Isotopic and geochemical constraints on the age and origin of granitoids from the central Mawson Escarpment, southern Prince Charles Mountains, East Antarctica |
| |
| Authors: | S D Boger R Maas C M Fanning |
| |
| Institution: | (1) School of Earth Sciences, The University of Melbourne, Melbourne, VIC, 3010, Australia;(2) Research School of Earth Sciences, The Australian National University, Canberra, ACT, 0200, Australia |
| |
| Abstract: | Granitoids from the central Mawson Escarpment (southern Prince Charles Mountains, East Antarctica) range in age from Archaean
to Early Ordovician. U–Pb dating of zircon from these rocks indicates that they were emplaced in three distinct pulses: at
3,519 ± 20, 2,123 ± 12 Ma and between 530 and 490 Ma. The Archaean rocks form a layer-parallel sheet of limited extent observed
in the vicinity of Harbour Bluff. This granitoid is of tonalitic-trondhjemitic composition and has a Sr-undepleted, Y-depleted
character typical of Archaean TTG suites. εNd and TDM values for these rocks are −2.1 and 3.8 Ga, respectively. Subsequent Palaeoproterozoic intrusions are of granitic composition
(senso stricto) with pronounced negative Sr anomalies. These rocks have εNd and TDM values of −4.8 and 2.87 Ga, indicating that these rocks were probably melted from an appreciably younger source than that
tapped by the Early Archaean orthogneiss. The remaining intrusions are of Early Cambrian to Ordovician age and were emplaced
coincident with the major orogenic event observed in this region. Cambro–Ordovician intrusive activity included the emplacement
of layer-parallel pre-deformational granite sheets at approximately 530 Ma, and the intrusion of cross cutting post-tectonic
granitic and pegmatitic dykes at ca. 490 Ma. These intrusive events bracket middle- to upper-amphibolite facies deformation
and metamorphism, the age of which is constrained to ca. 510 Ma—the age obtained from a syn-tectonic leucogneiss. Nd–Sr isotope
data from the more felsic Cambro–Ordovican intrusions (SiO2 > 70 wt%), represented by the post-tectonic granite and pegmatite dykes, suggest these rocks were derived from Late Archaean
or Palaeoproterozoic continental crust (TDM ∼ 3.5–2.3 Ga, εNd ∼ −21.8 to −25.9) not dissimilar to that tapped by the Early Proterozoic intrusions. In contrast, the compositionally more
intermediate rocks (SiO2 < 65 wt%), represented by the metaluminous pre-tectonic Turk orthogneiss, appear to have melted from a notably younger lithospheric
or depleted mantle source (TDM = 1.91 Ga, εNd ∼ −14.5). The Turk orthogneiss additionally shows isotopic (low 143Nd/144Nd and low 87Sr/86Sr) and geochemical (high Sr/Y) similarities to magmas generated at modern plate boundaries—the first time such a signature
has been identified for Cambrian intrusive rocks in this sector of East Antarctica. These data demonstrate that: (1) the intrusive
history of the Lambert Complex differs from that observed in the adjacent tectonic provinces exposed to the north and the
south and (2) the geochemical characteristics of the most mafic of the known Cambrian intrusions are supportive of the notion
that Cambrian orogenesis occurred at a plate boundary. This leads to the conclusion that the discrete tectonic provinces observed
in the southern Prince Charles Mountains were likely juxtaposed as a result of Early Cambrian tectonism. |
| |
| Keywords: | Gondwana Antarctica Prince Charles Mountains Lambert Complex SHRIMP Granites High Sr/Y |
| 本文献已被 SpringerLink 等数据库收录！ |
|
