Microdiamond in high-grade metamorphic rocks of the Western Gneiss region, Norway

Dobrzhinetskaya, L.; Eide, Elizabeth A.; Larsen, Rune B.; Sturt, B. A.; Trønnes, Reidar G.; Smith, David; Taylor, W. Rowland; Posukhova, T. V.

doi:10.1130/0091-7613(1995)023<0597:mihgmr>2.3.co;2

Cited by 321 publications

(171 citation statements)

References 19 publications

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“…Because exhumed rocks in the metamorphic core complex of the Western Gneiss Region, record high-and ultra-high-pressure metamorphism (cf. Smith, 1984;Griffin, 1987;Jamtveit, 1987), it is suggested that the Caledonian Orogen developed extremely thick continental crust capable of stabilising coesite (Smith, 1984) and micro-diamonds (Dobrzhinetskaya et al, 1995). Subduction of continental crust, however, requires pervasive eclogitizaton in order to maintain a reasonable topography above the thickened crust (Richardson and England, 1979;Dewey et al, 1993).…”

Section: Discussionmentioning

confidence: 99%

Extensional tectonics in the Caledonides of southern Norway, an overview

1998

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The extensional collapse of the Scandinavian Caledonides resulted in rapid tectonic denudation of the orogen, exhumation of high-and ultra-high-pressure metamorphic rocks and provided a structural template for the formation of Devonian supra-detachment sedimentary basins. The geometry and intensity of the extensional deformation show considerable variation vertically in the crustal section as well as horizontally from east to west across the orogen. The most prominent structural feature related to the extension in central-south Norway is the change in the direction of tectonic transport, from the easterly directed nappe translation during the Silurian Scandian Orogeny, to top-westerly directed sense of shear during the extension. The Fennoscandian basement was little affected by extension in the eastern Caledonides. In the west, however, top-to-the-west shear zones are commonly observed in basement windows. Deformation affecting the Cambrian to Late Silurian rocks in the Caledonian foreland developed a typical of foreland fold and thrust belt geometry. Deformation in the foreland was apparently contemporaneous with the extension-related decompression of the high-pressure rocks in the hinterland. Thrusting in the foreland may thus have been driven by gravitational collapse, and as such have important similarities to the foreland-hinterland relationships of the Himalayan-Tibetan region. The basal contacts of the Jotun and other major nappes constitute prominent shear zones in which fabrics related to thrusting have been mostly destroyed by extensional shearing. The high structural levels of the Western Gneiss Region, adjacent to the western margin of the Jotun Nappe, were only moderately affected by the extensional deformation. Consequently, the Proterozoic orthogneiss complexes are generally well preserved in this area. The westernmost and structurally lowermost parts of the Western Gneiss Region have, however, been subjected to extreme overburden during the Caledonian continental collision. Initial, near-isothermal decompression of the high-pressure rocks occurred by non-rotational vertical shortening-horizontal stretching at eclogite-to amphibolite-facies conditions; at a later stage, decompression and cooling from amphibolite to greenschist facies occurred by rotational deformation associated with the large-scale extensional detachments. The initial extensional deformation in the hanging wall of the detachments in western Norway commenced at greenschist-facies conditions, and became progressively more brittle and localised as the complexes were exhumed in the Late Silurian to Middle Devonian. Major syn-depositional normal faults in the hanging wall of the extensional detachments eventually controlled sedimentation in the Devonian supra-detachment basins.

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Section: Discussionmentioning

confidence: 99%

Extensional tectonics in the Caledonides of southern Norway, an overview

1998

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“…The discovery of microdiamonds in garnets and zircons from metamorphic rocks of the Kokchetav Massif (3) and subsequently in other ultrahigh-pressure (UHP) metamorphic terranes (27)(28)(29)(30)(31)(32) is taken as evidence that the crustal rocks were subducted to considerable depths. FTIR microspectroscopy has revealed fluid inclusions in metamorphic diamonds (33); bulk chemical analyses of the Kokchetav microdiamonds demonstrated high contents of K and Cl (34).…”

