Genesis and evolution of low-Al orthopyroxene in spinel peridotite xenoliths, Grand Canyon field, Arizona, USA

Smith, Douglas J.; Riter, J. C. Alexis

doi:10.1007/s004100050288

Cited by 49 publications

(26 citation statements)

References 61 publications

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“…The orthopyroxenes in the OJOB metaperidotites are invariably enstatites that are abnormally low in Al 2 O 3 , Cr 2 O 3 , and CaO for magmatic phases, even considering the relatively depleted and hence distinctly low-Al nature of the host metaperidotites. Similarly low contents of these components are typically reported for metamorphic enstatites (Pinsent and Hirst, 1977;Gole et al, 1987;Mancini et al, 1996;Smith and Riter, 1997;Trommsdorff et al, 1998). The common occurrence of chromian chlorite inclusions in OJOB metaperidotite enstatites suggests that early-formed chlorite captured most of the primary silicate phase Al and Cr before enstatite crystallization.…”

Section: Factors Contributing To Mineral Compositionsmentioning

confidence: 87%

“…The common occurrence of chromian chlorite inclusions in OJOB metaperidotite enstatites suggests that early-formed chlorite captured most of the primary silicate phase Al and Cr before enstatite crystallization. Early crystallization of chlorite and its wide thermal stability in metamorphic ultramafic rocks has been observed elsewhere (Gole et al, 1987;Smith and Riter, 1997;Barnes, 2000). In the Rapasaari case (Zone D), Al is also present in the Mg-Al-spinel phases that replace early chlorite.…”

Section: Factors Contributing To Mineral Compositionsmentioning

confidence: 94%

“…Relatively low pressure amphibolite-facies regional metamorphism of Archean komatiites and orogenic ultramafic intrusives have been investigates by Gole et al (1987) and Mancini et al (1996), respectively, the former authors giving special emphasis to the role of the fluid phase. Conversely, Smith and Riter (1997), Trommsdorff et al (1998), and Puga et al (1999) have addressed the high-pressure metamorphism of ultramafic rocks.…”

Section: Introductionmentioning

confidence: 96%

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Metamorphism and Chromite in Serpentinized and Carbonate-Silica-Altered Peridotites of the Paleoproterozoic Outokumpu-Jormua Ophiolite Belt, eastern Finland

Säntti

Kontinen

Sorjonen-Ward

et al. 2006

International Geology Review

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The 1.95 Ga Outokumpu-Jormua ophiolite belt of eastern Finland contains numerous mafic-ultramafic, predominantly peridotitic bodies which, despite amphibolite-facies metamorphism and pervasive deformation, retain compelling evidence of a residual mantle origin. These rocks therefore currently represent the oldest documented examples of exhumed mantle lithosphere, so information concerning their primary igneous mineral assemblages and textures and chemical and isotopic characteristics is of considerable scientific value. Although several earlier studies have argued for the preservation of primary mineral assemblages, field and petrographic evidence presented here show that the protolith peridotites had already experienced pervasive low-T serpentinization prior to Svecofennian orogenic deformation, during which they were progressively deserpentinized via antigorite metaserpentinites to olivine-talc-anthophyllite-enstatite-bearing metaperidotites. Evidence is also presented to show that the premetamorphic serpentinization event was closely followed by extensive low-T (< 250°C) metasomatic alteration of the marginal parts of the ultramafic bodies to carbonate-silica rocks which, during the subsequent prograde metamorphism, were converted to the distinctive chromite-bearing carbonate-skarn-quartz rocks comprising the Outokumpu rock assemblage. Because these quartz rocks are intimately associated with the Outokumpu Cu-Co-Zn-Ni deposits and have generally been regarded as metamorphosed siliceous seafloor exhalative deposits, the revised interpretation presented here has important implications for ore formation as well. Equilibrium mineral assemblages in the interior parts of the ultramafic bodies (low XCO 2 ) define four regional metamorphic zones, expressed as an east to west increase in the peak dehydration temperatures from 500° to 775ºC, at 3-5 kbar. Large ultramafic bodies commonly show core to margin zoning from talc via anthophyllite-to enstatite-bearing assemblages, reflecting synmetamorphic core-margin gradients in XCO 2 , attributed to infiltration of CO 2 released by decarbonation reactions in previously formed talc-carbonate and carbonate-silica alteration zones.The only primary igneous phase identified in this study was chromite, which occurs as scattered relict cores within large altered grains. These are relatively common in metaserpentinites, but also occur in metaperidotites and even in carbonate-skarn-quartz rocks. Even though Mg, Fe 2+ , and Zn abundances in these relict chromites may have been somewhat modified, absolute concentrations and ratios of Cr and Al appear to be essentially unmodified. The lobate to amoeboid morphology and observed Cr# range (0.41-0.67) of the best-preserved grains are more consistent with residual depleted lherzolite to harzburgite textures than a cumulate origin. However, during regional metamorphism, most mantle chromites were either pervasively altered to ferrian chromites and Cr-magnetites or (where CO 2 and S fugacities were high, such as within smaller ultramafic bod...

