Igneous Albitite Dikes in Orogenic Lherzolites, Western Pyrenees, France: A Possible Source for Corundum and Alkali Feldspar Xenocrysts in Basaltic Terranes. Ii. Geochemical and Petrogenetic Considerations

Pin, Christian; Monchoux, Pierre; Paquette, Jean‐Louis; Azambre, Bernard; Wang, Ru Cheng; Martin, Robert F.

doi:10.2113/gscanmin.44.4.843

Cited by 46 publications

(34 citation statements)

References 73 publications

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“…While igneous albitite has been reported in some localities (e.g., [54]), these occurrences are rare compared to metasomatic albitites [17]. The meter-scale tabular or lenticular geometry of the Bear Basin albitite is quite similar to several other tabular white rock bodies that crop out within the biotite ± garnet gneiss in the region ( Figure 2E).…”

Section: Origin Of the Albititementioning

confidence: 81%

Dating Metasomatism: Monazite and Zircon Growth during Amphibolite Facies Albitization

et al. 2018

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Abstract:We present coupled textural observations and trace element and geochronological data from metasomatic monazite and zircon, to constrain the timing of high-grade Na-metasomatism (albitization) of an Archean orthogneiss in southwest Montana, USA. Field, mineral textures, and geochemical evidence indicate albitization occurred as a rind along the margin of a~3.2 Ga granodioritic orthogneiss (Pl + Hbl + Kfs + Qz + Bt + Zrn) exposed in the Northern Madison range. The metasomatic product is a weakly deformed albitite (Ab + Bt + OAm + Zrn + Mnz + Ap + Rt). Orthoamphibole and biotite grew synkinematically with the regional foliation fabric, which developed during metamorphism that locally peaked at upper amphibolite-facies during the 1800-1710 Ma Big Sky orogeny. Metasomatism resulted in an increase in Na, a decrease in Ca, K, Ba, Fe, and Sr, a complete transformation of plagioclase and K-feldspar into albite, and loss of quartz. In situ geochronology on zoned monazite and zircon indicate growth by dissolution-precipitation in both phases at~1750-1735 Ma. Trace element geochemistry of rim domains in these phases are best explained by dissolution-reprecipitation in equilibrium with Na-rich fluid. Together, these data temporally and mechanistically link metasomatism with high-grade tectonism and prograde metamorphism during the Big Sky orogeny.

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Section: Origin Of the Albititementioning

confidence: 81%

Dating Metasomatism: Monazite and Zircon Growth during Amphibolite Facies Albitization

et al. 2018

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“…Beside fragments of serpentinized and talcified lherzolites, the breccia contains angular clasts of undeformed to cataclastic granitoids, gneissic granitoids, various types of mica schists (some of them bearing andalusite or garnet porphyroblasts), abundant thinly layered quartz‐rich mylonites (previously considered as thinly bedded quartzites by Fortané et al, ), thinly foliated black schists, chlorite schists, and rare Jurassic and Cretaceous marbles (Figure ). Albitite clasts derived from corundum‐ and zircon‐bearing magmatic albitite intrusions crosscutting the ultramafic massif (Monchoux et al, ; Pin et al, ; Pin et al, ) are also found reworked in the breccia. Close to Mer de Her, to the NW of the massif, the breccia is monogenic and bears the characteristics of a tectonic breccia (Figures f and f).…”

Section: Lithology and Deformation Of The Continental Basement Unitsmentioning

confidence: 99%

How Do Continents Deform During Mantle Exhumation? Insights From the Northern Iberia Inverted Paleopassive Margin, Western Pyrenees (France)

et al. 2019

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Extreme crustal thinning associated with subcontinental mantle exhumation characterizes the distal domain of some current, magma‐poor continental passive margins. Since these domains lie at abyssal depths and are hardly accessible, their internal structure and the finite strain of the stretched crust are not directly observed and are only inferred. A detailed field study was conducted on exceptionally preserved Cretaceous distal margin analogs in two key areas of the western Pyrenees (North Pyrenean Zone): the Urdach and Saraillé ultramafic massifs in the Chaînons Béarnais range. A tight sampling allowed us to characterize the conditions of the ductile deformation of the continental crust exhumed together with the mantle. New 40Ar/39Ar dating on muscovite constrains the timing of the last deformation of the continental crust in relation with mantle exhumation to the late Albian. We propose a new reconstruction for the distal part of the North Iberian paleopassive margin based on the following constraints: (i) post‐Silurian Paleozoic rocks are never found in the distal domain; (ii) lower crustal levels are not found in the exhumed crustal units; (iii) extension in the pre‐Silurian series is accomplished by lenticular deformation and pervasive ductile flattening through anastomosing extensional mylonitic shear zones at temperatures of 350–450 °C; and (iv) at the final step of exhumation, only pre‐Silurian crustal lenses remained welded on the exhumed mantle. Finally, we discuss the importance of the crustal structure inherited from previous Paleozoic and Mesozoic tectonic events and we state that mantle exhumation was partially achieved before the Cretaceous North Pyrenean rifting.