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confidence: 99%

The role of mantle ultrapotassic fluids in diamond formation

Palyanov

Shatsky

Sobolev

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

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Analysis of data on micro-and nano-inclusions in mantle-derived and metamorphic diamonds shows that, to a first approximation, diamond-forming medium can be considered as a specific ultrapotassic, carbonate/chloride/silicate/water fluid. In the present work, the processes and mechanisms of diamond crystallization were experimentally studied at 7.5 GPa, within the temperature range of 1,400 -1,800°C, with different compositions of melts and fluids in the KCl/K 2CO3/H2O/C system. It has been established that, at constant pressure, temperature, and run duration, the mechanisms of diamond nucleation, degree of graphite-to-diamond transformation, and formation of metastable graphite are governed chiefly by the composition of the fluids and melts. The experimental data suggest that the evolution of the composition of deep-seated ultrapotassic fluids/melts is a crucial factor of diamond formation in mantle and ultrahigh-pressure metamorphic processes. high-pressure experimentA n important stage in solving problems of diamond genesis is constructing a clear physical model of diamond formation (1). One of the key parameters to be modeled is the composition of the diamond crystallization medium, with a fluid being largely considered as a crucial agent in diamond formation. It is generally agreed that the mantle media of diamond crystallization were volatile-saturated melts or fluids (1-7). Carbonbearing fluids and carbonates could be sources of carbon, and the medium could have been saturated with it by redox reactions. Recent studies have been aimed at searching and examining fluid and fluid-containing inclusions in genetically different diamonds. Also, experiments have been performed to model the processes of diamond crystallization in the media compositionally corresponding to the inclusions. It is the combination of these two approaches that permits us to gain deeper insight into diamond genesis and to better understand the specific character of processes of deep-seated mineral formation.Studies of mineral inclusions in diamonds have determined the main types of diamondiferous parageneses: ultramaffic, eclogitic (4,8,9), and intermediate websterite (10) and calc-silicate types (11). Some mineral inclusions, e.g., intergrowths of phlogopite with pyroxene (8, 12, 13) and phlogopite with calcite (14), are unambiguously evidence that K and H 2 O were present in the diamond-forming medium. It is pertinent to note that, as early as 30 years ago, neutron activation analysis of diamonds without visible inclusions, taken from three South African deposits, revealed a mixture of mostly K and of other components, which was interpreted as evidence of the presence of entrapped melt (15). Principally, more recent information has accrued from micro-and nano-inclusions in mantle-derived and metamorphic diamonds. Analysis of the composition of the inclusions in fibrous or cloudy mantle diamonds shows that, at the time of entrapment, the inclusion matter was a specific fluid whose composition belongs to one of the three main types: (i) ...

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“…Terry et al 2000;Tucker et al 2004;Root et al 2005). In this last phase of the collision, however, both Baltic basement and a number of nappe units were buried to depths of c. 125 km, resulting in the formation of diamond-and coesite-bearing eclogites (Dobrzhinetskaya et al 1995;Wain 1997). Burial and ultrahigh-pressure metamorphism was rapidly followed by substantial denudation (Terry et al 2000;Terry & Robinson 2003).…”

Section: Geological Settingmentioning

confidence: 99%

Kinematics of the Høybakken detachment zone and the Møre–Trøndelag Fault Complex, central Norway

Osmundsen

Eide

Haabesland

et al. 2006

JGS

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The tectonic disintegration of the Caledonian orogen through combined extension, contraction and strike-slip was characterized by spatial and temporal strain partitioning through a period of at least 30 Ma. Early to Mid-Devonian exhumation of the Central Norway basement window was associated with retrograde, top-to-the-SW extensional shearing in the Høybakken detachment zone, sinistral shearing along the Møre-Trøndelag Fault Complex, and formation of extension-parallel folds. Progressive exhumation led to increasing strain localization and to the transition from ductile to brittle deformation. In the interval between c. 370 and 320 Ma, the Høybakken detachment fault cut previously folded detachment mylonites, capturing mylonites in its hanging wall. 40 Ar/ 39 Ar mica and K-feldspar ages indicate a Late Devonian or younger age for the uppermost parts of the adjacent 'Old Red' basin. Gentle folding of this stratigraphic level attests to the continuation of shortening and orogen-oblique extension into Late Devonian-Carboniferous time. Shortening was intensified along strands of the Møre-Trøndelag Fault Complex, as shown by mutually cross-cutting reverse and strike-slip faults. 'Flower structures' may be particularly common in constrictional strain systems where strike-slip faults develop parallel to the principal elongation trend, but normal to the principal axis of shortening.

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Microdiamond in high-grade metamorphic rocks of the Western Gneiss region, Norway

Cited by 321 publications

References 19 publications

Extensional tectonics in the Caledonides of southern Norway, an overview

Extensional tectonics in the Caledonides of southern Norway, an overview

The role of mantle ultrapotassic fluids in diamond formation

Kinematics of the Høybakken detachment zone and the Møre–Trøndelag Fault Complex, central Norway

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