Caledonian Fold Belt Research Articles

The geochronology of the Scoresby Sund area Progress report 2: Rb/Sr mineral ages

The reconnaissance age determination programme started at the "Institute für Kristallographie und Petrographie" of the "Eidg. Technische Hochschule" in Zürich has been continued. To verify the pre-Caledonian ages found last year in the Stauning Alper, additional minerals were analysed from some of the previously dated rock samples. The results on these, and on a group of other samples, clearly confirm the presence of extensive Precambrian rock units within the Caledonian fold belt. In table 6 the rocks are subdivided into four main groups on the basis of their geological relations.

Caledonian Geology of Scoresby Sund Region, Central East Greenland: ABSTRACT

The Geological Survey of Greenland has completed the first 3 years of a 5-year mapping campaign in the Scoresby Sund region which includes the southernmost Caledonian fold belt of East Greenland. The preliminary results show that it is possible to distinguish 4 main geologic units in the Caledonian fold belt. (1) A Precambrian crystalline basement with a cover of Precambrian metasediments and metavolcanics. These rocks are reworked by Caledonian folding to a varying degree. (2) A metamorphosed but nonmigmatized supracrustal complex composed of psammitic and pelitic rocks with occasional bands of calcareous rocks and totaling several kilometers in thickness. These rocks represent Caledonian geosynclinal deposits of miogeosynclinal aspect and are probably of very late Precambrian age. (3) A Caledonian infracrustal complex of mainly gneisses, migmatites and synkinematic granites. This unit is formed by migmatization of Caledonian geosynclinal deposits. (4) Late- to post-Caledonia intrusions, mainly of granitic type. Westward directed thrust-sheets with a displacement of several tens of kilometers are present along the western rim of the fold belt. They comprise largely Caledonian supracrustal rocks, but in places basement rocks are incorporated in the thrust sheets. The central part of the N-S directed fold belt is characterized by infracrustal rocks which exhibit simple low-dipping macroscopic structures, which in parts of the area can be shown to be the limbs of major recumbent folds. The Caledonian supracrustal rocks in the western part of the region were metamorphosed under high-pressure facies conditions and are characterized by kyanite-bearing rocks, whereas the central migmatitic part of the region was formed under low-pressure conditions and is characterized by cordierite-bearing assemblages. End_of_Article - Last_Page 2485------------

Isotopic ages from the Appalachians and their tectonic significance

Geological field relationships and previously reported isotopic age determinations throughout the Appalachians provided evidence for a pattern of Lower Paleozoic tectogenesis. The regional isotopic age pattern indicates that intrusion of ultramafic and mafic igneous materials and major episodes of metamorphic recrystallization throughout the Appalachians were completed before the end of the Silurian Period.New K–Ar ages of metamorphic rocks from Vermont and adjacent regions in the Northern Appalachians are reported and confirm this pattern. Whole-rock ages of slates from the Taconic Klippe (460–445 m.y.) indicate that metamorphism and initial formation of slaty cleavage occurred during Middle to Late Ordovician times. Mica ages of Paleozoic schists exposed along the Green Mountain Anticlinorium (425–375 m.y.) are indicative of prolonged post-metamorphic uplift and cooling of this structure during the Silurian Period and Early Devonian Epoch. Local recrystallization and consequent loss of argon from the Taconic slates also occurred during this time. Ages obtained from a variety of metamorphic rocks from eastern Vermont fall in a narrow range (345 ± 7 m.y), indicating that renewed uplift and rapid cooling of this area, east of a line of ultramafic intrusions, occurred during Late Devonian time.Comparison of isotopic age data from the Appalachian and British Caledonian fold belts indicates that a broadly synchronous sequence of Lower Paleozoic tectonic and magmatic activity, lasting approximately 100 m.y., occurred in both regions.

