A Chemical Study of Serpentinization--Burro Mountain, California

Coleman, Robert G.; Keith, Terry E.C.

doi:10.1093/petrology/12.2.311

Cited by 179 publications

(80 citation statements)

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“…These observations are consistent with synkinematic growth of fibres around clasts and do not support the possibility of a concentration and reorientation of shorter, pre-existing fibres. This mechanism, which increases the abundance of chrysotile by creating newly formed crystals in the schistose zones, is also in accordance with field observations in low-temperature sheared serpentinites that indicate an increase of chrysotile abundance with increasing deformation degree (Page, 1968;Coleman and Keith, 1971;Wicks, 1984).…”

Section: The Formation Mechanism Of Schistosity: a Creep Processsupporting

confidence: 87%

Development of schistosity by dissolution–crystallization in a Californian serpentinite gouge

Andréani

Boullier

Gratier

2005

Journal of Structural Geology

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To understand the behaviour and deformation mechanisms of serpentinites in the seismogenic zone we study the deformation macro-and microstructures of serpentinites along the Santa Ynez Fault in the San Andreas System. At the outcrop scale, deformation is localized in a gouge zone that shows three different structures: (1) micrometric undeformed fragments (clasts) of the previously serpentinized peridotite, (2) localized shear planes (Y and R) and (3) a penetrative schistosity (S). Observations under SEM and TEM reveal that the schistosity corresponds to serpentine fibres, parallel to each other, and whose orientation varies as they wrap around clasts. TEM micro-textures indicate that these long fibres result from continuous syntectonic growth rather than from reorientation of pre-existing fibres implying a slow transfer process that occurs at short distances. We propose a dissolution-diffusion-crystallization process for the formation of the schistosity that corresponds to a low strain-rate creeping process of deformation that can be effective in aseismic fault segments.

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Section: The Formation Mechanism Of Schistosity: a Creep Processsupporting

confidence: 87%

Development of schistosity by dissolution–crystallization in a Californian serpentinite gouge

Andréani

Boullier

Gratier

2005

Journal of Structural Geology

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“…The low CaO contents of the serpentinite relative to Al 2 O 3 indicate Ca loss during serpentinization (Coleman and Keith 1971); a fractionation typically observed during open-system alteration of the oceanic lithosphere. Also, the serpentinites have a higher SiO 2 /MgO than normal Table 2).…”

Section: Discussionmentioning

confidence: 96%

The importance of talc and chlorite “hybrid” rocks for volatile recycling through subduction zones; evidence from the high-pressure subduction mélange of New Caledonia

Spandler

Hermann

Faure

et al. 2007

Contrib Mineral Petrol

161

111

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The transfer of fluid and trace elements from the slab to the mantle wedge cannot be adequately explained by simple models of slab devolatilization. The eclogite-facies mélange belt of northern New Caledonia represents previously subducted oceanic crust and contains a significant proportion of talc and chlorite schists associated with serpentinite. These rocks host large quantities of H 2 O and CO 2 and may transport volatiles to deep levels in subduction zones. The bulk-rock and stable isotope compositions of talc and chlorite schist and serpentinite indicate that the serpentinite was formed by seawater alteration of oceanic lithosphere prior to subduction, whereas the talc and chlorite schists were formed by fluid-induced metasomatism of a mélange of mafic, ultramafic and metasedimentary rocks during subduction. In subduction zones,

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“…Three processes are thought to be the most important in determining the chemical composition of the serpentinite surface rock: magmatic differentiation; sulphide saturation leading to chalcophile element depletion in ultramafic silicates within fertile serpentinites; and chemical weathering, considered to vary in intensity due to differences in the amount of sulphide and subsequent sulphuric acid generation in fertile and sterile serpentinites. Serpentinization can take place without significant metasomatism (Coleman and Keith, 1971;Komor et al, 1985;Donaldson et al, 1986) so that the serpentinization process is probably not as important as magmatic differentiation and sulphur saturation in generating Ni-sulphide ore bodies from ultramafic hosts or in generating the chemical signatures which distinguish the ultramafic hosts.…”

Section: Discussion and Interpretationmentioning

confidence: 99%

An application of lithogeochemistry to the evaluation of the Ni-sulphide ore potential of weathered serpentinites in the Fortaleza de Minas Greenstone Belt, Minas Gerais, Brazil

Oostindiër

Taufen

Vriend

1988

Journal of Geochemical Exploration

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Oostindi~r, J., Taufen, P.M. and Vriend, S.P., 1988. An application of lithogeochemistry to the evaluation of the Ni-sulphide ore potential of weathered serpentinites in the Fortaleza de Minas greenstone belt, Minas Gerais, Brazil. J. Geochem. Explor., 31: 57-73.A practical application of lithogeochemistry to the classification of weathered serpentinites as to whether or not serpentinites are host rocks to Ni-sulphide ore is presented. An effort is made to apply existing concepts used to distinguish between fertile and sterile unweathered ultramafics to explain the observed chemical differences between fertile and sterile weathered serpentinites in southwestern Minas Gerais, Brazil.The data comprise total-attack chemical analyses for A1, Ca, Cr, Cu, Fe, Mg, Mn, Ni, Si, Ti, V, and partial-attack determinations of Cu and Ni as ascorbic acid, hydrogen peroxide-soluble metal. Student's t-tests are used to identify element concentration differences between the two serpentinite groups. Discriminant analysis is used to classify the weathered fertile and sterile serpentinites. Non-linear mapping and fuzzy c-means clustering help to assess the validity of the discriminant analysis. Finally, chemical element associations provide extra information on geological and mineralogical causes that can be responsible for the identified differences.It is found that a clear separation and classification of weathered serpentinites is possible using the procedures presented. The observed chemical differences between fertile and sterile serpentinites are interpreted in terms of original magmatic differentiation, the degree of sulphur saturation of the original magma and the behavior of the derived ultramafic rocks in a tropical weathering environment.+Present address: Shell Internationale Petroleum Maatschappy. B.V.,

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A Chemical Study of Serpentinization--Burro Mountain, California

Cited by 179 publications

References 0 publications

Development of schistosity by dissolution–crystallization in a Californian serpentinite gouge

Development of schistosity by dissolution–crystallization in a Californian serpentinite gouge

The importance of talc and chlorite “hybrid” rocks for volatile recycling through subduction zones; evidence from the high-pressure subduction mélange of New Caledonia

An application of lithogeochemistry to the evaluation of the Ni-sulphide ore potential of weathered serpentinites in the Fortaleza de Minas Greenstone Belt, Minas Gerais, Brazil

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