摘要:

The Munni Munni Complex is a layered sequence of clinopyroxenite, peridotite, and gabbro within the Archean Pilbara Block, Western Australia. The intrusion has been tilted, exposing some 2000 m of layered ultramafic rocks overlain by over 3500 m of gabbroic rocks. The top of the intrusion is hidden under younger sedimentary rocks. It displays many of the features of layered intrusions: rhythmic and cryptic layering, igneous lamination, pseudo‐gravity stratification, slump structures, and cumulus textures. Bulk‐rock analyses for major and trace elements show similar variation with structural height to that described from the Skaergaard, Bushveld, and Stillwater intrusions, although the mineralogical features of the Munni Munni Complex are slightly different. Olivine, clinopyroxene, and plagioclase are the only cumulus phases, and orthopyroxene, clinopyroxene, plagioclase, and Fe‐Ti oxides are the major intercumulus phases. The original magma was probably a tholeiitic basalt which differentiatedin situby fractional crystallization due to effective removal of early formed crystals by settling. Temperatures of crystallization were apparently in the range 1250° to 1200°C, and cooling rates were slow, as evidenced by exsolution features in the pyroxenes and oxides. Pressure was probably low (1–4 kb), indicating normal crystallization in the upper crust.

ISSN:0016-7614    

DOI:10.1080/00167617408728831

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

The term ‘Eyrian Series’, proposed by Woolnough and David in 1926, is here redefined in terms of the Australian Code of Stratigraphic Nomenclature. In conformity with the code the orignal term is changed toEyre Formation.

ISSN:0016-7614    

DOI:10.1080/00167617408728832

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

Pyrite‐rich sulphide with minor chalcopyrite, sphalerite, marcasite, and pyrrho‐tite, occurs in low‐grade metabasaltic rocks near Tumut, New South Wales. The rocks are chemically akin to modern abyssal tholeiites and form part of a well‐developed ophiolite rock assemblage. Rock alteration and sulphide mineral assemblages are similar to those found in pyrite‐rich sulphide deposits in the Troodos ophiolite complex, Cyprus, and in other ophiolite complexes, although low‐grade regional metamorphism has caused textural and mineralogical changes. It is suggested that the Tumut occurrences formed from submarine volcanic exhalations, associated with abyssal theoliite volcanism; and that the ophiolite rock assemblage formed contemporaneously with a sea‐floor spreading episode. The ophiolite rock assemblage was later obducted, perhaps during continental collision.

ISSN:0016-7614    

DOI:10.1080/00167617408728833

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

Igneous rocks dominate over sedimentary rocks in the Mullaley area and are divided, on the basis of field relationships and petrochemistry, into six groups: Garrawilla Volcanics, Nombi Extrusives, Glenrowan Intrusives, Napperby Limburgite, Tambar Trachybasalt, and Bulga Complex.

ISSN:0016-7614    

DOI:10.1080/00167617408728834

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

Over much of arid Western Australia a red and brown hardpan occurs on broad plains; it may lie either on the surface or buried beneath a shallow mantle of soil. It is proposed that, because of its lithological character and its considerable thickness and extent, it should be given the name of Wiluna Hardpan. The proposed type section is north of Wiluna, near Bulloo Downs homestead, where headward erosion of the Ashburton River is exposing sections 30 m deep. Although both ferruginous and calcareous cement may be present, Wiluna Hardpan is largely indurated with silica. It is younger than laterite, but broadly contemporaneous with calcrete and Robe Pisolite. Initially it was probably geographically restricted by a coincidence of suitable conditions of low relief and a climate resulting in episodic flooding and desiccation. Its present distribution is partly controlled by current erosional and depositional processes.

ISSN:0016-7614    

DOI:10.1080/00167617408728835

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

Total fusion40Ar/39Ar ages have been determined on 22 samples, including biotite, muscovite, sanidine, hornblende, plagioclase, pyroxene, and whole rock samples of volcanics. The samples have conventional K‐Ar ages ranging from 14 m.y. to 2000 m.y. The neutron irradiations for the40Ar/39Ar dating were made in the HIFAR reactor, using the standard biotite GA1550 as the flux monitor. The40Ar/39Ar total fusion ages of 14 samples agree to within 2 percent with the conventional isotope dilution K‐Ar ages. The remaining 8 give measured40Ar/39Ar ages from 3 to 9.5 percent greater than the conventional K‐Ar ages. These systematic discrepancies are due to significant neutron flux gradients in the reactor which become apparent because larger amounts of sample, compared with the amount of flux monitor, were used in these cases. With samples laid out in the reactor can as in the present study the precision of the40Ar/39Ar ages is about 2 percent (standard deviation) in the ideal case. Correction factors for interfering argon istopes in HIFAR have been determined: (39Ar/37Ar)ca= 7.44 (± 0.24) x 10‐4; (36Ar/37Ar)ca= 3.05 (± 0.10) x 10‐4; (40Ar/39Ar)K= 0.28±0.03.

ISSN:0016-7614    

DOI:10.1080/00167617408728836

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

The Serpentine Hill Complex is an ophiolite dismembered by tectonic emplacement and subsequent faulting. It consists of ultramafics, gabbros, dolerites, and volcanics (mainly basaltic). The layered ultramafics (dominantly orthopyroxenite and harzburgite) and layered hypersthene gabbro are thought to be cumulates, and have been intruded by pegmatitic gabbro and microgabbros. Three types of serpentinite can be recognized in the western part of the complex, black serpentinites, green serpentinites, and sheared contact serpentinites. The black serpentinites are generally unsheared, consist essentially of lizardite, and have preferentially replaced olivine‐bearing ultramafics. The sheared contact serpentinites consist mainly of chrysotile and antigorite, and may have formed during tectonic emplacement. The formation of the green serpentinites (lizardite‐chrysotile mixtures) appears to have accompanied localized deformation which occurred after tectonic emplacement of the complex.

ISSN:0016-7614    

DOI:10.1080/00167617408728837

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

A matrix of the primary sedimentary features of modern depositional environments has been used as a key for the interpretation of the environments of deposition of the Gosford Formation, which comprises the uppermost 212 m of the Triassic Narrabeen Group on the Central Coast of New South Wales.

ISSN:0016-7614    

DOI:10.1080/00167617408728838

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

ISSN:0016-7614    

DOI:10.1080/00167617408728830

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor