摘要:

Field and petrographic studies on granitic, hematitic and chloritic breccias in the central portion of the Mount Painter Inlier, South Australia, indicate that: (i) breccias and brecciated basement extend to depths exceeding 400 m and have gradational contacts; (ii) clasts are mainly autochthonous and contain fine‐scale hematite, chlorite or quartz veinlets and fractures; (iii) K‐metasomatism preceded hematitisation and chloritisation; (iv) hematitic breccia intrudes a pegmatite dyke correlated with the Ordovician Arkaroola Pegmatite; and (v) U, F and REE‐containing minerals are present in the Proterozoic basement rocks, and concentrated in the breccias.

ISSN:0016-7614    

DOI:10.1080/00167618208729199

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

In the Buckambool area, Cobar, New South Wales, the boundary between dominantly shallow‐water, shelf sediments of the Winduck Group and fluviatile sediments of the Mulga Downs Group has been established as a small hiatus not resolvable by available fossil age data. Although dips are parallel over much of the area, disconformable and locally angular unconformable relations are present. This hiatus, late‐Early to Middle Devonian in age, marks a period of uplift, localised folding and erosion. These reflect movement of basement blocks along major fractures that are now revealed as lineaments.

ISSN:0016-7614    

DOI:10.1080/00167618208729200

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Biotite igneous ages and well‐defined isochron ages of plutons from the composite Blue Tier Batholith and the Coles Bay area in northeastern Tasmania range from 395 to 370 Ma. The older limit of this range, for the George River granodiorite, is considerably older than any age previously recorded for NE Tasmania. The ages of the youngest plutons (Mt Paris and Anchor granites), which host cassiterite ores, record pervasive hydrothermal alteration events. The initial87Sr/80Sr ratios of the granitoids range from 0.7061 to 0.7136 and suggest different protolith compositions, consistent with mineralogical and geochemical characteristics of each pluton. The S‐type garnetbiotite granites (Ansons Bay and Booby alia granites) have initial ratios greater than 0.7119, indicative of enriched, high Rb/Sr ratio, crustal source‐rocks of Proterozoic age (1700–800 Ma). The S‐type biotite granites (Poimena and Pearson granites) have relatively high initial87Sr/86Sr ratios (0.7070, 0.7105) but overlap with those of the I‐type granodiorites (George River, Scamander Tier, Pyengana and Coles Bay granodiorites) which are in the range of 0.7061 to 0.7073. The initial ratios of the enriched altered plutons are poorly constrained, and on both hand‐specimen and thin‐section scales, reveal open‐system Sr isotopic patterns.

ISSN:0016-7614    

DOI:10.1080/00167618208729201

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Lake Tyrrell is a large ephemeral salt lake, the level of which is controlled by climate and groundwater. Up to a metre of water fills the basin during the wetter and cooler winter season, but evaporates during the summer, precipitating up to 10 cm of halite. Each year essentially the same pool of ions is redissolved by this annual freshening. The small percentage of gypsum precipated (< 2%) in the surface salt crust reflects the low calcium content of the brine which, in turn, is a function of the negligible net discharge of calcium from the groundwater system. The small influx of fine‐grained clastic sediment to the lake floor comes from surface runoff, wind, and reworking of older sediment from the shoreline.

ISSN:0016-7614    

DOI:10.1080/00167618208729202

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The anorthositic Windimurra Gabbroid is the largest gabbroid body in the central Yilgarn Block of Western Australia, and is approximately equivalent in size to the Stillwater Complex. It contrasts with most other Yilgarn layered gabbroid bodies in its generally fresh mineralogy, anorthositic affinities, apparent lack of regional or static metamorphic effects, and unusual greenstone setting, wherein mafic and ultramafic volcanics are absent. The contacts with surrounding granitoids and greenstones are tectonic, and it has not been possible to establish direct age relationships.

ISSN:0016-7614    

DOI:10.1080/00167618208729203

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

A detailed analysis of field exposures and grain‐size distribution data for the Pilliga Sandstone within the southern Coonamble Embayment and Oxley Basin indicates a braided stream depositional environment for this unit. From the palaeocurrent data, it is concluded that deposition was dominated by two fluvial systems, one draining Lower Palaeozoic basement rocks to the SW, and the other originating from the SE and possibly fed from uplifted Triassic quartz‐rich sediments of the Sydney Basin. A matrix‐cement of coarse‐grained, well‐ordered kaolinite is typical of this porous sandstone unit, and available evidence points to much of this material being authigenic. The author considers this to have developed during diagenesis of the sandstone through the alteration of unstable detrital minerals by reaction with mobile groundwater.

ISSN:0016-7614    

DOI:10.1080/00167618208729204

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The Spring Well volcanic complex in the Eastern Goldfields Province of Western Australia, is a relatively fresh and well exposed Archaean felsic volcanic centre that is preserved in a synclinal structure at the top of the local greenstone succession. Subaerial acid pyroclastic deposits and subordinate lava flows, intruded by anastomosing intermediate‐acid dykes and sills, comprise the near‐vent facies. In the distal regions of the centre, subaqueous crystal tuff and other tuff units are intercalated with epiclastic sediments.

ISSN:0016-7614    

DOI:10.1080/00167618208729205

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Detailed structural mapping on NE Eyre Peninsula, South Australia, has led to a revised stratigraphy and model of sedimentation for Early Proterozoic metasediments of the Gawler Craton. Four stages of deformation have been recognised; three stages are associated with the Kimban Orogeny (c. 1820–1580 Ma) and a fourth stage is known as the Wartakan Event (c. 1500–1450 Ma). The recognition of major D2folds has shown the previously used stratigraphy to be incorrect and has necessitated its revision. At the base of the sequence, unconformably overlying a 2300 Ma or older basement, is the Warrow Quartzite. A transgressive cycle of schist, dolomite (Katunga Dolomite) and iron formation (Lower Middleback Jaspilite) overlies the quartzite, and this is overlain in turn by a regressive semipelitic unit containing local amphibolites (Cook Gap Schist), and another transgressive iron‐formation bearing cycle (Upper Middleback Jaspilite). At the top of the sequence is the Yadnarie Schist. All units overlying the older basement to the top of the Yadnarie Schist are defined collectively as the Hutchison Group. The Middle‐back ‘Group’ consisting of units from the top of the Warrow Quartzite to the base of the Yadnarie Schist is redefined as the Middleback Subgroup. Sediments of the Hutchison Group were probably derived from 2300+ Ma rocks on western Eyre Peninsula and deposited on a shallow platform now oriented approximately N‐S.

ISSN:0016-7614    

DOI:10.1080/00167618208729206

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The Middle Shoalhaven Plain is a large, tray‐like depression bounded in the west by the Mulwaree fault and in the east by cliffed Permian sediments. The plain is probably Mesozoic in origin and was partially alluviated during the Early to mid‐Eocene. Much of the plain and sediments were covered by basalts during the Late Eocene. This was followed by an episode of deep weathering, which culminated in the formation of widespread bauxitic and lateritic crusts and manganocrete and silcrete during the mid‐Tertiary. A second minor weathering event is recorded during the latest Tertiary to Early Pleistocene. Two new basalt dates are consistent with earlier ones at about 43 Ma. Palaeomagnetism shows bauxites and ferricretes to be mid‐Tertiary.

ISSN:0016-7614    

DOI:10.1080/00167618208729207

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

ISSN:0016-7614    

DOI:10.1080/00167618208729208

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor