摘要:

A nephrite jade deposit within the Great Serpentine Belt of N.S.W., near Tamworth, occurs as several tabular bodies up to 3.5 m thick on the serpentinite country‐rock contact. The occurrence is interpreted as a low‐temperature reaction zone, similar to those observed around Alpine serpentinites elsewhere. The nephrite probably formed as a result of dynamothermal metasomatism associated with the emplacement of serpentinites along the Peel Fault.

ISSN:0016-7614    

DOI:10.1080/00167617808729033

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

A new Precambrian palaeomagnetic pole has been obtained for the Gawler Craton, South Australia. The pole is based on results obtained from the accurately dated Gawler Range Volcanics (1525±15 m.y.) and is situated 230°E 60.4°N witha95 = 6.2°. The pole is in excellent agreement with poles previously determined from the negatively magnetized ore of Iron Monarch and the negatively magnetized dykes that intrude the Gawler Craton. The results suggest that the iron ore‐forming process is closely related to igneous activity and supports the hypothesis of a hypogene origin for the ore.

ISSN:0016-7614    

DOI:10.1080/00167617808729034

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The late Palaeozoic granitoids of the Moonbi district are derived both from igneous (I‐type) and sedimentary (S‐type) sources. Field and petrographic observations and chemical data on theI‐type granitoids show that they are derived from four separate and distinct source‐rock compositions and that, consequently, these granitoids may be grouped into four suites. Mafic xenoliths and microxenoliths are relatively more abundant in more maficI‐type granitoids. Such xenoliths are interpreted as restite, or material residual from partial melting of the source rocks. Variation within the granitoids is ascribed to varying degrees of separation of restite from the melt produced during each fusion event. The source material of theI‐type granitoids is considered to have been material underplated beneath the crust during an earlier subduction event. Two suites ofS‐type granitoids can be recognized. These are derivatives of pelitic materials that have undergone only a small amount of chemical weathering.

ISSN:0016-7614    

DOI:10.1080/00167617808729035

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

Polygonal ridge patterns with intervening hollows some 400 m across and with a relief of about 100 m are common as low hills on the northern dissected part of the Sepik piedmont. They are developed in Pliocene mudstone and sometimes in marl and greywacke. The crests of the highest flat‐topped hills have a veneer of Pleistocene fanglomerate on them.

ISSN:0016-7614    

DOI:10.1080/00167617808729036

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

Within the complexly deformed and metamorphosed middle Precambrian Willyama Complex in western New South Wales, two distinct sedimentary sequences are recognized at the top of the succession. The fine‐grained carbonaceous Bijerkerno Beds conformably overlie a very thick psammopelitic unit termed the Wookookaroo Beds. These two sequences record different depositional histories, though they probably have similar source areas. The base of the Wookookaroo Beds is terminated against a significant tectono‐stratigraphic boundary, which may represent a major stratigraphic break within the Willyama Complex. Beneath this boundary, felsic and mafic gneisses and high‐grade metasediments are correlated with mine‐sequence rocks such as are developed within the vicinity of the main Broken Hill lode. Correlations between the stratigraphy, as established at Bijerkerno, and other areas from the Willyama Complex, help provide a fuller understanding of this Precambrian terrain.

ISSN:0016-7614    

DOI:10.1080/00167617808729037

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The term ‘Zamu Dolerite’ is proposed here to replace ‘Zamu Complex’, the name originally applied to the predominantly mafic intrusives of the South Alligator River area, and to include the other mafic supracrustal intrusive rocks that, with minor felsic differentiates, were emplaced into the strata of the Pine Creek Geosyncline before an 1800 m.y. phase of regional metamorphism. This suite of lower Proterozoic rocks generally forms conformable intrusive tabular bodies which are folded and, in most places, metamorphosed with the enclosing strata. The intrusions are mostly now amphibolite, but in the type area of Zamu Creek, folded but unaltered dolerite rocks are found. The Zamu Dolerite occurs in two broad zones of regional meta‐morphic grade: medium and/or high grades in the northeastern part of the region, and low grade elsewhere. Late‐orogenic Carpentarian granite diapirs have, however, locally superimposed a contact metamorphism on the low‐grade regional metamor‐phic event. Low‐temperature retrograde metamorphism is locally present throughout the Pine Creek Geosyncline, being particularly prevalent within areas of uranium mineralization.

ISSN:0016-7614    

DOI:10.1080/00167617808729038

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

Fission‐track ages have been determined on sphene and apatite from 28 granitic intrusions across the western half of Victoria. The sphene ages compare closely with independent K‐Ar biotite ages for the same intrusions, where these are available, and are invariably older than apatite ages by 35 to 135 m.y. This is in accord with the effective geological track annealing temperatures for these two minerals which are estimated to be 260 ± 20°C and 80 ± 10°C respectively. Both sphene and apatite ages decrease from west to east across western Victoria, the sphenes ranging from 470±28 to 355±19 m.y. The Wando Vale granodiorite and Dergholm granite from the Dundas Tableland of far‐western Victoria have sphene ages of 470 ± 28 m.y. and 452 ±16 m.y. respectively, clearly suggesting a relationship to the Ordo‐vician granitic rocks of southeastern South Australia. Fission‐track ages from the numerous post‐tectonic granites in the Ballarat Trough fall into two distinct groups. Rocks from the western area have sphene ages in the relatively narrow range 393 ± 14 m.y. suggesting emplacement in the Early Devonian time whereas those in the east have sphene ages of 362±7 m.y. (near the Devonian‐Carboniferous boundary). Over the temperature interval recorded by sphene‐apatite pairs, cooling of the granitic rocks was very slow ranging from 0.8 to 5.3°C/m.y. Cooling in this range was probably controlled by uplift and erosion of overburden during a long period of post‐tectonic relaxation. Corresponding uplift rates are estimated to be 0.03 to 0.18 km/ m.y. assuming a normal continental geothermal gradient of 30°C/km. Below 80°C average cooling and uplift rates were probably about l°C/m.y. and 0.03 km/m.y. respectively so that cooling was essentially complete within about 80 m.y. of the apatite ages.

ISSN:0016-7614    

DOI:10.1080/00167617808729039

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The granulite‐facies rocks in the Tomkinson Ranges of central Australia are dominated by layered felsic (quartzofeldspathic) gneisses with minor interbanded mafic, calcareous, ferruginous, and quartzitic granulites. They are regarded as representing a middle Proterozoic metasedimentary and/or metavolcanic sequence which has undergone anhydrous granulite‐facies metamorphism approximately 1200 m.y. ago. Conditions of metamorphism have been derived from a petrogenetic grid based on several experimentally determined reactions and give estimates of 10–11 kb pressure and 950–1000°C. Such metamorphism could take place close to the base of the crust with a moderate geothermal gradient of 25–30°C/km.

ISSN:0016-7614    

DOI:10.1080/00167617808729040

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

ISSN:0016-7614    

DOI:10.1080/00167617808729041

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

ISSN:0016-7614    

DOI:10.1080/00167617808729042

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor