Low-potassium, trondhjemitic to granodioritic plutonism in the eastern Blue Ridge, southwestern North Carolina-northeastern Georgia

Abstract

Plutons and dikes of the eastern Blue Ridge, North Carolina and northeasternGeorgia, were emplaced syntectonically ca. 400 Ma in the evolving southern Appalachian orogen. These intrusive rocks are uniformly felsic and peraluminous, ranging continuously from trondhjemitic to granodioritic in composition with no associated mafic or intermediate rocks. The trondhjemites are very low in K and in incompatible and high field strength trace elements; are rich in Al, Na, and Sr; and have low 87 Sr/ 86 Sr and δ 18 O and high ε Nd . Granodiorites are less extreme, having elemental and isotopic compositions that are more typical of continent margin granitoids.Their compositions require that the rocks near the trondhjemitic end of the spectrum had a relatively mafic source that was young and derived from depleted mantle. Trace-element modeling and isotopic constraints suggest that this source had the geochemical characteristics of a primitive arc basalt, and that the residue of melting was garnet amphibolite. The granodiorite end of the compositional continuum was derived in large part from the Proterozoic continental basement of the region. The most plausible genetic model involves development of an early Paleozoic magmatic arc, underthrusting of arc rocks during subsequent orogeny, heating of the deep crust as a consequence of crustal thickening, and anatexis within a heterogeneous lower crust. Magmas generated within this crust ranged from trondhjemite to granodiorite, depending upon the source rock, and coalesced in the source region or during ascent to yield the observed compositional continuum.

Paired plutonic belts in convergent margins and the development of high Sr/Y magmatism: Peninsular Ranges Batholith of Baja California and Median Batholith of New Zealand

“…of Rahu are due to contamination of Separation Point magmas with Paleozoic continental crust (e.g., Waight et al, 1998). A similar model has been proposed by Miller et al (1997) for trondhjemitic to granodioritic plutonism in the southern Appalachians. Figure 9.…”

Linking metamorphism, magma generation, and synorogenic sedimentation to crustal thickening during Southern Appalachian mountain building, USA

“…Importantly, these two overlapping belts occur within the eastern Blue Ridge and are not separated by major faults (e.g., Brevard fault zone), as observed in Georgia and North Carolina, thereby limiting uncertainties associated with younger fault displacements. Geochemical models for the trondhjemite and granodiorite magmas in the eastern Blue Ridge of Georgia and North Carolina are consistent with intracrustal partial melting involving amphibole and biotite dehydration reactions, leaving behind a plagioclase-poor, garnet-bearing residue at deep-crustal levels (>30 km depth; Miller et al, 1997). Highly variable and negative zircon Hf isotope data from the Alabama plutons support an intracrustal melting origin; however, some weakly positive ε Hf(i) values are compatible with contributions from a mantle source.…”

Re‐creation of the 1744 Heylyn and Frye ceramic patent wares using Cherokee clay: Implications for raw materials, kiln conditions, and the earliest English porcelain production

“…The parent rock to unaker might appear to be a coarse-grained granite or feldsparbearing pegmatite. Ramsay et al (2001) have demonstrated that the parental rocks for this primary clay assemblage are a suite of essentially northeast-trending pegmatite intrusions and quartz veins that were syntectonically emplaced during the Acadian Orogeny (Miller et al, 1997). Again, the description suggests that both Heylyn and Frye had firsthand experience of this material and were not hastily filing a patent to stop other competitors, such as Andrew Duché (Watney, 1973:10) from obtaining exclusive rights.…”