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J.J. Villalaín, P. Calvín, M. F. Bógalo, I. Falcón, and A. M. Casas Villalaí
n et a
l.
EGU 2020
Basque-
Cantabrian
BACKGROUND Widespread cretaceous remagnetizations
in inverted Mesozoic basins of the Iberia and North Africa
- Thick lower cretaceous syn-rift sediments in Iberia
- Thick lower Jurassic syn-rift sediments in Atlas ranges. Villa
laín e
t al.
EGU 2020
3
North Iberian cretaceous remagnetizations
ChRM
Systematic Normal polarity
E. Cameros Basin
Cabuérniga Basin
Aralar stratigraphic coordinates
Aralar
Polientes Basin
Organyà Basin
(Gong et al., 2008)
Iberian Range
Palencia, 2006
W. Cameros Basin
Iberian Ranges
Juarez, 1994
etc… Villa
laín e
t al.
EGU 2020
Timing of Iberian remagnetizations
AGE: - Pre basin-inversion (Oligocene) - Post- o syn- extensión - Post Aptian sediments - Normal polarity (K Superchron)
CRETACEOUS REMAGNETIZATION
Rem
agn
etiz
ed u
nit
s
TE
RT
IAR
Y
LA
TE
CR
ET
.
JUR
AS
SIC
EA
RL
Y C
RE
T.
CR
ET
AC
EO
US
T
RIA
SS
IC
LA
TE
J.
MID
. J.
EA
R. J
.
60
100
140
200
No
rmal
Cre
t.
Sup
erch
ron
Tect
on
ic s
ub
sid
ence
Ex
ten
sio
n
Tect
on
ic
inve
rsio
n
Villalaí
n et a
l.
EGU 2020
High Atlas cretaceous remagnetization
N
90
180
270
TILT CORR
(Lambert)
Down
Up
ChRM
Systematic Normal polarity
Villalaí
n et a
l.
EGU 2020
Dating from the Remagnetization Direction
nA
HYPOTHESIS
- If the different sites were remagnetized at
the same time.
- If the deflection of the magnetization is only due to tilting around the bedding
strike.
- The remagnetization direction is the intersection of the SC.
SC must intersect at the Remagnetization
direction Contours of A values
SCI REMAGNETIZATION DIRECTION
A min
- SC gives all possible original direction in a rotation of the magnetization around the strike.
Small Circle Intersection method (SCI)
Shipunov, 1997; Waldhor & Appel, 2006;
Callvín et al. 2017
Interfolding remagnetization
Small Circles Intersection (SCI) method
Villalaí
n et a
l.
EGU 2020
Aparent Polar Wander Path of Africa (APWP)
136 Ma
136 Ma 77 Ma 40 Ma
50º of cretaceous rotation
Systematic paleomagnetic studies in the Moroccan High Atlas
Expected directions in The High Atlas
Villalaí
n et a
l.
EGU 2020
Systematic paleomagnetic studies in the Moroccan High Atlas
Villalaí
n et a
l.
EGU 2020
Systematic paleomagnetic studies in the Central High Atlas (CHA)
Villalaí
n et a
l.
EGU 2020
NRM OF REMAGNETIZED JURASSIC LIMESTONE
The CHA cretaceous remagnetization has been observed in all these sites with the same magnetic properties: a viscous paleomagnetic component with maximum unblocking temperatures of 200-250ºC and the remagnetization normal polarity component up to 450–500ºC.
Villalaí
n et a
l.
EGU 2020
Magnetic properties: SD-SP uniaxial magnetite
Villalaí
n et a
l.
EGU 2020
Aiming to perform a 3D palinspastic restorations using interfolding remagnetizations a high resolution sampling has been made.
- 10.000 Km2
- 20 profiles - 600 paleomagnetic sites (calculating 600 paleobeddings)
0 100 km
Villalaí
n et a
l.
EGU 2020
All 526 sites
Before BC After total BC
After partial BC
Dec = 336.0° Inc = 43.7° η95 = 1.8 ° ζ 95 = 1.0 °
Direction of remagnetization from Small Circle Intersection Method over 526 sites
Very high accuracy Villalaí
n et a
l.
EGU 2020
Before BC After total BC
After partial BC
Dec = 336.0° Inc = 43.7° η95 = 1.8 ° ζ 95 = 1.0 °
All 526 sites
Exp
ecte
d p
aleo
mag
net
ic d
irec
tio
ns
at t
he
Hig
h A
tlas
DATING THE REMAGNETIZATIION
Villalaí
n et a
l.
