O and H isotopic evidence for a mantle source of water in appinite magma: An example from the late Neoproterozoic Greendale Complex, Nova Scotia

Cawood, Ian P.; Murphy, J. Brendan; McCarthy, William; Boyce, Adrian J.

doi:10.1016/j.lithos.2021.105997

Cited by 4 publications

(4 citation statements)

References 71 publications

(134 reference statements)

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“…McCarthy and Müntener 2016). This interpretation is supported by recent δ 18 O and δD isotopic studies of hornblende in ultramafic appinite of the Neo-proterozoic Greendale Complex, Nova Scotia (Cawood et al 2021), which imply growth of a generation of hornblende from magma with a significant component of mantle-derived water (δ 18 O, 4.7-6.8‰; δD < −90‰). This generation of hornblende preferentially occurs in lamprophyric sheets and pods (sheets dismembered by later intrusions) within the complex where they poikilitically enclose olivine and clinopyroxene.…”

Section: Conceptual Model For Coeval Appinite Suite and Granitoid Com...mentioning

confidence: 66%

“…4). As such, although their composition may be modified during their ascent, appinite complexes (especially their most mafic components) may provide a window into the composition of the mafic underplate in arc systems (Cawood et al 2021).…”

Section: Discussionmentioning

confidence: 99%

“…Although a study of the aureole of the Greendale Complex indicates emplacement at 3-5 kbar (Abad et al 2011), hornblende with mantle water isotopic signatures has an Al content (e.g. high total Al, high Al iv ) consistent with crystallization between 5 and 8 kbar (Murphy et al 2012;Pe-Piper and Piper 2018;Murphy 2020;Cawood et al 2021). More generally, experiments suggest crystallization conditions of at least 1000°C at P > 6 kbar for the beginning of hornblende crystallization under water-saturated conditions (Krawczynski et al 2012).…”

Section: Conceptual Model For Coeval Appinite Suite and Granitoid Com...mentioning

confidence: 99%

“…Pitcher and Berger 1972;Bowes and McArthur 1976;Pitcher and Hutton 2003;Murphy 2013Murphy , 2020. Although data are very limited, recently published O-and H-isotope data from magnesio-hornblende in an appinite body (Greendale Complex, Nova Scotia, Canada) identified a mantle component to the water incorporated in the hornblende crystal structure of mafic-ultramafic appinite (Cawood et al 2021), suggesting a connection to the mantle processes that may have stimulated the generation of coeval granitoid magma. However, the potential importance of appinite in understanding the origin of batholiths in continental arcs (and by implication, the generation of continental crust) is often overlooked, possibly because of its subordinate volume relative to the adjacent batholith.…”

Section: Introductionmentioning

confidence: 99%

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Logan Medallist 7. Appinite Complexes, Granitoid Batholiths and Crustal Growth: A Conceptual Model

Murphy

Collins

Archibald

2022

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Appinite bodies are a suite of plutonic rocks, ranging from ultramafic to felsic in composition, that are characterized by idiomorphic hornblende as the dominant mafic mineral in all lithologies and by spectacularly diverse textures, including planar and linear magmatic fabrics, mafic pegmatites and widespread evidence of mingling between coeval mafic and felsic compositions. These features suggest crystallization from anomalously water-rich magma which, according to limited isotopic studies, has both mantle and meteoric components. Appinite bodies typically occur as small (~2 km diameter) complexes emplaced along the periphery of granitoid plutons and commonly adjacent to major deep crustal faults, which they preferentially exploit during their ascent. Several studies emphasize the relationship between intrusion of appinite, granitoid plutonism and termination of subduction. However, recent geochronological data suggest a more long-lived genetic relationship between appinite and granitoid magma generation and subduction.Appinite may represent aliquots of hydrous basaltic magma derived from variably fractionated mafic underplates that were originally emplaced during protracted subduction adjacent to the Moho, triggering generation of voluminous granitoid magma by partial melting in the overlying MASH zone. Hydrous mafic magma from this underplate may have ascended, accumulated, and differentiated at mid-to-upper crustal levels (ca. 3–6 kbar, 15 km depth) and crystallized under water-saturated conditions. The granitoid magma was emplaced in pulses when transient stresses activated favourably oriented structures which became conduits for magma transport. The ascent of late mafic magma, however, is impeded by the rheological barriers created by the structurally overlying granitoid magma bodies. Magma that forms appinite complexes evaded those rheological barriers because it preferentially exploited the deep crustal faults that bounded the plutonic system. In this scenario, appinite complexes may be a direct connection to the mafic underplate and so its most mafic components may provide insights into processes that generate granitoid batholiths and, more generally, into crustal growth in arc systems.

