2- Geodynamics of Sedimentary Viking Graben ... Thin-skinned vs thick-skinned extensional tectonics - Rift geometry . Master1 Gologie des Rservoirs Dynamique des Bassins

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Text of 2- Geodynamics of Sedimentary Viking Graben ... Thin-skinned vs thick-skinned extensional...

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    2- Geodynamics of Sedimentary Basins

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    http

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    2.1 Basins due to divergence - Rifts - Subsidence analysis - Passive continental margins

    Lakes Tanganyika & Victoria Gulf of Suez & Red Sea USA Atlantic Margin

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    2.1.1. Rifts a. stretching Subsidence analysis b. kinematics of rifting c. Rift basin architecture

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    a. Stretching

    Extension => deformation = stretching

    Stretching thinning (volume conservation)

    thinitial

    linitial

    lfinal

    thfinal

    Stretching factor (): lfinal/linitial (always >1) Thinning factor: thfinal/thinitial (always

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    Stretching (extensional stress)

    a) Stretching => thinning b) Deformation = Normal faults in upper crust and

    uplift of Lithos/asthenos boundary c) N. Faults => initial subsidence d) LAB isotherm uplift =>increased geotherm

    a) Stop of extensional stress => and faults b) Cooling of thinned lithosphere c) Cooling => density increase => subsidence d) Subsidence => sediment deposition

    Considere

    d

    instantane

    ous

    10s Million

    s

    of years

    Lithospheric Stretching

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    Rifting and subsidence processes

    Cooling

    Stretching/ thinning

    Loading

    Rifting (lithosphere stretching and thinning) involves the 3basic subsidences processes,

    simultaneously or successively. 0C

    1300C

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    Geological example of a rift : Viking Graben

    Moho

    Thinned cont. Crust (lithosph. also affected)

    Synrift sequence (initial subsidence)

    Postrift sequence Rift axis

    Postrift basin

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    How does it work ? -> the McKenzie model = Subsidence Analysis

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    Computing the value of initial subsidence

    local

    isostacy

    instantane

    ous

    Mass

    Conservat

    ion

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    Sediment-fill = load => extra-subsidence

    Subsidence without

    sediment

    sediment

    Subsidence with sediment

    Extra Subsid. due to

    sediment load

    local

    isostacy

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    Computing the subsidence due to Sediment-load

    3.15

    2.3

    1

    Sload = 0.60 hs

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    subsidence in rift basins

    Temporal subdivision

    Processes

    Driving mechanisms

    Syn-rift

    (intantaneous, initial)

    + Post-rift (long-term)

    Fault activity

    + Thermal recovery

    Sediment load + Geodynamics

    (tectonic)

    Total subsidence in rift basins (measured in borehole)

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    12 True f

    or any

    type of ba

    sin

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    Exercise: Viking Graben

    Considering a pre-rift crustal thickness of 35km, what is the total subsidence at points A, B, C ? Same question, considering that Trias + U. Palaeozoic belong to pre-rift. What are the stretching and thinning factors at each point?

    A B C

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    Subsidence evolution of sedimentary basins

    g h+ag udv br

    oa&hg hl +

    udcal br g a++hd

    annw0ban ial odhr r ba

    nar w&+dbl h

    &bn+& h+ & anh&

    inw0ban &al p&+ul h&

    h0avudb+h&

    vna+hiudg h r adoul a+h

    vna+hiudg g adn&

    &nuvh

    g adn& &bn+&

    +wdobpb+h& r al l hn&

    2 a+hd

    nobal

    v+bal

    addhg bal

    8ur ug bal

    d8r ag odbal

    a+h dh+ar huw&

    adn4 mhd+bad4

    nbcur hl h huchl h

    dh&hl +

    +da+bcdav 4 hv+ sg

    b+ unuc4 ch 4

    ag vu& a&bl

    sg

    hdg bhl mdba&

    ur nh

    wda&&bf wh

    g u4hl h+ &wv

    wda&&bf wh l i

    d8+ar 8 l i

    d8+ar 8 wv

    an8uc1l h

    8uc1l h

    cd1&

    inw0ba+bnh&

    cd1&

    +wdobpb+bf wh

    adcbnh&

    g adbl h&

    haw

    cd1&nb++udaw6

    ch 4 ebsbl c daohl

    Age (My)

    Dep

    th

    (km

    ) D

    epth

    g h+ag udv br

    oa&hg hl +

    udcal br g a++hd

    annw0ban ial odhr r ba

    nar w&+dbl h

    &bn+& h+ & anh&

    inw0ban &al p&+ul h&

    h0avudb+h&

    vna+hiudg h r adoul a+h

    vna+hiudg g adn&

    &nuvh

    g adn& &bn+&

    +wdobpb+h& r al l hn&

    2 a+hd

    nobal

    v+bal

    addhg bal

    8ur ug bal

    d8r ag odbal

    a+h dh+ar huw&

    adn4 mhd+bad4

    nbcur hl h huchl h

    dh&hl +

    +da+bcdav 4 hv+ sg

    b+ unuc4 ch 4

    ag vu& a&bl

    sg

    hdg bhl mdba&

    ur nh

    wda&&bf wh

    g u4hl h+ &wv

    wda&&bf wh l i

    d8+ar 8 l i

    d8+ar 8 wv

    an8uc1l h

    8uc1l h

    cd1&

    inw0ba+bnh&

    cd1&

    +wdobpb+bf wh

    adcbnh&

    g adbl h&

    haw

    cd1&nb++udaw6

    ch 4 ebsbl c daohl

    Data Campos Basin

    nar w&+dbl h

    inw0ban &al p&+ul h&

    h0avudb+h&h0avudb+h&

    vna+hiudg h r adoul a+h vna+hiudg h r adoul a+h

    vna+hiudg g adn& vna+hiudg g adn&

    &nuvh

    g adn& &bn+&

    +wdobpb+h& r al l hn&

    2 a+hd2 a+hd

    b+ unuc4

    130My ago

    Deposits a

    t

    Surface

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    g h+ag udv br g h+ag udv br

    udcal br g a++hd

    annw0ban ial odhr r ba

    &bn+& h+ & anh&

    Today,

    basement

    at

    10km dept

    h

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    Exercices: subsidence evolution of basins

    15

    Plot the total subsidence curve from different types of data

    g h+ag udv br

    oa&hg hl +

    udcal br g a++hd

    annw0ban ial odhr r ba

    nar w&+dbl h

    &bn+& h+ & anh&

    inw0ban &al p&+ul h&

    h0avudb+h&

    vna+hiudg h r adoul a+h

    vna+hiudg g adn&

    &nuvh

    g adn&am