کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
4715838 1638673 2014 24 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
In search of transient subduction interfaces in the Dent Blanche–Sesia Tectonic System (W. Alps)
موضوعات مرتبط
مهندسی و علوم پایه علوم زمین و سیارات ژئوشیمی و پترولوژی
پیش نمایش صفحه اول مقاله
In search of transient subduction interfaces in the Dent Blanche–Sesia Tectonic System (W. Alps)
چکیده انگلیسی


• The Dent Blanche Complex: a stack of blueschist metamorphic continental slices.
• Younger ages towards lowermost structural levels indicate underplating processes.
• Insights onto 30–40 km depths subduction dynamics at early Cenozoic times.

In this paper we study the Alpine metamorphic history of a major tectonic zone which formed during Alpine orogeny, the Dent Blanche Thrust (DBT). This contact, located in the Northern Western Alps, juxtaposes some ophiolitic metasediment-rich remnants of the Liguro-Piemontese ocean (Tsaté Complex) with a composite continental, km-sized complex (Dent Blanche Tectonic System, DBTS) of Adriatic affinity thrusted over the ophiolite. In order to better understand the geodynamic meaning of the DBT region and adjacent units, we have reconstructed the pressure–temperature–time–deformation (P–T–t–d) history of these two units using modern thermobarometric tools, Rb/Sr geochronology, and field relationships.We show that the Tsaté Complex is formed by a stack of km-thick calcschists-bearing tectonic slices having experienced variable maximum burial temperatures between 360 °C and 490 °C at depths of ca. 25–40 km. Associated deformation ages span a range between 37 Ma and 41 Ma. The Arolla gneissic mylonites at the base of the DBTS experienced high-pressure (12–14 kbar), top-to-NW deformation at ca. 450 °C between 43 and 48 Ma. A first age of ca. 58 Ma has been obtained for high-pressure ductile deformation in the Valpelline shear zone, atop Arolla gneisses. Some of the primary, peak metamorphic fabrics have been reworked and later backfolded during exhumation and collisional overprint (ca. 20 km depth, 37–40 Ma) leading to the regional greenschist-facies retrogression which is particularly prominent within Tsaté metasediments.We interpret the Dent Blanche Thrust, at the base of the Arolla unit, as a fossilized subduction interface active between 43 and 48 Ma. Our geochronological results on the shear zone lining the top of the Arolla unit, together with previous P–T–t estimates on equivalent blueschist-facies shear zones cutting the Sesia unit, indicate an older tectonic activity between 58 and 65 Ma. We demonstrate here that observed younger ages towards lowermost structural levels are witness of the transient, downwards migration of the Alpine early Cenozoic blueschist-facies subduction interface. This down-stepping is interpreted to reflect the progressive underplating acting between 30 and 40 km depth in the Alpine subduction zone between late Cretaceous and late Eocene. Underplating involved first continental material derived from the stretched Adriatic margin followed by underplating of ocean-derived rocks in the Eocene. These results shed light on subduction-zone accretion processes and therefore provide a new perspective for the understanding of geophysical results imaging the plate-interface region in active subduction zones.

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ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Lithos - Volume 205, 15 September 2014, Pages 298–321
نویسندگان
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