Geochemistry and petrology of komatiites of the Pioneer Ultramafic Complex of the 3.3 Ga Weltevreden Formation, Barberton greenstone belt, South Africa

Stiegler, M. Thompson; Cooper, M.; Byerly, Gary R.; Lowe, Donald R.

doi:10.1016/j.precamres.2012.04.017

Cited by 31 publications

(9 citation statements)

References 43 publications

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“…Their Al 2 O 3 /TiO 2 ratios range from 16 to 29 (Fig. 8), which is similar to ranges reported by Kareem (2005) and Thompson Stiegler et al (2012). There are komatiites in the upper silicified portion of M2v and M4v-l that are similarly Al-undepleted.…”

Section: Handheld X-ray Fluorescencesupporting

confidence: 87%

“…However, there is no apparent genetic relationship between these formations and there is no evidence of rocks of the Weltevreden Formation at the top of the Mendon. The Weltevreden contains Al-undepleted and Al-enriched komatiitic flows and tuffs and Al-depleted tuffs, which are all interstratified throughout the formation (Thompson Stiegler et al, 2012). By contrast, the Mendon Formation contains a wider range of komatiitic compositions that are ordered in a predictable stratigraphy.…”

Section: Relationship To the Weltevreden Formationmentioning

confidence: 99%

“…Because Al 2 O 3 /TiO 2 ratios reflect deep mantle processes, these chemical stratigraphic differences suggest that the Weltevreden was far removed from the eruptive source(s) that produced the komatiitic magmas of the Mendon. The Weltevreden likely represents a period of volcanism in a location affected by one or more sources of magma generated by melting at different depths (Thompson Stiegler et al, 2012). Meanwhile, the Mendon appears to have had a more complex compositional history that is probably the result of multiple sources.…”

Section: Relationship To the Weltevreden Formationmentioning

confidence: 99%

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High resolution tephra and U/Pb chronology of the 3.33–3.26Ga Mendon Formation, Barberton Greenstone Belt, South Africa

Decker

Byerly

Stiegler

et al. 2015

Precambrian Research

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a b s t r a c tThe Mendon Formation in the Barberton Greenstone Belt of South Africa marks the boundary between the Onverwacht and Fig Tree Groups. These groups are characterized by mafic to ultramafic volcanism and felsic volcanism with related epiclastic sedimentation, respectively. This transition marks the end of komatiitic volcanism in the Barberton Greenstone Belt and is accompanied by numerous impact-related spherule layers. This study characterizes the upper Mendon Formation texturally and geochemically over a wide areal extent and across structure and facies changes in an attempt to better understand the evolution of tectonic processes at this boundary. A suite of whole rock and handheld X-ray fluorescence analyses are presented in conjunction with textural information, stratigraphic relationships, and U/Pb ages to create a temporal and chemostratigraphic framework for the Mendon Formation. Local and regional stratigraphic variations, including absence of distinctive layers and variation in layer thickness, seen across the Mendon preclude ascription of a single stratigraphy that accurately describes the >1.2 km of section present in this formation. These variations indicate diachronous deposition of the Mendon Formation over a wide areal extent and into multiple basins or sub-basins by more than one magmatic source. 204 Pb-corrected 206 Pb/ 238 U and 207 Pb/ 235 U concordia model ages of 3279 ± 9.1 Ma and 3287.3 ± 2.9 Ma for two samples from upper portions of the Mendon Formation provide temporal context for deposition. Two samples from the basal 10 m of the Fig Tree Group, above the S2 spherule bed that marks the boundary between the Onverwacht and Fig Tree Groups, give model ages of 3267.8 ± 6.9 Ma and 3261 ± 18 Ma. These ages provide added constraints for the Onverwacht-Fig Tree boundary and confirm that the Weltevreden Formation is roughly age-correlative with the uppermost Mendon Formation.While the Mendon and Weltevreden Formations are in part age-correlative and have similar lithologies, they do not appear to be genetically related. The dominance of ultramafic volcanic rocks and the paucity of felsic volcanic and terrigenous sedimentary rocks within the Mendon and Weltevreden Formations indicate that the primary mode of crustal formation was likely plume-related magmatic accretion and not subduction. The relatively sharp transition within the Barberton Greenstone Belt from ultramafic volcanic sequences to more felsic volcanic and epiclastic sedimentary sequences is everywhere marked by impact-related spherule layers, which suggest that major impacts may have played a role in the evolution of early tectonics to more modern, subduction-related styles.

