Cenozoic Earth History I

Transcription

1 Cenozoic Earth History I Cenozoic plate tectonics Tertiary, Quaternary, Paleogene, Neogene Tejas Transgression North America s east coast geology Laramide Orogeny Post-Laramide mountain building and volcanism The Rocky Mountains Yellowstone Hotspot Alpine-Himalayan Orogenic Belt Circum-Pacific Orogenic Belt

2 The Cenozoic Era The Cenozoic is the shortest era of the Phanerozoic Eon. It starts with the second largest mass extinction in Earth s history and includes the Recent today. There is now agreement in the Earth science community about how the Cenozoic should be sub-divided: Paleogene, Neogene and Quaternary.

3 The Cenozoic Era The Tejas transgression began and ended during the Paleogene. Starting at about the middle of the period, cooling at both poles led to a long period of global cooling and sea level fall. The fall in sea level led to the development of many of the Atlantic Coastal Plain s interesting geologic features like a stair-step series of scarps (paleoshorelines) and terraces (wave-scoured sea floor). By the Neogene, the Earth s polar climate had cooled to the point that both sea ice and continental glaciers began to grow, locking Earth s climate into Icehouse Earth the Earth s climate was (and still is) cold enough that minor changes in the shape of the planet s orbit causes extensive ice ages.

4 The flat-lying Atlantic Coastal Plain (ACP) contains a thick sequence of sediments weathered from the Appalachians and deposited during the Zuni (Cretaceous) and Tejas (early Tertiary) transgressions. The ACP strata at the surface are progressively younger, with Cretaceous and Eocene strata cropping out farthest inland. The ACP sedimentary wedge thickens toward the ocean, reaching a thickness of several kilometers in offshore canyons.

5 The scarps mark places where coastal erosion occurred in the past. In other words, they mark the positions of shorelines in the past. The terraces were formed by slightly offshore erosion and deposition in the shallow ocean.

6 Relatively flat lying sedimentary rocks deposited during the major transgressions and orogenies of the Paleozoic. The hilly topography is controlled by river drainage. Coal in the Appalachian Plateau strata are targets for strip mining and mountaintop removal mining because it is relatively flat lying seams.

7 The deformed and faulted sedimentary rocks of this province were deposited at the same time as the flat lying rocks of the Appalachian Plateau. These strata were deformed and faulted by the great Alleghanian Orogeny, which shoved giant blocks westward for dozens of miles. These blocks are bounded by very large thrust faults.

8 This province contains primarily Proterozoic and Paleozoic aged plutonic, metamorphic and sedimentary rocks, including parts of the Grenville orogen. The amount of uplift necessary to expose these deep crustal rocks is on the kilometer scale. All three Paleozoic orogenies contributed to this massive uplift.

9 Usually heavily weathered rock similar to the Blue Ridge as well as rocks that formed during the rifting of Pangaea (rift basin sediments and igneous dikes). Piedmont Province rocks underlie the sedimentary deposits of the Atlantic Coastal Plain.

10 Lightly lithified and unconsolidated sediment deposited during marine transgressions in the Cretaceous Period and Cenozoic Era. The province extends into the Atlantic Ocean to the edge of the continental shelf. This sedimentary material is more easily eroded than crystalline rock, so the eastern boundary is a fall zone, where the gradients of rivers steepen suddenly as they dig into the softer material of the coastal plain.

11 Fall Zone The eastern margin of North America has been folded into a series of arches and embayments by tectonism associated with formation of the Caribbean plate and persistent northward movement of Cuba. The bays fill with thick packages of sediment when sea level is high.

12 Eastern North America is presently a passive continental margin Ultimately oceanic crust will break along the continental margin and subduction of Atlantic basin crust will begin, just as it did with the Iapetus Ocean during the Paleozoic.

13 The Cenozoic Era The Laramide Orogeny ended during the Paleogene. However even with the end of active subduction along the continental margin, the Rocky Mountains went through several periods of rapid uplift, especially during the Neogene. The modern shape of the Rocky Mountains is the result of erosion of this uplifted material, primarily during the Neogene. The Neogene was also a time of great change in other parts of the Cordilleran, with the development of the San Andreas fault system, the Basin and Range province, and the extrusion of lava to form the Columbia Plateau s Large Igneous Province (LIP). Part of the North American Plate dragged over the Yellowstone hot spot causing a series of volcanoes to pop up along its track.

