The nature of zircon inheritance in two granite plutons

Abstract

Using zircons taken from two granite plutons, Strontian (Caledonian, northwestern Scotland) and Kameruka (Bega Batholith, southeastern Australia), this study presents observations that have a bearing on refractory zircons as provenance indicators. Two broad textural types of refractory zircon were identified: (1) those which show simple two-stage growth histories; and (2) those which have apparently undergone repeated periods of growth, resorption, mechanical abrasion, fracturing and fracture-healing. SHRIMP U-Pb ages obtained from the Kameruka zircons indicate that the cores are the textural manifestation of inheritance. The shapes of refractory cores are not unambiguously indicative of their ultimate origin, since they may also be modified by processes that occur before and after incorporation into the magma. The cores within the two populations show a great diversity in types and styles of zoning, and in composition, implying that they have not chemically equilibrated internally, or externally with their host melt.

Dedication

“…This was an extension of earlier work by Pupin (1980) who had classified zircon morphologies and attempted to relate them to the temperature and composition of the host magma. High-quality BSE images of inherited cores in zircons that had been dated by SHRIMP were published by Paterson et al (1992). Hanchar and Miller (1993) discussed the potential of BSE and CL imaging combined with SHRIMP as a tool for investigating complex growth histories due either to changes within the crystallization sequence or to episodic growth events that were sufficiently different in age to be dated separately.…”

Detrital zircon geochronology: enhancing the quality of sedimentary source information through improved methodology and combined U–Pb and fission‐track techniques

“…The area of a zircon grain to be probed is governed by the zircon type and structure. There are two reasons for this; of prime concern is Pb loss associated with metamictization, overgrowths over old recrystallized cores and metamict zircons that have recrystallized during high‐grade metamorphism ( Patterson et al ., 1992 ). Pb loss leads to unreliable discordant grain ages, i.e.…”

“…The outer rims, commonly exhibiting oscillatory growth lines, grew within the granitic melt and contain the true age of the granite. Similarly, gneiss and other high‐grade metamorphic rocks may have cores that relate to the original metamorphic, igneous or sedimentary lithologies ( Patterson et al ., 1992 ). Figure 3(A) is an electron backscattered image of an igneous zircon with a rounded inherited core, probably of sedimentary origin.…”

Poly-Orogenic Melting of Metasedimentary Crust From a Granite Geochemistry and Inherited Zircon Perspective (Southern Calabria-Peloritani Orogen, Italy)

“…The analysis of age patterns of detrital and inherited zircon in metasedimentary and igneous rocks, respectively, is commonly used in provenance studies aimed at reconstructing the geodynamic evolution of continents (e.g., Nance et al, 2014 and references therein). On the other hand, zircon inheritance patterns in igneous rocks have been employed relatively little as a petrogenetic tool, despite their considerable potential to provide key information on both magma sources and petrogenetic processes (e.g., Chen and Williams, 1990;Paterson et al, 1992;Williams, 1992Williams, , 2001Zeck and Williams, 2002;Fiannacca et al, 2008Fiannacca et al, , 2013Fiannacca et al, , 2017Jeon et al, 2012;Samperton et al, 2015;Díaz-Alvarado et al, 2016;Jeon and Williams, 2018;Schaltegger and Davies, 2018).…”