P-T conditions and the origin of quartzo-feldspathic veins in metasyenites from the Central Zone of the Limpopo Belt, South Africa

Rigby, Martin J.; Mouri, Hassina; Brandl, G.

doi:10.2113/gssajg.111.2-3.313

Cited by 14 publications

(12 citation statements)

References 78 publications

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“…The peak metamorphic P-T conditions agree well with the peak P-T estimates obtained by Droop (1989) and Hisada and Miyano (1996). However, the retrograde path, defined by matrix assemblages, garnet resorption textures, mineral zoning and diffusion patterns (Zeh et al, 2004) requires a simultaneous P-T decrease, in agreement with the DC paths defined by Perchuk et al (2000), Van Reenen et al (2004), Hisada et al (2005) and Rigby et al (2008b) but in stark contrast to retrograde paths defined by ITD (e.g. Droop, 1989;Hisada and Miyano, 1996) and subsequent IBC (Hisada and Miyano, 1996).…”

Section: P-t-t Evolution Of the Central Zonesupporting

confidence: 78%

“…A single metamorphic event was further supported by the petrological data obtained by Rigby et al (2008b) from metasyenites in the West Alldays region. Results from conventional thermobarometry and pseudosection modelling in the chemical system Na 2 O-CaO-K 2 O-FeO-MgO-Al 2 O 3 -H 2 O-TiO 2 -Fe 2 O 3 indicate the metasyenites underwent a metamorphic evolution that was characterized by a maximum pressure of 8 kbar and temperatures of $770°C.…”

Section: P-t-t Evolution Of the Central Zonementioning

confidence: 54%

“…Subsequent retrogression involved a simultaneous P-T decrease via decompression-cooling to 4 kbar at temperatures <550°C. The inferred P-T path was used in combination with the petrological data of Zeh et al (2004Zeh et al ( , 2005 to postulate the existence of a metamorphic field gradient (Rigby et al, 2008b).…”

Section: P-t-t Evolution Of the Central Zonementioning

confidence: 99%

“…Whereas, the relative timing, style and extent of metamorphic activity in CZ has, over the years, come into question by numerous workers (e.g. Harris and Holland, 1984;Droop, 1989;Hisada and Miyano, 1996;Jaeckel et al, 1997;Holzer et al, 1998;Kröner et al, 1998Kröner et al, , 1999Smit et al, 2001;Van Reenen et al, 2004;Zeh et al, 2004;Zeh et al, 2005a,b;Hisada et al, 2005;Boshoff et al, 2006;Zeh et al, 2007;Rigby et al, 2008b;Gerdes and Zeh, 2009;Van Reenen et al, 2008;Perchuk et al 2008) who have defined different P-T paths. This has ultimately led to a great deal of controversy surrounding the tectonic evolution of the Limpopo Belt (Rigby et al, 2008a).…”

Section: Introductionmentioning

confidence: 99%

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Conflicting P–T paths within the Central Zone of the Limpopo Belt: A consequence of different thermobarometric methods?

Rigby

2009

Journal of African Earth Sciences

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a b s t r a c tA single metapelitic sample from the Verbaard locality, near Messina was investigated in order to construct a P-T path and moreover, highlight pertinent contradictions in the current P-T database. Interpretations based on P-T pseudosections, garnet isopleth thermobarometry and mineral mode/isopleth modelling indicate that the mineral assemblages, textures and zonations developed in the metapelite formed along a single clockwise P-T path. The metamorphic evolution is characterized by an early high-pressure phase at 10-11 kbar/800°C, followed by a simultaneous pressure decrease and temperature increase to $8/850°C and subsequent retrogression via decompression-cooling to 4-5 kbar at T < 650°C. Growth zoning in garnet provides evidence for an earlier, prograde history, however, as potential melt-loss was not accounted for this must be deemed speculative. The results of this study agree entirely with that of [Zeh, A., Klemd, R., Buhlmann, S., Barton, J.M. 2004. Pro-and retrograde P-T evolution of granulites of the Beit Bridge Complex (Limpopo Belt, South Africa); constraints from quantitative phase diagrams and geotectonic implications. Journal of Metamorphic Geology 22, 79-95], who adopted a similar approach to thermobarometry i.e. pseudosections. The results are, however, inconsistent with recent publications that argue for a twofold, metamorphic history defined by two decompression-cooling paths (DC1 $2.6 Ga and DC2 $2.0 Ga) that are separated by an isobaric heating path ($2.0 Ga). The disparity in the results obtained from different workers can be explained by an examination of the thermobarometric methods employed. The methodology employed to derive the twofold, polymetamorphic P-T path appears to be erroneous. At present, the most reliable and robust method for determining P-T paths is the pseudosection approach to thermobarometry. Future modelling of Limpopo Belt granulites should adopt this strategy and ensure potential melt-loss is taken into account. Alternatively, this potential problem can be avoided altogether by investigating rocks of mafic composition.

