摘要:

The southern part of the New England Orogen in the Hunter‐Myall region of NSW consists of the southeasterly extremity of the Tamworth Belt, a region of Devonian‐Carboniferous shelfal deposition between a volcanic arc in the west and a deep water accretionary wedge in the east. These depositional elements, which may have been separated from the Australian continent during the Devonian‐Middle Carboniferous, were deformed during the Permian and Triassic by up to four folding events separated by episodes of granitoid emplacement. Depositional patterns were influenced by five major cycles of sea level changes between the Late Devonian and Permian, an influx of volcanic detritus from an arc which changed in composition from andesitic in the Devonian, through dacitic in the Early Carboniferous to mainly rhyolitic in the Late Carboniferous, and in the Early Carboniferous by penecontemporaneous faulting within the shelf. The overall Carboniferous pattern of deposition was regressive. Rapid southerly movement of the Yarrol‐New England Orogen and possible accretion with the Australian continent in the mid‐Carboniferous coincided with the culmination of volcanic activity, a widespread disconformity, and a rapid change of climate that led to the extinction of the cosmopolitan marine invertebrate fauna, its replacement by the cold water Gondwanan fauna, and establishment of a widespread ice cap. The first orogenic event late in the Carboniferous was followed by rifting and subsidence of the Sydney Basin on the south and west flanks of New England. Folding of the southern Tamworth Belt and injection of serpentinite into the Peel and Manning Fault Systems took place in the Early Permian and was followed by emplacement of the Barrington Tops Granodiorite, and further folding in the Late Permian was similarly followed by intrusion of the New England Batholith. The initial folding generated active basins of deposition (Stroud‐Gloucester Syncline) in which Permian marine and coal measure sediments were deposited. Uplift associated with Late Permian or Triassic granitoid intrusion caused the detachment of Carboniferous blocks which slid south and southwest, generating a low angle thrust along southern parts of the Hunter Fault System. Final folding in the Late Triassic may have been related to dextral movement along the Demon Fault in the northern New England Orogen.

ISSN:0812-0099    

DOI:10.1080/08120098708729391

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The Early Devonian Boggy Plain Supersuite is a belt of I‐type granitic and volcanic rocks extending for over 500 km in the central Lachlan Fold Belt. It has a distinctive composition and origin. Compared with other Lachlan Fold Belt I‐types, rocks of the supersuite are high in Cu and incompatible elements (K, Ba, Sr, Rb, La, Ce, U, and Th). The source for the magmas is interpreted to have been an incompatible element‐rich gabbroic layer, underplated at the base of the crust in the Ordovician. This layer is inferred to correspond to a belt of Ordovician shoshonitic basaltic volcanic rocks that has a strikingly similar geographical distribution to the supersuite. Compositional variation in the supersuite is ascribed to fractional crystallization, in contrast to most other I‐type magmas of the Lachlan Fold Belt which owe most of their compositional variation to fractionation by restite unmixing. This contrast resulted from differences in source rocks, with the Boggy Plain Supersuite being derived from basaltic sources at high temperatures, and the restite‐bearing I‐types being derived from more felsic sources at lower temperatures. The proposed crustal source for the supersuite magmas is consistent with the orogenic evolution in the Lachlan Fold Belt being mainly related to reworking of pre‐existing crust, and has no analogy in the evolution of modern continental margin orogenic zones.

ISSN:0812-0099    

DOI:10.1080/08120098708729392

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Detailed geological mapping and drilling has shown that the contact between the Cambrian volcano‐sedimentary sequence at Rosebery and the Mt Read Volcanics is formed by a major thrust fault dipping east at 40° and having a displacement of at least 1.5 km. The sedimentary sequence is part of the Dundas Group, a Middle to Late Cambrian forearc‐like sequence which unconformably overlaps the volcanics south of Rosebery. The Rosebery Thrust Fault marks the eastern boundary of a zone of folding, faulting and disruption which affects the Dundas Group and the tectonically interfingered and underlying basaltic greywacke‐mudstone sequence of the Crimson Creek Formation. At least some of this deformation occurred prior to deposition of the Ordovician Limestone, as evidenced by marked angular discordances. The complex area can be interpreted as a Cambrian accretionary prism‐forearc‐arc sequence developed above an east‐dipping subduction zone.

ISSN:0812-0099    

DOI:10.1080/08120098708729393

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Along part of the Precambrian‐Palaeozoic boundary in northern Queensland adjacent Palaeozoic flysch sequences (1) are separated by major reverse faults, (2) differ markedly in sedimentary characteristics and (3) have anomalous stratigraphic relations suggesting that they were originally deposited far apart. Internally, the sequences young mainly to the west towards the basement. These relationships suggest a tectonic model in which the Palmerville Fault is the principal fault in a complex imbricate thrust system that has resulted in the basement rocks over‐riding sediments of the Hodgkinson Province. The Palmerville Fault has been steepened by later movements on the underlying faults and by regional shortening. The fault is localized along a pre‐existing (?)Precambrian mylonite zone. A minimum age of Late Carboniferous (300 Ma) has been obtained for the last major fault movement by K‐Ar dating of granitoids intruding the fault.

