Title: Integrated 2-D and 3-D Structural, Thermal, Rheological and Isostatic Modelling of Lithosphere Deformation:
1Integrated 2-D and 3-D Structural, Thermal,
Rheological and Isostatic Modelling of
Lithosphere Deformation
- Application to Deep Intra-Continental Basins
Stuart Egan
2Contents
- 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
3The McKenzie Model (Uniform Lithosphere Extension)
(McKenzie, 1978)
4Subsidence curve generated by McKenzie model
5BIRPS Seismic Data
British Institutions Reflection Profiling
Syndicate
6Integrated Model - parameters
7Integrated Model - extension
8Integrated 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.
9Integrated Model - shortening
10Black Sea Location
11Black 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
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14Uniform lithosphere extension
15..followed by shortening at margins
16Crustal thickness can be used to define a Beta
(stretching) profile
17Uniform lithosphere extension based upon
magnitude of crustal thinning
18Depth dependent stretching -enhanced extension
of lower crust and mantle lithosphere
19Lithosphere strength distribution and inferred
depth of necking/detachment
Adapted from Braun and Beaumont, 1989
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23South Caspian Basin
24Confidential Data
25SW-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
26Fault 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.
27Uniform 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.
29Estimation of Moho Depth
Confidential Data
- Moho depth based upon limited information (e.g.
Mangino Priestley 1998). - Bmax 3.5
30Reconciliation 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!).
31Summary
- 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.
32Summary - 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 (?).