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Ladakh Batholith Tectonic Model (Kirstein Model (Stage 1 (~60Ma) (Soft…
Ladakh Batholith Tectonic Model
Kirstein Model
Stage 1 (~60Ma)
Soft collision of leading plate edges
--> causes tilting & exposure of S. margin (Khardung volcanics)
Tethys closure
Stage 2
(40 Ma)
along steep decollement on main part batholith
More rapid exhumation
End Miocene
Reinvigoration of thrusting to North
Model inferred from data on ladakh batholith
2 approaches
A. Kirstein et al
Collect sample, interpret data, infer exhumation Ladakh batholith
B. Robert et al 2009
Predicted thermal profile & ages each tectonic scenario would produce
Recognised 2 models for how Central Himalayas exhumed - Avouac vs Hodges
∴ Age distribution across structures expected:
Avouac
Shortening concentrated on MHT
Hodges
Out-of-sequence faulting @ topog transition
Robert (2009)
Avouac model (2003)
Thermochron ages
should
young toward MCT
Crustal ramp = below topog transition
Shortening concentrated on MAin Himalayan Thrust
Younging @ topog transition
Hodges model (2004)
Out of sequence faulting @ topog transition (central himalaya)
Lotsa faults propagate from MHT to/toward surface
Thermochron ages
Jump/break @ out-of-seq thrusts
Other side thrust - older ages appear then young
Break @ topog transition
Models produce fundamentally different ages @ topog transition
Robert Data (2009)
Central Nepal data
Found topog transition
sampled N & S of it
No jump in AFT ages observed across topog transition
Age-elevation profiles either side topog transition
quantified ramp geometry
taken either side topog transition = further supporting evidence
Is topog transition thrust-controlled ?
Avouac - overthrusting
One main basal thrust (MHT)
Hodges - Out of sequence thrusting
Series of other thrust propagate & intersect surface
Robert interp
Overthrusting of a crustal ramp, thus
No out-of-sequence thrusting
Only one MHT affecting geometry of Central Himalaya
Case studies summary
Local
Entire Ladakh Batholith evo
Compare tectonic models validity
--> for generation of Central Himalaya