Challenges in high‐pressure granulite metamorphism in the era of pseudosections: reaction textures, compositional zoning and tectonic interpretation with examples from the Bohemian Massif

O’Brien, Patrick J.

doi:10.1111/j.1525-1314.2007.00758.x

Cited by 80 publications

(49 citation statements)

References 76 publications

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“…Occurrences of diamondiferous quartz-feldspathic rocks, sunken blocks of garnet peridotites in granulites and almost entirely felsic undepleted granulite chemistry different from granulites of the stable lower crust (Fiala et al 1988), support this interpretation. Moreover, O'Brien (2008) demonstrated the equilibrium metamorphic state of ternary feldspar within granulites substantiating their HP-HT subcrustal origin.…”

Section: Rock Complexes Along the St/tb Boundarymentioning

confidence: 93%

Bottom to top lithosphere structure and evolution of western Eger Rift (Central Europe)

Babuška

Fiala

Plomerová

2009

Int J Earth Sci (Geol Rundsch)

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We present model of the structure and development of the entire lithosphere beneath the western Eger Rift (ER). Its crustal architecture and paths of volcanic products are closely related to sutures/boundaries of uppermost mantle domains distinguished by different orientations of olivine fabric, derived from 3-D analysis of seismic anisotropy. Three different fabrics of the mantle lithosphere belong to the Saxothuringian (ST), Teplá-Barrandian (TB) and Moldanubian (MD) microplates assembled during the Variscan orogeny. Dipping fossil (pre-assembly) olivine orientations, consistent within each unit, do not support any voluminous mantle delamination. The variable rift structure and morphology depend on the character of the pre-rift suture between the northern ST unit and the TB/MD units in the southern rift flank. The proper rift with typical graben morphology has developed above the steep lithosphere-scale suture between the ST and TB units. This subduction-related boundary originated from the closure of the ST Ocean. Parts of the crust and mantle lithosphere were dragged there into asthenospheric depths and then rapidly uplifted. The suture is marked by abrupt change in the mantle fabric and sharp gradients in regional gravity field and in metamorphic grade. The secular TBside-down normal movement is reflected in deep sedimentary basins, which developed since the Carboniferous to Cenozoic and in topography. The graben morphology of the ER terminates above the ''triple junction'' of the ST, TB and MD mantle lithospheres. The junction is characterized by offsets of surface boundaries of the tectonic units from their mantle counterparts indicating a detachment of the rigid upper crust from the mantle lithosphere. The southwest continuation of the rift features in Bavaria is expressed in occurrences of Cenozoic sediments and volcanics above an inclined broad transition zone between the ST and MD lithospheres. Schematic scenario of evolution of the region consists mainly of a subduction of the ST lithosphere to depths around 140 km, exhumation of HP-HT rocks and the post-tectonic granitoid plutonism.

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Section: Rock Complexes Along the St/tb Boundarymentioning

confidence: 93%

Bottom to top lithosphere structure and evolution of western Eger Rift (Central Europe)

Babuška

Fiala

Plomerová

2009

Int J Earth Sci (Geol Rundsch)

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“…The HPG conditions are suggested to have been produced by continental subduction terminated by delamination of the lowermost subducted crust and its lithospheric mantle (O'Brien, 2008), leading to a transition from a longer-lived colder orogenic regime to that of a hot orogen dominated by felsic crust with relatively high heat productions at deep levels in the thickened orogenic architecture. In the southern Bohemian Massif the HPG gneisses underwent post-peak ITD through near-UHT to granulite P-T conditions of 12-7 kbar at 880-800°C within 5-10 Ma of the 340 Ma metamorphic peak.…”

Section: Rapid Buoyancy-driven Vertical Extrusion Of Highpressure Gramentioning

confidence: 99%

“…The Variscan orogen in the Bohemian Massif is typified by gneisses of upper crustal derivation, metamorphosed at 16-22 kbar and 850-1000°C at 340 Ma to produce garnet + kyanite leucogranulites (O'Brien, 2008), classic examples of High Pressure granulites (HPG) (O'Brien and Rötzler, 2003;Brown, 2006). The HPG conditions are suggested to have been produced by continental subduction terminated by delamination of the lowermost subducted crust and its lithospheric mantle (O'Brien, 2008), leading to a transition from a longer-lived colder orogenic regime to that of a hot orogen dominated by felsic crust with relatively high heat productions at deep levels in the thickened orogenic architecture.…”

