Silurian deformation and metamorphism of Ordovician arc rocks of the Casco Bay Group, south-central Maine

2003 ◽  
Vol 40 (6) ◽  
pp. 887-905 ◽  
Author(s):  
David P West Jr. ◽  
Heather M Beal ◽  
Timothy W Grover
Keyword(s):  
Middle Devonian ◽  
Elevated Temperatures ◽  
Early Carboniferous ◽  
Low Pressure ◽  
Late Ordovician ◽  
Early Ordovician ◽  
Late Cambrian ◽  
South Central ◽  
Intrusive Activity ◽  
Back Arc

The Casco Bay Group in south-central Maine consists of a sequence of Late Cambrian to Early Ordovician interlayered quartzofeldspathic granofels and pelite (Cape Elizabeth Formation) overlain by Early to Late Ordovician back-arc volcanic (Spring Point Formation) and volcanogenic sedimentary rocks (Diamond Island and Scarboro formations). These rocks were tightly folded and subjected to low-pressure amphibolite-facies metamorphism in the Late Silurian. This phase of deformation and metamorphism was followed by the development of a variety of structures consistent with a period of dextral transpression in Middle Devonian – Early Carboniferous time. Previously dated plutons within the sequence range in age from 422–389 Ma and record a period of prolonged intrusive activity in the region. Similarities in age, volcanic rock geochemistry, and lithologic characteristics argue strongly for a correlation between rocks of the Casco Bay Group and those in the Miramichi belt of eastern Maine and northern New Brunswick. The Cape Elizabeth Formation correlates with Late Cambrian to Early Ordovician sediments of the Miramichi Group (Gander Zone) and the Spring Point through Scarboro formations correlate with Early to Late Ordovician back-arc basin volcanics and volcanogenic sediments of the Bathurst Supergroup. The folding and low-pressure metamorphism of the Casco Bay Group is attributed to Late Silurian to Early Devonian terrane convergence and possible lithospheric delamination that would have resulted in a prolonged period of intrusive activity and elevated temperatures at low pressures. Continued convergence and likely plate reconfigurations in the Middle Devonian to Carboniferous led to widespread dextral transpression in the region.

Composition, structure and tectonic analysis of the Shangrimuce arc-continent collision zone on the northern margin of the Central Qilian, NW China

2021 ◽  
Author(s):  
Hongyuan Zhang ◽  
Zhibin Lei ◽  
Bo Yang ◽  
Qing Liu ◽  
Haijun Zhang ◽  
...  
Keyword(s):  
Shear Zones ◽  
Oceanic Lithosphere ◽  
Late Ordovician ◽  
Island Arc ◽  
Qilian Mountain ◽  
Northern Margin ◽  
Early Ordovician ◽  
Collision Zone ◽  
Two Stages ◽  
Back Arc

<p>A 1:50000 regional survey, covering an area of about 2000 km<sup>2</sup>, was carried out in the Shangrimuce area of Qilian Mountain in Northwest China. The results show that during Caledonian, the northern margin of the Central Qilian block experienced collision with mature island arcs and subsequently northward expansion. In the Shangrimuce study area, five geological units have been identified; they are, form south to north, back-arc basin, early Ordovician island arc, inter arc basin, middle Late Ordovician island arc, and fore-arc and oceanic lithosphere amalgamation zone. </p><p>(1) back-arc basin. In the Yangyuchi- Shule River- Cuorigang- Wawusi area, there may be a back-arc spreading basin, and there should be spreading basins in this area. It is speculated that there was a northward reverse subduction in the late Ordovician, accompanied by a syenite body, a broad spectrum dyke swarms and an accretionary wedge zone in the whole area.</p><p>(2) early Ordovician island arc. In the Shangrimuce-Dander area, the Proterozoic basement granitic gneiss, the early Ordovician island arc block and the high-pressure geological body all occur in the form of thrust horses, forming a double metamorphic belt, which reveals the existence of ocean subduction to south in the early Ordovician. </p><p>(3) inter arc basin. On both banks of Tuolai River to the east of Yanglong Township, there are early Middle Ordovician inter-arc basins with oceanic crust. </p><p>(4) middle Late Ordovician island arc. To the north of Tuolai River, there is a middle Late Ordovician island arc belt. Both sides of the island arc zone experienced strong ductile shear deformation, which recorded a complex arc-continent collision. </p><p>(5) fore-arc and oceanic lithosphere amalgamation zone (Fig.1). The Yushigou area has developed a fore-arc and oceanic lithospheric amalgamation zone, with weakly deformed fore-arc flysch basin, strongly deformed siliceous rocks, pillow Basalt, diabase, gabbro, peridotite and other rock assemblages.</p><p>Combined with the characteristics of arc-continent collision zone in the Western Pacific, there are two stages of shear zone series (Fig.2). One is ductile shear zones formed by the South dipping gneissic belt, revealing the existence of oceanic subduction accretion wedge and emplacement of high-pressure rocks. Another superimposed one is north dipping. This indicates that the arc-continent collision caused by back-arc reverse subduction, which ultimately controls the overall geometric and kinematic characteristics of the shear zones in the region.</p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gepj.8219836ca50067454890161/sdaolpUECMynit/12UGE&app=m&a=0&c=40b3389c641f2d0ca723e1527c32927e&ct=x&pn=gepj.elif&d=1" alt=""></p><p>Figure 1 United sections showing a Caledonian trench-arc system in the Qilian Mountain, NW China.</p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gepj.8def566da50066084890161/sdaolpUECMynit/12UGE&app=m&a=0&c=e82258ecc235c4e618abd6c035b58232&ct=x&pn=gepj.elif&d=1" alt=""></p><p>Figure 2 Structural analysis at Hongyahuo, indicating two stages of deformation.</p><p>The research has been supported by projects from the Ministry of Land and Resources (No.201211024-04; 1212011121188) and the 2020 undergraduate class construction project from China University of Geosciences (Beijing) (No. HHSKE202003).</p><p> </p>

Parallel geological development in the Dunnage Zone of Newfoundland and the Lower Palaeozoic terranes of southern Scotland: an assessment

1992 ◽  
Vol 83 (3) ◽  
pp. 571-594 ◽  
Author(s):  
S. P. Colman-Sadd ◽  
P. Stone ◽  
H. S. Swinden ◽  
R. P. Barnes
Keyword(s):  
Volcanic Rocks ◽  
Foreland Basin ◽  
Late Ordovician ◽  
Marine Transgression ◽  
Early Ordovician ◽  
Sedimentary Sequences ◽  
Structural Regime ◽  
Lower Palaeozoic ◽  
Back Arc ◽  
Combined Data

AbstractThe Notre Dame and Exploits subzones of Newfoundland's Dunnage Zone are correlated with the Midland Valley and Southern Uplands of Scotland, using detailed comparisons of two key Lower Palaeozoic successions which record similar histories of extension and compression. It follows that the Baie Verte Line, Red Indian Line and Dover Fault are equivalent to the Highland Boundary Fault, Southern Upland Fault and Solway Line, respectively.The Betts Cove Complex and overlying Snooks Arm Group of the Notre Dame Subzone are analogous to the Ballantrae Complex of the Midland Valley, both recording the Arenig evolution and subsequent obduction of an arc and back-arc system. The Early Ordovician to Silurian sequence unconformably overlying the Ballantrae Complex is poorly represented in the Notre Dame Subzone but important similarities can still be detected suggesting corresponding histories of continental margin subsidence and marine transgression.In the Exploits Subzone, Early Ordovician back-arc volcanic rocks are overlain by Llandeilo mudstones and Late Ordovician to Early Silurian turbidites. A similar stratigraphy occurs in the Northern and Central Belts of the Southern Uplands and both areas have matching transpressive structural histories. Deeper erosion in the Exploits Subzone reveals Cambrian and Early Ordovician volcano-sedimentary sequences structurally emplaced on the Gander Zone, and such rocks are probably present beneath the Southern Uplands. Combined data from the Notre Dame Subzone and Midland Valley suggest an Arenig southeast-dipping subduction zone. Early Ordovician volcanic rocks in the Exploits Subzone and Southern Uplands have back-arc basin geochemistry and support the model of the Southern Uplands as a transition from back-arc to foreland basin. Preferential emergence of the Dunnage Zone and contrasts between Exploits Subzone and Southern Uplands turbidite basins are attributed to collision of Newfoundland with a Laurentian promontory and Scotland with a re-entrant. This hypothesis also explains the transpressive structural regime common to both areas.

