Eclogites with a short-lived granulite facies overprint in the Moldanubian Zone, Czech Republic: petrology, geochemistry and diffusion modelling of garnet zoning

O’Brien, Patrick J.; Vrána, Stanislav

doi:10.1007/s005310050019

Cited by 89 publications

(35 citation statements)

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“…The chemical potential of Al increases towards garnet–kyanite, whilst the chemical potential of Na increases towards clinopyroxene, and the various layers in the corona could reflect compositional differences in the original reaction domains (e.g. O’Brien, 1997a). Thus, the symplectite of orthopyroxene and edenite may have replaced a rim of sodic pyroxene that previously mantled the igneous augite (e.g.…”

Section: Textural Relationships In the Eclogitic Rocksmentioning

confidence: 56%

“…Thus, the symplectite of orthopyroxene and edenite may have replaced a rim of sodic pyroxene that previously mantled the igneous augite (e.g. O’Brien, 1997a; Indares, 1997), whilst the pargasite–anorthite–spinel intergrowth has replaced garnet–kyanite ( O’Brien, 1997a), with spinel possibly nucleating in the kyanite domains. Phases such as sapphirine and corundum described from textures in Variscan and Grenvillean eclogites ( O’Brien, 1997a; Indares, 1997) have not been observed.…”

Section: Textural Relationships In the Eclogitic Rocksmentioning

confidence: 84%

“…5a). The development of complex zonal coronas in which different igneous domains react separately reflects an incomplete gabbro to eclogite transformation probably aided by low fluid activities ( Mørk, 1985; O’Brien et al ., 1990 ; Rubie, 1990; O’Brien, 1997a). Of the original igneous phases, only clinopyroxene is preserved.…”

Section: Textural Relationships In the Eclogitic Rocksmentioning

confidence: 99%

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Eclogites in the Makuti gneisses of Zimbabwe: implications for the tectonic evolution of the Zambezi Belt in southern Africa

Dirks

Sithole

1999

Journal Metamorphic Geology

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The gneisses of the Makuti Group in north‐west Zimbabwe are characterized by complex geometries that resulted from intense non‐coaxial deformation in a crustal scale high‐strain zone that accommodated extensional deformation along the axis of the Zambezi Belt at c. 800 Ma. Within low‐strain domains in the Makuti gneisses, undeformed metagabbroic lenses preserve eclogite and granulite facies assemblages, which record a part of the metamorphic history that predates Pan‐African events. Eclogitic rocks can be subdivided into: (1) corona‐textured metagabbros that preserve igneous textures, and (2) garnet–omphacite rocks in which primary textures are destroyed. The lenses of eclogitic rocks are enveloped in a mantle of garnet–clinopyroxene–hornblende gneiss, which is a common rock type in the Makuti gneisses. The eclogites preserve multi‐staged, domainal, symplectic reaction textures that developed progressively as the rocks experienced loading followed by decompression–heating. In the metagabbros, the original clinopyroxene, plagioclase and olivine domains acted separately during the peak of metamorphism, with plagioclase being replaced by garnet and kyanite, and olivine being replaced by orthopyroxene and possibly omphacite. The peak assemblage was overprinted by: (1) the multi‐mineralic corona assemblage pargasite–orthopyroxene–spinel–plagioclase replacing garnet–kyanite–clinopyroxene (possibly at c. 19 kbar, 760±25 °C); (2) orthopyroxene–pargasite–plagioclase–scapolite coronas replacing orthopyroxene (15±1.5 kbar, 750±50 °C); and (3) moats of orthopyroxene–plagioclase replacing garnet (10±1 kbar, 760±50 °C). The garnet–omphacite rocks record similar peak conditions (15±1.1 kbar, 760±60 °C). Garnet–clinopyroxene–hornblende–plagioclase gneisses envelop the eclogites and record matrix conditions of 11±1.5 kbar at 730±50 °C using assemblages that are oriented in the regional fabric. These rocks are characterized by decompression‐heating textures, reflecting temperature increases during exhumation of the Makuti gneisses. The eclogite facies rocks formed during a collisional event prior to 850 Ma. Their formation could be related to a suture zone that developed along the axis of the Zambezi Belt during the formation of Rodinia (between 1400 and 850 Ma). The main deformation‐metamorphism in the Makuti gneisses occurred around 800 Ma and involved extension and exhumation of the high‐P rocks (break‐up of Rodinia), which experienced a high‐T metamorphic overprint. Around 550–500 Ma, a collisional event associated with the formation of Gondwana resulted in renewed burial and metamorphic recrystallization of the Makuti gneisses.

