DARWIN Digitale Dissertationen German Version Strich

FU Berlin
Digitale Dissertation

Jörg Ebbing :
3-D density structure and isostatic state of the lithosphere in the Eastern Alps
3-D Dichteverteilung und isostatisches Verhalten der Lithosphäre in den Ostalpen

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Abstract

The aim of this study is to investigate the structure of the Eastern Alpine lithosphere using different techniques to analyze the gravity field. Of particular interest are the lithospheric characteristics caused by the collision of the Adriatic and European plate.
Direct interpretation techniques allow only a first estimate of the  main sources of the gravity field. In the case of the Eastern Alps the main sources are the density distribution at the crust-mantle boundary and density variations within the uppermost crust.
Consideration of the constraining information from different sources has resulted in two alternative models for the 3D density structure of the Eastern Alps. Both of these models feature the same structure within the uppermost 10 km of the crust, which is well constrained and directly related to the tectonic  formations visible at the surface. The uppercrustal density distribution contributes up to one third to the total Bouguer gravity field of the Eastern Alps.
The first model is based on the velocity model  Eschen-38 and features mainly density contrasts in the vertical direction. The second model is based on the results of reflection seismic and receiver function analysis by the TRANSALP experiments. Based on these results the geometry of the crust-mantle boundary within the Adriatic plate is very different.
From the 3D models of density structure the internal loads of the Eastern alpine lithosphere can be calculated. These loads are necessary to investigate isostatic compensation and to estimate the flexural rigidity of the lithospheric plate. An investigation of isostasy in the sense of an Airy isostatic model shows that the internal loads strongly influence the isostatic compensation.
The isostatic residual field correlates with geological formations, visible at the surface and structures within the the uppermost 10 km of the crust.
Regional compensation is analyzed using a convolution method based on flexural models , i.e. Vening-Meinesz isostatic model. Over broad areas the lithosphere of the Eastern Alps features small values of flexural rigidity  (D < 10E21 Nm). But within the lithosphere of the TRANSALP model high values of flexural rigidity (D > 100E21 Nm) are detected in the southern Alps. The high values are connected to the strong internal loading of the plate caused by the thick Adriatic lower crust and its high density.
Together, the results suggest that the Eschen-38 model is more realistic. The high densities within the Adriatic lower crust of the TRANSALP model and the related  large internal loads and high flexural rigidity indicate that the modeled crust-mantle boundary is not the Adriatic Moho. Instead this boundary is likely to be the boundary between subducted European crust and Adriatic crust, or a boundary within the upper mantle. Therefore, the geometry of the crust-mantle boundary as featured in the Eschen-38 model seems to be more reliable.

Table of Contents

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Titel und Inhalt
1 Einführung 1
2 Methoden der Interpretation 4
2.1 Potentialfelder 4
2.2 Direkte Methoden 5
2.3 Indirekte Methoden 10
3 Geologie und Tektonik der Ostalpen 17
3.1 Der Prozess der Alpinen Gebirgsbildung 18
3.2 Die Geologischen Einheiten der Ostalpen 19
3.3 Geologische Szenarien 21
4 Datenbasis 24
4.1 Topographische Daten 24
4.2 Potentialfelder 24
4.3 Weitere Datensätze 32
4.4 Seismische Ergebnisse vor TRANSALP 33
4.5 Ergebnisse des seismischen Experiments TRANSALP 37
5 Direkte Auswerteverfahren 42
5.1 Tiefenabschätzung 42
5.2 Wellenlängenfilterung 42
5.3 Feldfortsetzung 43
5.4 Krusten-Mantel-Grenze durch Inversion 47
5.5 Euler-Dekonvolution 49
5.6  Diskussion und Beurteilung 51
6 Die 3D-Dichtestruktur der Ostalpen 53
6.1 Oberflächennahe Dichteverteilung 53
6.2  Dichtemodelle der Kruste 59
6.3 Dichtemodelle der Lithosphäre 72
6.4 Allgemeine Einordung der Modelle 74
7 Isostasie und flexurelle Rigidität 76
7.1 Modelle der lokalen und regionalen Isostasie 76
7.2 Flexurelle Rigidität 79
7.3 Lokales isostatisches Verhalten der Ostalpen 92
7.4 Flexurelle Rigidität der Ostalpen 95
8 Lithosphärenspannung und dynamische Betrachtungen 107
8.1  Spannungsberechnung mit Hilfe der Krümmung 107
8.2 Finite Elemente 115
9 Interpretation und Ausblick 118
Literaturverzeichnis 123
A Euler-Dekonvolution von Modelldaten 133
B Admittanzfunktion der dünnen, elastischen Platte 138
Danksagung 141

More Information:

Online available: http://www.diss.fu-berlin.de/2002/192/indexe.html
Language of PhDThesis: german
Keywords: Eastern Alps, gravity, density structure, isostasy, flexural rigiditiy
DNB-Sachgruppe: 31 Geowissenschaften
Date of disputation: 16-Jul-2002
PhDThesis from: Fachbereich Geowissenschaften, Freie Universität Berlin
First Referee: Prof. Dr. Hans-Jürgen Götze
Second Referee: Prof. Dr. Volker Haak
Contact (Author): jebbing@geophysik.fu-berlin.de
Contact (Advisor): hajo@geophysik.fu-berlin.de
Date created:16-Sep-2002
Date available:18-Sep-2002

 

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