Dynamic Metasomatism: Stable Isotopes, Fluid Evolution, and Deformation of Albitite and Scapolite Metagabbro (Bamble Lithotectonic Domain, South Norway)

Engvik, Ane K.; Taubald, Heinrich; Solli, Arne; Grenne, Tor; Austrheim, Håkon

doi:10.1155/2018/9325809

Cited by 8 publications

(3 citation statements)

References 68 publications

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“…Antigorite might also release water and produce olivine during deserpentinisation caused by frictional heat, or heat from other sources. As observed by Engvik et al (2018), other mineral systems in the lower crust, involving scapolite metagabbro and scapolite-bearing amphibolites might also show brittle/ductile behaviour. Soret et al (2019) studied the deformation mechanisms in mafic amphibolites and granulites at relevant temperatures and pressures.…”

Section: Constraining the Properties Of The Lcbmentioning

confidence: 54%

The "Global Salt Cycle": Formation of Giant Salt Accumulations, a Result of Subduction, Mantle Upwelling, and Rifting

Johnsen¹,

Rueslåtten²,

Hovland³

2021

Preprint

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The main objective of this communication is to describe the ‘Global Salt Cycle’. Giant salt accumulations are commonly found along continental margins of former rifts. The first stage in the accumulation process is saturation of newly formed oceanic crust with seawater. Final mobilisation and accumulation of the salts occurs during rifting, localised in the vicinity of relict subduction zones. Oceanic crust is created along the spreading ridges in the deep oceans of the Earth. It exchanges mass and energy with seawater in hydrothermal circulation cells that penetrate deep into the new and fractured crust. Water-rock interactions include the formation of hydrated and hydroxylated minerals, e.g., serpentinites and clay minerals. By incorporating hydroxyl groups and water in their crystal lattices, the salinity of remaining brines increases. Subduction of oceanic crust and serpentinised lithosphere transports water, hydrated minerals, and marine salts deep into the crust and mantle. Upon pressurisation and heating of the subducting slab, different parts of this water are expelled at different depths/temperatures. The resulting fluids will contain salts brought in with the slab, as well as new salts formed by water-rock interaction. The combination of elevated pressures and temperatures, water, salinity, and CO2, create permeability in the normally impermeable, peridotitic mantle, by altering the fluid-rock dihedral angles of mineral grains. This P/T-determined intergranular permeability allows ascent of saline fluids, under lithostatic pressure, within the mantle wedge, or the slab itself. The fluids produce a mechanically weakened and buoyant zone within the mantle wedge due to high pore pressure between mineral grains and reduced mantle density. During the lifetime of a subduction zone, a substantial accumulation of saline fluids within the mantle wedge and crust, is evident. Deep, fluid reservoirs accumulate between the subduction trench and the volcanic front. They may exist for hundreds of millions of years, even after the extinction of the subduction zone. Saline fluids may escape to the surface along deep faults, due to overfilling of available pores/fractures. Fluids within the mantle wedge may form rock melts or exist as supercritical, mineral rich fluids. The combination of reduced pressure due to rifting, and a saline and buoyant mantle, creates a mantle circulation that brings the accumulated, saline fluids, to crustal levels. Salts will therefore accumulate during initial stages of rifting as a result of massive fluid expulsion, phase change and boiling of mantle fluids. No extra energy is required to produce phase change and boiling. The result is formation of solid salts or dense brines/slurries invading fractured crustal rocks, or escaping to the surface/seabed. This process may take place both before and after the sea has invaded a continental rift.

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Section: Constraining the Properties Of The Lcbmentioning

confidence: 54%

The "Global Salt Cycle": Formation of Giant Salt Accumulations, a Result of Subduction, Mantle Upwelling, and Rifting

Johnsen¹,

Rueslåtten²,

Hovland³

2021

Preprint

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“…S.1), as observed in this sample. Indeed, scapolisation of plagioclase feldspar has been attributed to the infiltration of NaCl fluids at 600-700 o C in metagabbros of the Bamble Lithotectonic Domain, South Norway (Engvik et al, 2011(Engvik et al, , 2018. We note that ST_16_005, which contains some clay minerals, has a noble gas isotope (and halogen) composition similar to the samples from the intrusion, suggesting that low temperature alteration has not affected its volatile geochemistry, e.g., by imparting an air-like signature (Fig.…”

Section: Evaluating the Effects Of Late-stage Metamorphism On Halogen Budgetsmentioning

confidence: 74%

Magmatic volatiles and platinum-group element mineralization in the Stillwater layered intrusion, U.S.A.

