Frontiers and Opportunities in Antarctic Geosciences * Certosa di Pontignano * 29-31 July 2004
Multi-Phase History of the mid-Cretaceous Palmer Land Event in the Southern
Antarctic Peninsula:
Implications for Terrane Boundaries and Kinematic Evolution
A.P.M. VAUGHAN
Geological Sciences Division, British Antarctic Survey, High Cross, Madingley Rd, Cambridge, CB3 0ET, UK (a.vaughan@bas.ac.uk)
In the southern Antarctic Peninsula, new and existing structural data (e.g. Vaughan & Storey, 2000), combined with
published radiometric ages for pluton emplacement (Pankhurst & Rowley, 1991) and deformation (Vaughan et al.,
2002a; Vaughan et al., 2002b) suggest that the mid-Cretaceous Palmer Land event (Vaughan et al., 2002b) was a two
stage event with kinematically distinct deformation pulses at c. 107 Ma and c. 103 Ma. The geological understanding
of the Antarctic Peninsula has recently changed, with the recognition that the peninsula is made up of a mosaic of 100to 1000-km scale fault-bounded blocks (Vaughan and Storey, 2000). These blocks may or may not have been in their
present day position at the time of formation and may have arrived from distant original locations by tectonic processes
(e.g. Vaughan et al., 2002a; Vaughan et al., 2002b). The focus of current study is the deformation history of one of
these blocks, the Eastern Domain, that forms the southern and eastern part of the Antarctic Peninsula and was once part
of the margin of Gondwana. The Eastern Domain terrane (Fig. 1) is made up of Neoproterozoic metamorphic rocks
(Millar & Pankhurst, 1987) and Palaeozoic sedimentary rocks (Laudon & Ford, 1997), overlain by Lower to Middle
Jurassic volcanic rocks of the Mount Poster Formation (Riley and Leat, 1999; Rowley et al., 1983) and Jurassic marine
mudstones and sandstones of the Latady Formation (Rowley et al., 1983). These host a suite of major intrusions
emplaced in a short time period during the middle of the Cretaceous, the Lassiter Coast Intrusive Suite (LCIS) (Vennum
& Rowley, 1986). The LCIS consists of calc-alkaline stocks and batholiths of Early Cretaceous age, ranging in age
from 123–96 Ma based on Rb–Sr, K–Ar, and U–Pb techniques (Pankhurst & Rowley, 1991; Vaughan et al., 2002b).
Plutons of the suite range in composition from granite to gabbro, and intrude rocks of the Latady Fm, Mount Poster Fm
and older rocks over an area of 500 x 100 km. The LCIS contains one major batholith (Werner: 225 x 50 km) and ~60
smaller stocks and plutons (from ~1 km across, up to 20 x 20 km). Plutons have thin mafic rims and intermediate to
felsic cores, with thermal aureoles 1–2 km wide. Metamorphic grade ranges up to hornblende-hornfels facies with
andalusite hornfels common in the Latady Formation and minor migmatisation in Mount Poster rhyolites. Intrusion of
the LCIS coincided with a major mountain building event approximately 100 million years ago, called the Palmer Land
Event (Kellogg & Rowley, 1989; redated by Vaughan et al., 2002b) that deformed Eastern Domain rocks. Cumulative
frequency plotting of pluton age data (Ludwig, 1999), combined with known ages of deformation and regional and
depth-related variations in structural style, suggest that the Palmer Land event consists of two phases of deformation
coincident with major pulses of LCIS magmatism: a NW–SE-directed episode of shortening at c. 107 Ma and an E–Wdirected episode of dextral transpression at 103 Ma. This change in kinematics coincided with spreading changes in the
Weddell Sea and major changes in and around the Pacific basin at this time (Vaughan et al., 2002a). Locally, the
relationship between these kinematic changes and the emplacement of the LCIS, implies that plutonism may not be arcrelated, and places better temporal constraints on terrane boundary activity.
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