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Section: P-t-t Evolution Of the Central Zonesupporting

confidence: 78%

Section: P-t-t Evolution Of the Central Zonementioning

confidence: 54%

Section: P-t-t Evolution Of the Central Zonementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Conflicting P–T paths within the Central Zone of the Limpopo Belt: A consequence of different thermobarometric methods?

Rigby

2009

Journal of African Earth Sciences

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“…The epicontinental metasediments and emplacement of the layered gabbroanorthosite intrusion indicate intracontinental development. In addition, it seems impossible to link the long metamorphic history of the Limpopo Belt that also contains evidence for a prominent succession of high-grade repetitions with a single collisional event, as supported by a body of more recent literature [Boshoff et al, 2006;Zeh et al, 2007: Gerdes, Zeh, 2009van Reenen et al, 2008;Millonig et al, 2008;Perchuk et al, 2008;Rigby et al, 2008;Rigby, 2009;Rigby, Armstrong, 2011]. In our view, the time of tectonic compression, extrusion of metavolcanic-metasedimentary fill of the palaeobasin, and formation of synformal thrust-nappe ensemble can be most reliably constrained by intersection of the northern synform limb by the Great Dyke.…”

Section: Superplume-related Evolution Beyond Lauroscandiamentioning

confidence: 99%

Age and isotopic geochemical characteristics of Archean carbonatites and alkaline rocks of the Baltic shield

2007

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Paradoxically, the lists of "proxies" of both plate-and plume-related settings are devoid of even a mention of the high-grade metamorphic rocks (granulite, amphibolite and high-temperature eclogite facies). However, the granulite-gneiss belts and areas which contain these rocks, have a regional distribution in both the Precambrian and the Phanerozoic records. The origin and evolution of the granulite-gneiss belts correspond to the activity of plumes expressed in vigorous heating of the continental crust; intraplate magmatism; formation of rift depressions filled with sediments, juvenile lavas, and pyroclastic flow deposits; and metamorphism of lower and middle crustal complexes under conditions of granulite and high-temperature amphibolite facies that spreads over the fill of rift depressions also. Granulite-gneiss complexes of the East European Craton form one of the main components of the large oval intracontinental tectonic terranes of regional or continental rank. Inclusion of the granulite-gneiss complexes from Eastern Europe, North and South America, Africa, India, China and Australia in discussion of the problem indicated in the title to this paper, suggests consideration of a significant change in existing views on the relations between the plate-and plume-tectonic processes in geological history, as well as in supercontinent assembly and decay. The East European and North American cratons are fragments of the long-lived supercontinent Lauroscandia. After its appearance at ~2.8 Ga, the crust of this supercontinent evolved under the influence of the sequence of powerful mantle plumes (superplumes) up to ~0.85 Ga. During this time Lauroscandia was subjected to rifting, partial breakup and the following reconstruction of the continent. The processes of plate-tectonic type (rifting with the transition to spreading and closing of the short-lived ocean with subduction) within Lauroscandia were controlled by the superplumes. Revision of the nature of the granulite-gneiss complexes has led to a fundamental new understanding of: a more important role than envisaged previously for mantle-plume processes in the juvenile additions to the continental crust, especially during the Neoarchaean-Proterozoic; the existence of the supercontinent Lauroscandia from ~2.80 to 0.85 Ga; the leading role of mantle plumes in the interaction of plate-and plume-tectonics in the Neoarchaean-Proterozoic history of Lauroscandia and perhaps of the continental crust as a whole. We propose that the evolution of the geodynamic settings of the Earth's crust origin can be represented as a spiral sequence: the interaction of mantle-plume processes and embryonic microplate tectonics during the Palaeo-Mezoarchaean (~3.8-2.8 Ga) → plume-tectonics and local plume-driven plate-tectonics (~2.80-0.55 Ga) → Phanerozoic plate tectonics along with a reduced role of mantle plumes.Key words: Precambrian; plate-tectonics; plume-tectonics; granulite-gneiss belts; supercontinent; intracontinent oval orogenRecommended by E.V. Sklyarov Аннотация: Ка...

