Tectonic significance of the meta-evaporitic magnesite and scapolite deposits in the Seve Nappes, Sarek Mts., Swedish Caledonides

Svenningsen, Olaf

doi:10.1016/0040-1951(94)90119-8

Cited by 28 publications

(31 citation statements)

References 26 publications

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“…Before the opening, however, rift basins developed, and syn‐rift sediments were deposited. These sediments consisted primarily of Neoproterozoic sandstone and shale overlain by a sequence of carbonate, which locally show evidence for evaporite deposits (Svenningsen, ). Locally, the carbonate sequence is overlain by a diamictite unit, which again is overlain by thick clastic packages, comprised by up to several kilometers of shallow marine sandstone (Nystuen et al, ; Stølen, ; Svenningsen, ; Zwaan & van Roermund, ).…”

Section: Geological Settingmentioning

confidence: 99%

Timing of Breakup and Thermal Evolution of a Pre‐Caledonian Neoproterozoic Exhumed Magma‐Rich Rifted Margin

et al. 2019

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During the terminal stages of Wilson cycles, remnants of magma‐poor margins may be incorporated into the orogens, whereas the magma‐rich margins often are lost in subduction due to low buoyancy. The understanding of magma‐rich margins is therefore mostly based on drill holes and geophysical observations. In this contribution, we explore the temporal evolution and the ambient conditions of a magma‐rich rifted margin preserved within the Scandinavian Caledonides. The Scandinavian Dike Complex was emplaced into a sedimentary basin during the initial breakup and opening of the Iapetus Ocean 615 to 590 million years ago. The dike complex constitutes 70–90% of the magma‐rich, syn‐rift basins and is locally well preserved despite the complex Caledonian history. This contribution provides new observations about the geometry, relative timing, and development of the margin. Jadeite‐in‐clinopyroxene geothermobarometry, titanium‐in‐biotite geothermometry, and garnet isopleth modeling show that the ambient pressure and temperature conditions were similar for the entire dike complex at 0.25 to 0.45 GPa, with contact metamorphic temperatures up to approximately 700 °C. In the northernmost part of the study area, U‐Pb dating of magmatic zircon shows that partial melting of the sedimentary host rock, at relatively shallow levels, occurred at 612 Ma. This shows that the crust was molten already 6 million years before the northernmost dike swarm was emplaced at 605.7 ± 1.8 Ma. We propose that the locally pervasive partial melting occurred due to high geothermal gradients and introduction of mafic melt in the lower crust. These processes significantly reduced the strength of the crust, eventually facilitating continental breakup.

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Section: Geological Settingmentioning

confidence: 99%

Timing of Breakup and Thermal Evolution of a Pre‐Caledonian Neoproterozoic Exhumed Magma‐Rich Rifted Margin

et al. 2019

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“…1a). The sediments consist of metapsammite, and to some extent of carbonates and calcsilicates metamorphosed to a scapolite rich, hornfelsic rock during dyke intrusion (Svenningsen 1994a). The diabases have T‐MORB chemistry (Andréasson et al 1992).…”

Section: The Scandinavian Caledonides and The Seve Nappe Complexmentioning

confidence: 99%

“…2a). Intercalations on a cenimetre scale of these rocks occur, and the metapsammite was metamorphosed into hornfels during dyke intrusion (Svenningsen 1994a). Alterations to garnet‐diopside skarn are common in the metasediments indicating vast circulation of water.…”

Section: The Scandinavian Caledonides and The Seve Nappe Complexmentioning

confidence: 99%

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Preservation of a magnetization carried by magnetite-inclusions during amphibolite grade metamorphic conditions? An example from the Sarek Dykeswarm, Northern Swedish Caledonides

