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The Deccan beyond the plume hypothesis Hetu Sheth , Indian Institute of Technology (IIT) Bombay

The Deccan beyond the plume hypothesis Hetu Sheth , Indian Institute of Technology (IIT) Bombay. Structure of India. India-Seychelles break-up. Basic geology. The Dediapada dyke swarm. Bouguer anomaly map. 16-24-km-thick igneous layer under the region.

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The Deccan beyond the plume hypothesis Hetu Sheth , Indian Institute of Technology (IIT) Bombay

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  1. The Deccan beyond the plume hypothesis Hetu Sheth, Indian Institute of Technology (IIT) Bombay

  2. Structure of India India-Seychelles break-up

  3. Basic geology

  4. The Dediapada dyke swarm

  5. Bouguer anomaly map 16-24-km-thick igneous layer under the region

  6. Heat flow, thermal springs, high gravity anomalies

  7. Normal crustal thickness – 35 to 41 km

  8. P-wave velocity anomaly

  9. Hotspot tracks

  10. India and Indian Ocean • Must consider: • Palaeolatitudes • Vishnu FZ • 60-61 Ma volcanism • Age data questioned • Deccan plume died at 30 Ma?

  11. Late-stage Deccan volcanism

  12. The pre-volcanic uplift issue: regional vs. local • The plume head model predicts broad lithospheric uplift of 1 to few km, a few m.y. before flood volcanism. • Small local vertical motions not diagnostic; indicate local tectonics

  13. Local uplift and subsidence • Locality - picrites underlain by tilted sediments and conglomerate • Basement and basalt clasts in conglomerate • Uplift before and also after eruption • Bagh beds in western India are marine – subsidence over plume head centre

  14. Physio-graphy of India

  15. Regional pre-volcanic uplift? (1) • The 1500-km-long Western Ghats are very youthful, and form the precipitous edge of an elevated, tilted plateau. • The plateau has a mature topography (flat, ancient land surface getting dissected again). • The highest peaks of the Ghats (up to 2,695 m) are in the charnockite region of southern India

  16. Regional pre-volcanic uplift? (2) • Abundant evidence for major post-Deccan uplift of the Western Ghats • Prominent easterly drainage not a result of plume-head-caused pre-volcanic doming • Easterly drainage is antecedent

  17. Regional pre-volcanic uplift? (3) • Base of Deccan lavas is not exposed over much of the province • In most cases where base is exposed, no evidence for basin shallowing, no basement-derived conglomerates • Flat-lying lavas cover extensive flat erosion surfaces cut across varied rocks (e.g., central India) • Thin, local Lameta sediments

  18. The basement: Archaean crystallines, the great Vindhyan Basin (Mid-Late Proterozoic), the Gondwana basin (Permo-Carboniferous to Upper Jurassic)

  19. Pachmarhi: planation surfaces on Mid-Triassic Gondwana sandstone, covered by Deccan lavas • Spectacular post-Deccan uplift

  20. Jabalpur Patalkot Pachmarhi

  21. Conclusions • Circular outcrop – intersecting rifts • Crust and lithosphere unaffected by volcanism; normal thickness • 8-9 m.y. total duration of volcanism • Pre-volcanic regional doming: absence of evidence, evidence of absence • Major (~1-2 km) post-volcanic uplift • Continental rifting and break-up is a good and sufficient explanation

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