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

Himalayan Foreland Basin and The Major Lithotectonic Divisions of the Himalaya

Bera et al., 2010

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

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.,

Chronologyof the majorTectonic Activity for the NW Himalayas

Yin, 2006

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)

Previous Work : Burbank, 2000; Meigs, 1995

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

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

Study Area – Kangra Ranital

Deformed…change it

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

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)

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

Methods for Petrographic Analysis- Gazzi-Dickinson Point Counting

Methods

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.

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

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

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

Source change hypothesis • Possible sources are

the Lesser Himalayan Metasedimentary Sequences

• Shale and Carbonates Dominant

• Low Quartz proportions•

Causes• Drainage

Reorganization

• Hinterland Tectonics

• Increased SAR at around 11.5 – 9 Ma

• Paleocurrent (Burbank, 1991; 1992; 1994)

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

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

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

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

Similar work done in Nepal Siwaliks• Decelles et al, GSA

Bulletin, 1998

• Sr isotope and Rock Fragment Types in Nepal Siwaliks•

RF Ternary, Maps, Sr Details, slides to add gravel progradation of Meigs model

Sinha, 2007

Tectonic Activity stages for the NW Himalayas

Sedimentary Fill character and rates controlled bySubsidence due to Active Thrusting climate change hinterland rock types exposed due to erosion and thrusting

Causes• Possible causes for

the sedimentary souce change may have been exposure of the LHS to ersoion due to thrusting