Hydration, melt production and rheological weakening within an intracontinental gneiss dome

Varga, Jan; Raimondo, Tom; Hand, Martin; Curtis, Stacey; Daczko, Nathan R.

doi:10.1016/j.lithos.2022.106872

Cited by 2 publications

(3 citation statements)

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“…One consequence of this thermal regime is the lower crust would have almost certainly been hot, as evidenced by the incorporation of crust into the felsic magmas (Chapman et al, 2019; Stewart & Foden, 2003; Wade et al, 2019). In addition, the migmatitic nature of the Mabel Creek Ridge granulites suggests they would have been characterized by melt‐weakened rheology that would have facilitated flow (Rey et al, 2011; Varga et al, 2022), as shown by Figure 12, a typical example of the formation of a gneiss dome based on numerical models (Korchinski et al, 2018). We tentatively suggest the Mabel Creek Ridge is a record of early Mesoproterozoic extension in the Gawler Craton during which thermally perturbed lower crustal rocks were exhumed within a broad approximately east–west elongate dome‐like culmination reminiscent of a gneiss dome (Rey et al, 2011; Teyssier & Whitney, 2002; Yin, 2004).…”

Section: Discussionmentioning

confidence: 99%

“…In our samples, the growth of cordierite coronas at the expense of garnet and sillimanite is consistent with decompression at high temperatures as the footwall (Mabel Creek Ridge) is exhumed, whereas the hanging wall (GOMA DH4) was at shallower levels and does not record this event. The inward flow of the hot lower crust may result in the viscous collision below the zone of upper crustal extension, leading to the formation of gneiss domes that contain internal sub‐domes (Figure 12; Korchinski et al, 2018; Rey et al, 2011, 2017; Varga et al, 2022). Although speculative because of the obscuring cover, the magnetic trend lines in the Mabel Creek Ridge appear to delineate two ovoid structural domains that bear a resemblance to outcrop‐generated structural maps of gneiss domes containing internal sub‐domes (Figure 2a).…”

Section: Discussionmentioning

confidence: 99%

“…Gneiss domes typically represent the localized rise of lower crustal material into the mid and upper crust during extension (Korchinski et al, 2018;Rey et al, 2009Rey et al, , 2011Whitney et al, 2015). Similar to metamorphic core complexes, the exhumed material within a gneiss dome is commonly characterized by decompressional thermobarometric evolutions (Korchinski et al, 2018;Teyssier & Whitney, 2002;Varga et al, 2022;Whitney et al, 2004). In contrast, the surrounding crust comprising the upper plate shows lower pressure metamorphism and comparatively modest baric change or even an absence of metamorphism of the same age as within the gneiss dome (Rey et al, 2011;Teyssier & Whitney, 2002).…”

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A buried gneiss dome in the northern Gawler Craton: The record of early Mesoproterozoic (ca. 1600–1560 Ma) extension in southern Proterozoic Australia

Yu,

Hand,

Morrissey

et al. 2024

Journal Metamorphic Geology

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Mabel Creek Ridge, in the northern Gawler Craton, is a granulite‐facies domain recording early Mesoproterozoic metamorphism, flanked by less metamorphosed rocks and dissected by crustal‐scale divergent structures. The nature of early Mesoproterozoic events is poorly understood due to the lack of basement outcrop. Calculated metamorphic phase diagrams and geochronology are used to decipher the tectonic regime of a potential gneiss dome. Pressure–temperature (P–T) modelling of metapelites from five drill holes across Mabel Creek Ridge suggests it has experienced conditions of ~6.4–7.4 kbar and 800–850°C and the growth of suprasolidus cordierite after garnet indicates subsequent decompression. In situ U–Pb monazite and Lu–Hf garnet geochronology constrains the granulite‐facies metamorphism of Mabel Creek Ridge to ca. 1600–1560 Ma. In contrast, drill hole GOMA DH4 located to the north of Mabel Creek Ridge records conditions of 2.2–5.4 kbar and 710–740°C at ca. 1520 Ma, with no evidence for 1600–1560 Ma metamorphism. Our new P–T pseudosection results and geochronology data from Mabel Creek Ridge and adjacent crust, coupled with the regional seismic and airborne magnetic data, reveal that Mabel Creek Ridge represents a record of early Mesoproterozoic extension in the Gawler Craton, during which thermally perturbed lower crustal rocks were exhumed within a gneiss dome. Early Mesoproterozoic extension took place within a complex geodynamic regime resulting from the interplay between final Nuna convergence along the margin of northeast Australia at ca. 1600 Ma and subduction to the southwest at ca. 1630–1610 Ma.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

