The upper mantle beneath Patagonia, Argentina, documented by xenoliths from alkali basalts

Bjerg, Ernesto; Ntaflos, Theodoros; Kurat, G.; Dobosi, G.; Labudia, Carlos Horacio

doi:10.1016/j.jsames.2004.09.002

Cited by 48 publications

(69 citation statements)

References 25 publications

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“…The values of CaO, Na O and Al O in clinopyroxene, and the Mg# and Cr# of spinels, show a range of variation comparable to previous data from Paso de Indios peridotites [8,10], and are signi cantly depleted compared to the fertile mantle below the Agua Poca region (Group 1 xenoliths of [34]]), and below the Cerro de los Chenques volcano (sample CD61 of [10,28]), which are among the very few examples of fertile spinel lherzolites with Depleted Mantle a nity found in the Argentinean extraAndean back-arc [28,34].…”

Section: Major-element Composition Of Mineralssupporting

confidence: 87%

“…% of clinopyroxene provides evidence that the mantle column beneath the Paso de Indios is signicantly depleted with respect to the modal composition of the Primitive Mantle proposed by Johnson et al [32] (Figure 3). This tendency appears in the majority of Patagonian occurrences of mantle xenoliths [8,10,28,41,42]. The possible relationship of the overall depleted character with episodes of partial melting can be inferred from the relative variation of orthopyroxene (Opx) versus clinopyroxene (Cpx) in the analyzed samples as shown in the Cpx/Opx vs. Cpx plot.…”

Section: Discussionmentioning

confidence: 99%

“…Textures identi ed, in order of decreasing abundance are: porphyroclastic (53%), porphyroclastic to equigranular [32]. The yellow eld represents the variation of anhydrous Patagonian xenoliths from Bjerg et al [8] and Rivalenti et al [10].…”

Section: Petrography and Classi Cation Of The Xenolithsmentioning

confidence: 99%

“…These xenoliths were rst mentioned by Alric et al [18], Labudía [19] and Alric [20]. Later, Rivalenti et al [10] and Bjerg et al [8] included microanalyses obtained in samples from the Paso de Indios area in their regional studies on the Patagonian mantle.…”

Section: Introductionmentioning

confidence: 99%

“…Later, Bjerg et al [7,8], Barbieri et al [9] and Rivalenti et al [10] conducted regional studies based on spinel facies xenoliths collected in the Río Negro, Chubut and Santa Cruz provinces. Among these localities (more than 20), only two contain garnet-bearing peridotites: Pali Aike located in southern Patagonia [11][12][13][14] and Prahuaniyeu, located in northern Patagonia [8,[15][16][17].…”

Section: Introductionmentioning

confidence: 99%

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Short-scale variability of the SCLM beneath the extra-Andeanback-arc (Paso de Indios, Argentina): Evidence from spinel-faciesmantle xenoliths

et al. 2015

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Cenozoic basalts carrying ultrama c mantle xenoliths occur in the Matilde, León and Chenque hills in the Paso de Indios region, Argentina. The mantle xenoliths from the Chenque and León hills mainly present porphyroclastic textures, whereas the Matilde hill xenoliths have coarse-grained to porphyroclastic textures. The equilibrium temperatures are in the range of 780 to 940• C, indicating a provenance from shallow sectors of the lithospheric mantle column that were subjected to a relatively low heat ux at Cenozoic Era. According to the modal compositions of xenoliths, the mantle beneath Matilde and León hills was a ected by greater than 22% partial melting, while less depleted peridotites occur in the Chenque suite (starting from 10% partial melting). Such an observation is con rmed by the partial melting estimates based on Cr# Sp , which vary from 8 to 14% for the selected Chenque samples and from 14 to 18% for the Matilde ones. The common melting trend is overlapped by small-scale cross cutting local trends that may have been generated by open-system processes, such as open-system partial melting and/or post partial-melting metasomatic migration of exotic Na-Cr-rich melts. The two main mineralogical reaction schemes are: i) the dissolution of pyroxenes and the segregation of new olivine in olivine-rich peridotites, and ii) the replacement of primary olivine by orthopyroxene±clinopyroxene in orthopyroxene-rich peridotites. These were produced by channelled and/or pervasive melt extraction/migration. Enhanced pyroxene dissolution is attributed to channelling of silica-undersaturated melts, whereas the replacement of primary olivine by orthopyroxene±clinopyroxene points to reaction with silica-saturated melts. Late disequilibrium reactions identi ed in the xenoliths comprise: the breakdown of orthopyroxene in contact with the host basalt, and (rarely) reaction coronae on orthopyroxene, clinopyroxene and spinel linked to glassy veins. Such features are apparently related to the injection of melt, likely during entrainment into the host basalts and ascent to the surface.

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