EGU 2020
Sector east 77 sites
Central sector 257 sites
Sector west 118 sites
PALEOMAGNETIC DIRECTION AND LOCATION
Homogeneous direction (and age) in different areas
Villalaí
n et a
l.
EGU 2020
Bathonian and lower Cretaceous - 51 sites
Middle Jurassic 166 sites
Toarcian-Aalenian 89 sites
Lower Jurassic 89 sites
STRATIGRAPHIC UNITS
PALEOMAGNETIC DIRECTION AND STRATIGRAPHIC UNIT
Red-beds
Limestones
Limestones
Limestones
Homogeneous direction (and age) in different units of limestone
Villalaí
n et a
l.
EGU 2020
Red beds 51 sites
Carbonates 401 sites
PALEOMAGNETIC DIRECTION AND LITHOLOGIES
Villalaí
n et a
l.
EGU 2020
Timing of the remagnetization
The mechanism proposed for this type of this burial widespread remagnetizations in limestones is the generation of magnetite grains due to the heating related with burial. The homogeneous direction of the remagnetization seems to suggest an acquisition for a short event at 100 Ma. However, the extensional stage of these basins lasts tens of millions years keeping the necessary burial conditions for growth of magnetite grains covering several polarity chrons including the CNS.
AGE (Ma) 200 150 100 50 0
360 350 340 330 320 310 300
DEC
LIN
ATI
ON
(º)
6
Burial timing
6 km
0 km
Villalaí
n et a
l.
EGU 2020
Progressive or
punctual?
In this work we address the question of timing under with these processes happened, i.e. short vs. long remagnetization periods.
? Villa
laín e
t al.
EGU 2020
Punctual thermal event
model
Magnetic moment of SSD magnetite grains shows all Normal polarity It can explain the homogeneous direction and age of remagnetization
Villalaí
n et a
l.
EGU 2020
𝑀 = 𝑚𝑖
Progressive model for acquisition of remagnetization of limestones in deep sedimentary basins
Progressive generation of
magnetite during deep basin condition
Magnetite grow blocking the magnetic moment at Vc.
Two population of N and R SSD
magnetite grains
SP V>Vc
t <<
SSD V>Vc Blocked
magnetic moment
We propose the hypothesis that the ca. 100 Ma paleomagnetic direction shows by the remagnetization is just the average of magnetic moments of the entire SSD magnetite population that grow from the Middle Jurassic up to the Cenozoic. Grains block the magnetic moments when they grow above their critical volume, keeping the magnetic polarity generating over time a distribution of grains in normal and reverse polarity groups.
Villalaí
n et a
l.
EGU 2020
160-84 Ma
SM = 33,6 u.a.
SIMULATION model for calculating remagnetization direction as sum of magnetic moments of grains with different directions and polarities.
For each time interval ∆𝑡𝑖 the corresponding magnetic moment is calculated with polarity from GPTS (Gradstein et al., 2004) and direction from the GAPWP (Torsvik et al., 2012).
𝑀 = 𝑚𝑖 = 𝑘∆𝑡𝑖 𝑢𝑖
Villalaí
n et a
l.
EGU 2020
160-84 Ma
SM = 33,6 u.a.
SM = 38,0 u.a.
120-65 Ma
Villalaí
n et a
l.
EGU 2020
160-84 Ma
SM = 33,6 u.a.
SM = 38,0 u.a.
120-65 Ma
SM = 41,4 u.a.
160-65 Ma
The Progressive model allows to explain the homogeneity in the directions of remagnetization.
Villalaí
n et a
l.
EGU 2020
OBJETIVE: Quantify the effectiveness of the SSD magnetite grains contributing to the NRM
METHOD Sequence: - AF demagnetization of NRM - ARM acquisition - AF demagnetization of ARM - ARM acquisition in progressive DC field
Puntual thermal event (one
population of SSD magnetite)
Progresive model (two N and R population of
SSD magnetite)
vs
EXPERIMENT to test the presence of SSD magnetite grains with opposed magnetic moments.
Villalaí
n et a
l.
