Geology of the Sir Samuel 1:250 000 sheet, Western Australia

The Archaean granite-greenstones in the SIR SAMUEL 1:250 000 sheet area can be divided into three north- to north-northwest-trending strips of greenstones that are separated by large areas of granitoid.
The west strip varies in width from 2 to 17 km, and includes the Perseverance-Mount Keith, Agnew, and Yakabindie greenstone belts.  The far west part of the sheet is largely granitoid, with an arcuate belt  up to 18 km wide of highly deformed and gneissic granitoid west of the Waroonga Shear Zone.  The southern Yandal greenstone belt is separated from the Perseverance-Mount Keith greenstone belt by a large area of granitoid, including the sigmoidal Koonoonooka monzogranite, and a highly deformed zone, up to  12 km wide, of interleaved granitoid and greenstone west of the Mount McClure Fault.  Part of the Dingo Range greenstone belt occurs in the northeast.
The Yakabindie greenstone belt comprises a layered sequence of the Kathleen Valley Gabbro overlain by the massive tholeiitic Mount Goode Basalt. The Agnew greenstone belt comprises a lower sequence of metamorphosed ultramafic, mafic, felsic volcanic, and sedimentary rocks, which is exposed in the Lawlers and Leinster Anticlines. The upper sequence, as in the Mount White Syncline area, consists of metabasalt, metagabbro and metasedimentary rocks. Metamorphosed ultramafic, mafic, felsic volcanic and sedimentary rocks in the Perseverance area extend farther north to west of Mount Pasco. From Six Mile Well, ultramafic, sedimentary, and felsic volcanic/volcaniclastic rocks correlate well with the greenstone sequences through Mount Keith to Wiluna. The Jones Creek Conglomerate represents a late clastic sequence  and is restricted to a narrow, fault-bounded zone between the Yakabindie greenstone belt and granite in the west and the Perseverance-Mount Keith and Agnew greenstone belts to the east. 
The southern Yandal greenstone belt consists of two major packages of greenstones, i.e., mafic and som e ultramafic rocks in the Bronzewing - Mount McClure, Hartwell, Yandal Well and Darlot areas, and felsic rocks along the Ockerburry Fault Zone and Spring Well area. In the Dingo Range greenstone belt, the Dingo Range antiform is interpreted to be a refolded earlier fold of banded iron formation/chert, ultramafic and basaltic rocks. In the Mount Harold area some felsic volcanic/volcaniclastic rocks occur.  The Stirling Peaks area is largely little deformed fine grained metabasalt. 
Three major deformation events are recognised in the granite-greenstones in the SIR SAMUEL area. The first deformation, although poorly understood, produced bedding-parallel foliation including flattened pillow structures in basalt, and some tight to isoclinal folds.  Major orogenic compression during D2 produced the north-northwest greenstone belt trends and linear structures including faults, shear zone s and folds.  During D3, deformation appears to have been largely concentrated along major shear zones.  Some north- to north-northeast-trending structures were probably produced, or reoriented into their current positions, during D3, which shaped the current structural architecture.  Structures in the southern Yandal greenstone belt are best configured in terms of a compressional jog. Post-D3 deformation is represented by normal faults, fractures, and sub-horizontal crenulations. A major phase of regional metamorphism was initiated during D2 and peaked late during or after D2. Granite intrusion occurred throughout the deformation and metamorphic history in the SIR SAMUEL area.
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Tags: AU-WA, Earth Sciences, GA Publication, Published_External, Record, geology
Organization: Geoscience Australia Data