Granite Harbor Intrusives

Granite Harbor Intrusives Ross Supergroup Koetthtz and Skelton groups... 

The basement rocks of southern Victoria Land defined in Fig. 3.1 are exposed in an irregular belt along the coast and consist primarily of the Granite Harbor Intrusives of Cambrian age which intruded the folded metasedimentary rocks of the Ross Supergroup of Cambrian and Neoproterozoic age (Warren 1969). This outcrop belt extends from the David Glacier south to the Byrd Glacier and includes the basement rocks... 

Fig. 3.12 Inclusion of metasedimentary rocks in the Granite Harbor Intrusives of the Brown FBlls being investigated by Robert Felder during the 1978(79 Antarctic field season (Photo by G. Faure)...

A mixture of biotite and hornblende from a post-kinematic porphyry dike dated by Deutsch and Webb (1964) yielded a Rb-Sr date of 467 15 Ma (recalculated to 1.42 X10 " year ). This Middle Ordovician date may approach the crystallization age of this rock because the porphyry dikes in the basement of southern Victoria Land are thin (less than 1 m) and therefore cooled more rapidly than the much more voluminous Granite Harbor Intrusives (e.g., Olympus, Dais, Theseus, Vida, and Irizar). 

Fig. 3.14 Rb-Sr isochron defined by whole-rock samples of two Vanda Porphyry dikes (R1 and R2) and K-feldspar concentrates (FI and F2). The date of 460 7 Ma is the crystallization age of these dikes which were intruded into the metasedimentary rocks of the Asgard Formation, and into the plutonic igneous rocks of the Granite Harbor Intrusives in Wright Valley during the Middle Ordovician Epoch after the Ross Orogeny (Plotted from data by Jones and Faure 1967)...

Fig. 4.2 Northern Victoria Land consists of three terranes that are separated from each other by the Leap Year and Lanterman faults. Each terrane is composed of characteristic assemblages of metasedimentary and metavolcanic rocks of Neoproterozoic and Cambrian ages. These basement rocks were locally intruded by plutons of the Granite Harbor Intrusives and by the younger Admiralty Intrusives. Rocks of the Beacon Supergroup occur only in a few places in northern Victoria Land including in the Morozumi Range and HeUiwell HiUs, in the adjacent Freyberg Mountains, and in the Lichen HiUs. The Kukri Peneplain, which is so prominent in southern Victoria Land, is only preserved in these locations (Adapted from Stump 1995)...

Fig. 4.6 The basement rocks of southern Victoria Land extend northward across the David Glacier into the Terra-Nova-Bay region of the Wilson Terrane of northern Victoria Land (NVL). The basement rocks of this region consist mainly of Granite Harbor Intrusives and of metasedimentary rocks of Neoproterozoic to Cambrian age. The rocks above the Kukri Peneplain are not shown (i.e., Beacon Supergroup, Ferrar Dolerite, and McMurdo Volcanics). This area contains several prominent mountains including Mt. Melbourne which is an extinct volcano of the Cenozoic McMurdo Volcanics (Adapted from Warren 1969 Gair et al. 1969 Skinner 1983)...

Fig. 4.7 The rocks exposed in the Deep Freeze Range between the Campbell and Priestley Glaciers include the folded metasedimentary rocks of the Priestley Schist which was intruded by the composite Terra Nova batholith of the Granite Harbor Intrusives (GHI). The metamorphic grade of the Priestley Schist increases until it grades into the Snowy Point Gneiss (SPG) which is a paragneiss composed of coarse and lenticular layers of quartz, microcline, oligoclase, biotite, and muscovite (Adapted from Skinner 1983)...

Isotopic age determinations of the basement rocks of the Terra-Nova-Bay area are listed in Appendix 4.8.1 based primarily on the work of Kreuzer et al. (1981, 1987), Vetter et al. (1984), Borsi et al. (1988), Armienti et al. (1990), and Adams (2006). The whole-rock Rb-Sr dates reported by Armienti et al. (1990) prove that the age of the Granite Harbor Intrusives of the Deep Freeze Range is Middle Cambrian based on the time scale of the lUGS (2002). All of the whole-rock samples they analyzed define a straight line in Fig. 4.8 that yields a date of507 7 Ma and an initial Sr/ Sr ratio of 0.71034 0.00022. 

