Rock Nomenclature with Particular Relation to Deformation and Recrystallisation Textures in Olivine-Bearing Xenoliths

Harte, B.

doi:10.1086/628299

Cited by 300 publications

(118 citation statements)

References 15 publications

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“…Textures were described using the classification commonly used for mantle peridotites from massifs and xenoliths [Harte, 1977;Mercier, 1985;Mercier and Nicolas, 1975;Nicolas, 1986a]. The modal composition of peridotites has been obtained by image analysis following the procedure developed by Launeau and Robin [1996] (see Table 1).…”

Section: Methodsmentioning

confidence: 99%

“…[19] The peridotites display three types of textures irrespective of their mineralogy: 30% have granoblastic textures (Figure 3b), 60% coarseporphyroclastic textures (Figure 3c) and 10% fine-porphyroclastic to mylonitic textures in the sense defined by [Harte, 1977;Mercier, 1985;Mercier and Nicolas, 1975;Nicolas, 1986a]. In the granoblastic rocks, olivine is up to 4 to 5 mm in diameter, has subisotropic shapes with curvilinear Du…”

Section: Peridotite Petrography and Texturesmentioning

confidence: 99%

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Along‐ridge petrological segmentation of the mantle in the Oman ophiolite

Monnier

Girardeau

Mée

et al. 2006

Geochem Geophys Geosyst

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[1] Oman ophiolite mantle has been sampled over a distance of about 400 km, all along the paleo-ridge axis. Primary phases have been analyzed in 174 peridotites (mainly harzburgites) and major and trace element contents measured in 90 and 156 samples, respectively. Most samples display depleted characteristics with very low incompatible element bulk rocks and very low HREE contents. On the basis of the spinel Cr# and in agreement with Yb concentrations in the bulk rocks, an average of 16.5% (F max ) of melt extraction is estimated. These rocks show light REE enrichments marked by high LREE/MREE ratios that well correlate with the extent of melting. The light REE were possibly gained during the latest stage of melting in an open-system melting model, or through interaction with influxed fluid after melting. Chemical data have been processed Fourier Transforms to study the along-ridge variations, which gives results similar to those obtained using the seven point running average . When plotted along ridge, spinel Cr# display variations with two types of wavelengths, defining four 50-100 km long segments (70 km in average) and numerous 10-20 km shorter ones making undulations within the longer ones. All segments have a center marked by high values of spinel Cr# (% F max ) and edges with the lowest values. The large, 50-100 km segments (70 km in average) may correspond to large asthenospheric mantle upwellings between major deep mantle discontinuities, while the smaller ones possibly relate more superficial mantle instabilities similar to the structural diapirs of Nicolas et al. (1988a). We consider that the variation in degree of melting in the short-scale instabilities relates fluid/melt flux melting variations. By comparison with mid-oceanic ridge models, the long Oman segments can correspond to second-order segments and the smallest to third-to fourth-order ones. Our data on the geometry of the melting zones will constrain models of the dynamics of the mantle beneath ridges. They provide a new perspective for further characterization of the segments in the Oman ophiolite.

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Section: Methodsmentioning

confidence: 99%

Section: Peridotite Petrography and Texturesmentioning

confidence: 99%

Along‐ridge petrological segmentation of the mantle in the Oman ophiolite

Monnier

Girardeau

Mée

et al. 2006

Geochem Geophys Geosyst

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“…Petrofabric measurements of olivine grains in a representative type "A" spinel lherzolite xenolith indicate a preferred orientation which most closely resembles that of porphyroclastic texture (Mercier & Nicolas 1975), and other crystallographic features are typical of mosaic-porphyroclastic texture described by Harte (1977). Porphyroclastic textures in peridotites are attributed to plastic flow due to mantle shear stress.…”

Section: Discussionmentioning

confidence: 87%

Mafic and ultramafic mantle and deep crustal xenoliths from Banks Peninsula, South Island, New Zealand

