Anorthosite Belts, Continental Drift, and the Anorthosite Event

Herz, Norman

doi:10.1126/science.164.3882.944

Cited by 74 publications

(12 citation statements)

References 17 publications

(2 reference statements)

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“…The results of this study indicate that the REE-enriched hematite breccias at Olympic Dam formed by hydrothermal processes with no evidence of intrusion of unusual, Fe-rich magmas at the present level of exposure. Large-scale hydrothermal activity at Olympic Dam probably required a magmatic heat source, perhaps related to incipient rifting of a Proterozoic supercontinent (Herz, 1969;Burke, 1977;Piper, 1983;Bond et al, 1984;Lindsay et al, 1987;Hoffman, 1989).…”

Section: Discussionmentioning

confidence: 99%

Origin of rare earth element-enriched hematite breccias at the Olympic Dam Cu-U-Au-Ag deposit, Roxby Downs, South Australia

Орескес

Einaudi²

1990

Economic Geology

234

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Hematite breccias, the host rocks to Cu-U-Au-Ag ore at the Olympic Dam deposit, occur as steeply dipping, northwest-striking, dikelike bodies within fractured granite. The breccia complex has a strike length of over 5 km and extends to depths greater than 1 km. Both the deposit as a whole and the individual breccia bodies are zoned from weakly brecciated, sericitized and hematized granite on the margins, through heterolithic breccias, to hematite-quartz microbreccia at the center. Hematite occurs as euhedral laths and fine-grained aggregates in the matrices of all breccia types, in veins and fragments, as pseudomorphs after feldspar, and rarely as pseudomorphs after siderite and magnetite. Relict magnetite is rare, and most iron oxide was deposited as hematite. Heterolithic breccias include fragments of earlier breccia and veins. Minor sedimentary rocks, including bedded hematite and laminated barite, also are present as clast components. In the upper portion of the deposit, volcaniclastic conglomerate and siltstone occur in a fault-bounded block approximately 500 X 500 m in plan view.Copper-iron sulfides occur as interstitial grains (most common), microveinlets, and rare clasts. They are most abundant in heterolithic breccias and are zoned laterally from chalcocitebornitc to chalcopyrite-pyrite. Zonal boundaries are subparallel to steep breccia contacts. Copper-iron sulfides commonly are intergrown with fluorite and locally rim corroded quartz grains. The breccias are highly enriched in light (LREE) and heavy rare earth elements (HREE) (avg = '--5,000 ppm REE in hematite-rich rocks). Total LREE content and La/Lu ratios are correlated with hematite abundance; maximum La values (10,000 X chondrite) occur in hematite-quartz microbreccias from the geographic center of the deposit. Five hydrothermal REE phases have been identified: bastnaesite, fiorencite, monazite, xenotime, and britholite(?). They occur in all breccia types and in a variety of habits: disseminated in quartz-sericite matrices of granite breccia, in quartz-sericite veins, interstitial to hematite laths, intergrown with barite in laminated sedimentary rocks, and as inclusions in hematite and in sulfide grains.The hematite breccias formed by progressive hydrothermal brecciation and iron metasomatism of the granite host. Minor sedimentary components preserved as blocks and fragments within the upper portion of the deposit point to a near-surface environment for the breccia complex. Textural relations indicate that most of the copper was introduced late relative to hematization and brecciation. Based on spatial relations between barren zones, oxidized sulfide grains, and high-grade chalcocite ore, some supergene redistribution of copper probably occurred. The abundance of REE in hydrothermal phases, REE enrichment of altered relative to unaltered wall rock, concentration of REE in the center of the system, and variable slopes of chondrite-normalized patterns, combined with the lack of evidence of intrusion of unusual magmas at the present level of exposu...