Fig. 4.8 Whole-rock Rb-Sr isochron of Granite Harbor Intrusives (GHI) of the Terra Nova batholith in the Deep Freeze Range and from Timber Peak, Ogden Heights, and Mt. Nansen in the Terra-Nova-Bay area of the Wilson Terrane. All of the samples of the GHI he close to the straight line that was fitted by linear least-squares regression. The slope (m = 0.00722569) yields a date of 507.0 7 Ma and an initial Sr/ Sr ratio of 0.71034 0.00022 (o ). A migmatite (x) that was intruded by the Mt. Abbott pluton in the Deep Freeze Range (Fig. 4.7) is either much older (about 820 Ma) or has a higher initial ration (0.72709) than the rocks that define the straight line in this diagram (Data from Armienti et al. 1990)...

The display of dates in Fig. 4.9 also demonstrates that the whole-rock K-Ar dates of the Priestley Schist are lower than those of the Priestley Slate and that they overlap the K-Ar and Rb-Sr dates of biotite of the Granite Harbor Intrusives of the Terra-Nova-Bay area. This observation confirms the hypothesis that the rocks of the Priestley Schist were outgassed during the magmatic activity that accompanied the Ross Orogeny. The Granite Harbor Intrusives and the Priestley Schist subsequently cooled at about the same rate until the Middle Ordovician at about 450 Ma. 

Rb-Sr dates and initial Sr/ Sr ratios of the Granite Harbor Intrusives of southern Victoria Land (Table 3.3, Section 3.4.2 and Appendix 3.6.3). 

Fig. 4.11 The Wilson Gneisses and Rennick Schist of the Wilson Group in the southern part of he Daniels Range (Fig. 4.1), USARP Mountains, northern Victoria Land, were intruded by granitic plutons of the Granite Harbor Intrusives. This area exemplifies the complex relationships among the metamorphic gneisses and biotite schists that characterize...

Biotite and muscovite of the Granite Harbor Intrusives and biotite of a tonalite dike cooled to about 300°C at about 475 3 Ma based on K-Ar dates measured by Kreuzer et al. (1981). In contrast to the wide range of whole-rock K-Ar dates of gneisses in the Wilson Hills reported by Ravich and Krylov (1964), the K-Ar dates of the basement rocks in the Daniels Range measured by Kreuzer et al. (1981) vary only from 471.5 to 478.5 Ma with a mean of 474.3 2.4 Ma for ten samples of biotite and muscovite. 

These isotopic data combined with the chemical compositions published by Borg et al. (1986) strongly support the conclusion that the Granite Harbor Intrusives of northern Victoria Land are S-type granitoids. This conclusion applies also to the Wright and Vanda Intrusives of the ice-free valleys of southern Victoria Land and perhaps to some of the Cambro-Ordovician granitic plutons elsewhere in the Transantarctic Mountains. 

Granite Harbor Intrusives in the southern Daniels Range and elsewhere in northern Victoria Land. Therefore, the Granite Harbor pluton in the Morozumi Range formed from a sedimentary proto-liths without achieving complete homogenization of the isotopic composition of strontium. 

Fig. 4.16 The Granite Harbor Intrusives of the Morozumi Remge in the Wilson Terrane crystaUized between 510 and 520 Ma and then reached the blocking temperature of biotite and muscovite between 460 and 490 Ma after coofing for about 35 million years fiom 515 to 480 Ma (Data from Kreuzer et al. 1981, 1987)...

The comparison of the initial Sr/ Sr ratios in Fig. 4.17 supports the conclusion that the feldspar in the till of the Morozumi Range originated primarily from the Granite Harbor Intrusives (GHI) and not from the Rennick Schist (RS) and the Wilson Gneiss (WG) which are exposed in the Daniels Range and in the adjacent Lanterman and Salamander ranges in Fig. 4.14. 

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