40Ar/39Ar and K-Ar geochronology and tectonic significance of the Upper Cretaceous Adel Mountain volcanics and spatially associated Tertiary igneous rocks, northwestern Montana

2005 ◽  
Author(s):  
Stephen S. Harlan ◽  
Lawrence W. Snee ◽  
Mitchell W. Reynolds ◽  
Harald H. Mehnert ◽  
R.G. Schmidt ◽  
...  
Keyword(s):  
Upper Cretaceous ◽  
Igneous Rocks ◽  
Northwestern Montana ◽  
Tectonic Significance ◽  
Ar Geochronology

Provenance and U–Pb geochronology of the Upper Cretaceous El Chanate Group, northwest Sonora, Mexico, and its tectonic significance

2009 ◽  
Vol 51 (9-11) ◽  
pp. 1051-1077 ◽  
Author(s):  
César Jacques-Ayala ◽  
Andrew P. Barth ◽  
Joseph L. Wooden ◽  
Carl E. Jacobson
Keyword(s):  
Upper Cretaceous ◽  
Tectonic Significance

scholarly journals A new, transitional centrosaurine ceratopsid from the Upper Cretaceous Two Medicine Formation of Montana and the evolution of the ‘ Styracosaurus -line' dinosaurs

2020 ◽  
Vol 7 (4) ◽  
pp. 200284 ◽  
Author(s):  
John P. Wilson ◽  
Michael J. Ryan ◽  
David C. Evans
Keyword(s):  
North America ◽  
Late Cretaceous ◽  
Upper Cretaceous ◽  
Frames Of Reference ◽  
Unique Combination ◽  
Holotype Specimen ◽  
Intermediate Morphology ◽  
Northwestern Montana ◽  
Phylogenetic Framework ◽  
Stratigraphic Succession

Ceratopsids are among the most ubiquitous dinosaur taxa from the Late Cretaceous terrestrial formations of the Western Interior of North America, comprising two subfamilies, Chasmosaurinae and Centrosaurinae. The Two Medicine Formation of northwestern Montana has produced numerous remains of centrosaurine dinosaurs, which represent three taxa previously considered valid: Rubeosaurus ovatus , Einiosaurus procurvicornis and Achelousaurus horneri . Here, we reassess the previous referral of specimens to Rubeousaurus ovatus and demonstrate that this taxon is represented solely by its holotype specimen, which was first diagnosed as Styracosaurus ovatus . One of the specimens previously referred to ‘ Rubeosaurus ’ ovatus instead represents a new eucentrosauran centrosaurine taxon diagnosed here, Stellasaurus ancellae gen. et sp. nov. Stellasaurus expresses a unique combination of eucentrosauran centrosaurine characters, including an elongate nasal horncore, diminutive supraorbital horncores, and a parietal bearing straight, elongate P3 processes, semi-elongate P4 processes and non-elongate P5, P6 and P7 processes. Within the stratigraphic succession of Eucentrosaura, Stellasaurus occurs intermediate to Styracosaurus albertensis and Einiosaurus , and likewise reflects intermediate morphology. Assessed within the stratigraphic, geographical, taphonomic, ontogenetic and phylogenetic framework of Unified Frames of Reference, we fail to reject the hypothesis that Stellasaurus ancellae represents a transitional taxon within an anagenetic lineage of eucentrosauran centrosaurines.

The final closure of the Vardar Ocean: paleomagnetic, AMS and structural results

2020 ◽  
Author(s):  
Emö Márton ◽  
Marinko Toljić ◽  
Vesna Lesić ◽  
Vesna Cvetkov
Keyword(s):  
Upper Cretaceous ◽  
National Development ◽  
Upper Jurassic ◽  
Igneous Rocks ◽  
Magmatic Activity ◽  
Ministry Of Education ◽  
Bedding Planes ◽  
The Republic ◽  
Final Closure ◽  
Oceanic Domain

<p>The Vardar zone divides units of African affinity from units of the European margin. It is characterized by extensional opening of an oceanic domain during the Triassic and Jurassic followed by divergent simultaneous obduction of the oceanic litoshphere over the continental units in the Upper Jurassic. However, a stripe of the oceanic domain persisted till the Cretaceous and Paleogene convergence. The remnants of the last closing part of the Vardar ocean are found in the Sava zone.</p><p>In this paper recently published and new paleomagnetic, AMS results in combination with structural observations will be presented from Upper Cretaceous sediments and Oligocene –Lower Miocene igneous rocks representing the areas bordering the Sava zone from the western and eastern sides, respectively and from the upper Cretaceous flysch deposited in the Sava zone.</p><p>In the areas W and E of the Sava zone, respectively, the primary remanences of the igneous rocks point to post-Oligocene CW rotation of about 30°. The sediments carry secondary magnetizations, imprinted during magmatic activity. Compared to the areas flanking it, the sediments of the Sava zone were intensively folded during the Upper Cretaceous and Paleogene and the paleomagnetic signals, which exhibit smeared distribution close to the present N, are of post-folding age. The AMS foliation and bedding planes are sub-parallel, thus the deformation must have been weak. Fold axes and AMS lineations are roughly N-S oriented, pointing to the deformational origin of the AMS lineations. These observations form the Sava zone will be discussed in the context of the post-Oligocene CW rotation of the flanking areas and the general NE-SW orientation of the compressional stress field outside of the zone.</p><p>Acknowledgement. This work was financially supported by the National Development and Innovation Office of Hungary, project K 128625 and by the Ministry of Education and Science of the Republic of Serbia, project 176015.</p>

The tectonic significance of Ordovician basic igneous rocks in the Southern Uplands, southwest Scotland

1995 ◽  
Vol 132 (5) ◽  
pp. 549-556 ◽  
Author(s):  
E. R. Phillips ◽  
R. P. Barnes ◽  
R. J. Merriman ◽  
J. D. Floyd
Keyword(s):  
Volcanic Rocks ◽  
Accretionary Prism ◽  
Igneous Rocks ◽  
Geochemical Data ◽  
Published Data ◽  
Volcanic Material ◽  
Tectonic Significance ◽  
Arc Setting ◽  
Back Arc ◽  
Midocean Ridge

AbstractIn the northern part of the Southern Uplands, restricted volumes of basic igneous rocks occur at or near the base of the Ordovician sedimentary strata. These rocks have previously been interpreted as ocean-floor tholeiites representative of the subducted Iapetus oceanic plate, preserved as tectonic slivers in a fore-arc accretionary prism. The alternative, back-arc basin model proposed for the Southern Uplands on sedimentological evidence raises questions over the origin of these rocks. New geochemical data and previously published data clearly indicate that the volcanic material does not have a simple single source. The oldest (Arenig) volcanic rocks from the Moffat Shale Group associated with the Leadhills Fault include alkaline within-plate basalts and tholeiitic lavas which possibly display geochemical characteristics of midocean ridge basalts. In the northernmost occurrence, alkaline and tholeiitic basalts contained within the Caradoc Marchburn Formation are both of within-plate ocean island affinity. To the south, in the Gabsnout Burn area, the Moffat Shale Group contains lenticular bodies of dolerite and basalt which have characteristics of island-arc to transitional basalts. This complex association of basaltic volcanic rocks is, at the present time, difficult to reconcile with either a simple fore-arc or back-arc setting for the Southern Uplands. However, the increasing arc-related chemical influence on basic rock geochemistry towards the southeast may tentatively be used in support of a southern arc-terrane, and as a result, a back-arc situation for the Southern Uplands basin. An alternative is that these volcanic rocks may represent the local basement to the basin and include remnants of an arc precursor to the Southern Uplands basin.

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