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Section: Textural Relationships In the Eclogitic Rocksmentioning

confidence: 56%

Section: Textural Relationships In the Eclogitic Rocksmentioning

confidence: 84%

Section: Textural Relationships In the Eclogitic Rocksmentioning

confidence: 99%

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Eclogites in the Makuti gneisses of Zimbabwe: implications for the tectonic evolution of the Zambezi Belt in southern Africa

Dirks

Sithole

1999

Journal Metamorphic Geology

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“…1; Gil Obrien and Vrana, 1995;Lardeaux et al, 2001;Massone, 2001;Arenas and Martínez Catalán, 2002). This type of units contains important information about the tectonothermal evolution of the Variscan or eo-Variscan accretionary complex, mainly because of the extreme metamorphic conditions attained and the superposition of deformational events that they register.…”

Section: Introductionmentioning

confidence: 99%

The eclogite facies gneisses of the Cabo Ortegal Complex (NW Iberian Massif): Tectonothermal evolution and exhumation model

Albert

Arenas

Martı́nez

et al. 2013

Journal of Iberian Geology

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The tectonothermal evolution of the eclogite facies gneisses of the Cabo Ortegal Complex has been investigated using new field and petrologic studies. This gneissic unit is included in the high-pressure and high-temperature (HP-HT) upper units of the allochthonous complexes of NW Iberia, a Cambrian arc-derived peri-Gondwanan terrane emplaced above ophiolitic units considered to represent the Rheic Ocean suture. Two detailed cross-sections performed in excellent exposures on the Cantabrian coast allows a clear understanding of the lithological constitution and deformations affecting the unit. The eclogitic gneiss unit is constituted by metasedimentary gneisses with abundant mafic inclusions, felsic rocks and rare ultramafic inclusions. The felsic rocks range from centimetric leucosomes to metric bodies and most of them were generated during extensive partial melting affecting the unit. The first tectonic fabric detected in the unit is a rarely preserved S1 foliation developed during subduction (ca. 400-390 Ma; 22 kbar). A drastic and fast exhumation (ca. 390 Ma; 12-10 kbar) generated a regional mylonitic foliation which represents the most prominent structural feature in the HP-HT upper units. The consecutive generation of extensional detachments, recumbent folds and a basal thrust occurred during the change from continental-type subduction to the underthrusting of ophiolitic units. These consecutive structures are probably related and the consequence of a long and pronounced exhumation of the subducted complex. The tectonothermal evolution of the eclogite facies gneisses of the Cabo Ortegal Complex represents an illustrative example of the intricate history of these deeply subducted units, which are relatively frequent in the suture zone of the Variscan Belt. It is important to remark that the structural, metamorphic and geochronological patterns in the evolution of this gneissic unit follows almost perfectly the ISSN (print): 1698-6180. ISSN (online): 1886-7995

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confidence: 99%

The eclogites in the Monotonous Series of the Moldanubian zone and the theory of thermal pulses: a discussion

Petrakakis¹

1997

Geologische Rundschau

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O'Brien and Vra´na (1995) recently interpreted textural and paragenetic relations as well as garnet zoning occurring in the rare eclogites of the Monotonous Series as evidence of (a) prograde evolution from lower pressures, (b) eclogite facies overprint and (c) granulite facies overprint caused by a thermal pulse of less than 1-Ma duration. The thermal pulse was interpreted as the result of the convergence of the thermal patterns of a hot-rock association over the cooler Monotonous Series metabasites. Re-evaluation of the data presented shows that the postulated prograde evolution is not supported. Similarly, the Fe-Mg-partitioning relations at garnet rims and associated orthopyroxene in these rocks point to cooling rather than heating. The age of less than 1 Ma dates a certain stage during cooling of the rocks, rather than the duration of a thermal pulse. The rare metabasites of the Monotonous Series are re-interpreted as tectonically incorporated bodies derived from the higher Moldanubian units during the intra-Moldanubian nappe stacking.

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Eclogites with a short-lived granulite facies overprint in the Moldanubian Zone, Czech Republic: petrology, geochemistry and diffusion modelling of garnet zoning

Cited by 89 publications

References 0 publications

Eclogites in the Makuti gneisses of Zimbabwe: implications for the tectonic evolution of the Zambezi Belt in southern Africa

Eclogites in the Makuti gneisses of Zimbabwe: implications for the tectonic evolution of the Zambezi Belt in southern Africa

The eclogite facies gneisses of the Cabo Ortegal Complex (NW Iberian Massif): Tectonothermal evolution and exhumation model

The eclogites in the Monotonous Series of the Moldanubian zone and the theory of thermal pulses: a discussion

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