Fluid inclusions in granulites and eclogites from the Bergen Arcs, Caledonides of W. Norway

Andersen, Torgeir B.; Austrheim, Håkon; Burke, E. A. J.

doi:10.1180/minmag.1990.054.375.02

Cited by 59 publications

(20 citation statements)

References 24 publications

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“…This indicates that the granulite-facies overprinting on UHP eclogite followed isothermal decompression (Fig. Origin of N 2 Several studies have been made on eclogite containing N 2 -rich fluids, for example, in the Caledonides (Andersen, Burke & Austrheim, 1989;Andersen, Austrheim & Burke, 1990;Andersen et al 1993) and the Münchberg complex in Bavaria (Klemd, Van den Kerkhof & Horn, 1992), although fluids from eclogites from the Alps are chiefly aqueous brines without evidence of N 2 (Selverstone et al 1984;Philippot & Selverstone, 1991;Philippot, 1993). This type of high-density CO 2 is also reported from ultrahightemperature granulites from North China (Santosh et al 2008).…”

Section: C Source Of Fluidmentioning

confidence: 98%

Fluids in coesite-bearing rocks of the Tso Morari Complex, NW Himalaya: evidence for entrapment during peak metamorphism and subsequent uplift

Mukherjee

Sachan

2009

Geol. Mag.

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Fluid inclusions trapped in coesite-bearing rocks provide important information on the fluid phases present during ultrahigh-pressure metamorphism. The subduction-related coesite-bearing eclogites of the Tso Morari Complex, Himalaya, contain five major types of fluids identified by microthermometry and Raman spectroscopy. These are: (1) high-salinity brine, (2) N 2 , (3) CH 4 , (4) CO 2 and (5) low-salinity aqueous fluids. These fluids were trapped during both deep subduction and exhumation processes. The coesite-bearing rocks are inferred to have been buried to a depth of > 120 km, where they experienced ultrahigh-pressure metamorphism. The fluid-rock interaction provides direct evidence for fluid derivation during a deep subduction process as demonstrated by silica-carbonate assemblages in eclogite. High salinity brine, N 2 and CH 4 inclusions are remnants of prograde and peak metamorphic fluids, whereas CO 2 and low-salinity aqueous fluids appear to have been trapped late, during uplift. The high-salinity brine was possibly derived from subducted ancient metasedimentary rocks, whereas the N 2 and CH 4 fluids were likely generated through chemical breakdown of NH 3 -bearing K minerals and graphite. Alternatively, CH 4 might have been formed by a mixed fluid that was released from calcareous sediments during subduction or supplied through subducted oceanic metabasic rocks. High density CO 2 is associated with matrix minerals formed during granulite-facies overprinting of the ultrahigh-pressure eclogite. During retrogression to amphibolitefacies conditions, low-salinity fluids were introduced from external sources, probably the enclosing gneisses. This source enhances salinity differences as compared to primary saline inclusions. The subducting Indian lithosphere produced brines prior to achieving maximal depths of > 120 km, where fluids were instead dominated by gaseous phases. Subsequently, the Indian lithosphere released CO 2rich fluids during fast exhumation and was then infiltrated by the low-salinity aqueous fluids near the surface through external sources. Elemental modelling may improve quantitative understanding of the complexity of fluids and their reactions.

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Section: C Source Of Fluidmentioning

confidence: 98%

Fluids in coesite-bearing rocks of the Tso Morari Complex, NW Himalaya: evidence for entrapment during peak metamorphism and subsequent uplift

Mukherjee

Sachan

2009

Geol. Mag.

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“…1). Fluid inclusion data from several eclogites in the WGR and BAS suggest that the eclogite facies¯uids were both N 2 ±CO 2 ±H 2 O¯uids (Andersen et al, 1989(Andersen et al, , 1990(Andersen et al, , 1993 and brines (Andersen et al, 1993;Svensen et al, 1999). This bimodality in the composition of these¯uid inclusions has been recognized in other eclogite terranes as well (see Philippot et al, 1995, and references therein), but there is no systematic regional pattern in the distribution of the two types of inclusion¯uid in the WGR/ BAS.…”

Section: Geological Settingmentioning

confidence: 99%

Halogen contents of eclogite facies fluid inclusions and minerals: Caledonides, western Norway

