New insights into the processes controlling compositional zoning in plagioclase

Üstünışık, Gökçe; Kilinc, A.; Nielsen, Roger L.

doi:10.1016/j.lithos.2014.03.021

Cited by 60 publications

(21 citation statements)

References 32 publications

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“…Compositional variations, especially in the concentrations of Fe, Mg, Sr and Ba and the contents of anorthite [An; Ca/(Ca + N + K)], and textural zoning patterns that develop during primary growth are preserved in plagioclase, on account of the slow rates of CaAl–NaSi diffusion (Morse, ; Smith et al ., ). The composition of plagioclase is sensitive to the composition of the melt and to physical conditions such as temperature, pressure and H 2 O content (Blundy and Wood, ; Housh and Luhr, ; Putirka, ; Ustunisik et al ., ). Hence, plagioclase in volcanic rocks is often adopted to constrain magmatic processes (e.g.…”

Section: Introductionmentioning

confidence: 97%

Back‐arc magma processes in the Okinawa Trough: new insights from textural and compositional variations of plagioclase in basalts

et al. 2016

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The evolution of magma during ascent through the crust in the region of the Okinawa Trough is recorded by its mineralogy. In this study, we utilized the characteristics of plagioclase minerals in basaltic magma to deduce magma generation processes, by examining (via back‐scattered electron images) the compositional features of plagioclase phenocrysts in basalts dredged from the middle and southern portions of the Okinawa Trough, which provided a detailed account of the evolution and crystallization of the magma. The crystallization and evolutionary histories of magmas from the middle Okinawa Trough are distinct from those in the southern Okinawa Trough. In the middle Okinawa Trough, we identified seven textural varieties of plagioclase: homogeneous‐core, fine oscillatory‐zoned, core‐sieved, mantle‐sieved, patchy‐core, glomerocrystic and microlitic. Anorthite (An) contents in the cores of plagioclase crystals are 80–87%, while concentrations of Fe, Mg and Sr vary more strongly, especially in patchy‐core plagioclase. The homogeneous‐core, fine oscillatory‐zoned and glomerocrystic plagioclase crystallized in deep‐seated chambers. In contrast, the core‐sieved, mantle‐sieved and patchy‐core textures developed when magmas ascended slowly and were injected into shallow chambers, during which plagioclase was resorbed and dissolved due to decompression. In the southern Okinawa Trough, homogeneous‐core plagioclase crystallized when magma ascended rapidly through deep conduits and was injected into a shallow chamber; under these conditions, only homogeneous‐core and core‐sieved plagioclase phenocrysts crystallized in the shallow chamber. The core of homogeneous‐core plagioclase (An86–An93) was partially resorbed and contaminated by crustal material. Degassing and undercooling promoted the rapid crystallization of microlitic plagioclase, especially in the outermost rims, during and after the extraction of magma from shallow chambers, in both the middle and southern Okinawa Trough. Copyright © 2016 John Wiley & Sons, Ltd.

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Section: Introductionmentioning

confidence: 97%

Back‐arc magma processes in the Okinawa Trough: new insights from textural and compositional variations of plagioclase in basalts

et al. 2016

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“…The chemical zonation in plagioclase phenocrysts has already been widely employed to better understand magma dynamics within the crust in arc systems (Bindeman & Bailey, 1999;Davidson et al, 2005;Ginibre et al, 2002;Lange et al, 2013;Nielsen, 2011;Singer et al, 1995;Ustunisik et al, 2014Ustunisik et al, , 2016. Plagioclase crystallization is also limited to maximum pressures of~1 GPa in dry MORB type magmas (Fram & Longhi, 1992;Kohut & Nielsen, 2003;Tepley et al, 2000;Ustunisik et al, 2018), which restricts plagioclase occurrence to the crust and upper mantle.…”

Section: Introductionmentioning

confidence: 99%

Trace Element and Isotopic Characteristics of Plagioclase Megacrysts in Plagioclase Ultraphyric Basalts (PUB)

