Sources of post-orogenic calcalkaline magmas: The Arrochar and Garabal Hill–Glen Fyne complexes, Scotland

Abstract

The 425 Ma Arrochar and Garabal Hill-Glen Fyne complexes of highland Scotland are examples of post-orogenic magmatism accompanying extensional collapse of an orogen, in this case the Caledonian. The rocks are dominantly high-K series, but range from medium-K to shoshonitic. Mantle upwelling, melting and the intrusion of large volumes of mafic magma into the crust are inferred to have accompanied lithospheric thinning, and to have provided the heat source for melting of young arc crust accreted during the preceding subduction epoch.Fluids evolved from the subducting slab are inferred to have caused high degrees of enrichment in the overlying mantle wedge. Deep in the crust, the mantle-derived, K-rich mafic to intermediate magmas mixed with felsic crustal melts to form the spectrum of magmas intruded in the two complexes. Microgranular enclaves in the granitic rocks represent mafic magmas derived from the enriched mantle and hybridised by reaction, diffusion and mechanical mixing with their host felsic magmas, but they do not form part of the evolutionary series that produced the host magmas. Rather than inheriting its LILEenriched character directly from crustal melts, or from crustal assimilation by mafic magmas, the high-K series may commonly owe at least part of its potassic character to the involvement of mantle (highly metasomatised by slab-derived fluids) as a major magma source. Enclave suites, though prominent in some granitic rocks should not be assumed to represent magmas that played a significant role in the production of the chemical variations in their host magmas.

Source-inherited compositional diversity in granite batholiths: The geochemical message of Late Paleozoic intrusive magmatism in central Calabria (southern Italy)

“…The latter geochemical features do not necessarily imply a crustal source. Clemens et al (2009) have for example proposed, to explain similar features in post-orogenic mafic to intermediate rocks from Scotland, an origin by partial melting of mantle that had been highly enriched by subduction derived fluids. Nevertheless, in cases like that of Clemens et al (2009), the mantle linkage is made apparent by the large proportions of mafic and intermediate rocks and the diffuse occurrence of ultramafic cumulates in the plutonic complex, as well as by the common presence of both orto-and clinopyroxene and of olivine-pyroxene bearing MME, associated to whole rock Mg numbers up to ca.…”

The Tynong pluton, its mafic synplutonic sheets and igneous microgranular enclaves: the nature of the mantle connection in I-type granitic magmas

“…Simply put, when tested (e.g. Clemens et al 2009), the amounts of assimilation that are required to produce the compositional spectra of granitic suites are not balanced by the amounts of energy or parent magma volume available.…”

Implications from zircon-saturation temperatures and lithological assemblages for Early Permian thermal anomaly in northwest China

“…2; Jahn, 2004;Renna et al, 2006Renna et al, , 2007. Inherited zircon cores have been reported for the samples from European orogenic belts (Appleby et al, 2009;Clemens et al, 2009;Skjerlie, 1992;Zeck et al, 2007), hence their zircon saturation temperatures represent maximum estimates for the formation temperature of granitoids. 44 samples for Caledonides and 63 samples for Hercynides give zircon saturation temperatures from 731 to 884°C with majority being b 800°C (Fig.…”