14 The Farallon Plate continued to subduct under North America until today only the Juan de Fuca and Cocos plates remain. Along the way, many, many terranes that were originally embedded in the Farallon Plate became part of North America. The subduction of the Farallon-Pacific spreading center caused many geologic changes, including the establishment of the San Andreas fault system

15 Increased heat beneath the Cordilleran plus stress from interactions between the North American and Pacific Plates caused crustal extension such as that found in the Basin and Range Province during the Neogene. The crust and mantle in this region have stretched up to 100% of it s original width. In the brittle upper crust, this stress caused multiple normal faults and a characteristic valleys separated by ridges (basin and range) topography NAWestBasin&Range.jpeg

16 The same temperature increase caused the Laramide Orogeny, which included the initial uplift of the massive Colorado Plateau followed by more intense uplift during the Neogene. Marine rocks (deposited below sea level) are now found well over a mile above sea level. The best exposure of these rocks are found in the Grand Canyon, a great series of canyons carved by the Colorado River. Igneous intrusions formed along the edges of the Colorado Plateau during the Cenozoic both during the Laramide Orogeny and again starting in the late Miocene and continuing until quite recently.

17 Cascade Range Columbia plateau flood basalts Yellowstone hot spot Snake River Plain San Juan volcanic field Arizona volcanic field Volcanic activity in the Cordilleran continued through the Cenozoic due to subduction of the Juan de Fuca and Farallon plates, flood basalt formation in the Columbia plateau and hot spot volcanism caused by the movement of the North American Plate over the Yellowstone hot spot.

18 The Columbia Plateau is an enormous Large Igneous Province (LIP) formed during the Miocene and Pliocene Epochs. Most of the basalt was extruded in a geologically short time at the beginning of the igneous activity in the area during the late Miocene (~17 Ma 14 Ma). The basaltic lava erupted from a series of large vents, some dozens of miles long, and from classic shield volcanoes. The source of the basalt and cause of the extensive eruption is debatable. Almost every known cause of volcanism has been hypothesized for this massive event, including that it was the result of an asteroid impact. One of the most popular current theory is that the eruptions were the results of a short-lived mantle plume, similar to the more permanent plumes that form hotspots.

19 Present of hot spot volcanism at 4.5 Ma volcanism at 16 Ma volcanism at 9 Ma The track of the North American Plate s southeastern movement over a hot spot during the Neogene is marked by a trail of volcanoes. The hot spot doesn t move, the continent moves over it. Volcanic activity in Yellowstone national park like geysers and hot springs indicates that the hot spot is still active.

20 Yellowstone s Dormant (Extinct?) Volcanoes Island Park Caldera Erupted Huckleberry Ridge tuff 2 Ma Yellowstone Caldera Erupted at Lava Creek tuff 600,000 years ago Henry s Fork Caldera Erupted Mesa Falls tuff 1.3 Ma

21 Previous eruptions at the Yellowstone hotspot produced enormous amounts of air-borne volcanic ash and debris, leading to Yellowstone s designation as a Supervolcano. An eruption of that size today be an unimaginable disaster for the western hemisphere.

22 The Cascade Range volcanoes are the result of partial melting of the Juan de Fuca as it subducts. The range has been active into historical times with the Mt. St. Helen s eruption of 1980 being the most recent major eruption. The Juan de Fuca plate is a remnant of the great Farallon plate. This small oceanic plate is bounded by a spreading center to the west and a subduction zone to the east, where it dives beneath the North American Plate.

23 Recent Earth s Major Orogenic Belts The Circum-Pacific and Alpine-Himalayan orogenic belts are Earth s presentday major mountain building belts.

24 The Alpine-Himalayan Orogenic Belt Volcanism, seismicity, and deformation in the Alpine-Himalayan orogenic belt extends eastward from Spain through the Mediterranean region into Southeast Asia. This tectonism is due to collision of the Arabian, African and Indo-Australian plates with the Eurasian plate. Eocene (50 40 Ma) Miocene (25-15 Ma)

25 The Himalayan Orogeny The movement of the Indian-Australian plate northward caused this orogeny, with oceanic crust subducting beneath Eurasia followed by the collision of the Indian continental block with the Eurasian plate. Although the orogeny is over, the area still experiences massive earthquakes as the leftover stress is accommodated by large earth movement.

26 The Alpine Orogeny This complicated orogenic event is occurring in response to northward movement of the African and Arabian plates toward southern Europe. The convergence is causing deformation along a linear zone from Spain eastward through Greece and Turkey and along Africa's northwest coast, producing many of Europe s largest mountain chains. Tectonic map of southern Europe and the Middle East, showing tectonic structures of the western Alpide mountain belt. Only Alpine (Tertiary) structures are shown.

27 Mediterranean Tectonics Subduction of Mediterranean crust under Italy, Greece, and Turkey continues to cause volcanism and seismicity. Mount Vesuvius and several other Italian volcanoes have erupted several times during the last 4,000 years. Greece and Turkey have more earthquakes than volcanoes. In 1999 an earthquake near Izmit killed 17,000 people in Turkey.

28 Circum-Pacific Orogenic Belt Subduction Zones (Ring of Fire) Pacific plate under western Eurasian plate Phillipine plate under Eurasian plate Pacific plate under the North American plate Juan de Fuca plate under North American plate Cocos plate under South American plate Pacific plate under Indian- Australian Plate Nazca plate under South American plate Subduction causes mountain building and volcanic activity all around the Pacific Ocean. Note the number of different plates involved!