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| Titel |
Crustal structure of a Proterozoic craton boundary: east Albany-Fraser Orogen, Western Australia, imaged with passive seismic and gravity anomaly data |
| VerfasserIn |
Christian Sippl, Lucy Brisbout, Catherine Spaggiari, Klaus Gessner, Hrvoje Tkalčić, Brian Kennett, Ruth Murdie |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250141903
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| Publikation (Nr.) |
 EGU/EGU2017-5457.pdf |
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| Zusammenfassung |
| We use passive seismic and gravity data to characterize the crustal structure and the
crust-mantle boundary of the east Albany-Fraser Orogen in Western Australia, a Proterozoic
orogen that reworked the southern and southeastern margin of the Archean Yilgarn
Craton. The crustal thickness pattern retrieved from receiver functions shows a belt of
substantially thickened crust - about 10 km thicker than the surrounding regions - that
follows the trend of the orogen, but narrows to the southwest. Common conversion
point profiles show a clear transition from a wide, symmetric Moho trough in the
northeast to a one-sided, north-western Moho dip in the southwest, where the Moho
appears to underthrust the craton towards its interior. The change from a Moho
trough to an underthrust Moho appears to coincide with the inferred trace of the
Ida Fault, a major terrane boundary within the Yilgarn Craton. Bulk crustal vp/vs
ratios are mostly in the felsic to intermediate range, with clearly elevated values
(≥1.8) at stations in the Fraser Zone granulite facies, dominantly mafic metamorphic
rocks.
Forward modelling of gravity anomaly data using the retrieved Moho geometry as a
geometric constraint shows that a conspicuous, elongated gravity low on the northwestern
side of the eastern Albany-Fraser Orogen is almost certainly caused by thickened Archean
crust. To obtain a model that resembles the regional gravity pattern the following assumptions
are necessary: high-density rocks occur in the upper crustal portion of the Fraser Zone, at
depth inside the Moho trough and in parts of the eastern Nornalup Zone east of
the Moho trough. Although our gravity models do not constrain at which crustal
level these high-density rocks occur, active deep seismic surveys suggest that large
extents of the east Albany-Fraser Orogen’s lower crust include a Mesoproterozoic
magmatic underplate known as the Gunnadorrah Seismic Province. The simplest
interpretation of the imaged crustal structure is that the Gunnadorrah Seismic Province is
underthrust beneath the Yilgarn Craton, most likely as a consequence of crustal
shortening during accretion further east. The imaged geometry overall appears to
show a wedge of Archean lower crust that was driven between the exhumed Fraser
Zone and the Gunnadorrah Seismic Province, effectively splitting the Paleo- to
Mesoproterozoic crust of the east Albany-Fraser Orogen. The vertical splitting of
Proterozoic crust by a cratonic crustal wedge, comparable to what we image in this
study, may be a process that contributed to forming many craton margins around the
world. |
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