Integrated 2-D and 3-D Structural, Thermal, Rheological and Isostatic Modelling of Lithosphere Deformation: - PowerPoint PPT Presentation

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Integrated 2-D and 3-D Structural, Thermal, Rheological and Isostatic Modelling of Lithosphere Deformation:

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The acquisition of deep seismic reflection and refraction data has played a key role in helping to understand the structure and rheological ... Like the Black Sea, ... – PowerPoint PPT presentation

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Title: Integrated 2-D and 3-D Structural, Thermal, Rheological and Isostatic Modelling of Lithosphere Deformation:


1
Integrated 2-D and 3-D Structural, Thermal,
Rheological and Isostatic Modelling of
Lithosphere Deformation
  • Application to Deep Intra-Continental Basins

Stuart Egan
2
Contents
  • Introduction
  • Modelling lithosphere extension and basin
    formation - basic concepts and initial models
  • Importance of geological and geophysical data in
    model development
  • Processes and modelling theory
  • Structural processes
  • Thermal effects - perturbation and
    re-equilibration
  • Isostasy
  • Surface processes and the development of basin
    stratigraphy
  • Case studies
  • Eastern Black Sea
  • South Caspian basin

3
The McKenzie Model (Uniform Lithosphere Extension)
(McKenzie, 1978)
4
Subsidence curve generated by McKenzie model
5
BIRPS Seismic Data
British Institutions Reflection Profiling
Syndicate
6
Integrated Model - parameters
7
Integrated Model - extension
8
Integrated Model of Lithosphere Extension
  • Basins are generated by extension along a
    sequence of closely spaced faults, which flatten
    within the crust.
  • Pure shear/stretching is assumed to deform the
    lithosphere below the faults and is distributed
    regionally.
  • The large subsidence within the basin is partly
    attributable to the effects of sediment infill
    and isostatic loading.
  • The Footwall and Moho are raised beneath the
    basin mostly as an isostatic response to crustal
    thinning.
  • The stratigraphy in the basin shows post-rift
    thermal subsidence overlying syn-rift
    megasequences.

9
Integrated Model - shortening
10
Black Sea Location
11
Black Sea Tectonics
Northwestern Shelf
Crimean Peninsula
Moesian Platform
Dolna - Kamchia depression
Caucasus
Western Black Sea Basin
Eastern Black Sea Basin
Mid - Black Sea High
Balkanides
W. Pontides
E. Pontides
12
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13
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14
Uniform lithosphere extension
15
..followed by shortening at margins
16
Crustal thickness can be used to define a Beta
(stretching) profile
17
Uniform lithosphere extension based upon
magnitude of crustal thinning
18
Depth dependent stretching -enhanced extension
of lower crust and mantle lithosphere
19
Lithosphere strength distribution and inferred
depth of necking/detachment
Adapted from Braun and Beaumont, 1989
20
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21
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23
South Caspian Basin
24
Confidential Data
25
SW-NE Cross-Section
Part 1
  • Sections produced from interpretation of seismic
    data by BP geoscientists.
  • Note depth is in TWT
  • There is an overlap and slight offset where
    sections intersect (see next slide)

Confidential Data
Part 2
Confidential Data
26
Fault Deformation Model input parameters
  • Fault heave values are very approximate as they
    are difficult to estimate from data.
  • However, extension due to faulting is very low
  • Also, difficult to quantify the compressional
    deformation, which intensifies to NE.

27
Uniform Lithosphere Extension(based upon fault
heave values)
Time 150Ma Te 5 10 km ri 2500 kg.m-3 rc
2850 kg.m-3
  • Subsidence in the basin is far too low.
  • Bmax 1.11!

28
.followed by compression
  • Subsidence in the basin is still far too low.

29
Estimation of Moho Depth
Confidential Data
  • Moho depth based upon limited information (e.g.
    Mangino Priestley 1998).
  • Bmax 3.5

30
Reconciliation of fault-controlled extension and
attenuation of the crust
  • Enhances syn-rift subsidence due to thinning of
    the lower crust.
  • Enhances post-rift subsidence through increased
    initial heating of the lithosphere (Bmax 3.5).
  • Overall subsidence is comparable to data.
    However, NE of section clearly not deep enough
    (more data required!).

31
Summary
  • The first numerical models of lithosphere
    extension were developed about 25 years ago.
    These models were successful in showing how
    crustal attenuation, thermal perturbations and
    local isostatic compensation control basin
    subsidence and the evolution of syn- and
    post-rift stratigraphic sequences.
  • The acquisition of deep seismic reflection and
    refraction data has played a key role in helping
    to understand the structure and rheological
    layering of the continental lithosphere. This led
    to the development of more realistic models of
    continental lithosphere tectonics.
  • The most up to date models of lithosphere
    deformation take into account the complex
    interaction, in 4-dimensions, of structural,
    thermal, isostatic, rheological, metamorphic and
    surface processes to simulate the evolution of
    extensional basins and thrust belt-foreland basin
    couplets.

32
Summary - Black Sea and South Caspian Sea case
studies
  • It is not possible to reproduce basin subsidence
    when the magnitude of lithosphere extension is
    based on the amount of fault controlled
    deformation.
  • The large magnitude of Tertiary ("post-rift")
    subsidence observed in the basins cannot be
    explained by loading and flexure caused by
    surrounding thrust belts.
  • Models in which the magnitude of deformation is
    constrained using crustal thinning/thickening
    generate amounts of total subsidence that are
    comparable with that observed. These models rely
    upon a depth dependent extension mechanism to
    reconcile the observed (small) magnitude of
    faulting with overall attenuation of the crust.
  • 3-D modelling of the eastern Black Sea shows that
    the magnitude of total subsidence is
    significantly reduced when accounting for a
    realistic bathymetry, a late stage Upper Miocene
    - Quaternary infill and regional flexure. The
    observed subsidence can only be accounted for by
    the extension of thickened crust or additional
    subsidence mechanisms (?).
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