Download - Clues to the Timing of MBT intiation
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Timing of MBT* Initiation, deduced from Petrography of Late Miocene
Foreland Basin Fill Sandstones, from NW Himalayas
Presented ByPraveen Kumar Maruthamuthu
09MS046
Guided ByDr. Prasanta Sanyal
* Main Boundary Thrust
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Himalayan Foreland Basin and The Major Lithotectonic Divisions of the Himalaya
Bera et al., 2010
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Introduction- The Himalayan Foreland Basin
• Started forming due to the Lithospheric subsidence and flexure of the Indian Plate when the Indian Plate started colliding with the Asian Plate.
• Episodic Tectonic Loading and Unloading• It contains Marine deposits as well as fluvial sedimentary deposits
derived from major litho-tectonic zones of the Himalayas
Catuneanu, 1998
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Himalayan Foreland Fill Stages• Two major stages of
Foreland Basin Fill1. Marine Underfill
(Subathu)2. Overfill stages
1. Dharmashala –Daghshai Kasauli (Early)
2. Siwalik Molasses (Late )
Int. Stratigraphic Commission Chart for India: DNS Raju et al.,
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Chronologyof the majorTectonic Activity for the NW Himalayas
Yin, 2006
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MBT: Main Boundary Thrust Initiation previous Work• Southern most thrust before the MFT
• Lesser Himalayan Rocks over the Siwaliks
• A crude age bracket of present to < 20 Ma (Hodges et al., 1988; Macfarlane, 1993; Yin, 2006).
• Age of >10 Ma ; Gravel Progradation sugested by (Meigs, 1995)
• (Problems with estimate)
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Previous Work : Burbank, 2000; Meigs, 1995
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Gravel Progradation: Syntectonic Indicator ?• Middle Siwalik Conglomerate 8.7 Ma -- Jwalamukhi Section
• Conglomerate clasts MBT Hanging Wall rocks (eg. Deoban Formation)
• Burbank (1988) Gravel Progradation syntectonic with thrusting
• Age estimates Highly Uncertain
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Gravel Progradation- Syntectonic for an overfilled basin?
• High slope Tectonic unloading
• Gravel progradation Unloading Phase
• Gravel Post Tectonic
• New syntectonic Proxy?
• Sandstone Petrography
Catuneanu, 2001
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Study Area – Kangra Ranital
Deformed…change it
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Study Area• Ranital Kangra, Kangra Sub basin
• Late Miocene
• Section Dated by Burbank (1996)
• Middle Siwalik Thick sandstone channel fills bodies
• Upper Siwalik Conglomerate 7Ma
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Methods
• Facies and Litholog
• Sampling of Sandstone and Paleosols
• Petrographic Analysis Quartz, Feldspar and Rock Fragment variation
• Rock fragment Better Understanding
7
8
9
10
11
Age (Ma)
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Facies Analysis and Sampling• Thickness Sandstones, Mudstones
• Facies Classification Miall, 1985
• Set and Coset Thickness Paleo-hydraulics
• Dominant Facies: St, Sh, Sp.
• In addition, we also encountered Sl, Gmm, Gmh, Gt etc and Fm, Fr, P for soil facies
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Methods for Petrographic Analysis- Gazzi-Dickinson Point Counting
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Methods
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Results and Discussions• Sublithic to Lithic
Arenites
• They fall in the region of Recycled Orogen- (Dickinson , 1975)Increase Symbol size
Mark the different fields e.g., craton interior, recycled orogen etc.
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Results and Discussions
• 3 RF Peaks 11.3 Ma , 10.5 ̴
Ma, 9 Ma.
• Abrupt decrease of Quartz and Feldspar 9 Ma ̴
• Rock Fragment types Better insights
Y axis values are absolute proportions
Increase resolution
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Rock Fragment Types
• 1̴1.3 Ma , 10.5 Ma : TRF possibly from the Greater Himalayan Formations
• Increased RF detritus - Higher erosion of MBT Hanging Wall Block
Increase resolution
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Rock Fragment Types
• 9 Ma SRF peak + Decrease in Quartz and Feldspar Modal percentages
• May indicate 2 events
• Change in RF Source or Drainage Reorganization
Increase resolution
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Source change hypothesis • Possible sources are
the Lesser Himalayan Metasedimentary Sequences
• Shale and Carbonates Dominant
• Low Quartz proportions•
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Causes• Drainage
Reorganization
• Hinterland Tectonics
• Increased SAR at around 11.5 – 9 Ma
• Paleocurrent (Burbank, 1991; 1992; 1994)
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Conclusions• MBT initiation 11.3 Ma ̴ or prior
• Major thrusting episode 10.5 Ma ̴
• 9Ma Change in source to LHS
• Drainage Reorganization
• A detailed study of palecurrent directions, Sr and Apatite Fission Track Dating is necessary to ascertain the event and possibly delineate the actual cause out of the two
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Conclusions—Cont..• This study documents for the first time the initiation of MBT in
the North-Western part of the Himalayas with a narrow age estimate
• The age is in agreement with the proposed age bracket of > 10 Ma and possibly > 11 Ma by Meigs (1995) deduced from the gravel progradation rate modeling
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Acknowledgements• I express my sincere gratitude to Dr. Prasanta Sanyal and Dr
Melinda Bera for allowing me to work on this project and for all the guidance and mentoring.
• I am indebted to Mr. Sambit Ghosh for without his help, I could not have done this work
• The entire Stable Isotope Lab Members for support
• Mr Rupam Rakshit for tirelessly making the Thin sections.
• And lastly , the entire DES, IISER K
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References• GSA Bulletin; January 1998; v. 110; no. 1; p. 2–21• Earth-Science Reviews, 22 (1985) 261-308• Earth-Science Reviews 76 (2006) 1 –131• Geology; May 1995; v. 23; no. 5; p. 423–426• Royal Society of London Philosophical Transactions, v. 326, p.
257–280• African Earth Sciences 33 (2001) 579–595• GSA Bulletin; March 2000; v. 112; no. 3; p. 394–412• Geological Society of America Special Paper 328 1999
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Similar work done in Nepal Siwaliks• Decelles et al, GSA
Bulletin, 1998
• Sr isotope and Rock Fragment Types in Nepal Siwaliks•
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RF Ternary, Maps, Sr Details, slides to add gravel progradation of Meigs model
Sinha, 2007
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Tectonic Activity stages for the NW Himalayas
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Sedimentary Fill character and rates controlled bySubsidence due to Active Thrusting climate change hinterland rock types exposed due to erosion and thrusting
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Causes• Possible causes for
the sedimentary souce change may have been exposure of the LHS to ersoion due to thrusting