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Section: Handheld X-ray Fluorescencesupporting

confidence: 87%

Section: Relationship To the Weltevreden Formationmentioning

confidence: 99%

Section: Relationship To the Weltevreden Formationmentioning

confidence: 99%

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High resolution tephra and U/Pb chronology of the 3.33–3.26Ga Mendon Formation, Barberton Greenstone Belt, South Africa

Decker

Byerly

Stiegler

et al. 2015

Precambrian Research

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“…Cr/Al relationship between spinel and bulk rock: indicator of source lithology Figure 8 shows the relationship between the bulk-rock Cr/Al and spinel Cr/Al ratios of the Ethiopian ferropicrite in comparison with mafic-ultramafic rocks of other igneous provinces. Based on this, the Cr/Al ratio of spinels of Ethiopian ferropicrite is similar to those of Archean komatiite (Stiegler et al, 2012), Siberian ferropicrite (Arndt et al, 1995), and boninite (Sobolev and Danyushevsky, 1994), although the bulk-rock Cr/Al ratio (<0.005) is significantly lower than those mentioned above.…”

Section: High Degree Melting Of the Source Mantle?supporting

confidence: 62%

“…Dashed arrows indicate the possible eclogitic and peridotitic sources. Data sources: Ethiopian LIP low-Ti and HT2 suits (Beccaluva et al, 2009); Abitibi komatiite (Barnes, 1985); Pioneer komatiite (Stiegler et al, 2012); Gorgona komatiite (Dietrich et al, 1981); Emeishan picrites (Kamenetsky et al, 2012); Siberian ferropicrite (Arndt et al, 1995); Karoo meimechite and ferropicrite Luttinen, 2008, 2010); West Greenland picrite (Larsen and Pedersen, 2000); Hawaii picrite (Wilkinson and Hensel 1988); Tonga boninite (Sobolev and Danyushevsky, 1994); Sorachi-Yezo picrite (Ichiyama et al, 2012); Tango picrite (Ishiwatari and Imasaka, 2002); depleted (D-type) and enriched (E-type) picrites from Mikabu belt (Ichiyama et al, 2014); high magnesian andesite (HMA) and tholeiite lava Noto Peninsula (López and Ishiwatari, 2002); Mongolian high magnesian andesite and picrite (Erdenesaihan et al, 2013).…”

Section: Primary Bulk-rock Nature Of the Meltmentioning

confidence: 99%

Ferropicrite from the Lalibela area in the Ethiopian large igneous province

Desta

Ayalew

Ishiwatari

et al. 2014

Journal of Mineralogical and Petrological Sciences

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Ferropicrite (FeO* = 14.0 wt% and MgO = 13.9 wt%) and picritic ferrobasalt (FeO* = 14.7 wt% and MgO = 10.8 wt%) lava flows are found near Lalibela in the Oligocene (~30 Ma) Ethiopian large igneous province (LIP) in association with ultratitaniferous transitional basalt and picrite of the second high-Ti (HT2) series. The dominant phenocryst in the studied samples is Mg-rich olivine (up to Fo 88.9) with high CaO contents (to 0.42 wt%) without any kink band structure, indicating that the olivines are crystallized from a magnesian melt. Spinel microphenocrysts and inclusions in olivine are characterized by extremely high Cr# (79-84), moderate Mg# (18-51), moderate Fe 3+ # (11-39) and high TiO 2 (3.6-14.8 wt%). The clinopyroxene phenocrysts are Mg#=74-88, TiO 2 = 0.84-1.82 wt%, and Al 2 O 3 = 1.2-3.2 wt% in the cores. The REE contents of clinopyroxenes display enrichment in LREE (La N /Yb N = 1.2-1.9) and MREE (Eu N /Yb N = 3.3-4.3) relative to HREE. Relative depletion of HFSE (e.g., Nb and Zr) is also observed. In general, these trace element characteristics of clinopyroxene are similar to those of the HT2 basalts. Some of the clinopyroxene crystals show strong reverse zoning with abrupt increase in Cr, Ni and Mg# from core to rim, which may be resulted from reaction of melt with mantle peridotite during magma ascent. Bulk rock chemistry of the studied samples exhibits very low Al 2 O 3 /TiO 2 (1.8-2.2) and high Zr/Y (8.2-10.2) ratios. These may indicate the important role for garnet during melting and that the lavas were formed by a small degree of partial melting which apparently contradicts to the high Cr# of spinel. In view of low Cr/Al ratio of the bulk rock, the high Cr# of spinel suggests very high temperature of the magma (and the mantle plume). The origin of these ferropicrite and picritic ferrobasalt could be attributed to high pressure partial melting of peridotite-eclogite (pyroxenite) mixture that possibly incorporated recycled oceanic crust components.

