Tectonics of the Simplon massif and Lepontine gneiss dome: deformation structures due to collision between the underthrusting European plate and the Adriatic indenter   总被引：1，自引：0，他引：1  

Albrecht Steck 《Swiss Journal of Geoscience》2008,101(2):515-546

This study presents a review of published geological data, combined with original observations on the tectonics of the Simplon massif and the Lepontine gneiss dome in the Western Alps. New observations concern the geometry of the Oligocene Vanzone back fold, formed under amphibolite facies conditions, and of its root between Domodossola and Locarno, which is cut at an acute angle by the Miocene, epi- to anchizonal, dextral Centovalli strike-slip fault. The structures of the Simplon massif result from collision over 50 Ma between two plate boundaries with a different geometry: the underthrusted European plate and the Adriatic indenter. Detailed mapping and analysis of a complex structural interference pattern, combined with observations on the metamorphic grade of the superimposed structures and radiometric data, allow a kinematic model to be developed for this zone of oblique continental collision. The following main Alpine tectonic phases and structures may be distinguished:

1.	NW-directed nappe emplacement, starting in the Early Eocene (~50 Ma);
2.	W, SW and S-verging transverse folds;
3.	transpressional movements on the dextral Simplon ductile shear zone since ~32 Ma;
4.	formation of the Bergell – Vanzone backfolds and of the southern steep belt during the Oligocene, emplacement of the mantle derived 31–29 Ma Bergell and Biella granodiorites and porphyritic andesites as well as intrusions of 29–25 Ma crustal aplites and pegmatites;
5.	formation of the dextral discrete Rhone-Simplon line and the Centovalli line during the Miocene, accompanied by the pull-apart development of the Lepontine gneiss dome – Dent Blanche (Valpelline) depression.

It is suggested that movements of shortening in fan shaped NW, W and SW directions accompanied the more regular NW- to WNW-directed displacement of the Adriatic indenter during continental collision.

---

Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Editorial Handling: Stefan Bucher  相似文献   

The mafic-ultramafic complex near Finero (Ivrea-Verbano Zone), I. Chemistry of MORB-like magmas     

Meihua Lu  Albrecht W. Hofmann  Maurizio Mazzucchelli  Giorgio Rivalenti 《Chemical Geology》1997,140(3-4):207-222

Geochemical data are presented for the meta-igneous, mafic-ultramafic complex near Finero. This complex is in contact with a phlogopite-bearing mantle peridotite and is subdivided into the Internal Gabbro unit, the Amphibole Peridotite unit, and the External Gabbro unit. The Internal Gabbro and the Amphibole Peridotite units consist of coarse-grained, chemically heterogeneous cumulates, whereas the External Gabbro unit is generally massive, chemically more uniform and approximately representative of the residual melt with MgO contents between 6.6 and 9.1% and Mg numbers between 38 and 58. Both whole-rock and mineral contents of Ni and Cr are significantly higher (at similar Mg numbers) in the Amphibole Peridotite unit than in the Internal Gabbro unit. The most straightforward interpretation of this is that the Amphibole Peridotite unit accumulated after the influx of fresh mafic (or ultramafic) magma into the magma chamber. Major-element chemical trends are continuous from the Amphibole Peridotite unit to the External Gabbro unit and are consistent with closed-system fractionation with no further addition of magma or contamination by wall or roof rock assimilation. In the External Gabbro unit, total FeO and TiO₂ contents are strongly correlated with each other (and with P₂O₅ and Zr) and reach values as high as 19 and 4%, respectively, indicating an advanced degree of crystal fractionation along a tholeftic trend. The External Gabbro samples have generally smooth normalized trace element patterns, which are consistent with being representative of a liquid composition. The residual nature of the External Gabbro magma is also indicated by negative Eu and Sr anomalies, clear evidence for prior feldspar fractionation. REE patterns are otherwise indistinguishable from N-type MORB, but Th and U are significantly more depleted than in MORB. This Th and U depletion is similar to that found in olivine basalts and picrites on Iceland and Hawaii; its origin is not well understood. No evidence is seen for any assimilation of crystal material, in sharp contrast with the situation of the igneous complex in Val Sesia near Balmuccia, where the magma composition is dominated by assimilation of crust. We suggest that the heat provided by at most two injections of magma near Finero was insufficient to induce crystal anatexis, in contrast with the excess heat supplied by multiple magma injections at Balmuccia.  相似文献   

Alpine thermal events in the central Serbo-Macedonian Massif (southeastern Serbia)     

Milorad D. Antić  Alexandre Kounov  Branislav Trivić  Andreas Wetzel  Irena Peytcheva  Albrecht von Quadt 《International Journal of Earth Sciences》2016,105(5):1485-1505