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Section: Discussionmentioning

confidence: 99%

Origin of rare earth element-enriched hematite breccias at the Olympic Dam Cu-U-Au-Ag deposit, Roxby Downs, South Australia

Орескес

Einaudi²

1990

Economic Geology

234

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“…It has been suggested that certain unusual igneous changes, apparently restricted to certain times, such as the "anorthosite event" (Herz, 1969) may have been related to extraterrestrial processes such as large meteorite impacts or to the proposed earth-moon separation. The resolation of such questions is still far in the future, but it is reasonablE!…”

Section: Discussionmentioning

confidence: 99%

Possible relations between meteorite impact and igneous petrogenesis, as indicated by the Sudbury structure, Ontario, Canada

French

1970

Bull Volcanol

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“…and in Archaean terrains (>2500 m.y.) and seem to constitute, in paleogeodynamic reconstructions before drifting of the continents, either two broad belts (one in Laurasia and the other in Gondwana) [2] or a unique great circle belt in a super-continent [3]. They are usually associated with mafic rocks of gabbroic or noritic types which may also include troctolites, with intermediate jotunitic rocks (hypersthene monzodiorite, monzonorite) and with acidic rocks (hypersthene monzonite, mangerite, quartz mangerite, charnockite, etc.).…”

Section: Introductionmentioning

confidence: 99%

Trace elements and anorthosite genesis

Duchesne

Demaiffe

1978

Earth and Planetary Science Letters

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Terrestrial massif anorthosites have gained new interest for the understanding of the deep zones of the crust and for the reconstitution of its history in Proterozoic time. The purpose of this paper is to show how trace elements can enlighten two controversial questions in the problem of anorthosites, namely the nature of the parental magma and the process which gives rise to related acidic rocks. Data obtained on rocks and minerals coming from the Rogaland anorthositic province, South Norway, are presented together with those available in the literature. The Sr and Ba in plagioclase and their relationship with Ca and K, K and Rb in rocks and plagioclases, rare earth elements (REE) in cumulate minerals and in various liquids, 87 Sr/ 86 Sr initial ratios on rocks and minerals as well as a few data on transition elements and on 18 O/ 16 O ratios are discussed in the different sections. Quantitative modelling of the behaviour of trace elements is realized mainly by graphical methods in the Bjerkrem-Sogndal layered lopolith and in the Hidra body, both andesine-type massifs. The major conclusions are as follows:(1) The parental magma of the andesine-type massifs has a jotunitic (hypersthene-monzodioritic) composition characterized by variable K/Rb ratios (from 480 to 1700), by the absence of an Eu anomaly, by variable REE contents (from 50 to 220 for La chondrite-normalized content) and by La/Yb ratios almost constant (from 6 to 12), as well as by high Ti and Fe contents, by transition elements indicating calc-alkaline affinities and by 87 Sr/ 86 Sr initial ratios similar to those of rocks derived from the upper mantle or the deep crust.(2) A jotunitic composition appears not to be compatible with the parental magma of the labradorite-type massif anorthosite. The relationship between andesine anorthosite and labradorite anorthosite cannot be described simply in terms of fractional crystallization.(3) Fractional crystallization can explain the succession of rocks from andesine anorthosite to leuconorite, to norite and finally to acidic rocks. In some cases however, namely the Bjerkrem-Sogndal lopolith in Rogaland, contamination by supracrustal material must be invoked and seems to have superimposed its effects on those of fractional crystallization.(4) Deformation, granulation and recrystallization do not appear to fractionate both the major and trace elements of the plagioclase, except Ti which is lowered.

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Anorthosite Belts, Continental Drift, and the Anorthosite Event

Cited by 74 publications

References 17 publications

Origin of rare earth element-enriched hematite breccias at the Olympic Dam Cu-U-Au-Ag deposit, Roxby Downs, South Australia

Origin of rare earth element-enriched hematite breccias at the Olympic Dam Cu-U-Au-Ag deposit, Roxby Downs, South Australia

Possible relations between meteorite impact and igneous petrogenesis, as indicated by the Sudbury structure, Ontario, Canada

Trace elements and anorthosite genesis

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