Section: Rapid Buoyancy-driven Vertical Extrusion Of Highpressure Gramentioning

confidence: 99%

A matter of time: The importance of the duration of UHT metamorphism

Harley

2016

Journal of Mineralogical and Petrological Sciences

142

110

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The duration of granulite (G) and ultra-high temperature (UHT) conditions in regional metamorphism is critical to arguments regarding the tectonic settings of granulites and their relationships to Supercontinent assembly. Analysis of zircon geochronology integrated with trace element (REE) constraints on the timing of zircon growth or modification and evidence for metamorphic temperatures from Ti-in-zircon reveals that zircon can form episodically at or near the metamorphic peak in long-lived UHT granulites. This reflects the segregation, transfer and stagnation or trapping of melts which leads to local melt-rock interactions that promotes zircon crystallisation. In contrast, although rutile can retain UHT information in short duration ('fast') G-UHT terrains it is afflicted by Zr loss in long duration ('slow') terrains and yields temperatures significantly lower than those preserved by zircons formed in the same G-UHT events. An assessment of the age-duration evidence from several well-documented G-UHT terrains reveals that most are 'slow', having durations of UHT, Δt 900 , in the range 30-100 Myr. Some UHT terrains previously considered to be short-lived (Δt 900 < 10 Myr) have longer durations of UHT in the light of recent geochronology and hence are also classed as 'slow'. Of the models proposed to account for UHT metamorphism, the 'large hot orogen' (LHO) model for collisional orogeny provides the best setting for the formation of such 'slow' UHT granulites. LHO models can account not only for the P-T paths, which can range from UHT with near-isothermal decompression (UHT-ITD) through to decompression-cooling and UHT followed by near-isobaric cooling (UHT-IBC), but also for residence times under UHT conditions. The Napier Complex, the Earth's premier UHT terrain, probably formed as trapped deep crust in the hot underbelly of a late-Archaean LHO. Shorter duration UHT and near-UHT granulites also exist, mostly with Δt 900 less than 10 Myr. A number of these are likely to have formed as a consequence of severe lithospheric thinning and crustal extension accompanied by voluminous magmatism, which could occur in arc and back-arc settings affected by subduction roll-back or, as advocated by previous workers, continental arcs undergoing extension. However, attaining long-lived UHT conditions in these settings is unlikely unless the crust has inherently high radioactive heat production in addition to the transient heat added during extension and magmatism.

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“…with subordinate amount of orthopyroxene, rutile and magnetite. The peak granulite assemblage is represented by garnetclinopyroxene-plagioclase-quartz-ilmenite with/without orthopyroxene which is characteristic of many high-pressure rocks (O'Brien, 2008;Racek et al, 2008). This assemblage could have evolved through dehydration melting of hornblende-bearing assemblage.…”

Section: Textural and Mineralogical Evolutionmentioning

confidence: 99%

Tectonic juxtaposition of crust and continental growth during orogenesis: Example from the Rengali Province, eastern India

Bose¹,

Guha²,

Ghosh³

et al. 2015

Geoscience Frontiers

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a b s t r a c tThe southern boundary of the Singhbhum Craton witnessed multiple orogenies that juxtaposed thin slice of granulite suite of the Rengali Province against the low-grade granite-greenstone belt of the craton along the EeW trending Sukinda Thrust. The strong southerly dipping mylonitic foliation within the granulites along with the prominent down-dip mineral lineation, suggest a northerly-verging thrusting. Mylonitized charnockite at the contact zone contains enclaves of mafic and ultramafic granulite, whereas granitoid gneiss contains enclaves of pelitic granulite. Mafic granulite enclaves preserve an early (S 1M ) foliation that formed during D 1M deformation. This rock, along with the host charnockite, were intensely deformed by the D 2M thrusting event and resulting S 2M foliation development in both rock suites. Geothermobarometric and pseudosection analyses show that the garnet-clinopyroxene-plagioclaseorthopyroxene-ilmenite-quartz assemblage in mafic granulite was stabilized at high-pressure and temperature conditions (10À12 kbar, 860 C) and was overprinted by a fine-grained assemblage of clinopyroxene-plagioclase AE hornblende that developed during decompression (down to 5.5e7.5 kbar). Matrix hornblende shows incipient breakdown to garnet-clinopyroxene-quartz intergrowth due to a granulite facies reworking. A contrasting P-T history is preserved in the pelitic granulite. The peak assemblage garnet-orthopyroxene-cordierite-quartz-rutile was stabilized at w6.0 kbar, 730 C which resulted from heating of the mid crust magma during the D 2M thrusting. The contrasting P-T histories could result from the tectonic juxtaposition of lower-and mid-crustal section during the D 2M event. Evidences of an early orogenic imprint within the mafic granulite imply involvement of deep continental crust during southward growth of the Singhbhum Craton.Ó 2014, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/3.0/).

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Challenges in high‐pressure granulite metamorphism in the era of pseudosections: reaction textures, compositional zoning and tectonic interpretation with examples from the Bohemian Massif

Cited by 80 publications

References 76 publications

Bottom to top lithosphere structure and evolution of western Eger Rift (Central Europe)

Bottom to top lithosphere structure and evolution of western Eger Rift (Central Europe)

A matter of time: The importance of the duration of UHT metamorphism

Tectonic juxtaposition of crust and continental growth during orogenesis: Example from the Rengali Province, eastern India

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