032-01.jpg 032-03.jpg

THE HIMALAYA ~40 million years  

The Himalayas are among the youngest mountain ranges on the planet and consist mostly of uplifted sedimentary and metamorphic rock. According to the modern theory of plate tectonics, their formation is a result of a continental collision or orogeny along the convergent boundary between the Indo-Australian Plate and the Eurasian Plate. This is referred to as a fold mountain.

The collision began in the Upper Cretaceous period about 70 million years ago, when the north-moving Indo-Australian Plate, moving at about 15 cm per year, collided with the Eurasian Plate. About 50 million years ago, this fast moving Indo-Australian plate had completely closed the Tethys Ocean, the existence of which has been determined by sedimentary rocks settled on the ocean floor and the volcanoes that fringed its edges. Since these sediments were light, they crumpled into mountain ranges rather than sinking to the floor. The Indo-Australian plate continues to be driven horizontally below the Tibetan plateau, which forces the plateau to move upwards. The Arakan Yoma highlands in Myanmar and the Andaman and Nicobar Islands in the Bay of Bengal were also formed as a result of this collision.

The Indo-Australian plate is still moving at 67 mm per year, and over the next 10 million years it will travel about 1,500 km into Asia. About 20 mm per year of the India-Asia convergence is absorbed by thrusting along the Himalaya southern front. This leads to the Himalayas rising by about 5 mm per year, making them geologically active. The movement of the Indian plate into the Asian plate also makes this region seismically active, leading to earthquakes from time to time. (click to see all the article on Wikipedia)

 

喜馬拉雅山脈 ~4千萬年前

喜馬拉雅山脈是地球上最為年輕的山脈,大部分是由沈積岩與變質岩抬升所形成的。根據最新的版塊構造理論,其形成起因於大陸碰撞,或是印澳版塊與歐亞版塊的匯聚邊界的造山運動。因此造成了山脈皺褶的情形。

這碰撞開始於白堊紀初期,約7千萬年前,向北移動的印澳版塊,與歐亞版塊發生碰撞。約5千萬年前,移動迅速的印澳版塊將提特斯洋(古地中海)完全封閉了,經由位居於海底的沈積岩,與海底火山邊緣殘留的冷卻熔岩可以證明其存在。由於這些沉積物較輕,因此產生了皺摺的山脈,而非沉入了地殼當中。印澳版塊繼續水平地沒入西藏高原之下,驅使著該高原向上抬升。緬甸的阿拉干山脈高地與孟加拉灣的安達曼-尼科巴群島,也是因此碰撞而形成的。

目前印澳版塊每年仍以67公釐的速度移動著,下一個1千萬年將前往亞洲15百公里。印度-亞洲的合聚是由喜馬拉雅山脈南端的前緣的掩衝斷層作用而吸收所致,每年約20mm。這樣的地質活動下,喜馬拉雅山脈每年上升5公釐。印度版塊進入亞洲版塊的運動,導致了該地區不時地有地震發生。

(維基連結:喜馬拉雅山脈提斯特洋)

    全站熱搜

    北極海 發表在 痞客邦 留言(0) 人氣()