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GEOLOGICAL HISTRORY OF NEPAL
HIMALAYA
•
Himalaya was formed by the collision of Indian
Plate with Eurasian Plate around 55 million years ago.
•
The major events in the geological history of
Himalaya are well recognizable in Nepalese sector. They are: Sedimentation in
the Purana Sea, Pan African Diastrophism, Sedimentation in Paleothethys,
Hercynian Diastrophism, Gondwana Sedimentation, Sedimentation in Neotethys,
beginning of Himalayan Orogeny, formation of foreland basin and tremendous rise
of Himalaya
A. Precambrian Events
•
Deep and Shallow marine sedimentation in
Purana Sea.
•
Wide distribution of Precambrian rocks in LH and
HH.
•
Very early during Paleozoic, there was a very
wide sea covering the vast territory of LH and the central and northern parts
of India.
•
Deep marine sedimentation in early phases and
shallow marine deposition in later phases dominantly of carbonate succession
with stromatolites.
B. Paleozoic Events
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It includes Pan African Diastrophism,
Sedimentation in Paleothethys, breaking of sedimentation due to Hercynian
Diastrophism and Early Gondwana Sedimentation
•
Pan African Diastrophism: long cycle of
Purana Sedimentation came to end towards the close of early Cambrian, sea was
forced to recede form LH and sedimentation was interrupted. Intrusion of
Cambrian Ordovician granites.
•
Sedimentation in Paleothethys:
Sedimentation was restarted in Tethyan Himalayan zone with abundant marine
fossils of barchipods, corals graptolites etc.
•
Hercynian Diastrophism: Interruption of
sedimentation in TH (regional unconformity). Rifting and volcanism in LH and
widespread glaciation.
•
Early Gondwana Sedimentation: at the end
of Paleozoic era along with some explosive volcanoes in rift valleys.
C. Mesozoic Events
•
Sedimentation in Neotethys and continetal
sedimentation of Late Gondwana.
•
Sedimentation in Neotethys: Tibetan
landmass in North was broken away due to rifting and opened new sea called
Neotethys between India and Tibet. Deep
marine sedimentation in northern part excluding Nepal Himalaya.
•
Sedimentation of Late Gondwana: continental sedmentaion of Upper Gondwana
unconfromably over Lower Gondwana.
D. Cenozoic Events
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Disappearance of Neotethys: due to plate
collision emplacement and squeezing of sea floor rocks. Formation of elongated
basins in North and south and rise of Himalaya.
•
Formation of MCT about 21 Ma. Around 25
to 15 Ma Granites and migmatites in TH
and HH. Also development of Nappe and Klippe.
•
Formation of MBT about 18 to 20 ma and
Siwalik Basin.
•
Formation of HFT, Dun Valley and Terai basin.
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