  相似文献   

Tectonic significance of Triassic mafic rocks in the June Complex,Sanandaj–Sirjan zone,Iran     

Farzaneh Shakerardakani  Franz Neubauer  Xiaoming Liu  Manfred Bernroider  Behzad Monfaredi  Albrecht von Quadt 《Swiss Journal of Geoscience》2018,111(1-2):13-33

This study concentrates on the petrological and geochemical investigation of mafic rocks embedded within the voluminous Triassic June Complex of the central Sanandaj–Sirjan zone (Iran), which are crucial to reconstruct the geodynamics of the Neotethyan passive margin. The Triassic mafic rocks are alkaline to sub-alkaline basalts, containing 43.36–49.09 wt% SiO₂, 5.19–20.61 wt% MgO and 0.66–4.59 wt% total alkalis. Based on MgO concentrations, the mafic rocks fall into two groups: cumulates (Mg# = 51.61–58.94) and isotropic basaltic liquids (Mg# = 24.54–42.66). In all samples, the chondrite-normalized REE patterns show enrichment of light REEs with variable (La/Yb)_N ratios ranging from 2.48 to 9.00, which confirm their amalgamated OIB-like and E-MORB-like signatures. Enrichment in large-ion lithophile elements and depletion in high field strength elements (HFSE) relative to the primitive mantle further support this interpretation. No samples point to crustal contamination, all having undergone fractionation of olivine + clinopyroxene + plagioclase. Nevertheless, elemental data suggest that the substantial variations in (La/Sm)_PM and Zr/Nb ratios can be explained by variable degrees of partial melting rather than fractional crystallization from a common parental magma. The high (Nb/Yb)_PM ratio in the alkaline mafic rocks points to the mixing of magmas from enriched and depleted mantle sources. Abundant OIB alkaline basalts and rare E-MORB appear to be linked to the drifting stage on the northern passive margin of the Neotethys Ocean.  相似文献   

Evaluating igneous sources of the Taveyannaz formation in the Central Alps by detrital zircon U–Pb age dating and geochemistry     

Gang Lu  Wilfried Winkler  Meinert Rahn  Albrecht von Quadt  Sean D. Willett 《Swiss Journal of Geoscience》2018,111(3):399-416

Late Palaeogene syn-tectonic volcanic products have been found in the Northern Alpine foreland basin and in the South Alpine hemipelagic basin. The source of abundant volcanic fragments is still in debate. We analyzed the geochronology and geochemistry of detrital zircons, and evaluated their temporal and genetic relationships with potential volcanic sources. The study shows that the detrital zircon U–Pb age patterns have two major age groups: a dominance (ca. 90%) of pre-Alpine zircons was found, as commonly observed in other Alpine flysch formations. These zircons apparently derived from erosion of the early Alpine nappe stack in South Alpine and Austroalpine units. Furthermore, a few Neo-Alpine zircons (ca. 10%) have ages ranging from Late Eocene to Early Oligocene (~ 41–29 Ma). Both source materials were mixed during long riverine transport to the basin margins before being re-deposited by gravity flows. These Palaeogene ages match with the activity of Peri-Adriatic magmatism, including the Biella volcanic suite as well as the Northern Adamello and Bergell intrusions. The values of REE and ¹⁷⁶Hf/¹⁷⁷Hf_(t) ratios of the Alpine detrital zircons are in line with the magmatic signatures. We observe an in time and space variable supply of syn-sedimentary zircons. From late Middle Eocene to Late Eocene, basin influx into the South Alpine and Glarus (A) basins from the Northern Adamello source is documented. At about 34 Ma, a complete reorganisation is recorded by (1) input of Bergell sources into the later Glarus (B) basin, and (2) the coeval volcaniclastic supply of the Haute-Savoie basin from the Biella magmatic system. The Adamello source vanished in the foreland basin. The marked modification of the basin sources at ~ 34 Ma is interpreted to be initiated by a northwestern shift of the early Alpine drainage divide into the position of the modern Insubric Line.  相似文献   

Fe and O isotope composition of meteorite fusion crusts: Possible natural analogues to chondrule formation?          下载免费PDF全文

Dominik C. Hezel  Graeme M. Poole  Jack Hoyes  Barry J. Coles  Catherine Unsworth  Nina Albrecht  Caroline Smith  Mark Rehkämper  Andreas Pack  Matthew Genge  Sara S. Russell 《Meteoritics & planetary science》2015,50(2):229-242