Eneroth

2002

Geophysical Journal International

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Summary An outcrop consisting of a 608 Myr old sheeted dyke complex and dyke‐intruded metasediments has been investigated palaeomagnetically. It is located in the interior of a nappe the basal and upper parts of which suffered penetrative deformation and amphibolite grade metamorphism during the Caledonian orogeny. The only trace from the orogeny at the outcrop is a widely spaced network of brittle and ductile shear zones crosscutting dyke contacts. Foliated amphibolite consisting of hornblende, quartz, plagioclase, garnet and sphene occur locally within them. The opaque mineralogy of the dykes differs from that commonly found in continental dykes, with ilmenite and pyrrhotite being the major visible opaque phases, and there are indications that magnetite inclusions exsolved from silicates carry a primary remanence even though 39Ar–40Ar mica ages were reset at ca. 430 Myr during the orogeny. A secondary component carried by pyrrhotite is less prominent but falls on the Baltican APW path at 430 Myr. The inferred primary component has a large directional uncertainty, but indicates low palaeolatitudes for the Baltscandian margin during rifting.

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“…Evaporites are not common in the Norwegian Caledonides, although meta-evaporitic magnesite and scapolite deposits have been described from the Skipa formation in the Swedish part of the Seve Nappe (Svenningsen, 1994). Also, if evaporates had been deposited along with the abundant carbonate bodies on the Laurentian continental margin, evidence of high-salinity fluids should be titanite was altered to ilmenite, restricting the event to high temperatures (Fig.…”

Section: Pressure and Temperature Constraintsmentioning

confidence: 99%

Orogenic degassing, scapolitization and K- metasomatism during Caledonian exhumation, Helgeland, Norway

Drivenes¹,

Sørensen²,

Larsen³

2016

NJG

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Metasomatism associated with barren quartz veins cross-cutting hornblende schist in the upper part of the metasedimentary sequence of the WMo-mineralized Bjellatinden area was studied using P-T modeling of the mafic schist host and alteration assemblages, fluid inclusions, and isocon diagrams. Two main alteration assemblages are associated with the quartz veins: A biotite-scapolite-dominated zone (BSZ), and a zone dominated by chlorite, muscovite and calcite (CMZ), replacing the former BSZ and extending further into the wall rock. Three types of fluid inclusions are observed: CO 2 -rich (type I), low-salinity H 2 O-rich (type II), and high-salinity H 2 O-rich (type III). Type III fluids are strongly associated with the CMZ, and are not observed in the BSZ, whereas type I and II fluids are observed in quartz and scapolite in the BSZ. Type I and II fluid inclusions found in quartz in the CMZ are interpreted to be relics from the earlier BSZ alteration. Plagioclase-amphibole thermobarometry of grains in the hornblende schist indicates a near-isothermal pressure drop from ca. 660 to ca. 560 MPa at ca. 690°C. Type I and II fluids are interpreted to have infiltrated extension fractures at ca. 240 MPa and 600°C giving rise to the BSZ, and only minor mass exchange with the hornblende schist. Type III fluids are responsible for K -metasomatism of the existing alteration assemblage, and infiltrated the pre-existing fracture system over a large temperature range, from ca. 600°C to ca. 350°C during near-isobaric cooling at ca. 200 MPa. The CMZ was stabilized towards the end of this fluid infiltration. The high-salinity fluids are interpreted to have exsolved from an underlying, unexposed, granitic intrusion. This intrusion may also be the source of the W-Mo mineralizations in the area.

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Tectonic significance of the meta-evaporitic magnesite and scapolite deposits in the Seve Nappes, Sarek Mts., Swedish Caledonides

Cited by 28 publications

References 26 publications

Timing of Breakup and Thermal Evolution of a Pre‐Caledonian Neoproterozoic Exhumed Magma‐Rich Rifted Margin

Timing of Breakup and Thermal Evolution of a Pre‐Caledonian Neoproterozoic Exhumed Magma‐Rich Rifted Margin

Preservation of a magnetization carried by magnetite-inclusions during amphibolite grade metamorphic conditions? An example from the Sarek Dykeswarm, Northern Swedish Caledonides

Orogenic degassing, scapolitization and K- metasomatism during Caledonian exhumation, Helgeland, Norway

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