UNIVERSITY OF SOUTH ALABAMA GY 112: Earth History Lectures 31: Mesozoic Tectonics Instructor: Dr. Douglas W. Haywick Last Time… Mesozoic Overview A) The end of the Paleozoic B) Mesozoic time frame and evolutionary developments C) Paleogeography and key tectonic events (web notes 30) Mass Extinctions Era Years Cenozoic (0 to 65 MA) Major Extinction Mesozoic (65 to 245 MA) Major Extinction Paleozoic (245 to 550 MA) Phanerozoic Phanerozoic Mass Extinctions Extinctions have always been a part of the rock record Mass Extinctions The cause(s) of the Permian-Triassic extinction remain uncertain. •Asteroid strike •Cosmic radiation •Climate change •Plate tectonics •“Nemesis” •Flood basalts Mass Extinctions The crater is approximately 180 km wide. The asteroid impacted in a shallow marine, tropical environment. Mass Extinctions The cause(s) of the Permian-Triassic extinction remain uncertain…. … but whatever it was, it caused unprecedented changes Mass Extinctions At the end of the Permian and the end of the Cretaceous, extensive basalt lava flows covered a good chunk of the surface up to 1000’s of feet thick. The Siberian Traps are much more extensive than the Deccan traps Major climate change! Mesozoic Overview Late Age of the Cretaceous (65-135 MA) Middle Angiosperms Early Mesozoic Jurassic Late Age of the (203-135 MA) Middle Cycads Early Triassic Late Age of the (245-203 MA) Middle Reptiles Early Mesozoic Overview Many major evolutionary changes occurred during the Mesozoic •Rise of the dinosaurs •Rise of the cephalopods •Major microfossils (coccoliths) •Rise of the angiosperms Mesozoic Paleogeography Mesozoic Paleogeography Mesozoic Paleogeography Mesozoic Paleogeography Mesozoic Tectonics (Key Events) Period North America Other Major Events Orogenies Cretaceous Separation of India from Gondwanna Jurassic Nevadan Orogeny (J-K) Opening of Atlantic Sevier Orogeny Ocean (J-K) Triassic Sonoma Orogeny Opening of Gulf of (Triassic) Mexico Devonian Antler Orogeny (Devonian) Today Mesozoic Tectonics A) The Triassic B) The Jurassic C) The Cretaceous (web notes 31) Mesozoic Tectonics The separation of Gondwanna and Laurentia began in the Triassic. Initial flooding of the “Atlantic Ocean” began in the Jurassic. (More on sedimentation next time ) This was the start of a new drift direction for North America; WNW Paleozoic Tectonics Now we have convergence along what had been a pretty stable (passive) continental margin (except for the Antler Orogeny) in the Devonian Paleozoic Tectonics Speaking of which… … when the Antler Orogeny occurred, an island arc stuck onto the side of Laurentia. This clump of “new continent” is called a terrane (specifically the Antler Terrane) Paleozoic Tectonics When terranes hit a continent, they are called docking events. Ultimately, continents grow bigger by scooping up geo-crap in their drift direction (Accretionary tectonics) Mesozoic Tectonics Into the Triassic, many more “terranes” (mostly island arcs) began to be scooped up by North America as it drifted WNW Mesozoic Tectonics Into the Triassic, many more “terranes” (mostly island arcs) began to be scooped up by North America as it drifted WNW •Brooke Range Terrane (Alaska) •Stikine Terrane (British Columbia) •Sonoma Terrane (Nevada) Mesozoic Tectonics Into the Triassic, many more “terranes” (mostly island arcs) began to be scooped up by North America as it drifted WNW •Brooke Range Terrane (Alaska) •Stikine Terrane (British Columbia) •Sonoma Terrane (Nevada) Mesozoic Tectonics Mesozoic Tectonics The Sonoman Orogeny in the Triassic marks the start of the formation of the Cordilleran Mountains and the current active margin Mid-Triassic Paleogeography (source http://jan.ucc.nau.edu/~rcb7) Mesozoic Tectonics In the Jurassic, we start to see terranes with mixed lithologies docking with North America (e.g., Klamath Terrane) •Major (felsic) intrusions begin Mesozoic Tectonics The culmination of several “hits” and docking events as well as major phases of felsic intrusions is collectively called the Nevadan Orogeny Mid-Jurassic Paleogeography (source http://jan.ucc.nau.edu/~rcb7) Mesozoic Tectonics In the Cretaceous, more hits and more intrusions. More uplift •Wrangellia Terrane docks Mesozoic Tectonics The culmination of several “hits” and docking events from the Jurassic to the Cretaceous produced major phases of thrust faulting and is collectively called the Sevier Orogeny Early Cretaceous Paleogeography (source http://jan.ucc.nau.edu/~rcb7) What’s the Point? What’s the Point? The Appalachians and Cordilleran Mountains were both formed via compressional tectonic events. Appalachians formed through collisions with other continents Cordilleran Mts. formed via accretionary tectonics What’s the Point? And once we get into the Cenozoic, deciphering the tectonic history of the Cordilleran Mountains gets really tricky… … stay tuned for details! Today’s Homework 1. Time Chart 3 due in one week (Hadean-Today ) Next Time 1. Mesozoic Sedimentation (Lectures 32 and 33) GY 112: Earth History Lectures 30 and 31: Mesozoic Geology Instructor: Dr. Doug Haywick [email protected] This is a free open access lecture, but not for commercial purposes. For personal use only. .