The origin of garnet and clinopyroxene in “depleted” Kaapvaal peridotites

Simon, Nina; Irvine, G. J.; Davies, Gareth R.; Pearson, D. Graham; Carlson, Richard W.

doi:10.1016/s0024-4937(03)00118-x

Cited by 200 publications

(107 citation statements)

References 71 publications

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“…Such metasomatic diopsides are well described from peridotite xenoliths from southern Africa (e.g. Erlank et al 1987;Simon et al 2003) but not from the Cenozoic volcanic fields in Central Europe. Despite our observations and mineral data, the exact origin of the resorbed patches in the dunites and harzburgite remains problematic.…”

Section: Mantle Metasomatismmentioning

confidence: 85%

Petrogenesis of ultramafic and mafic xenoliths from Mesozoic basanites in southern Sweden: constraints from mineral chemistry

Rehfeldt

Obst

Johansson

2006

Int J Earth Sci (Geol Rundsch)

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Jurassic basanite necks occurring at the junction of two major fault zones in Scania contain ultramafic (peridotites, pyroxenites) and mafic xenoliths, which together indicate a diversity of upper mantle and lower crustal assemblages beneath this region. The peridotites can be subdivided into lherzolites, dunites and harzburgites. Most lherzolites are porphyroclastic, containing orthopyroxene and olivine porphyroclasts. They consist of Mg-rich silicates (Mg# = Mg/(Mg + Fe tot ) · 100; 88-94) and vermicular spinel. Calculated equilibration temperatures are lower in porphyroclastic lherzolites (975-1,007°C) than in equigranular lherzolite (1,079°C), indicating an origin from different parts of the upper mantle. According to the spinel composition the lherzolites represent residues of 8-13% fractional melting. They are similar in texture, mineralogy and major element composition to mantle xenoliths from Cenozoic Central European volcanic fields. Dunitic and harzburgitic peridotites are equigranular and only slightly deformed. Silicate minerals have lower to similar Mg# (83-92) as lherzolites and lack primary spinel. Resorbed patches in dunite and harzburgite xenoliths might be the remnants of metasomatic processes that changed the upper mantle composition. Pyroxenites are coarse, undeformed and have silicate minerals with partly lower Mg# than peridotites (70-91). Pyroxenitic oxides are pleonaste spinels. According to two-pyroxene thermometry pyroxenites show a large range of equilibration temperatures (919-1,280°C). In contrast, mafic xenoliths, which are mostly layered gabbronorites with pyroxene-and plagioclase-rich layers, have a narrow range of equilibration temperatures (828-890°C). These temperature ranges, together with geochemical evidence, indicate that pyroxenites and gabbroic xenoliths represent mafic intrusions within the Fennoscandian crust.

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Section: Mantle Metasomatismmentioning

confidence: 85%

Petrogenesis of ultramafic and mafic xenoliths from Mesozoic basanites in southern Sweden: constraints from mineral chemistry

Rehfeldt

Obst

Johansson

2006

Int J Earth Sci (Geol Rundsch)

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“…Along the eastern Euro-Asian plate, especially in eastern China, which is known as the large-scale thinning of lithosphere beneath the eastern North China Craton from [200 km to present 60-80 km (Griffin et al 1992;Menzies et al 1993;Xu et al 1996Xu et al , 2003Fan et al 2000;Zheng et al 2004;Zhang 2005;Ying et al 2006;Chen et al 2006;Zhang et al 2006Zhang et al , 2007aZhang et al , b, 2008, many garnet peridotite xenoliths occurred from north Siberia (Russia) to the south Cathaysia block (China) (Fig. 1), but the amounts of garnet peridotites are less abundant than those in Tanzania (Tanzania), Kaapvaal (South Africa) and Slave (Canada) cratons where a thick ([150 km) lithosphere is still preserved at present (Henjes Kunst and Altherr 1992;Simon et al 2003;Kopylova and Caro 2004;Menzies et al 2004;Liati et al 2004;Boyd et al 2004;Viljoen et al 2005). The occurrence of all almost garnet peridotite xenoliths is related to subduction zones (e.g., eastern China) (e.g., Zheng et al 2006) or mantle plumes (e.g., Tanzania craton) (e.g., Henjes Kunst and Altherr 1992;Chesley et al 1999).…”

Section: Garnet Peridotite Xenoliths In Volcanic Rocksmentioning

confidence: 97%

Geochemical syntheses among the cratonic, off-cratonic and orogenic garnet peridotites and their tectonic implications

Zhang

Tang

et al. 2010

Int J Earth Sci (Geol Rundsch)

