Pb-Sr-Nd isotopic behavior of deeply subducted crustal rocks from the Dora Maira Massif, Western Alps, Italy

Tilton, G. R.; Schreyer, Werner; Schertl, Hans‐Peter

doi:10.1016/0016-7037(89)90071-9

Cited by 96 publications

(67 citation statements)

References 24 publications

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“…One possible interpretation is the incorporation of excess Ar. Several studies on highpressure white micas indicated that Ar-Ar ages are geologically meaningless due to excess Ar (Tilton et al 1991;Tonarini et al 1993;Li et al 1994;Arnaud and Kelley 1995;Hacker and Wang 1995). Li et al (1994) and Boundy et al (1997) suggested that excess Ar in Phe is mainly observed in Bt-free UHP-HP rocks.…”

Section: Discussionmentioning

confidence: 99%

Multichronometric Evidence for an In Situ Origin of the Ultrahigh‐Pressure Metamorphic Terrane of Dabieshan, China

Chavagnac

Jahn²,

Villa

et al. 2001

The Journal of Geology

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A B S T R A C TU-Pb zircon data on gneisses indicate a Late Proterozoic protolith at ∼700 Ma at Bixiling and a Late Archean to Early Proterozoic for the Shuanghe sheet within the ultrahigh-pressure metamorphic terrane of Dabieshan (China). U-Pb zircon and Sm-Nd dates on the gneisses of the Shuanghe sheet constrain a metamorphic peak at ∼230 Ma. Rb-Sr and 40 Ar-39 Ar analyses of phengite from five gneisses in the Bixiling Complex yield ages at 198-212 Ma, overlapping the 190-220-Ma age on eclogites. The host gneisses record a similar metamorphic evolution as the coesite-bearing eclogites since both the peak and the retrograde evolution were contemporaneous. This argues for an in situ tectonic relationship.

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Section: Discussionmentioning

confidence: 99%

Multichronometric Evidence for an In Situ Origin of the Ultrahigh‐Pressure Metamorphic Terrane of Dabieshan, China

Chavagnac

Jahn²,

Villa

et al. 2001

The Journal of Geology

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“…The Pb isotopic compositions fall above the Pb evolution curve for average crust and reflect a pre-metamorphic average Th/U atomic ratio of c. 6.3 (cf. Tilton et al 1989). Such high Th/U atomic ratios are typically found in high-grade metamorphic rocks and chemically deeply weathered sediments, as these rocks experienced loss of U and Pb relative to Th (e.g., Zartman and Haines 1988;Romer and Hahne 2010).…”

Section: Perspectives For Future Whiteschist Researchmentioning

confidence: 99%

“…Tilton et al (1989) used the isotopic composition of Sr, Nd, and Pb to demonstrate that the protolith of the Dora-Maira UHP rocks represents old continental crust, focusing on the point that continental crust may be subducted to mantle depth and that such material-when interacting with the mantle-may account for the enriched geochemical and isotopic signature of some mantle types. Their isotope data, however, provide also powerful constraints on the development of the protoliths.…”

Section: Perspectives For Future Whiteschist Researchmentioning

confidence: 99%

“…Their isotope data, however, provide also powerful constraints on the development of the protoliths. For instance, the Nd data (eNd T & -7.2; Tilton et al 1989) correspond to a T DM model age of 1,250-1,400 Ma for the crustal protolith and fall in the range typically encountered in mixed-source Paleozoic magmatic and sedimentary rocks of Central Europe (see compilation in Romer and Hahne 2010 Sr ratios as high as 0.745 ± 0.005 (Tilton et al 1989) Romer et al 2012). The Pb isotopic compositions fall above the Pb evolution curve for average crust and reflect a pre-metamorphic average Th/U atomic ratio of c. 6.3 (cf.…”

Section: Perspectives For Future Whiteschist Researchmentioning

confidence: 99%

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Protoliths and phase petrology of whiteschists