Svensen

Jamtveit

Banks

et al. 2001

Journal Metamorphic Geology

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Primary multiphase brine fluid inclusions in omphacite and garnet from low‐ to medium‐temperature eclogites have been analysed for Cl, Br, I, F, Li and SO4. Halogen contents and ratios provide information about trapped lower crustal fluids, even though the major element (Na, K, Ca) contents of inclusion fluids have been modified by fluid–mineral interactions and (step‐) daughter‐crystal formation after trapping. Halogens in the inclusion fluids were analysed with crush–leach techniques. Cl/Br and Cl/I mass ratios of eclogite fluids are in the range 31–395 and 5000–33 000, respectively. Most fluids have a Cl/Br ratio lower than modern seawater and a Cl/I ratio one order of magnitude lower than modern seawater. Fluids with the lowest Cl/Br and highest Cl/I ratios come from an eclogite that formed by hydration of granulite facies rocks, and may indicate that Br and I are fractionated into hydrous minerals. Reconstructions indicate that the inclusion fluids originally contained 500–4000 ppm Br, 1–14 ppm I and 33–438 ppm Li. Electron microprobe analyses of eclogite facies amphibole, biotite, phengite and apatite indicate that F and Cl fractionate most strongly between phengite (F/Cl mass ratio of 1469 ± 1048) and fluid (F/Cl mass ratio of 0.008), and the least between amphibole and fluid. The chemical evolution of Cl and Br in pore fluids during hydration reactions is in many ways analogous to Cl and Br in seawater during evaporation: the Cl/Br ratio remains constant until the aH2O value is sufficiently lowered for Cl to be removed from solution by incorporation into hydrous minerals.

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“…However, several recent studies have demonstrated that many eclogites or other types of H P rock samples do contain workable, sometimes spectacular inclusions, many of them related to peak metamorphic conditions (e.g. Selverstone et al ., 1984, 1992; Andersen et al ., 1989, 1990; Klemd et al ., 1992, 1995; Nadeau et al ., 1993; Giaramita & Sorensen, 1994; Philippot et al ., 1995; Scambelluri et al ., 1997, 1998).…”

Section: Introductionmentioning

confidence: 99%

Fluid inclusions in coesite‐bearing eclogites and jadeite quartzite at Shuanghe, Dabie Shan (China)

Touret

Zheng

2001

Journal Metamorphic Geology

126

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Fluid inclusions in coesite‐bearing eclogites and jadeite quartzite at Shuanghe in Dabie Shan, East‐central China, have preserved remnants of early, prograde and/or peak metamorphic fluids, reset during post‐UHP (ultrahigh‐pressure) metamorphic uplift. Inclusions occur in several minerals (e.g. omphacite & epidote), notably as isolated, primary inclusions in quartz included in various host minerals. Two major fluid types have been identified: non‐polar fluid species (N2 or CO2) and aqueous, the latter is by far the most predominant. Aqueous fluids cover a wide range of salinity, from halite‐bearing brines to low salinity fluids. For non‐polar fluids, few N2 inclusions occur in undeformed eclogite, whereas a number of CO2‐rich inclusions have been found in microshear zones of eclogite or jadeite quartzite in close proximity to marble occurrences. The primary character of N2 and high‐salinity aqueous inclusions indicates that they are remnants from UHP metamorphic fluids and for some there is the distinct possibility that they are ultimately derived from pre‐metamorphic fluids. This conclusion is supported by the preservation, in some samples, of microdomains containing synchronous inclusions of variable salinities, which tend to relate to the chemical composition of the host crystal. Carbonic fluids may be derived from neighbouring rocks, notably marble and carbonate‐bearing metasediments, during post‐metamorphic uplift. During post‐UHP exhumation, a limited decrease of the fluid density has occurred, with formation of new sets of fluid inclusions. Fluid movements, however, remained exceedingly limited, at the scale of the enclosing crystal.

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Fluid inclusions in granulites and eclogites from the Bergen Arcs, Caledonides of W. Norway

Cited by 59 publications

References 24 publications

Fluids in coesite-bearing rocks of the Tso Morari Complex, NW Himalaya: evidence for entrapment during peak metamorphism and subsequent uplift

Fluids in coesite-bearing rocks of the Tso Morari Complex, NW Himalaya: evidence for entrapment during peak metamorphism and subsequent uplift

Halogen contents of eclogite facies fluid inclusions and minerals: Caledonides, western Norway

Fluid inclusions in coesite‐bearing eclogites and jadeite quartzite at Shuanghe, Dabie Shan (China)

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