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Section: Conceptual Model For Coeval Appinite Suite and Granitoid Com...mentioning

confidence: 66%

Section: Discussionmentioning

confidence: 99%

Section: Conceptual Model For Coeval Appinite Suite and Granitoid Com...mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Logan Medallist 7. Appinite Complexes, Granitoid Batholiths and Crustal Growth: A Conceptual Model

Murphy

Collins

Archibald

2022

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Zircon Reveals Diverse Trends of Magma Crystallization from Two Types of Early Post-Collisional Diorites (Variscan Orogen, NE Bohemian Massif)

Pietranik

Farina

Derkowska

et al. 2022

Journal of Petrology

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Amphibole- and clinopyroxene-bearing monzodiorites were emplaced at 340 Ma (CA-ID-TIMS zircon age), suggesting the formation of hydrous and dry magmas closely related in space and time in the NE Bohemian Massif. Hafnium and oxygen isotopes of zircon in less evolved rocks (<55 wt% SiO2) are similar between Amp and Cpx monzodiorites (εHf = −3.3 ± 0.5 and − 3.5 ± 0.8; δ18O = 6.4 ± 1.0 and 6.8 ± 0.7, respectively), consistent with a common source—a contaminated mafic magma derived from an enriched mantle. At the same time, the conditions of crystallization are distinct and zircon appears to be an excellent tool for distinguishing between hydrous and anhydrous crystallization conditions, a process that may be more ambiguously recorded by whole rock and major mineral chemistry. In particular, elements fractionated by either amphibole or plagioclase crystallization, such as Hf, Dy, and Eu, differ in zircon from amphibole- and clinopyroxene-bearing rocks, and Zr/Hf, Yb/Dy, and Eu/Dy are therefore useful indices of crystallization conditions. We show that the composition of zircon from hydrous dioritic magmas is not comparable with that of typical zircon from dioritic-granitic suites worldwide, suggesting a specific process involved in their formation. Here, we propose that fluid-present remelting of a mafic underplate is necessary to explain the rock textures as well as the composition of the whole rock, zircon, and other minerals of amphibole-bearing monzodiorites and that a similar process may control the formation of amphibole-rich dioritic rocks worldwide, including appinitic suites. Overall, we show that dioritic rocks represent snapshots of differentiation processes that occur in the early stages of magma evolution before the magma is homogenized into large-scale batholiths.

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The genetic relationship between coeval Ediacaran mafic and granitoid plutons in the Antigonish Highlands, Nova Scotia

Archibald

Murphy

Creaser

2023

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Granitic plutons dominated by felsic-intermediate compositions are commonly spatially and temporally associated with mafic intrusions; however, the genetic relationship between the apparently coeval but compositionally dissimilar magmas is controversial. To better understand this relationship, we present new lithogeochemical and isotopic data from coeval late Neoproterozoic plutonic rocks in the Antigonish Highlands of Nova Scotia where the regional context is well documented. The predominantly mafic Greendale Complex contains lamprophyre, appinites, and leucocratic dykes. The appinites are remarkably variable in their textures, and consist of hornblende pegmatites, hornblende cumulates, porphyritic hornblende gabbro, and coarse-grained, equigranular hornblende gabbro. Geochemical data show enrichment in large-ion lithophile elements and depletion in the high field strength elements suggesting an arc setting. ε Nd (607) values from the Greendale Complex range from +3.2 to +5.0 that are on average slightly more juvenile than coeval granitic rocks which have petrological characteristics typical of continental arc magmas. Hydrous mafic magmas were likely contaminated by subducted sediments and their ascent was facilitated by lithospheric-scale faults. Felsic magmas were derived by anatexis of heterogeneous Avalonian crust that oscillated between fluid-saturated to fluid-deficient (dehydration) melting, consistent with the evolution from arc to intra-arc rift environment. Supplementary material at https://doi.org/10.6084/m9.figshare.c.6686462

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O and H isotopic evidence for a mantle source of water in appinite magma: An example from the late Neoproterozoic Greendale Complex, Nova Scotia

Cited by 4 publications

References 71 publications

Logan Medallist 7. Appinite Complexes, Granitoid Batholiths and Crustal Growth: A Conceptual Model

Logan Medallist 7. Appinite Complexes, Granitoid Batholiths and Crustal Growth: A Conceptual Model

Zircon Reveals Diverse Trends of Magma Crystallization from Two Types of Early Post-Collisional Diorites (Variscan Orogen, NE Bohemian Massif)

The genetic relationship between coeval Ediacaran mafic and granitoid plutons in the Antigonish Highlands, Nova Scotia

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