mountain building episodes

Transcription

1 EarlyTertiaryTectonicsand mountain building episodes Jarðsaga 2 - Saga Lífs og Jarðar - Ólafur Ingólfsson

2 The World as we know it largely a product of Cenozoic tectonics and volcanism...

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4 Mountain building (orogenic and volcanic) in process

5 Volcanism and the opening up of the North Atlantic During Cretaceous times, N America, Greenland, and Eurasia were part of a common land mass. Early in the Cenozoic, about 60 MY ago, sea-floor spreading began between Greenland and Europe. Continued sea-floor spreading between North America and Greenland led to opening of Baffin Bay. Volcanism on western Greenland, Greenland acted as an independent plate during the early Cenozoic. Thick basalt plateaus built up in eastern Greenland, western Scotland, northern Ireland and the Faeroes

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8 Cretaceous-Tertiary basalts in Arctic Canada and northern Greenland

9 Early Tertiary volcanism on central West Greenland Hyaloclastite breccias and lava flows of the Vaigat Formation on the south coast of Nuussuaq. Cretaceous and Paleocene sandstones and shales are present below the volcanic rocks. The cliff is about 1300 m high. Photo: Asger K. Pedersen, Geological Museum, Copenhagen.

10 Tertiary basalt plateau, Disko Island

11 Tertiary basalts, East Greenland In East Greenland early Tertiary volcanic rocks crop out between latitudes 68 o and c. 75 o N. South of Scoresby Sund/Kangertittivaq (c. 70 o N) plateau basalts cover an extensive region of c km 2

12 Flood basalts in Greenland

13 Major Tertiary intrusive centres in East Grennland

14 Basalt dykes, East Greenland An early Tertiary dike in Archean gneiss, Scoresby Sund area, E Greenland A Tertiary dike swarm, Scoresby Sund area, East Greenland

15 North Atlantic/Iceland Hotspot Circles indicate hypothesised locations of an Icelandic mantle plume at the times indicated in MY.

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17 Land bridge over Iceland... The Tertiary biota of Iceland is closely related to the modern Eastern Deciduous Forests of N America. Flora and fauna used the dynamic land bridge between North America and Europe via Greenland- Iceland as a migration route during the Paleogene. This land bridge emerged due to hotspot activity on the Mid Atlantic ridge in connection with the opening of the N Atlantic.

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19 Early Tertiary land bridge across Iceland Plate reconstruction to 60 Ma with simplified seafloor. The main dike trend in the British Volcanic Province schematically shown to extend to the West Greenland magmatic area

20 Tertiary basalts in Ireland 60 MY ago the Antrim area, Ireland, was subject to intense volcanic activity. There were three periods of volcanic activity which resulted in the flows, known as the Lower, Middle and Upper Basalts. It is the Middle Basalts rocks which forms the columns of the Giants Causeway.

21 ...and Scotland Staffa: Fingal's Cave and the columnar jointing in Tertiary volcanic flows In early Tertiary, a volcanic chain ran down what is now the west coast of Scotland. The islands of Skye, Rum, Mull, Arran and St. Kilda, along with the Ardnamurchan Peninsula were all volcanic centres (above sea level). Although the volcanoes themselves no longer remain apparent, their lava flows and their eroded internal structures are obvious in the geology of Scotland.

22 Three series of plateaux basalts on the Faeroe Islands There was extensive volcanism on thefaeroeislandsduringthe period MY. The Tertiary basalts on the Faeroe Islands are divided into three series, the Lower-, Middle- and Upper series.

23 Thick Cenozoic sediments on top of the basalt pile The possibility for striking it rich and finding oil on the Faeroe Island shelf has led to extensive geophysical surveying and drilling.

24 Denmark was a sedimentary basin......below sea level until Miocene. Thick deposits of limestones (Paleocene) and clays (Eocene-Oligocene).

25 The Fur Formation Volcanic ash beds of late Paleocene-Eocene age accumulated in the Fur Formation, N Denmark. This formation is famous for its fossils, volcanic ash beds, and economic uses. The ash has similar geochemistry to plateau basalts of the Faeroes-East Greenland province

26 North Sea Oil... North Sea oil and gas has been generated from deeply-buried mudstone source rocks. Commercial petroleum reservoirs occur in almost every sedimentary succession ranging in age from ca MY. Sandstone reservoirs of Paleogene age are estimated to contain about 20% of the oil province s proven hydrocarbon reserves

27 The Early Tertiary Laramide Orogeny The Laramide Orogeny started in the Late Cretaceous and continued into Oligocene, The Alpine Orogeny started in early Eocene and continued into Miocene

28 Tectonic maps of N America and the N Atlantic The Laramide Orogeny

29 The Laramide Orogeny TheLaramide orogeny was a 30 million year period of mountain building in western N America that started in the Late Cretaceous, 70 MY ago, and ended in the Late Paleogene 40 MY ago. The major feature that was created by this orogeny was the Rocky Mountains. Evidence of the Laramide orogeny is present from Mexico to Alaska.

30 Cretaceous Paleogeography The Cretaceous paleogeography reflected a large inland sea, the last time such a sea would exist in North America. The east and south parts of the U.S. were very broad, lowlying terranes, whereas the largest mountain ranges of the Mesozoic in the west existed in the Cretaceous.

31 Early Tertiary paleogography In the Early Cenozoic, the subduction continued along the west coast, producing some igneous rocks, such as those at Devil's Tower NM in Wyoming. The Rocky Mountains region was dominated by the fold and thrust belt of the Laramide Orogeny.