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Section: Factors Contributing To Mineral Compositionsmentioning

confidence: 87%

Section: Factors Contributing To Mineral Compositionsmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 96%

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Metamorphism and Chromite in Serpentinized and Carbonate-Silica-Altered Peridotites of the Paleoproterozoic Outokumpu-Jormua Ophiolite Belt, eastern Finland

Säntti

Kontinen

Sorjonen-Ward

et al. 2006

International Geology Review

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“…Similar orthopyroxene-rich mantle domains are found at many places worldwide: Papua New Guinea [7], USA [38,43,44], Kamchatka [40], Canada [45], Andes [46], Philippines [47], Zabargard peridotite, Red Sea [48], and Cabo Ortegal peridotite, Spain [49]. Most these localities have a close spatial and temporal relation to subduction.…”

Section: Geodynamic Implicationsmentioning

confidence: 54%

Olivine Websterite Veins Cutting the Rabrovo Serpentinites (South Macedonia): New Evidence of the Arc Setting of the East Vardar Ophiolites?

Boev¹,

Prelević²,

Božović³

et al. 2017

Contributions

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The study reports petrography and mineral chemistry data about an ultramafic vein that cuts the Rabrovo serpentinite (near Valandovo, Southern Macedonia). The serpentinite occurs as a block within a shearing zone of the East Vardar Zone tectonic mélange. The vein corresponds to medium-grained olivine websterite that sometimes displays cumulate-like textures. It is composed of low-Al orthopyroxene (Mg#[mol MgO*100/(MgO + FeO o C. Its pyroxene-rich modal composition suggests that this rock cannot represent a normal lithospheric mantle. Instead, it is supposed that it was formed via magmatic precipitations in the mantle lithosphere. In addition, the Rabrovo olivine websterite shows similar mineral chemical compositions to many other orthopyroxene-rich lithologies worldwide, which origin is commonly associated with subduction settings. Therefore, its presence is considered as additional evidence that the East Vardar ophiolites represent typical supra-subduction ophiolites.

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“…Such low‐Al orthopyroxene might indicate equilibrium with chlorite (cf. Smith & Ritter, 1996; Trommsdorff et al ., 1998 ). In garnet‐bearing harzburgite, orthopyroxene is richer in Fe, Al, Cr and Ca, and has less Mg than in olivine orthopyroxenite.…”

Section: Mineral Chemistrymentioning

confidence: 99%

Deformation, high‐pressure metamorphism and exhumation of ultramafic rocks in a deep subduction/collision setting (Cabo Ortegal, NW Spain)

Ibarguchi

Ábalos

Azcarraga

et al. 1999

Journal Metamorphic Geology

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New petrological and microstructural data from various metaperidotite ‘boudins’ within large ductile shear zones in the Cabo Ortegal allochthonous complex in NW Spain have important implications for the tectonic models of the area. The peridotites (mylonitic garnet harzburgite, Ti‐clinohumite and magnesite–olivine orthopyroxenite) contain mineral assemblages that equilibrated at high‐ to ultra‐high‐pressure metamorphic conditions as well as microstructures of tectonic origin formed at temperatures well above 800 °C. Olivine and orthopyroxene fabrics resulted from flow at high temperature (>1000 °C) and solid‐state non‐coaxial plastic flow at intermediate temperature (800–900 °C). Flow caused dynamic recrystallization and formation of moderate to strong lattice preferred orientations under low to moderate differential stresses and strain rates characteristic of upper mantle and deep crustal deformation. The microstructures and textural relationships suggest that the mylonitic garnet harzburgite represents mantle fragments with lithospheric and asthenospheric imprints, whereas the olivine orthopyroxenite resulted from serpentinite burial to depths where it acquired a characteristic high/ultra‐high‐pressure metamorphic signature. Both types of ultramafites converged to a common site in a subduction zone that was later incorporated during continental collision to the NW Iberian Massif as exotic, allochthonous complexes that record structural and metamorphic evidence of the earliest phases of the Hercynian orogeny.

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Genesis and evolution of low-Al orthopyroxene in spinel peridotite xenoliths, Grand Canyon field, Arizona, USA

Cited by 49 publications

References 61 publications

Metamorphism and Chromite in Serpentinized and Carbonate-Silica-Altered Peridotites of the Paleoproterozoic Outokumpu-Jormua Ophiolite Belt, eastern Finland

Metamorphism and Chromite in Serpentinized and Carbonate-Silica-Altered Peridotites of the Paleoproterozoic Outokumpu-Jormua Ophiolite Belt, eastern Finland

Olivine Websterite Veins Cutting the Rabrovo Serpentinites (South Macedonia): New Evidence of the Arc Setting of the East Vardar Ophiolites?

Deformation, high‐pressure metamorphism and exhumation of ultramafic rocks in a deep subduction/collision setting (Cabo Ortegal, NW Spain)

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