Mineral-scale Sr isotope variation in plutonic rocks — a tool for unravelling the evolution of magma systems

Abstract

Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. New single grain Sr isotope data are presented from the Dais Intrusion, Antarctica, which reflect an open system origin for the crystals. The crystal cargo appears to be aggregated and assembled during transport and emplacement. This model, as opposed to a magma body crystallising post emplacement, may be more applicable to plutonic rocks in general, and is testable using the in situ isotopic determination methods described here.

Oscillatory Sr isotopic signature in plagioclase megacrysts from the Damiao anorthosite complex, North China: Implication for petrogenesis of massif-type anorthosite

“…Similarly, as the effect of late isotopic equilibration after crystallization (i.e. diffusion) is very limited, Sr isotopic ratios of plagioclase should also retain Sr isotopic compositions of the magmas (e.g., Halama et al, 2002;Davidson et al, 2008). Therefore, the consistent oscillatory patterns of chemical and Sr isotopic compositions from center to rim suggest that these megacrysts have crystallized from a magma whose compositions change temporally in deep magma chambers at lower-crustal depths or crust-mantle boundary (Loomis and Welber, 1982).…”

“…Using the in-situ analytical technique of LA-MC-ICP-MS with high spatial-resolution, variations of elemental and Sr isotopic compositions across zoned minerals can be obtained, and thus can bring in the temporal aspect to in-situ mineral analyses along crystal growth zones (e.g., Simonetti et al, 1996;Davidson et al, 2001Davidson et al, , 2007Davidson et al, , 2008Bizzarro et al, 2003;Ramos and Reid, 2005;Pietranik and Koepke, 2009;Lackey et al, 2012). In this contribution, we present major, trace and in-situ Sr isotopic data of plagioclase megacrysts from the Damiao anorthosite complex, North China (Ye et al, 1996;Xie, 2005;Zhao et al, 2009).…”

Lattice-preferred orientations of late-Variscan granitoids derived from neutron diffraction data: implications for magma emplacement mechanisms

“…This requires that the phenocrysts crystallised early, which is documented by different composition and structure compared to the groundmass minerals, and by internal compositional zoning (e.g. Davidson et al 2008). Early crystallisation of the amphibole and feldspar phenocrysts in the monzonite magma is indicated by variable core to rim composition, the occurrence of diopside cores in amphibole grains and different compositions of groundmass and phenocryst feldspars (Pfeiffer 1964;Wenzel et al 1997).…”

An evolving magma chamber within extending lithosphere: An integrated geochemical, isotopic and zircon U–Pb geochronological study of the Gushan granite, eastern North China Craton

“…While crystal-isotope profile has been proved to be a very powerful tool in volcanic systems, only few studies have employed this approach to plutonic systems (e.g., Cox et al, 1996;Waight et al, 2000;Halama et al, 2002;Tepley and Davidson, 2003;Gagnevin et al, 2005;Davidson et al, 2008;Alves et al, 2009). One of the reasons for the scarcity of such studies is that plutonic rocks cool slowly and are thus affected by diffusive re-equilibration associated with long-term high-temperature environments, or by variable isotopic exchange associated with hydrothermal fluids (Davidson et al, 2005(Davidson et al, , 2008Siebel et al, 2005;Ramos and Tepley, 2008).…”

“…One of the reasons for the scarcity of such studies is that plutonic rocks cool slowly and are thus affected by diffusive re-equilibration associated with long-term high-temperature environments, or by variable isotopic exchange associated with hydrothermal fluids (Davidson et al, 2005(Davidson et al, , 2008Siebel et al, 2005;Ramos and Tepley, 2008). Although Sr and Pb isotopes are relatively sensitive to such disturbances, Nd isotope is a much more ''robust'' tracer, given its slow diffusion rates and low mobility (Lesher, 1994;Van Orman et al, 2001;Cherniak, 2003).…”