The Geochemistry of the Lower Proterozoic Willyama Complex Volcanics, Broken Hill Block, New South Wales

James, Sarah; Pearce, Julian A.; Oliver, R.

doi:10.1144/gsl.sp.1987.033.01.27

Cited by 24 publications

(15 citation statements)

References 25 publications

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“…Whereas in the Zr vs. Ti plot (Fig. 5b), samples show increasing of Ti trend with Zr, indicating clinopyroxene and plagioclase as crystallization phases (James et al, 1987). Geochemical data are thus consistent with clinopyroxene and plagioclase being the principal fractionating phases.…”

Section: Geochemical Characteristics and Classificationsupporting

confidence: 57%

Petrogenetic evolution of the felsic and mafic volcanic suite in the Siang window of Eastern Himalaya, Northeast India

Singh

2012

Geoscience Frontiers

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The Abor volcanics outcroping in the core of the Siang window in the Eastern Himalaya comprise voluminous mafic volcanics (47%e56% w(SiO 2 )), with subordinate felsic volcanics (67%e75% w(SiO 2 )). The felsic volcanics are dacitic to rhyolitic in composition and are typically enriched in LREE (La/Sm N Z 3.09e3.90) with high REE contents (256e588 ppm), moderately fractionated REE patterns (Ce N /Yb N Z 6.54e9.52) and pronounced negative Eu anomalies (Eu/Eu* Z 0.55e 0.72). Wide variations in Rb/Zr, K/Rb and La/Sm ratios suggest that they were derived from magmas which were randomly contaminated with crustal material. Chemical characteristics and petrogenetic modelling indicate that the dacites were generated by w15% partial melting of a mafic source leaving a residue with 55% plagioclase, 14% orthoclase, 18% clinopyroxene, 5% orthopyroxene, 8% hornblende. The silica-rich rhyodacites and rhyolites were derived from a dacite magma source by a higher degree (>45%) fractional crystallization of an assemblage consisting of 70% plagioclase, 12% clinopyroxene, 7% amphibole and 11% magnetite. The associated LREE-LILE enrichment and pronounced negative GEOSCIENCE FRONTIERS journal homepage: www.elsevier.com/locate/gsf GEOSCIENCE FRONTIERS 3(5) (2012) 613e634 anomalies for HFSE (Nb, P, and Ti) exhibited by these felsic volcanics are characteristic of continental rift volcanism, implying that they were emplaced during lithospheric extension. ª 2012, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. All rights reserved.

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Section: Geochemical Characteristics and Classificationsupporting

confidence: 57%

Petrogenetic evolution of the felsic and mafic volcanic suite in the Siang window of Eastern Himalaya, Northeast India

Singh

2012

Geoscience Frontiers

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“…The presence of deep-seated faults associated with rifting may have provided the pathways for hydrothermal fluid flow. In this model the metals may be leached from surrounding rocks by the convection of hot ocean water (as proposed by Phillips et al, 1985 andJames et al, 1987). The quartz + garnet + gahnite rocks may also have formed as exhalites as did siliceous ores at Kuroko (both sets of rocks have 81so values of around 10%o).…”

Section: Mineralization Associated With Volcanismmentioning

confidence: 93%

Regional oxygen isotope zonation at Broken Hill, New South Wales, Australia; large-scale fluid flow and implications for Pb-Zn-Ag mineralization