EGU 2020
Sequence: AF-ARM-AF
Comp. A
VRM
A. F.
20mT 80mT
140mT
N
Thermal
450ºC 300ºC
VRM
Comp. A
Villalaí
n et a
l.
EGU 2020
Sequence: AF-ARM-AF Two components: A: Cretaceous Remagnetization VRM: Viscous Normal Brunes component
Comp. A
VRM
A. F.
20mT 80mT
140mT
N
Thermal
450ºC 300ºC
VRM
Test the effectiveness: NRM VS ARM 0-20 mT fraction (paralels) 20-80 mT fraction (antiparaleles??)
0
0.2
0.4
0.6
0.8
1
1.2
0 50 100 150 200
ARM DEM / ARM AQ / NRM DEM
ARM DEMAG
ARM AQ
NRM DEMAG
Comp. A
Villalaí
n et a
l.
EGU 2020
Sequence: AF-ARM-AF
0
0.2
0.4
0.6
0.8
1
1.2
0 50 100 150 200
ARM DEM / ARM AQ / NRM DEM
ARM DEMAG
ARM AQ
NRM DEMAG
DT38-5B
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
0.05
-20 30 80 130 180
D ARM /DB D NRM / DB
D ARM /DB
D-NRM/DB
Type 1
y = -0.9173x + 0.9109
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.2 0.4 0.6 0.8 1
Arai diagram
ARM gained/ARMmax N
RM
left
/NR
Mo
-0.03
-0.025
-0.02
-0.015
-0.01
-0.005
0
0.005
0.01
0.015
0.02
-20 30 80 130 180
D ARM -D NRM / D B
Comp. A
VRM
Comp. A VRM
40 mT
20 mT
10 mT
70 mT
110 mT
170 mT
y = -0.573x + 0.6443 0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.5 1
Arai diagram (20-70 mT)
20 mT
70 mT
comparing the NRM -ARM signal through the pseudo-Thellier approach
Villalaí
n et a
l.
EGU 2020
0
0.2
0.4
0.6
0.8
1
1.2
0 50 100 150 200
ARM DEM / ARM AQ / NRM DEM
ARM DEMAGARM AQNRM DEMAG
Sequence: AF-ARM-AF Type 1
y = -0.8358x + 0.8624
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.2 0.4 0.6 0.8 1
Arai diagram
y = -0.3959x + 0.5439
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.5 1
Arair diagram (20-70 mT)
0
0.01
0.02
0.03
0.04
0.05
0.06
-20 30 80 130 180
D ARM /DB D NRM / DB
D ARM /DB
D-NRM/DB
-0.05
-0.04
-0.03
-0.02
-0.01
0
0.01
0.02
-20 30 80 130 180
D ARM -D NRM / D B
40 mT 20 mT
10 mT
70 mT
110 mT
170 mT
Comp. A
VRM
Comp. A VRM
Villalaí
n et a
l.
EGU 2020
Sequence: AF-ARM-AF Tipo 2
0
0.2
0.4
0.6
0.8
1
1.2
0 50 100 150 200
ARM DEM / ARM AQ / NRM DEM
ARM DEMAG
ARM AQ
NRM DEMAG
y = -0.9707x + 1.0073
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.2 0.4 0.6 0.8 1
Arai diagram y = -0.9856x + 1.0203
0
0.2
0.4
0.6
0.8
1
0 0.2 0.4 0.6 0.8 1
Arai diagram (20-70 mT)
0
0.005
0.01
0.015
0.02
0.025
0.03
-20 30 80 130 180
D ARM /DB D NRM / DB
D ARM /DB
D-NRM/DB
-0.012
-0.01
-0.008
-0.006
-0.004
-0.002
0
0.002
0.004
0.006
0.008
-20 30 80 130 180
D ARM -D NRM / D B
DT33-1B
ARM gained/ARMmax
NR
M le
ft/N
RM
o
Villalaí
n et a
l.
EGU 2020
Sequence: AF-ARM-AF
0
0.2
0.4
0.6
0.8
1
0 0.5 1
Arai diagram
0
0.2
0.4
0.6
0.8
1
0 0.5 1
Arai diagram
ARM gained/ARMmax
NR
M le
ft/N
RM
o
ARM gained/ARMmax
NR
M le
ft/N
RM
o
Type 2 Type 1
Consistent with progressive model (several polarities)
Consistent with Punctual thermal event model (one polarity)
Villalaí
n et a
l.
EGU 2020