Nielsen

Üstünışık

Lange

et al. 2020

Geochem Geophys Geosyst

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Major, trace, and isotopic compositions of plagioclase megacrysts from plagioclase ultraphyric basalts (PUB) from multiple mid‐ocean ridges were determined to characterize the liquid compositions from which they were derived. Large (up to 2 cm) plagioclase megacrysts exhibit homogeneous major element compositions, with variable degrees of trace element and isotopic heterogeneity. The pattern and degree of heterogeneity is itself variable between megacrysts, with some being homogenous and others exhibiting a wide range of trace element and isotopic zoning. Liquids calculated to be in equilibrium with the plagioclase megacrysts exhibit a range equivalent to lavas erupted from entire ridge segments. Many of the megacrysts may be considered to be cognate xenocrysts in that they are related to the same mantle material as the host lavas in which they were carried to the surface. The observed trace element patterns together with the isotopic diversity suggest a complex set of processes are active, that include mixing of distinct primitive melts, fractional crystallization, and diffusive reequilibration. The degree to which each process influences the megacrysts varies between individual crystals in each sample. Equally important is the range of composition we see within individual crystals. For example, Ba concentrations vary by as much as a factor of 5 but not systematically from core to rim.

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“…5) and zoned K-feldspar megacrysts (e.g., Sr, Ba and Rb) probably record the mixing of coexisting mafic and felsic magmas. The factors controlling compositional zoning in plagioclase include temperature and total pressure, as well as the full range of compositional controls, including the water content of the melts (Ustunisik et al, 2014). While the influence of temperature and/or pressure in the genesis of the oscillatory-zoned plagioclase cannot be ruled out, we emphasize here that the dominant control is still related to magma mixing.…”

Section: Mineralogical Evidence For Magma Mixingmentioning

confidence: 88%

Mineral chemistry and crystallization conditions of the Late Cretaceous Mamba pluton from the eastern Gangdese, Southern Tibetan Plateau

Scheltens

et al. 2016

J. Earth Sci.

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The Late Cretaceous Mamba granodiorite belongs to a part of the Mesozoic Gangdese continental magmatic belt. No quantitative mineralogical study has been made hitherto, and hence the depth at which it formed is poorly constrained. Here we present mineralogical data for the Mamba pluton, including host rocks and their mafic microgranular enclaves (MMEs), to provide insights into their overall crystallization conditions and information about magma mixing. All amphiboles in the Mamba pluton are calcic, with B (Ca+Na)>1.5, and Si=6.81-7.42 apfu for the host rocks and Si=6.77-7.35 apfu for the MMEs. The paramount cation substitutions in amphibole include edenite type and tschermakite type. Biotites both in the host rocks and the MMEs collectively have high MgO (13.19 wt.%-13.03 wt.%) contents, but define a narrow range of Al apfu (atoms per formula unit) variations (2.44-2.57). The oxygen fugacity estimates are based on the biotite compositions cluster around the NNO buffer. The calculated pressure ranges from 1.2 to 2.1 kbar according to the aluminum-in-hornblende barometer. The computed pressure varies from 0.9 to 1.3 kbar based on the aluminum-in-biotite barometer which corresponds to an average depth of ca. 3.9 km. Besides, the estimates of crystallization pressures vary from 0.8 to 1.4 kbar based on the amphibole barometer proposed by Ridolfi et al. (2010), which can be equivalent to the depths ranging from 3.1 to 5.2 km. The MMEs have plagioclase oscillatory zonings and quartz aggregates, probably indicating the presence of magma mixing. Besides, core-to-rim element variations (Rb, Sr, Ba, and P) for the K-feldspar megacrysts serve as robust evidence to support magma mixing and crystal fractionation. This indicates the significance of the magma mixing that contributes to the formation of K-feldspar megacryst zonings in the Mamba pluton. KEY WORDS: Mamba pluton, Gangdese terrane, MMEs, K-feldspar megacrysts, magma mixing, P-T conditions, oxygen fugacity, in-situ trace element. INTRODUCTIONPrevious studies have demonstrated that the composition and structure of feldspar, biotite and amphibole in felsic rocks can serve as ideal proxies for physico-chemical conditions of magmas, such as crystallization and emplacement temperature, pressure, oxygen fugacity, water activity and compositional variations (Ayati et al.

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New insights into the processes controlling compositional zoning in plagioclase

Cited by 60 publications

References 32 publications

Back‐arc magma processes in the Okinawa Trough: new insights from textural and compositional variations of plagioclase in basalts

Back‐arc magma processes in the Okinawa Trough: new insights from textural and compositional variations of plagioclase in basalts

Trace Element and Isotopic Characteristics of Plagioclase Megacrysts in Plagioclase Ultraphyric Basalts (PUB)

Mineral chemistry and crystallization conditions of the Late Cretaceous Mamba pluton from the eastern Gangdese, Southern Tibetan Plateau

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