ISSN:0812-0099    

DOI:10.1080/08120098708729394

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Foliated portions of the Early Devonian Bega Batholith were developed in an apparent flattening field contemporaneous with their plutonic emplacement. Overprinting the foliated portions of the granites are a series of Early‐Middle Devonian ductile shear zones characterized by mylonitic rocks with dextral horizontal movement. The principal shortening during the ductile shear zone development has a trend of 140°. Brittle deformation, confined to narrow gouge and microbreccia zones, is superimposed on the features of ductile deformation. The brittle features represent deformation at higher crustal levels with the orientation of the principal shortening becoming almost north‐south.

ISSN:0812-0099    

DOI:10.1080/08120098708729395

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Nepheline hawaiite southeast of Woolomin, NSW, has been examined in terms of its composition and inclusions. The host is a fine grained, occasionally vesicular nepheline hawaiite (100 Mg/Mg + Fe2+[henceforth Mg'] = 51.5;ne=11.93) with phenocryst olivine, and groundmass clinopyroxene, brown amphibole, titanomagnetite, and plagioclase. The inclusions are dominantly single crystals of kaersutite, anorthoclase, and rare brown mica, the latter falling into two groups based on TiO2content. Only two poly‐crystalline fragments have been recovered: one is a cumulate‐textured hornblende lherzolite (ol + cpx + amph + opx), and the second comprises complexly zoned clinopyroxene enclosing spinel and amphibole. In this second fragment, silicate compositions are similar to phenocrysts and groundmass, and this (combined with textural evidence for rapid cooling) suggests the xenolith is cognate and low pressure. Published experimental work supports both mica and amphibole as liquidus phases in chemically evolved (i.e. low Mg') rocks such as nepheline hawaiites and mugearites. However, as crystals are large, insufficient time would have elapsed for crystallization, Furthermore, two distinct compositions for biotite xenocrysts do not support a cognate origin. A ruptured vein system (suggested for other megacryst occurrences) is not favoured, as polycrystalline fragments are noticeably absent. Instead, it is speculated that both mica and amphibole grew as discrete crystals at low pressure in rock cavities and were mechanically stripped by the magma immediately prior to eruption. The absence of higher pressure (e.g. spinel‐bearing) inclusions and the low Mg’, Cr, and Ni of the host are consistent with slow magma rise and attendant gravitational settling of inclusions, and mafic mineral fractionation.

ISSN:0812-0099    

DOI:10.1080/08120098708729396

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The Late Ordovician Abercrombie Beds, south of Reids Flat, New South Wales, and adjacent to the Wyangala Batholith, show evidence of three successive fold episodes. First generation folds are tight to isoclinal, with fold axes ranging from vertical to horizontal and north‐trending, and steep axial‐plane slaty cleavage. Second generation folds are steeply plunging, tight to open with north‐striking axial planes. In pelitic rocks the axial plane structure is a crenulation cleavage which overprints the slaty cleavage. The first two fold episodes were accompanied by greenschist‐facies metamorphism. Granite emplacement occurred prior to the second fold episode. A third deformation was of relatively mild intensity and produced open, north‐trending folds with axial planes dipping moderately to the east, and crenulation cleavage as the axial plane structure in pelitic rocks. These latest folds are correlated with the latest folds in the Abercrombie Beds north of the Abercrombie River. The mapped area has no apparent macroscopic structure and may be considered as a single domain.

ISSN:0812-0099    

DOI:10.1080/08120098708729397

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Postcratonization intrusions in the Yilgarn Block of Western Australia are predominantly dykes with high length/width ratios and sharp contacts with minimal thermal metamorphism of country rock. Dyke frequency and number of relative age relationships increase towards the exposed margins of the Yilgarn Block. Dykes in the northern, southern and western margins of the Yilgarn Block are mafic, ranging from gabbro to magnetite‐rich leucodolerite, and have apparently been intruded over a long time interval in response to periodic reactivation of the tectonically active craton margins. Dykes in the central Yilgarn Block range from porphyritic olivine picrite to magnetite‐rich quartz dolerite and display a spectrum of chemical compositions with an overall trend of tholeiitic iron‐enrichment. The concentration of both Archaean and Proterozoic rocks of high‐Mg nature in the central Yilgarn Block is suggestive of a fundamental control, perhaps in the mantle source area, and also indicates that ultramafic magmas were generated in the area over an extensive time interval. Dykes in the central Yilgarn Block were emplaced in tensional fractures from the Late Archaean until the culmination of a major marginal crust‐forming event at about 2000 Ma. On the basis of the limited data available, the dykes are similar to poststabilization swarms in other cratonic nucleii.

ISSN:0812-0099    

DOI:10.1080/08120098708729398

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

ISSN:0812-0099    

DOI:10.1080/08120098708729399

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

ISSN:0812-0099    

DOI:10.1080/08120098708729400

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor