcanic sequence (Popelogan arc) in front of a growing back-arc basin, and erupted the upper tholeiitic sequence of the Boil Mountain ophiolite in a back-arc-basin setting. The tonalité sill formed during this event by partial melting of the lower volcanic–gabbroic sequence. Spreading in this back-arc basin (Tetagouche basin) brought a fragment of the Gander margin (Chain Lakes massif), along with an allochthonous ophiolitic cover (Boil Mountain complex) across Iapetus, where it collided with the Taconic modified margin of North America in the Late Ordovician and was then intruded by the Ashgillian Attean pluton.

The Caldwell Group lavas of southern Quebec: MORB-like tholeiites associated with the opening of Iapetus Ocean

1999 ◽  
Vol 36 (6) ◽  
pp. 999-1019 ◽  
Author(s):  
Jean H Bédard ◽  
Ross Stevenson
Keyword(s):  
Incompatible Element ◽  
Crustal Contamination ◽  
Isotopic Data ◽  
High Field Strength ◽  
Element Abundances ◽  
Incompatible Elements ◽  
Iapetus Ocean ◽  
Mid Ocean Ridge ◽  
Source Mantle ◽  
Ocean Ridge

The Caldwell Group belongs to the Internal Nappe Domain of the Humber Zone and consists of basaltic lavas, quartzo-feldspathic sandstones, and mudslates. The lavas are clinopyroxene ± plagioclase ± olivine-phyric tholeiites, and are typically altered to epidote-, chlorite-, carbonate-, and (or) hematite-rich secondary assemblages. In most cases, the high field strength elements do not appear to have been perturbed by the alteration, and preserve magmatic signatures. Most Caldwell basalts exhibit coupled major and trace element variations compatible with low- to medium-pressure ([Formula: see text] 10 kbar, where 1 kbar = 100 MPa) fractional crystallization. Paleotectonic discriminants imply an ocean-floor or normal mid-ocean ridge basalt (N-MORB) affinity. Most basalts have flat N-MORB-normalized profiles, except for the highly incompatible elements (Ba, Th, Nb), which show slight relative enrichment. Melting models suggest that most of these lavas formed by about 20% melting from a mantle slightly less depleted than fertile MORB mantle (FMM). Subpopulations of Caldwell lavas (types 1b and 1a) are characterized by slightly higher incompatible element abundances, with similarly shaped N-MORB-normalized profiles, and can be modeled by slightly smaller degrees of melting (6-15%) of a similar source mantle. The Caldwell basalts erupted in the final stages of Iapetus rifting, when the predominant mantle source involved in melting was the depleted asthenosphere. Isotopic data preclude significant crustal contamination, yet the basalts are associated with sandstones, implying that a mature continental crust was present nearby. Nd isotopic data on the sandstones suggest erosion of an ancient Archean-Proterozoic composite terrane.

Geology of the Charlie Gibbs transform system (52-53ºN, Mid Atlantic Ridge): preliminary results from Akademik Nikolaj Strakhov Expedition S50

2021 ◽  
Author(s):  
Alessio Sanfilippo ◽  
Sergey Skolotnev ◽  
Alexander Peyve ◽  
Keyword(s):  
North Atlantic ◽  
Large Scale ◽  
Single Channel ◽  
Continental Margins ◽  
Transform Faults ◽  
The North ◽  
Mid Ocean Ridge ◽  
Mid Atlantic Ridge ◽  
Ocean Ridge ◽  
Resolution Single

<p>The Charlie Gibbs offsetting by ~340 km the Mid Atlantic Ridge (MAR) axis between 52°-53° N is one of the main transform systems of the North Atlantic. Located between long mid-ocean ridge segments influenced to the south by the Azores and to the north by the Iceland mantle plume, this transform system has been active since the early phases of North Atlantic rifting. Object of several surveys in the ‘70 and ‘80, Charlie Gibbs received great attention for its unique structure characterized by two long-lived right-lateral transform faults linked by a short ~40 km-long intra-transform spreading centre (ITR) with parallel fracture zone valleys extending continuously towards the continental margins. In October 2020 expedition S50 of the R/V A.N. Strakhov surveyed an area of 54552 km<sup>2</sup> covering the entire Charlie Gibbs transform system and the adjacent MAR spreading segments. We collected new bathymetric, magnetic and high-resolution single channel seismic data, along with basaltic, gabbroic and mantle rocks from 21 dredges. In this contribution we present preliminary data from cruise S50 and discusses the large-scale architecture of this unique, long-lived transform system.</p>

Late stage rifting of the Laurentian continent: evidence from the geochemistry of greenstone and amphibolite in the central Vermont Appalachians1This article is one of a series of papers published in CJES Special Issue: In honour of Ward Neale on the theme of Appalachian and Grenvillian geology.

2012 ◽  
Vol 49 (1) ◽  
pp. 43-58 ◽  
Author(s):  
Raymond Coish ◽  
Jonathan Kim ◽  
Nathan Morris ◽  
David Johnson
Keyword(s):  
New England ◽  
East African ◽  
Alkali Basalts ◽  
Iapetus Ocean ◽  
Afar Region ◽  
Mid Ocean Ridge ◽  
African Rift ◽  
Type 3 ◽  
Ocean Ridge

Metamorphosed mafic rocks from west-central Vermont crop out in tectonic slices of the Stowe Formation within the Rowe–Hawley Belt of New England. The rocks include greenstone and amphibolite, which are interpreted to have been basaltic flows and gabbroic intrusions, respectively. Even though the rocks have been metamorphosed to greenschist or amphibolite facies, their igneous origins can be deciphered through careful use of geochemistry. Three geochemical types have been identified. Type 1 and 2 samples have geochemical characteristics similar to those found in mid-ocean ridge basalts (MORB), except that they have slightly elevated light rare-earth element (LREE) concentrations and are higher in Nb/Y ratios. Their Nb/Y ratios are similar to basalts found in Iceland and parts of the Afar region of the East African Rift. Types 1 and 2 are similar to metabasalts of the Caldwell and Maquereau formations in southern Quebec. The less-common type 3 samples have highly enriched LREE and are high in Nb/Y and Zr/Y ratios, similar to some alkali basalts from Afar and Iceland. Detailed analysis of the geochemistry suggests that greenstones and amphibolite from the Stowe Formation formed as basaltic eruptions during very late stages in rifting of the Rodinian continent that eventually led to formation of the Iapetus Ocean. This interpretation is consistent with tectonic models of the Vermont and Quebec Appalachians.

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