Authors / CoAuthors
Czarnota, K. | Blewett, R.S. | Champion, D.C. | Henson, P.A.
Abstract
A visually and conceptually helpful method for understanding a region's geodynamic evolution is a time-space-event chart. A new chart focussed on the time span of 2800 Ma to 2600 Ma has been constructed for the Eastern Goldfields Superterrane (EGST). This was a key period in the Neo-Archaean evolution of the Earth; when extensive crustal growth, cratonisation and mineralisation occurred. The new time-space-event incorporates geochronology, geochemistry, isotopic data, greenstone and magmatic stratigraphy, deep seismic profiles, 3D models and structural mapping/analysis. Immediately obvious from this chart is the temporally coupled relationship between the main elements of deformation/structure, greenstone volcanism and sedimentation, and felsic magmatism. That is, a change in one of these elements is marked by a change in all other elements. Similar patterns occur in the Pilbara, Superior, and Birrimian. The record from pre-2720 Ma is sparse and most supracrustal assemblages involved mafic and ultramafic volcanism and minor BIF. Andesitic volcanic and volcaniclastic rocks predominate between 2720 Ma and 2705 Ma, after which the mafic-ultramafic lavas and intrusive rocks form a volumetrically significant component of the greenstone stratigraphy. Volcanism changed to more felsic types, and by 2670-2665 Ma (epi)clastic rocktypes dominated. The record of felsic magmatism was limited prior to 2700 Ma, but increased from ~2680, and peaked at 2670 Ma for the High-Ca type granites (TTG). Extension was dominant in this early period (D1), with the orogen likely facing ENE and establishing the NNW-trending architecture preserved today. Granite domes initiated at this stage. Volcanism shut off at 2665 Ma with the onset of the first regional contraction, the short lived D2 event which accreted the terranes of the region. From 2665 Ma to ~2657 Ma greenstone stratigraphy changed to Late Basin sedimentation, with unroofing and deep exhumation into the granitic substrate during a major extensional (D3) event that involved doming and core-complex formation. An equally dramatic change is recorded in the felsic magmatism, with a change to Mafic-type granite and Syenite marking the introduction of melts from a metasomatised mantle wedge (and gold!). Extension was at first controlled by rising granite domes (partly radial extension), and evolved into ENE-directed regional extension. This extensional event had a profound influence on the architecture of the region, and it forms many of the "events" that are imaged by the deep seismic reflection profiling. By ~2655 Ma the Late Basins were inverted by ENE-oriented shortening (D4a) and was followed by sinistral transpressional strike-slip (D4b) shearing as the stratigraphy and some granite-greenstone contacts rotated to the vertical. The sinistral shear likely involved a rotation in the regional 1 to south of E-W. These sinistral faults linked with NNW-directed thrusts (previously ascribed D1), both being mineralised with significant gold. Felsic magmatism changed after 2655 Ma with the introduction of extensive crustal melts (Low-Ca granites). These granites were accompanied by a change from sinistral to dextral (D5) transtensional strike-slip faulting, and a rotation of 1 by 60º to NE-SW. Further gold accompanied this event (or was remobilised from earlier events). The last significant event was the collapse of the regional with D6 normal faults and flat-lying crenulations and folds. Further work will integrate the changing PT conditions and fluids/alteration through time. As direct dating of deposits become available these will be added.
Product Type
nonGeographicDataset
eCat Id
65331
Contact for the resource
Custodian
Owner
Point of contact
Cnr Jerrabomberra Ave and Hindmarsh Dr GPO Box 378
Canberra
ACT
2601
Australia
Keywords
-
- GA PublicationRecord
- ( Theme )
-
- geology
-
- AU-NT
- Australian and New Zealand Standard Research Classification (ANZSRC)
-
- Earth Sciences
-
- Published_Internal
Publication Date
2007-07-16T00:00:00
Creation Date
Security Constraints
Legal Constraints
Status
Purpose
Maintenance Information
unknown
Topic Category
geoscientificInformation
Series Information
Record
Lineage
Unknown
Parent Information
Extents
Reference System
Spatial Resolution
Service Information
Associations
Downloads and Links
Source Information
Source data not available.