Parker¹,

Clay

Boudreau³

et al. 2022

American Mineralogist

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The activity of volatile-rich fluids may be important in the evolution of basaltic magmatic systems and associated precious metal ore formation. There is evidence for Cl-rich fluids within the Stillwater Complex (Montana, USA), which have been linked to platinum and palladium mineralisation in the economically important J-M Reef ore body. We present the first dataset for heavy halogens (Cl, Br and I) and natural noble gas isotopes in bulk rock and mineral separates from the Peridotite Zone and the Olivine-Bearing Zone I of the Stillwater Complex, including samples from the J-M Reef and G Chromitite bodies. Our data reveal concentrations of 4 to 13500 ppm for Cl, 26 ppb to 360 ppm for Br and <1 ppb to 9 ppm I over This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America.The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press.

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“…The Bamble domain is known for its high‐grade granulite facies metamorphism, including the first mapped orthopyroxene isograde (Touret, 1971), and for being extensively metasomatized. Metasomatism led to the formation of albitite bodies (Engvik et al, 2008, 2014, 2018), scapolite‐rich rocks (Engvik et al, 2009, 2011; Lieftink et al, 1993), orthoamphibole‐cordierite rocks (Engvik & Austrheim (2010); Hövelmann et al, 2014) and nodular gneisses (Nijland et al, 2014). Similar metasomatic rocks are also present in the Modum region of the Kongsberg domain.…”

Section: Geological Settingmentioning

confidence: 99%

Low‐grade prehnite‐pumpellyite facies metamorphism and metasomatism in basement rocks adjacent to the Permian Oslo rift: The importance of displacive reactions

Austrheim

Engvik

Ganerød

et al. 2022

Journal Metamorphic Geology

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The Kongsberg and Bamble lithotectonic domains of SE‐Norway are known as classical Precambrian high‐grade metamorphic terrains. The area has undergone extensive metasomatism with formation of albitites and scapolite‐rich rocks and numbers of previously economically important deposits including the Kongsberg Silver and the Modum Cobalt mines. We demonstrate here that the central part of the Bamble lithotectonic domain (Kragerø area) has locally developed low‐grade metamorphic minerals (prehnite, pumpellyite, analcime, stilpnomelane and thomsonite) belonging to the prehnite‐pumpellyite and zeolite facies. Structurally, the low‐grade minerals occur as fracture fills, in the alteration selvages around fractures where the rock is albitized, and along shear zones and cataclastic zones. The fracture fill and the alteration selvages vary from millimetres scale to 1 m in thickness. The fractures with low‐grade minerals are part of larger fracture systems. The low‐grade minerals typically formed by both displacive (swelling) and replacive reactions and in a combination of these. Prehnite together with albite, K‐feldspar, quartz, epidote and hydrogarnet form lenses along (001) faces in biotite and chlorite leading to bending of the sheet silicates through a displacive reaction mechanism. Numerous replacement reactions including the earlier minerals as well as the low‐grade minerals occur. As albite, K‐feldspar, talc, quartz, actinolite, titanite, calcite and hydrogrossular form in the same veins and in the same biotite grain as the classical low‐grade minerals, they probably belong to the low‐grade assemblage and some of the albitization in the region presumably occurred at low‐grade conditions. Alteration of olivine (Fo69) at low‐grade conditions results in the formation of clay minerals including ferroan saponite. Reconnaissance studies at the east (Idefjord lithotectonic domain) and the northwest (Kongsberg lithotectonic domain) sides of the Oslo rift together with reports of low‐grade assemblages in south‐western Sweden along the continuation of the rift into Skagerrak suggest that the low grade assembles occur in rocks adjacent to the Oslo rift along its full extent. Ar‐Ar dating of K‐feldspar from the low‐grade assemblages gave an age of 265.2 ± 0.4 Ma (MSWD = 0.514 and P = 0.766), suggesting that the low‐grade metamorphism and some of the metasomatism is induced by fluids and heat from the magmatic activity of the Permian Oslo rift, which requires transport of fluid over distances of several kilometres. The metamorphic conditions are constrained by stability fields of prehnite, pumpellyite and analcime to be less than 250°C and at a pressure less than 5 kbars. The displacive reactions created micro‐fractures and porosity in the adjacent minerals that enhance fluid flow and low‐grade mineral formation on a local scale. On a thin section scale, the displacive growth of albite in biotite results in a local volume increase of several 100%. Whether the opening of the larger, horizontally oriented fracture systems...

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Dynamic Metasomatism: Stable Isotopes, Fluid Evolution, and Deformation of Albitite and Scapolite Metagabbro (Bamble Lithotectonic Domain, South Norway)

Cited by 8 publications

References 68 publications

The "Global Salt Cycle": Formation of Giant Salt Accumulations, a Result of Subduction, Mantle Upwelling, and Rifting

The "Global Salt Cycle": Formation of Giant Salt Accumulations, a Result of Subduction, Mantle Upwelling, and Rifting

Magmatic volatiles and platinum-group element mineralization in the Stillwater layered intrusion, U.S.A.

Low‐grade prehnite‐pumpellyite facies metamorphism and metasomatism in basement rocks adjacent to the Permian Oslo rift: The importance of displacive reactions

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