32 Laramide Orogeny At the end of the Cretaceous and through the early Cenozoic, the Laramide orogeny, a huge deformational event, reached from the west coast deep into the continent to the Rocky Mountains and Great Plains. Extensive thrusting of Mesozoic and older rocks on top of younger rocks occurred throughout the Rocky Mountains, as well as broad warping of the continental basement (uplifting the Black Hills of South Dakota).

33 Laramide Orogeny very complex tectonics The Laramide orogeny originally was a poly- phaselatecretaceous- Oligocene orogeny, consisting of many disparate pulses of deformation that varied in intensity and age from place to place in western North America. /1998_Laramide/1998_Laramide.htm

34 Laramide Orogeny and sedimentary basins As the Rocky Mountains are uplifting, basins form between major uplifts. Huge lakes fill the basins during the Eocene.

35 A Rocky Mts transect Uplifted blocks and down-dropped basins in central western USA. Very huge lake deposits (Green River Formation). Beginning of Yellowstone volcanism (a mantle plume underneath the American West)

36 The Lewis Thrust Fault A km long thrust fault, formed MY ago The Lewis thrust fault. The white Paleozoic limestone has been thrust over the brown Mesozoic shales

37 Rocky Mts still in the making The cause of the Laramide Orogeny is still debated, and may have been due to collision of an oceanic terrane to the west, or an nearly flat-dipping subduction zone that extended deformation deep into the continental interior. In the middle Cenozoic, the Laramide Orogeny Rocky Mts would be eroded down, only to be rejuvenated in the last 30 MY by the change in tectonic setting that occurred along the west coast, when the spreading center and subduction zone collided off the west coast, changing the plate boundary to the transform fault system of the San Andreas. Recent uplift and formation of the Sierra Nevada, Basin and Range, Colorado Plateau and modern Rocky Mountains occurred after this change in plate tectonic setting along the western margin.

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39 Japan a product of Cenozoic tectonic events pics/2004/tp html

40 ...and so is Indonesia

41 Tectonic activity in Eurasia EarlytomiddleTertiarywasa periodof intense tectonic activity in Eurasia

42 The Alpine Orogeny The Alpine Orogeny was a mountain-building event that affected southern Europe and the Mediterranean region during the early-middle Tertiary Period. The Alpine orogeny produced intense metamorphism of preexisting rocks, crumpling of rock strata, and uplift accompanied by both normal and thrust faulting. It was responsible for the elevation of the present Alps, and for the uplifting of plateaus in the Balkan Peninsula and in Corsica and Sardinia.

43 The Alps seen from space

44 Collision of the African and Eurasian Plates In the late Cretaceous period, the African and Eurasion plates began to converge, closing the Tethys Ocean basin. The Mediterranean sea is remnants of this ancient ocean.

45 Very complex tectonics There are three major geomorphical settings within the Mediterranean basin: Areas with stable margin characteristics; Areas with unstable convergent margin charactericstics; Areas with extensional margin (rifting) characteristics.

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47 The Mediterranean basin is a location of an intercontinental interplate system; with compressional and extensional events occurring within close proximity.

48 Mediterrean volcanic activity and earthquakes All of the volcanic and seismic activity in the Mediterranean area is related to one or more of these processes; subduction, extension, or other tectonic events throughout the Cenozoic.

49 A continuum between the Alps and the Himalayas... The reddish brown landform clearly visible in the middle of this image is a great fold structure extending to the arid highlands in Pakistan, Afghanistan, and Iran.

50 Raising the Himalayas

51 The Grand Tertiary Collision About 80 million years ago, India was located roughly 6,400 km south of the Asian continent, moving northward at a rate of about 9 cm/yr. When India rammed into Asia about 40 to 50 million years ago, its northward advance slowed by about half.

52 Formation of the Himalayas 60 MY ago

53 Formation of the Himalayas 40 MY ago

54 Formation of the Himalayas 20 MY ago

55 Formation of the Himalayas Today

56 Much of the uplift has occurred during the past 10 MY

57 Present rate of uplift... The Himalayas and the Tibetan Plateau to the north have risen very rapidly. In 50 million years, peaks such as Mt. Everest have risen to heights of more than 9 km. The impinging of the two landmasses has yet to end. The Himalayas continue to rise more than 0.5 cm a year - a growth rate of 5 km in a million years!

58 The isolation of Antarctica

59 ODP record of Antarctic cooling

60 Tectonic effects on climate 1 Computer model experiments performed to test the climate's sensitivity to mountains and high plateaus show that plateau uplift in Tibet and western North America has a small effect on global temperature but cannot explain the magnitude of the mid-late Tertiary cooling trend. Plateau uplift does, however, have a significant impact on climate, including the diversion of North Hemisphere westerly winds and intensification of monsoonal circulation.

61 Tectonic effects on climate 2 The collision of India and Asia led to the uplift of the Tibetan Plateau and the Himalayas. While topography may not be enough to explain the cooling trends, another mechanism may account for changing climate. The uplift may have caused both an increase in the global rate of chemical erosion, as well as erode fresh minerals that are rapidly transported to lower elevations, which are warmer and moister and allow chemical weathering to happen more efficiently. Through these mechanisms, then, it has been hypothesized that the tectonically driven uplift of the Tibetan Plateau and the Himalayas is one of the causes of the post-eocene cooling trend.

62 EarlyTertiarytectonicsgreatly effected global environments Oceanic circulation was strongly affected by the tectonic events that opened up the N Atlantic, closed the Tethys Sea and drove Antarctica towards a pole-centered position

63 References for this lecture Stanley: Earth System History. Arnold, London This Dynamic Earth