Granitoids of the Dry Valleys area, southern Victoria Land, Antarctica: Plutons, field relationships, and isotopic dating

Abstract

Detailed mapping throughout much of the Dry Valleys area indicates the region is underlain by 15 major granitoid plutons and numerous smaller plugs and dikes. Intrusive relationships of these plutons and dikes indicate repeated intrusion of superficially similar granitoids at different times. Sufficient internal lithologjc variation occurs within individual plutons, to allow correlation with several of the previously defined granitoid units based on lithologic character. Consequently, previous subdivision schemes based on lithology are no longer tenable and are here replaced with a G92026 Received 2 June 1992; accepted 29 April 1993subdivision scheme based on the identification of individual plutons.The elongate, concordant Bonney, Denton, Cavendish, and Wheeler Plutons, which range in composition between monzodiorite and granodiorite, are the oldest relatively undeformed plutons in the Dry Valleys area. Each pluton is characterised by flow alignment of K-feldspar megacrysts, hornblende, biotite, and mafic enclaves. Field relationships and radiometric dating indicate these are deep-level plutons, emplaced synchronous with upper amphibolite facies metamorphism of the adjacent Koettlitz Group between 589 and 490 Ma ago. Elongate, discordant plutons of equigranular homogeneous biotite granodiorite and granite (Hedley, Valhalla, St Johns, Suess) were subsequently emplaced by stoping at a relatively high crustal level at 490 Ma.These eight plutons are cut by numerous swarms of Vanda mafic and felsic porphyry dikes. The ovoid, discordant, high level Pearse, Nibelungen, Orestes, Brownworth, Swinford, and Harker Plutons, emplaced between c. 486 and 477 Ma, display mutually crosscutting relationships with the youngest of the Vanda dikes. These younger plutons range in composition between monzonite and granite. Some are characterised by K-feldspar megacrystic textures superficially similar to some of the oldest concordant plutons.

Age, Correlation, and Provenance of the Neoproterozoic Skelton Group, Antarctica: Grenville Age Detritus on the Margin of East Antarctica

“…2). The northern part is characterized by a north-northwest-striking structural grain that is evident in both metasedimentary and plutonic rocks (Findlay et al 1984;Allibone et al 1991Allibone et al , 1993aCox 1993). Structures, metasedimentary units, and granitoid plutons can be traced as continuous features for many tens of kilometers in some cases.…”

“…490 and ca. 480 Ma, respectively, after peak metamorphism in the northern part of the Skelton Group (Allibone et al 1991(Allibone et al , 1993a(Allibone et al , 1993bSmillie 1992;Turnbull et al 1994;Encarnacion and Grunow 1996).…”

The Fontaine Pluton: An early Ross Orogeny calc‐alkaline gabbro from southern Victoria Land, Antarctica

“…The high Sr DV1b suite is thought to be the result of melting of either subducted lithosphere or underplated mafic crustal material (Allibone et al 1993b). There are two distinct phases of DV1b magmatism-the "older" DV1b ranges in age from c. 531 to c. 516 Ma and the "younger" DV1b at c. 490 Ma (Allibone et al 1993a;Cox et al 2000;Allibone & Wysoczanski 2002). The DV2 suite consists of monzonite to granite plutons as well as high-K, calc-alkaline and shoshonitic dikes.…”

Amalgamation of disparate crustal fragments in the Walcott Bay‐Foster Glacier area, South Victoria Land, Antarctica

“…These general observations are in strong contrast to the Dry Valleys area to the north, which comprises c. 50% batholithic, granitoid I-type intrusions (Smillie 1992;Allibone et al 1993a). The metasedimentary host rocks in the Dry Valleys area are more thoroughly deformed and recrystallised than almost all those in the Walcott Block (Cook 1997) and metamorphic grade reaches upper amphibolite facies verging on granulite facies (Allibone 1992;Cox 1992).…”

“…Regionally, the orogen now consists of greenschist to amphibolite facies metasedimentary rocks intruded by granitoid and mafic bodies (as summarised by Stump 1995). Calc-alkaline I-type granites dominate the intrusive suite, and some intrusions are of batholithic scale (Cox 1992;Smillie 1992;Allibone et al 1993a).…”