Meteorite fusion crust formation is a brief event in a high‐temperature (2000–12,000 K) and high‐pressure (2–5 MPa) regime. We studied fusion crusts and bulk samples of 10 ordinary chondrite falls and 10 ordinary chondrite finds. The fusion crusts show a typical layering and most contain vesicles. All fusion crusts are enriched in heavy Fe isotopes, with δ⁵⁶Fe values up to +0.35‰ relative to the solar system mean. On average, the δ⁵⁶Fe of fusion crusts from finds is +0.23‰, which is 0.08‰ higher than the average from falls (+0.15‰). Higher δ⁵⁶Fe in fusion crusts of finds correlate with bulk chondrite enrichments in mobile elements such as Ba and Sr. The δ⁵⁶Fe signature of meteorite fusion crusts was produced by two processes (1) evaporation during atmospheric entry and (2) terrestrial weathering. Fusion crusts have either the same or higher δ¹⁸O (0.9–1.5‰) than their host chondrites, and the same is true for Δ¹⁷O. The differences in bulk chondrite and fusion crust oxygen isotope composition are explained by exchange of oxygen between the molten surface of the meteorites with the atmosphere and weathering. Meteorite fusion crust formation is qualitatively similar to conditions of chondrule formation. Therefore, fusion crusts may, at least to some extent, serve as a natural analogue to chondrule formation processes. Meteorite fusion crust and chondrules exhibit a similar extent of Fe isotope fractionation, supporting the idea that the Fe isotope signature of chondrules was established in a high‐pressure environment that prevented large isotope fractionations. The exchange of O between a chondrule melt and an ¹⁶O‐poor nebula as the cause for the observed nonmass dependent O isotope compositions in chondrules is supported by the same process, although to a much lower extent, in meteorite fusion crusts.  相似文献   

Organic matter of the Mulhouse Basin, France: a synthesis     

P. Hofmann  A.Y. Huc  B. Carpentier  P. Schaeffer  P. Albrecht  B. Kelly  J.R. Maxwell  J.S.Sinninghe Damst  J.W. de Leeuw  D. Leythaeuser 《Organic Geochemistry》1993,20(8)

The lower Oligocene evaporite sequence of the Mulhouse Basin (France) contains organic matter-rich marl deposits. These marls display an overall cyclic variation of sedimentation rate, organic carbon content, hydrogen index and selected molecular parameters over a 30 m thick stratigraphic interval. The integration of all sedimentological and geochemical parameters has allowed the reconstruction and characterization of the paleoenvironment of deposition. The marls were deposited in a perennial lake that was at times connected to the sea. Two organic facies end members could be assigned to a lake stage with a marine connection and a lake stage that received dominantly continental water input. The overall stratigraphic variation in the organic matter content is interpreted to reflect the adaptation of the Oligocene flora to the changing paleoclimate and environmental conditions.  相似文献   

Polar constituents of organic matter rich marls from evaporitic series of the Mulhouse basin     

P. Schaeffer  F. Fache-Dany  J.M. Trendel  P. Albrecht 《Organic Geochemistry》1993,20(8)

A suite of marl samples from the evaporitic series of the Mulhouse basin (France; Lower Oligocene) was studied for its biomarker content, in particular its polar constituents. Novel series of 3-carboxyalkyl steranes and 15-oxo triaromatic ketones were identified by synthesis. The 3-carboxyalkyl steranes probably originate from highly polar precursors yet unreported in living organisms. Our data suggest that micro-algae could be the major source of these compounds which seem to be indicators of high algal input rather than characteristic of evaporitic environments. The 15-oxo triaromatic ketones could be oxidation products of triaromatic steroid hydrocarbons formed during diagenesis, although their formation during work-up procedure could not be excluded.  相似文献   

Beschaffenheitslängsschnitt eines Flußgebietes mittels Regressionsanalyse     

A. Gnauck  E. Weber  U. Suhr 《洁净——土壤、空气、水》1991,19(4):363-373

Following a general representation of the regression analysis, especially concerning the relations between flow and concentrations of matter and loads, these relations are represented and discussed for the suspended solids, nitrate concentration, chloride content and oxygen concentration for seven sections of the Spree river. There result clear connections to the structure and utilizations of all of the parts of the river basin. Finally, the covering of the total river basin by models of water quality management in the form of regression, self-purification and eutrophication models-and their coupling is represented.  相似文献   

GALPERIN,M. V.: Applied Simulation of Marine Communities. Berlin,Akademie-Verlag, 1990, 205 S., 48 Abb., 19 Tab., DM 42,-, ISBN 3-05-500761-1     

A. Gnauck 《洁净——土壤、空气、水》1991,19(6):745-746

  相似文献