Sewell¹,

Hobden

Weaver

1993

New Zealand Journal of Geology and Geophysics

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Mafic and ultramafic xenoliths of spinel lherzolite, wehrlite, websterite, pyroxenite, and metagabbro (mafic granulite) occur in a basanite plug forming Le Bons Bay Peak on the eastern flanks of Akaroa volcano, Banks Peninsula. Spinel lherzolites are assigned to the Cr-diopside xenolith suite and are interpreted to represent fragments of depleted upper mantle derived from a depth of c. 60 km. Pyroxenites belong to the wehrlite series Al-augite xenolith suite and may represent basaltic cumulates derived from differentiation of mafic magma intruded at or near the crust/ mantle boundary. Mafic granulite of gabbroic composition represents a tectonised and partly recrystallised lower crustal basaltic cumulate. Mineral and bulk rock chemistry of the xenoliths suggests that chemical and mineralogical variation in Banks Peninsula magmas could reflect the development of a subcrustal basaltic "underplate". This might explain the trend from extensively modified to relatively unmodified mantlederived magmas through time. The Le Bons Bay Peak xenolith suite may be explained in terms of rapidly rising basanite magma, with entrained spinel lherzolite xenoliths, which incorporated ultramafic cumulates and metagabbro while passing through the crust/mantle boundary region.

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“…The terminology used for the different rock textures is after Harte (1977). Lherzolite vs. harzburgite assignment is based on the presence or absence of clinopyroxene, respectively.…”

Section: Petrography and Mineral Chemistrymentioning

confidence: 99%

Major element and isotope geochemistry (Sr Nd and Hf) of mantle derived peridotites carbonatites and kimberlites from Canada and Greeland insights into mantle dynamics

Bizzarro¹

2003

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Illhérité de la differentiation initiale de la Terre. Notre étude confirme donc qu'une telle hétérogénéité était toujours présente aux environ de 3 Ga, mais plus elusive dans les roches juvéniles d'âge <2.7 Ga. Les nouvelles données isotopiques de l'Hf ici présentées favorisent une source et origine communes pour les carbonatites, kimberlites et certain basaltes océaniques. IV ABSTRACTWe report on the major element composition of a suite of kimberlite-hosted peridotite xenoliths from the northern margin of the western Archean craton of Greenland, as well as the isotopic composition (Nd, Sr and Hf) of carbonatites and kimberlites from eastern Canada and southwestern Greenland.Our results indicate that the lithospheric mantle underneath the Sarfartoq area of southwestern Greenland extends to approximately 225 km, and consists of refractory (olivine Mg # >0.9) harzburgites and lherzolites. Moreover, the Sarfartoq peridotites are not characterized by the OPX enrichment observed in peridotites from the Kaapvaàl craton of South Africa, and show more affinity with peridotites from east Greenland (Wiedemann Fjord), Somerset Island (Canadian arctic) and Tanzania. Detailed analyses of constituent minerals reveal that the lithospheric mantle underneath the Sarfartoq area is compositionally layered as follows: (1) an internally stratified upper layer (70 to 180 km) consisting of coarse, un-deformed, refractory garnet-bearing and garnet-free peridotites and, (2) a lower layer (180 to 225 km) characterized by fertile, CPX-bearing, porphyroclastic garnet lherzolites. The stratification observed in the upper refractory harzburgite layer (70-180 km) is reflected by an increase in fertility (e.g. lower olivine abundance and fosterite content) with depth. The sharp nature of the stratification may indicate a two-step process for the formation of this lithosphère, i.e. multistage growth of the lithospheric root.In Sr values suggests that apatite and carbonate precipitated predominantly under non-equilibrium conditions. The isotopic variations observed within individual hand specimens may therefore reflect larger-(regional) scale open-system processes, possibly involving mixing of carbonatitic melts derived from distinct mantle sources, or from a common isotopically heterogeneous mantle. This analytical technique provides a rapid and effective approach to determine the extent of isotopic heterogeneity within a single sample or individual grains, with analytical precision approaching that obtained by conventional TIMS.High-precision Hf isotopic analyses and U-Pb ages of carbonatites and kimberlites from Greenland and eastern North America, including Earth's oldest known carbonatite (3 Ga), indicate derivation from an enriched mantle source. This previously unidentified mantle reservoir of unradiogenic Hf isotopic composition, preserved in the deep mantle for at least 3 billion years, may account for the mass imbalance in Earth's Hf-Nd budget. Our results show that the Early to mid-Archean terrestrial mantle was isotopically much more...

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Rock Nomenclature with Particular Relation to Deformation and Recrystallisation Textures in Olivine-Bearing Xenoliths

Cited by 300 publications

References 15 publications

Along‐ridge petrological segmentation of the mantle in the Oman ophiolite

Along‐ridge petrological segmentation of the mantle in the Oman ophiolite

Mafic and ultramafic mantle and deep crustal xenoliths from Banks Peninsula, South Island, New Zealand

Major element and isotope geochemistry (Sr Nd and Hf) of mantle derived peridotites carbonatites and kimberlites from Canada and Greeland insights into mantle dynamics

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