Geopshysical Studies in the Greenland Sea

Research Article| January 01, 1968 Geopshysical Studies in the Greenland Sea N. A OSTENSO N. A OSTENSO Geophysical and Polar Research Center, Department of Geology, University of Wisconsin, Madison, Wisconsin PRESENT ADDRESS: OFFICE OF NAVAL RESEARCH, CHICAGO, ILLINOIS Search for other works by this author on: GSW Google Scholar Author and Article Information N. A OSTENSO PRESENT ADDRESS: OFFICE OF NAVAL RESEARCH, CHICAGO, ILLINOIS Geophysical and Polar Research Center, Department of Geology, University of Wisconsin, Madison, Wisconsin Publisher: Geological Society of America Received: 29 Aug 1966 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1968, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1968) 79 (1): 107–132. https://doi.org/10.1130/0016-7606(1968)79[107:GSITGS]2.0.CO;2 Article history Received: 29 Aug 1966 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation N. A OSTENSO; Geopshysical Studies in the Greenland Sea. GSA Bulletin 1968;; 79 (1): 107–132. doi: https://doi.org/10.1130/0016-7606(1968)79[107:GSITGS]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Magnetic, gravity, and seismic sub–bottom profiles are used to contribute to the structural interpretation of the Greenland Sea and environs. The most anomalous feature of the magnetic survey is the subdued magnetic expression of the Mid–Atlantic Ridge north of the Jan Mayen fracture zone. Over the median rift valley magnetic anomalies are an order of magnitude smaller than those recorded in the Atlantic Ocean. A suggested explanation, supported by seismic data, is that crustal tension decreases northward along the ridge. The inferred structural consequence is that the tensional mid-oceanic ridge merges into the compressional Verkhoyansk Range beneath the Arctic Ocean. Gravity data suggest an abrupt increase in crustal thickness under the Greenland continental shelf. Maximum seismic penetration into the sediments of the ocean floor was 1.2 sec. Due to masking by strong bottom reflection multiples, poor sub–bottom resolution was obtained on the continental shelf. The steep and jagged continental slope off Kronprins Christian Land, the occurrence of seamounts, and the proximity of earthquake epicenters support the thesis that the Lena Trough is the medial rift of a northern extension of the Mid–Atlantic Ridge. The sub–bottom profile oft the east coast of Greenland reveals three widely separated faults. These correlate with projections of known tectonic features and suggest: (1) The thrust fault of the main Caledonian orogeny of northeastern Greenland extends to a depth in excess of 3 km and continues into the ocean floor at least 85 km from the coast; (2) the Jan Mayen fracture zone, which offsets the Mid–Atlantic Ridge, extends into Greenland at approximately 72° N.; and (3) the Caledonian fold belt may correlate directly between eastern Greenland and northern Britain. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The stratigraphy and structure of the Whithorn area of Wigtownshire, Scotland

Synopsis The rocks of the Whithorn area comprise two groups of Silurian strata: the Riccarton Beds, of Wenlock age, and the Hawick Rocks. The boundary between these groups is reinterpreted as a strike fault with major southward downthrow. Five fold movements have been recognised in the area. The first two comprise N.E.-S.W. folds and are responsible for the major monoclinal structure of the area. Folds of the third movement have E-W axial planes and steep plunges, and are considered contemporaneous with members of the Caledonian dyke suite. Fourth generation folds have low-angle axial planes, and are associated with late thrusts and mineralisation (probably Hercynian). The latest folds, dextral kink bands with N-S modal trend, are believed to post-date a Tertiary dyke series. Early thrusts are associated with the first folds, and a conjugate set of wrench faults with the second folds. It is suggested that strike faults originated as dip-slip fractures before or during the second fold movement, and were later reactivated by strike- and oblique-slip movement. The structural history of the area is found to be comparable with those of other parts of the southern Caledonian fold belt, especially the Silurian areas.

Tectonic Control of Sedimentation and the Interpretation of Sediment Alternation in the Tertiary of Prince Charles Foreland, Spitsbergen

Over 6000 feet of clastic sediments, probably of early Tertiary age, have been deposited in an actively developing graben. The sequence consists of beds mostly less than a foot thick, ranging in texture from conglomerate to shale, but dominantly of low rank graywacke. While much of the rapid vertical variation in lithology is erratic, some cyclic patterns are present. The sediments were derived from an area of low-grade metamorphic rocks only a short distance to the west and were deposited at the edge of a mountainous land which was actively rising by warping and perhaps by early movements on the faults that now separate the horst of Prince Charles Foreland from the graben of the Foreland Sound. Slump structures indicate considerable downward sliding of the sediments toward the center of the graben. Lithologic cycles in the sediments have been analyzed quantitatively in an attempt to assess their significance. Major cycles are attributed to variation in the balance between the rate of upward movement of the source area and the rate at which erosion reduced the resulting topographic relief. Minor cycles (mainly conglomerate-sandstone alternations and sandstone-shale alternations) are superimposed on the major cycles. Chiefly from an analysis of the ratios of thicknesses of beds in these cycles, it is argued that they represent short-term meteorologic variations. For each kind of rock, the thicknesses of beds have a log normal frequency distribution, and the geometric mean thicknesses increase with coarseness: shales 0.3 foot, siltstones 0.6 foot, sandstones 1.0 foot, conglomerates 1.4 feet. The sandstone thickness distribution, however, is a composite of two populations. The sandstones that are in cyclic alternation with conglomerates have a geometric mean thickness greater than that of the conglomerates; the sandstones that are in cyclic alternation with shales have a geometric mean thickness less than that of the shales. These data are compared with information on bedding thickness from other areas, and the interpretation of such data is discussed. The tectonic setting is taphrogeosynclinal; the rocks are dominantly low rank graywackes. The association of various kinds of sedimentary rocks with this tectonic setting is discussed. If general uplift occurs at the same time as the differential movement that forms the taphrogeosyncline, non-marine deposits will probably develop. Arkoses will be abundant if the source area consists of high-grade metamorphic and granitic rocks. Arkoses and non-marine deposits have developed in the past in a number of situations where block-faulting accompanied the uplift and deep erosion of the central part of an orogenic belt after an episode of orogenesis. In Prince Charles Foreland, however, the horst rose and the graben sank about a mean horizon of roughly constant elevation, and the “accidental” location on the western flank of the much older Caledonian fold belt of Spitsbergen resulted in a source area of low-grade metamorphic rocks and a sedimentary pile dominated by low rank graywackes.