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Garnet-bearing mantle peridotites, occurring as either xenoliths in volcanic rocks or lenses/massifs in high-pressure and ultrahigh-pressure terrenes within orogens, preserve a record of deep lithospheric mantle processes. The garnet peridotite xenoliths record chemical equilibrium conditions of garnet-bearing mineral assemblage at temperatures (T) ranging from *700 to 1,400°C and pressures (P) [ 1. 6-8.9 GPa, corresponding to depths of *52-270 km. A characteristic mineral paragenesis includes Cr-bearing pyropic garnet (64-86 mol% pyrope; 0-10 wt% Cr 2 O 3 ), Cr-rich diopside (0.5-3.5 wt% Cr 2 O 3 ), Al-poor orthopyroxene (0-5 wt% Al 2 O 3 ), high-Cr spinel (Cr/(Cr ? Al) 9 100 atomic ratio = 2-86) and olivine (88-94 mol% forsterite). In some cases, partial melting, re-equilibration involving garnet-breakdown, deformation, and mantle metasomatism by kimberlitic and/or carbonatitic melt percolations are documented. Isotope model ages of Archean and Proterozoic are ubiquitous, but Phanerozoic model ages are less common. In contrast, the orogenic peridotites were subjected to ultrahigh-pressure (UHP) metamorphism at temperature ranging from *700 to 950°C and pressure [3.5-5.0 GPa, corresponding to depths of [110-150 km. The petrologic comparisons between 231 garnet peridotite xenoliths and 198 orogenic garnet peridotites revealed that (1) bulk-rock REE (rare earth element) concentrations in xenoliths are relatively high, (2) clinopyroxene and garnet in orogenic garnet peridotites show a highly fractionated REE pattern and Ce-negative anomaly, respectively, (3) Fo contents of olivines for off-cratonic xenolith are in turn lower than those of orogenic garnet and cratonic xenolith but mgnumber of garnet for orogenic is less than that of offcratonic and on-cratonic xenolith, (4) Al 2 O 3 , Cr 2 O 3 , CaO and Cr# of pyroxenes and chemical compositions of whole rocks are very different between these garnet peridotites, (5) orogenic garnet peridotites are characterized by low T and high P, off-cratonic by high T and low P, and cratonic by medium T and high P and (6) garnet peridotite xenoliths are of Archean or Proterozoic origin, whereas most of orogenic garnet peridotites are of Phanerozoic origin. Taking account of tectonic settings, a new orogenic garnet peridotite exhumation model, crustmantle material mixing process, is proposed. The composition of lithospheric mantle is additionally constrained by comparisons and compiling of the off-cratonic, oncratonic and orogenic garnet peridotite.

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“…This, combined with the fact that a number of cratons with thick lithospheric roots such as the Kaapvaal and Siberian cratons are covered to some degree with Phanerozoic oceanic sediments, indicates that craton freeboard might have varied through time. Our modelling has the important implication that the common petrological processes that lead to an increase in the density of the cratonic root after their formation, such as refertilization of peridotites by silicate metasomatism (Simon et al, 2003;Schutt and Lesher, 2010) do not necessarily jeopardize the stability of cratons.…”

Section: Cratons In a Thermally Evolving Earthmentioning

confidence: 98%

Craton stability and longevity: The roles of composition-dependent rheology and buoyancy

Wang

Hunen

Pearson

et al. 2014

Earth and Planetary Science Letters

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. (2014) 'Craton stability and longevity : the roles of composition-dependent rheology and buoyancy.', Earth and planetary science letters., 391 . pp. 224-233.Further information on publisher's website:http://dx.doi.org/10. 1016/j.epsl.2014.01.038 Publisher's copyright statement: NOTICE: this is the author's version of a work that was accepted for publication in Earth and Planetary Science Letters. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reected in this document. Changes may have been made to this work since it was submitted for publication. A denitive version was subsequently published in Earth and Planetary Science Letters, 391, 2014Letters, 391, , 10.1016Letters, 391, /j.epsl.2014 Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Abstract:Survival of thick cratonic roots in a vigorously convecting mantle system for billions of years has long been studied by the geodynamical community. High strength of the cratonic root is generally considered to be the most important factor, but the role of lithospheric mantle depletion and dehydration in this strengthening is still debated. Geodynamical models often argue for a significant strength or buoyancy contrast between cratonic and non-cratonic mantle lithosphere, induced by mantle depletion and dehydration. But recent laboratory experiments argue for only a modest effect of dehydration strengthening. Can we reconcile laboratory experiments and geodynamical models?We perform and discuss new numerical models to investigate craton stability and longevity with different composition-dependent rheology and buoyancy. Our results show that highly viscous and possibly buoyant cratonic root is essential to stabilise a geometry in which thick cratonic lithosphere and thinner non-cratonic lithosphere coexist for billions of years. Using nonNewtonian rheology, a modest strengthening factor of Δη=3 can protect compositionally buoyant cratonic roots from erosion by mantle convection for over billions of years. A larger strengthening factor (Δη=10) can maintain long term craton stability even with little or no intrinsic buoyancy. Such composition-dependent rheology is comparable to the laboratory experiments. This implies that a strict isopycnic state of cratonic lithosphere may not be necessary for the preservation of a cratonic root, provided a sufficient level of compositional strengthening is present.

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The origin of garnet and clinopyroxene in “depleted” Kaapvaal peridotites

Cited by 200 publications

References 71 publications

Petrogenesis of ultramafic and mafic xenoliths from Mesozoic basanites in southern Sweden: constraints from mineral chemistry

Petrogenesis of ultramafic and mafic xenoliths from Mesozoic basanites in southern Sweden: constraints from mineral chemistry

Geochemical syntheses among the cratonic, off-cratonic and orogenic garnet peridotites and their tectonic implications

Craton stability and longevity: The roles of composition-dependent rheology and buoyancy

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