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Volcanic facies architecture of the Cambro-Ordovician Seventy Mile Range Group, Northern Queensland, Australia


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Simpson, K 2001 , 'Volcanic facies architecture of the Cambro-Ordovician Seventy Mile Range Group, Northern Queensland, Australia', PhD thesis, University of Tasmania.

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The Cambro-Ordovician Seventy Mile Range Group occurs within the Mount Windsor Subprovince in northern Queensland, Australia. It extends approximately 165 km east-west, consists of compositionally and texturally diverse submarine volcanic and sedimentary fades and hosts massive sulfide deposits. The Seventy Mile Range Group has undergone greenschistgrade regional metamorphism and three phases of deformation. It comprises four formations, the middle two of which are dominantly volcanic (Mount Windsor and Trooper Creek Formations).
Detailed volcanic fades mapping has been undertaken along spaced traverses throughout the
Seventy Mile Range Group. The main areas studied include Warawee, Brittania,
Highway /Reward, Mt. Farrenden, Mt. Windsor, Lion town and Thalanga. This research has
prompted a review of the existing stratigraphic framework. The Mount Windsor and Trooper
Creek Formations are amalgamated into one lithostratigraphic unit, informally termed the
Mount Windsor-Trooper Creek unit. The Mount Windsor-Trooper Creek unit overlies nonvolcanic
sandstone and mudstone of the Puddler Creek Formation. The contact with the
Puddler Creek Formation is either narrow (<100 m) or broad (up to 1000 m) and interfingering
or intrusive. The Mount Windsor-Trooper Creek unit is conformably overlain by non-volcanic
sandstone and mudstone of the Rollston Range Formation.
Twenty-three principal lithofacies have been identified in the Mount Windsor-Trooper Creek
unit and are organised into five groups: 1) coherent rhyolite, dacite and basaltic andesite; 2)
monomictic volcanic breccia and conglomerate; 3) polymictic volcanic breccia and
conglomerate; 4) volcanic sandstone and mudstone; and 5) non-volcanic sandstone and
mudstone. The volcanic succession is interpreted to comprise lavas and intrusions, syn-eruptive
pyroclastic sediment gravity flow deposits, bomb-rich fire-fountain deposits, syn-eruptive
resedimented pyroclastic and autoclastic deposits and post-eruptive and reworked volcaniclastic
deposits. Transport and deposition of monomictic and polymictic volcanic breccia and
conglomerate involved water-supported sediment gravity flows. Coherent and associated
autoclastic rhyolite fades are interpreted to be dominantly intrusions.
Regionally, the environment of deposition was submarine and below-storm-wave-base. The
products of both intrabasinal submarine and extrabasinal shallow-marine or subaerial volcanic
eruptions are preserved in the Mount Windsor-Trooper Creek unit. The volcanic fades
associations represent three and possibly four main intrabasinal volcano types: 1) rhyolite lava
and intrusion volcanic complexes, 2) basaltic andesite fire-fountain and lava volcanoes, 3) dacite dome volcanoes, and 4) possibly rhyolite lava-intrusion "tuff'' volcanoes. Rhyolite lava and
intrusion volcanic complexes are the most voluminous and common type of volcano identified.
The basaltic andesite fire -fountain eruptions generated a distinctive monomictic breccia
composed of fluidal and blocky basaltic andesite clasts. The fluidal clasts resemble subaerial
volcanic bombs and are interpreted to be the products of submarine fire fountaining of
relatively low-viscosity lava.
The stratigraphic thickness of the Mount Windsor-Trooper Creek unit varies across the belt
from ~1100 mat Thalanga to >7 km in the Mt. Farrenden and Mt. Windsor east areas.
Thickness variations of the volcanic stratigraphy are a product of accumulation of mass-flow
volcaniclastic fades in local depocentres and emplacement of voluminous felsic lavas and
intrusions at intrabasinal volcanic centres.
Lavas, intrusions and monomictic volcaniclastic fades can be divided into three geochemically
distinct suites. Suite I ranges in composition from rhyolite to basaltic andesite and is interpreted
to comprise a cogenetic suite related by variable degrees of crystal fractionation and crustal
assimilation. Suite II consists principally of rhyolites which are geochemically distinct from
Suite I rhyolites. Suite III consists of trachyandesites. Suite I occurs at all stratigraphic levels
within the Mount Windsor-Trooper Creek, Suite II is restricted to the lower Mount WindsorTrooper
Creek unit, and Suite III is largely restricted to the Puddler Creek Formation. All suites
occur across the length of the Seventy Mile Range Group. New U-Pb zircon ages for felsic
volcanic rocks from the Mount Windsor-Trooper Creek unit are 467.9 ± 4.1 Ma, 466.7 ± 2.6
Ma, and 465.4 ± 1.4 Ma.
Volcanic-hosted massive sulfide deposits occur in the middle to upper part of the Mount
Windsor-Trooper Creek unit. They have previously been interpreted to be spatially and
temporally associated with emplacement of rhyolite lavas and shallow-level intrusions (e.g.,
Thalanga and Highway /Reward) or hosted by volcaniclastic facies (e.g., Lion town). The
volcanic fades architecture of the Seventy Mile Range Group is similar to that of the Early
Proterozoic Skellefte District in Sweden, where numerous polymetallic massive sulfide deposits
are hosted within rhyolite volcanic centres and volcaniclastic deposits.

Item Type: Thesis - PhD
Authors/Creators:Simpson, K
Keywords: Volcanism
Copyright Information:

Copyright 2001 the author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).

Additional Information:

Includes one folded map in back pocket. For consultation only. No loan or photocopying permitted until 21 November 2002. Thesis (Ph.D.)--University of Tasmania, 2001. Includes bibliographical references

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