The magma mixing origin of mantled feldspars

Hibbard, M. J.

doi:10.1007/bf00371956

Cited by 358 publications

(140 citation statements)

References 45 publications

Supporting

Mentioning

123

Contrasting

Unclassified

Order By: Relevance

“…Therefore, underplating and/or magma mixing are the most plausible explanations for elevated temperature of outer shells. Textural evidence such as partial resorption or corrosion likely to occur under changing magmatic conditions further testifies to the magma mixing-mingling processes (see Hibbard 1981;Glazner et al 1990;Müller et al 2005). Likewise, the observed crystal fragmentation may be related to the magma mixing as well.…”

Section: Implications For Dyke Emplacement and Ore Genesismentioning

confidence: 81%

The nature of “quartz eyes” hosted by dykes associated with Au-Bi-As-Cu, Mo-Cu, and Base-metal-Au-Ag mineral occurrences in the Mountain Freegold region (Dawson Range), Yukon, Canada

Betsi¹,

Lentz

2012

J. Geosci.

View full text Add to dashboard Cite

Various origins have been assigned to rounded to subrounded and elliptical quartz megacrysts ("quartz eyes") in dyke rocks associated with mineral deposits/occurrences worldwide. An exact interpretation of their nature is likely to tightly constrain the petrogenesis of the host rocks, and by association may be critical in evaluating genetic models for spatially associated ore minerals. ChromaSEM-CL imaging and electron probe microanalysis (EPMA) of "quartz eyes" within porphyry dykes associated with Au-Bi-Cu-As, Mo-Cu, and base-metal-Au-Ag mineral occurrences across the Northern Freegold Resources (NFR) property in the Dawson Range of Yukon Territory, Canada, reveals that the cathodoluminescence (CL) response of quartz is a function of its trace-element abundance(s). Bright blue luminescent growth zones are in most cases richer in Fe (up to 8839 ppm) and Ti (up to 229 ppm) relative to CL dark growth zones, with up to 41 times lower concentration of these elements. Assuming a TiO 2 = 1, the Ti-poor dull cores consistently recorded lower temperatures (mostly < 600 °C) compared to Ti-rich brighter blue rims (up to 860 °C). This suggests either overgrowth on xenocrystic cores or an increase in crystallization temperature. The temperature rise likely reflects magma mixing, and is therefore consistent with the phenocryst/phenoclasts having formed in a magma chamber rather than by secondary processes. Also, the great variability in composition and temperature of crystallization and/or reequilibration of brighter blue growth zones of two quartz crystals (660 °C and 855 °C) from a single sample suggests that multiple episodes of magma mixing and incremental growth of parental magma chambers occurred. Some "quartz eyes" are overprinted by variably oriented, bifurcating, and anastomosing fluid migration trails ("splatter and cobweb textures") of red to reddish-brown CL quartz that is in most cases of low-temperature origin, and trace-elements poor, thus implying interaction of deuteric fluids with quartz phenocrysts/phenoclasts. The presence of "quartz eye" crystals with broken and angular blue cores, overgrown by oscillatory-zoned rims in which the zoning pattern does not correspond with the crystal boundaries, further suggests that some quartz crystals had been explosively fragmented (phenocrysts) and are now hosted in a recrystallized tuffisitic groundmass. The volatile exsolution that likely accompanied both magma mixing and decompression (as suggested by dendritic quartz, fine-grained recrystallized tuffisitic groundmass, and corroded quartz grains) was probably an important process that could have favoured the ore formation.

show abstract

Section: Implications For Dyke Emplacement and Ore Genesismentioning

confidence: 81%

The nature of “quartz eyes” hosted by dykes associated with Au-Bi-As-Cu, Mo-Cu, and Base-metal-Au-Ag mineral occurrences in the Mountain Freegold region (Dawson Range), Yukon, Canada

Betsi¹,

Lentz

2012

J. Geosci.

View full text Add to dashboard Cite

show abstract

“…The clinopyroxenes in the Hamsilos volcanic rocks (high-K calc-alkaline and shoshonitic rocks) show different types of disequilibrium textures, as zoning, resorbed, rounded crystals and embayed and breakdown clinopyroxenes megacryst (Figures 3 and 4). Clinopyroxenes are represented by rounded and embayed crystals similar to sieved plagioclase crystals that are generally caused by magma mixing (Hibbard, 1981;Simonetti Shore, Bell, 1996;Streck, 2008) or decompressional melting (Nelson & Montana, 1992). Normally zoned clinopyroxenes in the Hamsilos volcanic rocks represent more Mg-rich composition in the core compared to the rim coupled with higher Cr and lower Ti and Al contents (Figure 15(a) and (b)).…”

Section: Fractional Crystallisation and Assimilation Vs Magma Mixingmentioning

confidence: 99%

Subduction-related Late Cretaceous high-K volcanism in the Central Pontides orogenic belt: constraints on geodynamic implications