Cartwright

1999

Economic Geology

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Metasedimentary and metavolcanic rocks at Broken Hill, Australia, show regional-scale lowering of 8•sO values from as high as 16 per mil in Paragon Group metasedimentary rocks to values as low as 7 per mil within a few hundreds of meters of Pb-Zn-Ag orebodies. Such large-scale oxygen isotope resetting cannot be achieved by closed-system processes (such as partial melting or devolatization), implying that the rocks were affected by fluid flow. The preservation of peak metamorphic •sO fractionations between coexisting minerals, and a lack of correlation between 81sO values and the intensity of retrogression, suggests that oxygen isotope resetting occurred at, or prior to, the peak of regional metamorphism. Fluid flow during the peak of regional metamorphism is unlikely due to widespread fluid-absent partial melting and internal buffering of volatile activities at that time. Thus, fluid flow most probably predated regional metamorphism. The association of rocks with low 8•sO values with the Pb-Zn-Ag orebodies suggests a link with mineralization. The 8•sO values of rocks adjacent to the orebodies are similar to those recorded in volcanic-hosted massive sulfide deposits where convective circulation of ocean water has occurred. Base metal mineralization at Broken Hill may have occurred at hydrothermal vents at, or close to, the sea floor producing localized low 8•sO values with later kilometer-scale fluid circulation, possibly driven by the same or related intrusions, eausing regional resetting of oxygen isotopes. However, mineralization in skarn systems associated with pre-regional metamorphic granites is also a plausible model that could explain the regional 8•sO trends and much of the other geochemical data. Alternatively, the large-scale resetting of oxygen isotopes may be unrelated to mineralization. While the stable isotope data may not unambiguously constrain the origin of the base metal orebody, they indicate that mineralization most probably occurred prior to regional metamorphism.

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“… Mid‐ocean ridge basalt (MORB)‐normalized spidergram of Khetri volcanics (samples from Madhan–Kudhan and Kolihan sections) compared with those of basaltic rocks occurring in subduction related tectonic settings, namely, continental margin arc (Condie 1986) and evolved oceanic arc (Pearce 1983). Normalizing values are after Pearce (1982) & James et al . (1987).…”

Section: Discussionmentioning

confidence: 99%

Plate‐plume‐accretion tectonics in Proterozoic terrain of northeastern Rajasthan, India: Evidence from mafic volcanic rocks of north Delhi fold belt

Raza¹,

Khan²,

Azam³

2007

Island Arc

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The northern part of the Aravalli mountain belt of northwestern Indian shield is broadly composed of three Proterozoic volcano-sedimentary domains, i.e. the Bayana, the Alwar and the Khetri basins, comprising collectively the north Delhi fold belt. Major, trace and rare earth element concentrations of mafic volcanic rocks of the three basins exhibit considerable diversity. Bayana and Alwar volcanics are typical tholeiites showing close similarity with low Ti-continental flood basalts (CFB) with the difference that the former shows enriched and the latter flat incompatible trace element and rare earth element (REE) patterns. However, the Khetri volcanics exhibit a transitional composition between tholeiite and calc-alkaline basalts. It appears that the melts of Bayana and Alwar tholeiites were generated by partial melting of a common source within the spinel stability field possibly in the presence of mantle plume. During ascent to the surface the Bayana tholeiites suffered crustal contamination but the Alwar tholeiites erupted unaffected. Geochemically, the Khetri volcanics are arc-like basalts which were generated in a segment of mantle overlying a Proterozoic subduction zone. It is suggested that at about 1800 Ma the continental lithosphere in northeastern Rajasthan stretched, attenuated and fractured in response to a rising plume. The produced rifts have undergone variable degrees of crustal extension. The extension and attenuation of the crust facilitated shallowing of the asthenosphere which suffered variable degree of melting to produce tholeiitic melts -different batches of which underwent different degrees of lithospheric contamination depending upon the thickness of the crust in different rifted basins. The occurrence of subductionrelated basaltic rocks of Khetri Belt suggests that a basin on the western margin of the craton developed into a mature oceanic basin.

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The Geochemistry of the Lower Proterozoic Willyama Complex Volcanics, Broken Hill Block, New South Wales

Cited by 24 publications

References 25 publications

Petrogenetic evolution of the felsic and mafic volcanic suite in the Siang window of Eastern Himalaya, Northeast India

Petrogenetic evolution of the felsic and mafic volcanic suite in the Siang window of Eastern Himalaya, Northeast India

Regional oxygen isotope zonation at Broken Hill, New South Wales, Australia; large-scale fluid flow and implications for Pb-Zn-Ag mineralization

Plate‐plume‐accretion tectonics in Proterozoic terrain of northeastern Rajasthan, India: Evidence from mafic volcanic rocks of north Delhi fold belt

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