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An appraisal of geochemical signatures of komatiites from the greenstone belts of Dharwar Craton, India: Implications for temporal transition and Archean upper mantle hydration

2019

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Archean ultramafic–mafic magmatism associated with dynamic mantle melting processes represents an integral part of crustal evolution and continental growth. Archean mantle plumes and their high temperature derivatives in komatiitic magmas provide a cornerstone in understanding the thermal and chemical evolution of the early Earth and its mantle. In this study, we evaluate the geochemical characteristics of the temporally distinct Sargur Group and Dharwar Supergroup greenstone belts of Dharwar Craton in southern India. The komatiites associated with these greenstone belts are characterized by Al‐depleted and Al‐undepleted compositions. Their MgO, Ni, Co, and Cr concentrations reflect primitive, undifferentiated nature of precursor melts, whereas the HFSE and REE chemistry corroborates high‐degree (30–50%) partial melting of mantle with prominent role of majorite garnet and perovskite in the generation of komatiitic melts. The Al‐depleted komatiites were formed at a greater depth (~13 GPa) by equilibrium melting leaving a garnet‐bearing residue. The resultant komatiitic melt retained buoyancy under extreme pressure and high temperature conditions, segregated and accumulated in the ambient peridotite mantle source and subsequently escaped with progressive decrease in pressure in the ascending plume. The Al‐undepleted and relatively rare Al‐enriched komatiites were derived by fractional melting at intermediate to shallow depths after the discharge of a large proportion of melt ensued by the collapse and entrance of residual garnet into the melt phase. The Mesoarchean–Neoarchean Dharwar komatiites provide evidence for heterogeneous, hydrated Archean upper mantle trapped by ascending mantle plumes. The non‐plume, arc‐related signatures invoke contributions from (a) sub‐cratonic lithospheric mantle roots influenced by ancient subduction events and (b) hydrated Archean upper mantle. The Sargur Group and Dharwar Supergroup komatiites record a distinct temporal transition and geochemical heterogeneity in the Archean mantle beneath the Dharwar Craton and can be attributed to Archean upper mantle hydration by flat slab subduction of >3.3 Ga oceanic crust at shallow level with vestiges of primordial oceanic crust forming deep cratonic mantle roots beneath the Dharwar Craton. The temporal transition towards mantle hydration beneath Dharwar Craton during the Mesoarchean can be correlated with the onset of subduction‐driven plate tectonics and ocean–crust–mantle interactions.

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Geochemistry and petrology of komatiites of the Pioneer Ultramafic Complex of the 3.3 Ga Weltevreden Formation, Barberton greenstone belt, South Africa

Cited by 31 publications

References 43 publications

High resolution tephra and U/Pb chronology of the 3.33–3.26Ga Mendon Formation, Barberton Greenstone Belt, South Africa

High resolution tephra and U/Pb chronology of the 3.33–3.26Ga Mendon Formation, Barberton Greenstone Belt, South Africa

Ferropicrite from the Lalibela area in the Ethiopian large igneous province

An appraisal of geochemical signatures of komatiites from the greenstone belts of Dharwar Craton, India: Implications for temporal transition and Archean upper mantle hydration

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