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Structural and geochronological constraints of early Ross orogenic deformation in the Pensacola Mountains, Antarctica

Curtis, Michael L; Millar, Ian L; Storey, Bryan; Fanning, Christopher

Description

During end-Neoproterozoic to early Paleozoic time, the southern margin of Gondwana was affected by widespread subduction-related orogenesis. In East Antarctica this event is known as the Ross orogeny, whose manifestation is exposed along the 3500 km length of the Transant-arctic Mountains. In the Pensacola Mountains, the Ross orogeny is characterized by two contractional deformation events, which bracket a brief period of latest Middle Cambrian to early Late Cambrian extension and...[Show more]

dc.contributor.authorCurtis, Michael L
dc.contributor.authorMillar, Ian L
dc.contributor.authorStorey, Bryan
dc.contributor.authorFanning, Christopher
dc.date.accessioned2015-12-13T22:49:00Z
dc.date.available2015-12-13T22:49:00Z
dc.identifier.issn0016-7606
dc.identifier.urihttp://hdl.handle.net/1885/80336
dc.description.abstractDuring end-Neoproterozoic to early Paleozoic time, the southern margin of Gondwana was affected by widespread subduction-related orogenesis. In East Antarctica this event is known as the Ross orogeny, whose manifestation is exposed along the 3500 km length of the Transant-arctic Mountains. In the Pensacola Mountains, the Ross orogeny is characterized by two contractional deformation events, which bracket a brief period of latest Middle Cambrian to early Late Cambrian extension and sedimentation. The oldest and most intense of these deformation events effected a succession of latest Neoproterozoic metagraywackes (Hannah Ridge Formation), producing tight to isoclinal F1 folds that possess a slaty axial-planar cleavage. Steeply plunging asymmetric F2 folds and their associated cleavage are superimposed upon the NNE-SSW D1 structural grain, forming a consistent clockwise oblique angle. Together with several shear-sense indicators, the angular relationship of D2 and D1 suggests that the F2 folds formed as a result of sinistral reactivation of D1 structures. At Serpan Peak, new meso- and microstructural observations of the Serpan Peak granite suite reveal two phases of emplacement: an early granodioritic phase emplaced prior to the regional D1 deformation event, and a later phase of syntectonic biotite granites emplaced during D2. New U-Pb SHRIMP ages for three phases of the Serpan Peak granite suite constrain their emplacement-and, by structural relationship, the early Ross D1 and D2 deformation events-as having occurred at 505 ± 5 Ma. The ages of D1 and D2 are identical within error, and we interpret them as being the product of a single progressive sinistral transpressional deformation event. Our new structural and geochronological constraints necessitate that deformation of the Hannah Ridge Formation occurred in conjunction with exhumation from lower greenschist conditions prior to deposition of the upper Middle Cambrian Nelson Limestone (< 10 m.y.). Exhumation was closely followed by ca. 500 Ma bimodal volcanism inferred to represent an extensional continental backarc setting. During the latest Cambrian-Early Ordovician, a second, less intense contractional deformation event deformed and inverted the backarc region. Our new data reveal that, along the Pensacola Mountains sector of East Antarctica, the Ross orogeny was manifested as a condensed sequence of rapidly changing tectonic events along a continuously subducting margin, characterized by switches in deformation mode within the continental margin. We interpret such tectonic switching to be the result of the intermittent arrival of buoyant oceanic plateaus at the Ross subduction zone, resulting in short-lived periods of flat-slab subduction and contractional deformation that punctuated the neutral or extensional strain regime generally associated with "normal" subduction. Given the limited length of plate margin likely to be affected by oceanic plateau subduction, specific correlation of stratigraphic and tectonic events along the entire length of the Ross orogen are unlikely. Nonetheless, similar patterns of punctuated tectonic events associated with sinistral transpressional deformation during the Ross orogeny are observed elsewhere along the orogen.
dc.publisherAssociation of Engineering Geologists
dc.sourceGeological Society of America Bulletin
dc.subjectKeywords: East Antarctica; Mountains; Orogenic deformation; Ross orogeny; Deformation; Geochronology; Granite; Landforms; Limestone; Microstructure; Shrinkage; Stratigraphy; Tectonics; Structural geology; Gondwana; orogeny; Proterozoic; Antarctica; East Antarctica; Antarctica; Granite; Polyphase deformation; Transantarctic Mountains; Transpression
dc.titleStructural and geochronological constraints of early Ross orogenic deformation in the Pensacola Mountains, Antarctica
dc.typeJournal article
local.description.notesImported from ARIES
local.description.refereedYes
local.identifier.citationvolume116
dc.date.issued2004
local.identifier.absfor040203 - Isotope Geochemistry
local.identifier.absfor040312 - Structural Geology
local.identifier.ariespublicationMigratedxPub8607
local.type.statusPublished Version
local.contributor.affiliationCurtis, Michael L, Natural Environment Research Council
local.contributor.affiliationMillar, Ian L, Natural Environment Research Council
local.contributor.affiliationStorey, Bryan, Natural Environment Research Council
local.contributor.affiliationFanning, Christopher, College of Physical and Mathematical Sciences, ANU
local.bibliographicCitation.issue5/6
local.bibliographicCitation.startpage619
local.bibliographicCitation.lastpage636
local.identifier.doi10.1130/B25170.1
dc.date.updated2015-12-11T10:32:02Z
local.identifier.scopusID2-s2.0-2442595671
CollectionsANU Research Publications

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