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A buried gneiss dome in the northern Gawler Craton: The record of early Mesoproterozoic (ca. 1600–1560 Ma) extension in southern Proterozoic Australia

Yu,

Hand,

Morrissey

et al. 2024

Journal Metamorphic Geology

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Trapped K‐feldspar phenocrysts as a signature of melt migration pathways within active high‐strain zones

Silva

Piazolo

Daczko

2022

Journal Metamorphic Geology

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Melt migration through high‐strain zones in the crust fundamentally influences their rheological behaviour and is important for the transfer of fluids to upper crustal regions. The inference of former melt‐present deformation, based on field observations, may be hampered if the high‐strain zone experience a low time‐integrated melt flux or high melt volume expulsion during deformation. In these cases, typical macro‐scale field evidence of former melt presence limits interpretations. In this contribution, we investigate igneous field evidence ranging from obvious to cryptic in the Gough Dam shear zone (central Australia), a 2‐ to 4‐km‐wide high‐strain zone shown to have acted as a significant melt pathway during the Alice Springs Orogeny. Within bands of the high‐strain zone, granitic lenses are easily discernible in the field and are inferred to have formed during melt present deformation. Related coarse K‐feldspar is observed in biotite‐rich (>75 vol%) schist (glimmerite) as either isolated grains, forming trails (sub)parallel to the main foliation, or in aggregates with subordinate quartz. Detailed characterization of the granitic lenses shows that pockets of phenocrysts may be entrained in the shear zone. If melt expulsion and melt‐rock interaction is severe, isolated K‐feldspar grains in glimmerite may form. These grains exhibit (i) partially preserved crystal faces; (ii) a lack of internal grain deformation; (iii) reaction textures preferentially formed along the main crystallographic axes showing dissolution of K‐feldspar and precipitation of dominantly biotite; (iv) low‐strain domains between multiple K‐feldspar grains being inferred to enclose crystallized melt pockets, with some apparently isolated grains showing connectivity in three dimensions; and (v) a weak quartz and K‐feldspar crystallographic preferred orientation. These observations suggest an igneous phenocrystic origin for the isolated K‐feldspar grains hosted in glimmerite, which is consistent with the observed REE concentration patterns with positive Eu anomaly. We propose that the K‐feldspar phenocrysts are early‐formed crystals that were entrained into the glimmerite rocks as reactive melt migrated through the actively deformatting high‐strain zone. Previously entrained K‐feldspar phenocrysts were trapped during the collapse of the melt pathway when melt flux‐related fluid pressure waned while confining pressure and tectonic stress were still significant. The active deformation facilitated expulsion or loss of the melt phase but retainment and trapping of phenocrysts. Hence, the presence of isolated or ‘trains’ of K‐feldspar phenocrysts is a cryptic signature of syndeformational melt transfer. If melt transfer occurs in an open chemical system, phenocrysts will be entrained within the reaction product of melt‐rock interaction. We suggest that these so‐called trapped phenocrysts are a viable indicator of former syntectonic melt passage through rocks.

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Hydration, melt production and rheological weakening within an intracontinental gneiss dome

Cited by 2 publications

References 64 publications

A buried gneiss dome in the northern Gawler Craton: The record of early Mesoproterozoic (ca. 1600–1560 Ma) extension in southern Proterozoic Australia

A buried gneiss dome in the northern Gawler Craton: The record of early Mesoproterozoic (ca. 1600–1560 Ma) extension in southern Proterozoic Australia

Trapped K‐feldspar phenocrysts as a signature of melt migration pathways within active high‐strain zones

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