Early Ordovician alkali-ultramafic Zhilandy complex (Central Kazakhstan): structure and age of formation

2019 ◽  
Vol 484 (1) ◽  
pp. 61-65
Author(s):  
R. M. Antonuk ◽  
A. A. Tretyakov ◽  
K. E. Degtyarev ◽  
A. B. Kotov
Keyword(s):  
Complex Formation ◽  
Central Asian Orogenic Belt ◽  
Early Cambrian ◽  
Early Ordovician ◽  
Late Cambrian ◽  
Central Asian ◽  
Geochronological Study ◽  
Three Stages ◽  
Late Neoproterozoic ◽  
Quartz Monzodiorites

U–Pb geochronological study of amphibole-bearing quartz monzodiorites of the alkali-ultramafic Zhilandy complex in Central Kazakhstan, whose formation is deduced at the Early Ordovician era (479 ± 3 Ma). The obtained data indicate three stages of intra-plate magmatism in the western part of the Central Asian Orogenic Belt: Late Neoproterozoic stage of alkali syenites of the Karsakpay complex intrusion, Early Cambrian stage of ultramafic-gabbroid plutons of the Ulutau complex formation, and Late Cambrian–Early Ordovician stage of formation of the Zhilandy complex and Krasnomay complex intrusions.

scholarly journals Decoupled evolution of soft and hard substrate communities during the Cambrian Explosion and Great Ordovician Biodiversification Event

2016 ◽  
Vol 113 (25) ◽  
pp. 6945-6948 ◽  
Author(s):  
Luis A. Buatois ◽  
Maria G. Mángano ◽  
Ricardo A. Olea ◽  
Mark A. Wilson
Keyword(s):  
Late Ordovician ◽  
Hard Substrate ◽  
Cambrian Explosion ◽  
Early Cambrian ◽  
Continuous Increase ◽  
Late Cambrian ◽  
Unconsolidated Sediment ◽  
Underlying Causes ◽  
Hard Substrates ◽  
Shed Light

Contrasts between the Cambrian Explosion (CE) and the Great Ordovician Biodiversification Event (GOBE) have long been recognized. Whereas the vast majority of body plans were established as a result of the CE, taxonomic increases during the GOBE were manifested at lower taxonomic levels. Assessing changes of ichnodiversity and ichnodisparity as a result of these two evolutionary events may shed light on the dynamics of both radiations. The early Cambrian (series 1 and 2) displayed a dramatic increase in ichnodiversity and ichnodisparity in softground communities. In contrast to this evolutionary explosion in bioturbation structures, only a few Cambrian bioerosion structures are known. After the middle to late Cambrian diversity plateau, ichnodiversity in softground communities shows a continuous increase during the Ordovician in both shallow- and deep-marine environments. This Ordovician increase in bioturbation diversity was not paralleled by an equally significant increase in ichnodisparity as it was during the CE. However, hard substrate communities were significantly different during the GOBE, with an increase in ichnodiversity and ichnodisparity. Innovations in macrobioerosion clearly lagged behind animal–substrate interactions in unconsolidated sediment. The underlying causes of this evolutionary decoupling are unclear but may have involved three interrelated factors: (i) a Middle to Late Ordovician increase in available hard substrates for bioerosion, (ii) increased predation, and (iii) higher energetic requirements for bioerosion compared with bioturbation.

New Monoplacophora (Mollusca) from Late Cambrian and Early Ordovician of Missouri

1986 ◽  
Vol 60 (3) ◽  
pp. 606-626 ◽  
Author(s):  
Bruce L. Stinchcomb
Keyword(s):  
New Species ◽  
New Genus ◽  
New Genera ◽  
New Genus And Species ◽  
Upper Cambrian ◽  
Early Ordovician ◽  
New Family ◽  
Late Cambrian ◽  
Lower Ordovician ◽  
A New Species

Fourteen new species and six new genera of the molluscan class Monoplacophora are described from the Upper Cambrian Potosi and Eminence formations and the Lower Ordovician Gasconade Formation of the Ozark Uplift of Missouri and some new biostratigraphic horizons are introduced. A new superfamily, the Hypseloconellacea nom. trans. Knight, 1956, and a new family, the Shelbyoceridae, are named. The genus Proplina is represented by five new species: P. inflatus, P. suttoni from the Cambrian Potosi Formation, P. arcua from the Cambrian Eminence Formation and P. meramecensis and P. sibeliusi from the Lower Ordovician Gasconade Formation. A new genus and species in the subfamily Proplininae, Ozarkplina meramecensis, is described from the Upper Cambrian Eminence Formation. Four new monoplacophoran genera in the superfamily Hypseloconellacea and their species are described, including: Cambrioconus expansus, Orthoconus striatus, Cornuella parva from the Eminence Formation, and Gasconadeoconus ponderosa, G. waynesvillensis, G. expansus from the Gasconade Formation. A new genus in the new family Shelbyoceridae, Archeoconus missourensis, is described from the Eminence Formation and a new species of Shelbyoceras, S. bigpineyensis, is described from the Gasconade Formation.

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