Anscestors of the Himalayas

[Guest guest]

"OF IMMOVABLE OBJECTS, I AM THE HIMALAYAS."Sri Krsna in Bhagavad Gita

 

Rangi makes a good observation about the possible 'lost cousins' of

Indian subcontinent viz. Madagascar & Seychelles. The theory being

Indian subcontinent moved up north east from near African plate

somewhere between 50-65 million years back.

 

http://uanews.org/cgi-bin/WebObjects/UANews.woa/1/wa/MainStoryDetails?

ArticleID=7831

 

Here is an interesting article from Sciencedaily. I have highlighed

the parts which kinda nullify our Indian subcontinent moving north

East to form Himalayas theory... Comments welcome!

 

Scientists Find Half-Billion-Year-Old Ancestral Mountains In The

Himalaya

By Lori Stiles

The world's highest and most spectacular mountains, the Himalaya of

Nepal, India, and Bhutan, are built on the foundations of a much

older mountain system, University of Arizona geoscientists have

discovered.

 

They have dated rocks that show Earth's mightiest range is predated

by ancestral mountains that existed in the same area between 450

million and 500 million years ago, long before India began plowing

northward into Asia 55 million years ago.

 

Their findings not only revise ideas on the region's tectonic

history, they offer new insight on connections between uplift of the

Himalaya during the past 55 million years and simultaneous global

shifts in seawater chemistry and climate.

 

"We conclude that the modern Himalaya Mountains are built on the

foundations of an ancient mountain range that may have been of

similar dimensions," said UA geosciences Professor George Gehrels,

who used state-of-the-art radioisotope techniques to date rock

formations in the Himalayan thrust belt.

 

Gehrels, UA geosciences Professor Peter G. DeCelles, UA doctoral

candidate Aaron Martin, UA master's degree graduate Tank Ojha, UA

undergraduate geosciences major Guy Pinhassi, and geology Professor

Bishal Upreti of Tribhuvan University in Kathmandu, Nepal, have

collaborated in field expeditions in rugged areas of Nepal for the

past several years. They report on their research in the September

issue of GSA Today, a scientific journal of the Geological Society of

America, online at http://www.geosociety.org Tank Ojha (left), a UA

master's degree student who now runs a geo-trekking company in

Kathmandu, and Tribhuvan University geology Professor Bishal Upreti

here debate the origin of boulder-borne schist from the high

Himalaya.

 

"Our model is based on observations that, between 450 and 500 million

years ago, rocks in the Himalaya were pushed down to great depth and

metamorphosed," Gehrels said.

 

The buried rocks became so hot under great pressure that they melted,

producing large granite bodies. The metamorphic schists and granite

bodies contained garnets and zircon crystals that Gehrels dated to

around 500 million years using uranium-lead radioisotope techniques.

 

These deep-level rocks were brought back up to the surface by

processes of faulting, uplift, and erosion soon after burial, their

observations suggest. The processes of uplift and faulting formed

mountains, which eroded and produced huge volumes of sediment.

 

The scientists studied conglomerates and sandstones found in

these "ancestral Himalaya" sediments in many different areas of the

present-day range. Their main area of research, in the Annapurna

range of Nepal, is a 5-day walk from the end of the nearest road.

 

They hired porters to carry camp gear and field equipment. Because

most samples weighed around 5 kilograms (11 pounds) and were

collected many miles from the nearest road, the researchers processed

their samples in the field, crushing granite samples by hand and

extracting garnets and zircon crystals by the panning-for-gold method.

 

The Himalaya is the best place on the planet for studying what

happens when Earth's continents collide, Gehrels noted.

 

Earth's surface is covered by a series of tectonic plates. Heat from

deep within the Earth drives convection currents that move the plates

in different directions. India rides on a plate that steadily

advances north a couple of centimeters a year, about as fast as your

fingernails grow. During the past 55 million years, this action has

uplifted Earth's tallest mountains, capped by 29,000-foot-plus Mount

Everest.

 

"The birth of the Himalaya is indeed this great story of rocks being

shoved down and being brought to the surface, while huge amounts of

erosion take place. But we now think that much of the burial, uplift,

and erosion happened between 450 million and 500 million years ago,"

Gehrels said. "The ancestral Himalaya Mountains appear to also have

formed in a regime of continental collision, with the Indian

continent being shoved beneath another landmass."

 

However, WHICH landmass is not yet known, he said.

 

"According to our model, this collisional event began with a small

range forming at around 508 million years ago. The faulting, burial

of rocks, formation of granite bodies, and uplift then propagated

toward India through time, with the mountain range growing in width

and perhaps elevation," Gehrels said.

 

By about 450 million years ago, as the forces of mountain building

waned, erosion leveled the topography down to the deep-level

metamorphic rocks, generating enormous amounts of sediment.

Subsequently, the ancestral Himalaya Mountains disappeared and the

region eventually subsided below sea level as the landmass was rifted

away from India's northern margin, Gehrels said.

 

"The region remained buried below marine sediments until India

collided with southern Asia around 55 million years ago and the

modern Himalaya Mountains began to form," he added. More research is

needed to determine the relative proportions of faulting, burial,

metamorphism, generation of granites, uplift and erosion that

occurred during these two phases of mountain-building, he said.

 

The revised geologic history also challenges Earth scientists to

rethink ideas on global climate change and the global shift in

seawater chemistry of about 55 million years ago.

 

Global climate began to cool around 55 million years ago, and

scientists theorize that this may have been driven by weathering

reactions in the Himalaya that remove carbon dioxide from the

atmosphere, decreasing the greenhouse effect and cooling Earth.

 

At about the same time, Earth's oceans changed chemically, a possible

result of vast quantities of Himalayan sediments carried by great

rivers into the sea.

 

"Maybe the Himalayas have played such an important role in shaping

modern climate and seawater chemistry because rocks exposed in the

mountain belt were buried, metamorphosed, and uplifted during an

earlier phase of mountain building," Gehrels said. "This multistage

history may be key to understanding the genetic linkages between

mountain building, climate change, and seawater chemistry."

 

Photos on UA website: http://uanews.org