Origin of the Mt Ashmore structural dome, west Bonaparte Basin, Timor Sea

dc.contributor.authorGlikson, Andrew
dc.contributor.authorJablonski, D
dc.contributor.authorWestlake, S
dc.date.accessioned2015-12-10T22:16:46Z
dc.date.issued2010
dc.date.updated2016-02-24T08:22:51Z
dc.description.abstractNew insights into the 3D structure, composition and origin of the Mt Ashmore dome, west Bonaparte Basin, Timor Sea, are enabled by reprocessed seismic-reflection data and by optical microscopic, X-ray diffraction (XRD), scanning electron microscopy (SEM)/energy dispersive spectrometry (EDS) and transmission electron microscopy (TEM) analyses of drill cuttings. The structural dome, located below a major pre-Oligocene post-Late Eocene unconformity and above a ~ 6 km-deep-seated basement high indicated by marked gravity and magnetic anomalies, displays chaotic deformation at its core and a centripetal kinematic deformation pattern. A study of drill cuttings of Lower Oligocene to Lower Jurassic sedimentary rocks intersected by the Mt Ashmore 1B petroleum-exploration well reveals microbrecciation and extreme comminution and flow-textured fluidisation of altered sedimentary material. The microbreccia is dominated by aggregates of poorly diffracting micrometre to tens of micrometres-scale to sub-millimetre particles, including relic subplanar fractured quartz grains, carbonate, barite, apatite and K-feldspar. A similar assemblage occurs in fragments in basal Oligocene sediments, probably derived from the eroded top section of the dome, which protrudes above the unconformity. SEM coupled with EDS show the micrometre to tens of micrometres-scale particles are characterised by very low totals and non-stoichiometric compositions, including particles dominated by Si, Al-Si, Si-Ca-Al, Si-Al-Ca, Si-Mg, Fe-Mg-Ca, Fe-Mg and carbonate. XRD analysis identifies a high proportion of amorphous poorly diffracting material. TEM indicates internally heterogeneous, fragmented and recrystallised structure of the amorphous grains, which accounts for the low totals in terms of the high-volatile and porous nature of the particles. Another factor for the low totals is the uneven thin-section surfaces which affect the totals. No volcanic material or evaporites were encountered in the drillcore, militating against interpretations of the structure in terms of magmatic intrusion or salt diapirism. Such models are also inconsistent with the strong gravity and magnetic anomalies, which signify a basement high below the dome. An interpretation of the dome in terms of a central rebound uplift of an impact structure can not be proven due to the lack of shock metamorphic effects such as planar deformation features, impact melt or coesite. However, an impact model is consistent with the chaotic structure of the domal core, centripetal sense of deformation, microbrecciation, comminution and fluidisation of the Triassic to Eocene rocks. In this respect, an analogy can be drawn between the Mt Ashmore structural dome and likely but unproven impact structures formed in volatile (H2O, CO2)-rich sediments where shock is attenuated by high volatile pressure, such as Upheaval Dome, Utah. In terms of an impact hypothesis the Mt Ashmore dome is contemporaneous with a Late Eocene impact cluster (Popigai: D = 100 km, 35.7 ± 0.2 Ma; Chesapeake Bay: D = 85 km, 35.3 ± 0.1 Ma).
dc.identifier.issn0812-0099
dc.identifier.urihttp://hdl.handle.net/1885/51101
dc.publisherBlackwell Publishing Ltd
dc.sourceAustralian Journal of Earth Sciences
dc.subjectKeywords: apatite; barite; breccia; carbonate; deformation mechanism; dome; Eocene; hydrocarbon exploration; modeling; Oligocene; orthoclase; quartz; scanning electron microscopy; seismic reflection; structural geology; transmission electron microscopy; unconformit Bonaparte Basin; Eocene; Impact; Mt Ashmore 1B; Structural dome; Timor Sea
dc.titleOrigin of the Mt Ashmore structural dome, west Bonaparte Basin, Timor Sea
dc.typeJournal article
local.bibliographicCitation.issue4
local.bibliographicCitation.lastpage430
local.bibliographicCitation.startpage411
local.contributor.affiliationGlikson, Andrew, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationJablonski, D, Finder Exploration Pty Ltd
local.contributor.affiliationWestlake, S, Finder Exploration Pty Ltd
local.contributor.authoremailrepository.admin@anu.edu.au
local.contributor.authoruidGlikson, Andrew, a104733
local.description.embargo2037-12-31
local.description.notesImported from ARIES
local.identifier.absfor020108 - Planetary Science (excl. Extraterrestrial Geology)
local.identifier.ariespublicationf2965xPUB217
local.identifier.citationvolume57
local.identifier.doi10.1080/08120099.2010.481327
local.identifier.scopusID2-s2.0-77952557391
local.identifier.uidSubmittedByf2965
local.type.statusPublished Version

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