Franz

Romer

Capitani

2013

Contrib Mineral Petrol

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Whiteschists appear in numerous high-and ultrahigh-pressure rock suites and are characterized by the mineral assemblage kyanite ? talc (?-quartz or coesite). We demonstrate that whiteschist mineral assemblages are well stable up to pressures of more than 4 GPa but may already form at pressures of 0.5 GPa. The formation of whiteschists largely depends on the composition of the protolith, which requires elevated contents of Al and Mg as well as low Fe, Ca, and Na contents, as otherwise chloritoid, amphibole, feldspar, or omphacite are formed instead of kyanite or talc. Furthermore, the stability field of the whiteschist mineral assemblage strongly depends on XCO 2 and fO 2 : already at low values of XCO 2 , CO 2 binds Mg to carbonates strongly reducing the whiteschist stability field, whereas high fO 2 enlarges the stability field and stabilizes yoderite. Thus, the scarcity of whiteschist is not necessarily due to unusual P-T conditions, but to the restricted range of suitable protolith compositions and the spatial distribution of these protoliths: (1) continental sedimentary rocks and (2) hydrothermally and metasomatically altered felsic to mafic rocks. The continental sedimentary rocks that may produce whiteschist mineral assemblages typically have been deposited under arid climatic conditions in closed evaporitic basins and may be restricted to relatively low latitudes. These rocks often contain large amounts of the clay minerals palygorskite and sepiolite. Marine sediments generally do not yield whiteschist mineral assemblages as marine shales commonly have too high iron contents. Sabkha deposits may have too high CO 2 contents. Protoliths of appropriate geochemical composition occur in and on continental crust. Therefore, whiteschist assemblages typically are only found in settings of continental collision or where continental fragments were involved in subduction. Our calculations demonstrate that whiteschists can form by closed-system metamorphism, which implies that the chemical and isotopic composition of these rocks provide constraints on the development of the protoliths.

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“…A broadly continuous younging towards more westerly (or structurally lower) units is then apparent, from 44 to 35 Ma in the Internal Crystalline nappes (e.g. Tilton et al, 1991;Duchêne et al, 1997;Gebauer et al, 1997;Rubatto and Hermann, 2001;Meffan-Main et al, 2004;Lapen et al, 2007;Gabudianu Radulescu et al, 2009;Rosenbaum et al, 2012) …”

Section: Tectono-metamorphic Evolution Of the Western Alpsmentioning

confidence: 99%

Recognizing remnants of magma-poor rifted margins in high-pressure orogenic belts: The Alpine case study

Beltrando

Manatschal

Mohn

et al. 2014

Earth-Science Reviews

125

104

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This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. Magma-poor rifted margins are being increasingly recognized in present-day Atlantic-type systems. However, findings of fossil areas floored by exhumed mantle or hyper-extended crust are comparatively rare within orogenic belts that were originated through the inversion of pre-existing rifted margins. This discrepancy may be due to the common reactivation of lithological contacts during subduction/orogeny, potentially masking pre-orogenic relationships, and, most importantly, to the frequent lack of a preorogenic layer-cake architecture, hindering retro-deformation of multiply deformed tectonic units. This study outlines a methodology to detect sections of magma-poor, hyper-extended rifted margins without a layer-cake architecture in multiply deformed/metamorphosed terrains. This approach is defined by comparison to well studied examples of fossil analogues preserved in weakly deformed parts of Alpine orogens. In the latter domains, continental basement and hydrated peridotites were exhumed at the basin floor during Jurassic rifting along long-offset detachment systems. Extensional geometries locally resulted in tectonic sampling of laterally discontinuous slivers of allochthonous continental basement and pre-rift sediments from the hanging wall blocks. Lithostratigraphic associations consisting of continental basement rocks directly juxtaposed with syn-to post-rift meta-sediments and/or serpentinized subcontinental mantle are widespread within sections of Alpine-type orogenic belts that underwent high-to ultra-high-pressure metamorphism. However, similar associations may arise from a variety of processes other than rift-related lithospheric thinning in magma-poor environments, including subduction mélange dynamics or deposition of sedimentary mélanges along convergent/divergent margins. The partial preservation of rift-related lithostratigraphic associations may still be assessed, despite the lack of biostratigraphic evidence, by (1) the consistency of the lithostratigraphic architecture over large areas, despite pervasive Alpine deformation, which rules out chaotic mixing during subduction/ exhumation, (2) the presence of clasts of basement rocks in the neighboring meta-sediments, indicating the original proximity of the different lithologies, (3) evidence of brittle deformation in continental basement and ultramafic rocks pre-dating Alpine metamorphism, indicating that they were juxtaposed by fault activity prior to the deposition of post-rift sediments, and (4) the similar Alpine tectono-metamorphic evolution of ophiolites, continental basement and meta-sediments. A re-assessment of basement-cover relationships in...

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Pb-Sr-Nd isotopic behavior of deeply subducted crustal rocks from the Dora Maira Massif, Western Alps, Italy

Cited by 96 publications

References 24 publications

Multichronometric Evidence for an In Situ Origin of the Ultrahigh‐Pressure Metamorphic Terrane of Dabieshan, China

Multichronometric Evidence for an In Situ Origin of the Ultrahigh‐Pressure Metamorphic Terrane of Dabieshan, China

Protoliths and phase petrology of whiteschists

Recognizing remnants of magma-poor rifted margins in high-pressure orogenic belts: The Alpine case study

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