Aydınçakır

2016

Geodinamica Acta

View full text Add to dashboard Cite

Mineral chemistry, major and trace elements, 40 Ar/ 39 Ar age and Sr-Nd-Pb isotopic data are presented for the Late Cretaceous Hamsilos volcanic rocks in the Central Pontides, Turkey. The Hamsilos volcanic rocks mainly consist of basalt, andesite and associated pyroclastics (volcanic breccia, vitric tuff and crystal tuff). They display shoshonitic and high-K calc-alkaline affinities. The shoshonitic rocks contain plagioclase, clinopyroxene, alkali feldspar, phlogopite, analcime, sanidine, olivine, apatite and titanomagnetite, whereas the high-K calc-alkaline rocks contain plagioclase, clinopyroxene, orthopyroxene, magnetite / titanomagnetite in microgranular porphyritic, hyalo-microlitic porphyritic and glomeroporphyritic matrix. Mineral chemistry data reveal that the pressure condition of the clinopyroxene crystallisation for the shoshonitic rocks are between 1.4 and 6.3 kbar corresponds to 6-18-km depth and the high-K calc-alkaline rocks are between 5 and 12 km. 40 Ar/ 39 Ar age data changing between 72 ± .5 Ma and 79.0 ± .3 Ma (Campanian) were determined for the Late Cretaceous Hamsilos volcanic rocks, contemporaneous with the subduction of the Neo-Tethyan Ocean beneath the Pontides. The studied volcanic rocks were enriched in the large-ion lithophile and light rare earth element contents, with pronounced depletion in the contents of high-field-strength elements. Chondrite-normalised rare earth element patterns (La N /Lu N = 6-17) show low to medium enrichment, indicating similar sources of the rock suite. Pb/ 204 Pb values between 37.839 and 38.427. The main solidification processes involved in the evolution of the volcanic rocks consist of fractional crystallisation, with minor amounts of crustal contamination ± magma mixing. According to geochemical evidence, the shoshonitic melts in the Hamsilos volcanic rocks were possibly derived from the low degree of partial melting of a subcontinental lithospheric mantle (SCLM), while the high-K calc-alkaline melts were derived from relatively high degree of partial melting of SCLM that was enriched by fluids and/or sediments from a subduction of oceanic crust.

show abstract

“…Further evidence for recharge episodes is provided by, for example, corroded crystal cores in quartz and plagioclase, the fused and recrystallized domains, rounded and smudged growth zoning, and plagioclase mantles around alkali-feldspar phenocrysts that were related to changes in primary magma composition and environmental parameters (P, T, water content). This allowed plagioclase to nucleate on alkali-feldspar crystals (Hibbard 1981;Müller et al 2005). Dempster et al (1994) explained that the formation of a plagioclase mantle by redistribution of exsolved plagioclase from alkali-feldspar phenocrysts is linked to the high fluorine contents of magmas.…”

Section: Characteristics Of Alkali-feldspar and Plagioclasementioning

confidence: 99%

Multi-stage emplacement of the Götemar Pluton, SE Sweden: new evidence inferred from field observations and microfabric analysis, including cathodoluminescence microscopy

Friese

Vollbrecht

Tanner

et al. 2011

Int J Earth Sci (Geol Rundsch)

View full text Add to dashboard Cite

The emplacement of the Mesoproterozoic Götemar Pluton into Paleoproterozoic granitoid host rocks of the Transscandinavian Igneous Belt is re-examined by microfabric analysis, including cathodoluminescence microscopy. Field data on the pluton-host rock system are used to strengthen the model. The Götemar Pluton, situated on the Baltic Shield of SE Sweden, is a horizontally zoned tabular structure that was constructed by the intrusion of successive pulses of magma with different crystal/melt ratios, at an estimated crustal depth of 4-8 km. Initial pluton formation involved magma ascent along a vertical dike, which was arrested at a mechanical discontinuity within the granitoid host rocks; this led to the formation of an initial sill. Subsequent sill stacking and their constant inflation resulted in deformation and reheating of existing magma bodies, which also raised the pluton roof. This multi-stage emplacement scenario is indicated by complex dike relationships and the occurrence of several generations of quartz (Si-metasomatism). The sills were charged by different domains of a heterogeneous magma chamber with varying crystal/melt ratios. Ascent or emplacement of magma with a high crystal/melt ratio is indicated by syn-magmatic deformation of phenocrysts. Complex crystallization fabrics (e.g. oscillatory growth zoning caused by high crystal defect density, overgrowth and replacement features, resorbed and corroded crystal cores, rapakivi structure) are mostly related to processes within the main chamber, that is repeated magma mixing or water influx.

show abstract

The magma mixing origin of mantled feldspars

Cited by 358 publications

References 45 publications

The nature of “quartz eyes” hosted by dykes associated with Au-Bi-As-Cu, Mo-Cu, and Base-metal-Au-Ag mineral occurrences in the Mountain Freegold region (Dawson Range), Yukon, Canada

The nature of “quartz eyes” hosted by dykes associated with Au-Bi-As-Cu, Mo-Cu, and Base-metal-Au-Ag mineral occurrences in the Mountain Freegold region (Dawson Range), Yukon, Canada

Subduction-related Late Cretaceous high-K volcanism in the Central Pontides orogenic belt: constraints on geodynamic implications

Multi-stage emplacement of the Götemar Pluton, SE Sweden: new evidence inferred from field observations and microfabric analysis, including cathodoluminescence microscopy

Contact Info

Product

Resources

About