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“…These also have large Nb, Th, U and LREE contents and are inferred to have crystallized from volatile-rich sources within the mantle (Stähle et al, 1990). The probable relationship between the Pyrenean dykes and megacryst suites was recognized by Pin et al (2006). The relative abundance of anorthoclasite suite megacrysts and xenoliths in Scotland prompts the suggestion that comparable salic dykes play a significant role near the crustmantle boundary beneath much of Scotland, especially the Midland Valley.…”

Section: Salic Dykes and Veins In The Deep Lithospherementioning

confidence: 99%

Megacrysts and salic xenoliths in Scottish alkali basalts: derivatives of deep crustal intrusions and small-melt fractions from the upper mantle

Upton¹,

Finch²,

Słaby³

2009

Mineral. mag.

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ABSTR ACTCa-poor and typically Na-rich feldspar megacrysts are common associates of spinel lherzolitic and pyroxenitic xenoliths in Scottish alkalic basalts. Associated megacrysts and composite megacrysts and salic xenoliths include apatite, magnetite, zircon, biotite, Fe-rich pyroxene(s) and corundum. The salic xenoliths and related megacrysts are referred to collectively as the 'anorthoclasite suite': the majority of the samples are inferred to derive from the disaggregation of coarse-grained, typically Na-rich, syenitic protoliths at depth. Rare occurrences of euhedral anorthoclase megacrysts, together with zircon dating, imply that the suite crystallized at, or very shortly before, their entrainment by the basaltic host magmas. Some evidence suggests that the anorthoclasite suite protoliths lie within ultramafic (pyroxenitic) domains in the deep crust. The latter are inferred to be pegmatites, crystallized from carbonated trachytic magmas with widely variable Ca, Na, K, Ba and trace-element contents, and to have ranged from metaluminous to peraluminous. Crystal zonation and resorption textures within the salic xenoliths imply that the crystallization of the parent magmas was complex. Confirmation of this comes from cathodoluminescence studies of the feldspars showing that early ('primary') anorthoclases and potassian albites exhibit partial replacement by a more potassic feldspar. A third generation of potassic feldspar (enriched in an assortment of trace elements and deduced to have crystallized from a carbonated high-K melt) forms transecting zoned veins in which carbonate fills the axial zone.Whereas most of the anorthoclasite suite materials are inferred to have grown from metaluminous magmas, the occurrence of magmatic corundum in salic xenoliths indicates crystallization from magmas that were peraluminous. The corundum-bearing samples also contain Nb-rich oxide minerals and their associated feldspars have the highest rare-earth element (REE) contents. Accordingly, the peraluminous trachyte magmas are deduced to have been specifically enriched in high field-strength trace elements. It is proposed that formation of the anorthoclasite suite protoliths is a phenomenon closely related to that of salic glass 'pockets', well known from spinel lherzolite xenoliths around the world. Not only are there compositional affinities, but both sets of phenomena appear to have closely pre-empted the ascent of alkali basalt (host) magmas. We propose that the two sets of phenomena are linked and that the anorthoclasite suite derived from coarse-grained sheets, generated by the aggregation of salic melt fractions rising from the shallow mantle and heralding the onset of basaltic magmatism.

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Igneous Albitite Dikes in Orogenic Lherzolites, Western Pyrenees, France: A Possible Source for Corundum and Alkali Feldspar Xenocrysts in Basaltic Terranes. Ii. Geochemical and Petrogenetic Considerations

Cited by 46 publications

References 73 publications

Dating Metasomatism: Monazite and Zircon Growth during Amphibolite Facies Albitization

Dating Metasomatism: Monazite and Zircon Growth during Amphibolite Facies Albitization

How Do Continents Deform During Mantle Exhumation? Insights From the Northern Iberia Inverted Paleopassive Margin, Western Pyrenees (France)

Megacrysts and salic xenoliths in Scottish alkali basalts: derivatives of deep crustal intrusions and small-melt fractions from the upper mantle

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