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SHRIMP dating of titanite from metasyenites in the Central Zone of the Limpopo Belt, South Africa

Rigby¹,

Armstrong²

2011

Journal of African Earth Sciences

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SHRIMP dating of titanite from metasyenites in the Central Zone of the Limpopo Belt yields a mean 207 Pb/ 206 Pb age of 2010.3 +/-4.5 Ma calculated from twenty-three analyses. This age, combined with petrographic and field observations, suggests the metamorphism in the syenites occurred during the regional Palaeoproterozoic event.Keywords: Limpopo Belt; SHRIMP; titanite; geochronology; Palaeoproterozoic. IntroductionA unique body of (meta)-syenite intrudes the Alldays Gneiss and outcrops in an elongate, 6.25 x 1.25 km body WNW of Alldays within the Central Zone of the Limpopo Belt, South Africa (Fig 1a + b). A recent study by Rigby et al. (2008a) reveals the metasyenites underwent a metamorphic evolution characterized by a maximum pressure of 7-8 kbar and ~770 o C. The subsequent retrograde path involved a simultaneous P-T decrease along a decompression-cooling path to 4 kbar and ~550 o C. These P-T estimates are 'intermediate' between the high-grade conditions reported by Zeh et al. (2004) and Rigby (2009) for metapelites near Messina and the amphibolite-facies conditions reported by Zeh et al. (2005a,b) and Chudy et al. (2008) for rocks from the Venetia area. Collectively, this data led Rigby et al. (2008a) to postulate the existence of a metamorphic field gradient. However, there are two main tectonometamorphic episodes known in the Central Zone of Limpopo Belt, one in the Neoarchean (e.g. McCourt & Armstrong, 1998; Kroner et al., 1998;Bumby et al., 2001;Bumby & van der Merwe, 2004; Zeh et al., 2007; Millonig et al., 2008; Perchuk et al., 2008; Van Reenen et al., 2008; Gerdes & Zeh, 2009; Zeh et al. 2009) and one in the Palaeoproterozoic (e.g. Jaeckel et al., 1997; Holzer et al., 1998; Kroner et al., 1999; Zeh et al., 2004; Rigby et al., 2008b;Chudy et al., 2008;Eriksson et al., 2009; Gerdes & Zeh, 2009; Rigby et al., 2010; Eriksson et al., 2010a and b; Millonig et al., 2010) and without robust geochronological constraints it is not clear in which event the metasyenites were metamorphosed. Additionally, due to this uncertainty, the existence of the proposed metamorphic field gradient by Rigby et al (2008a) is, at present, mere speculation. In this short communication we present new U-Pb SHRIMP data obtained from titanite in the metasyenites to delineate their age and support the metamorphic field gradient hypothesis.

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P-T conditions and the origin of quartzo-feldspathic veins in metasyenites from the Central Zone of the Limpopo Belt, South Africa

Cited by 14 publications

References 78 publications

Conflicting P–T paths within the Central Zone of the Limpopo Belt: A consequence of different thermobarometric methods?

Conflicting P–T paths within the Central Zone of the Limpopo Belt: A consequence of different thermobarometric methods?

Age and isotopic geochemical characteristics of Archean carbonatites and alkaline rocks of the Baltic shield

SHRIMP dating of titanite from metasyenites in the Central Zone of the Limpopo Belt, South Africa

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