Origin of the Solar System

1. Origin of the Solar System • Nebula collapse • Imanuel Swedenborg, Immanuel Kant, Pierre-Simon LaPlace • Existence of early (~5bya) nebula in Milky Way galaxy • Compositional segregation • Denser, hotter materials (Fe, Ni) in inner zone • Lighter, colder materials (H, He) in outer zone • Planetary accretion • Inner rocky planets (Mercury, Venus, Earth, Mars) • Iron, Nickel, silicate minerals (oxygen and silicon) • Outer gas bags (Jupiter, Saturn, Uranus, Neptune) • Present solar system

2. Origin of the Solar System • Illustration of collapsing nebula • Angular momentum flattens disk & begins revolution of disk material around protostar material • Pressure of coalescing dust & gas elevate temps at center eventually igniting fusion (development of true star) • Accretion process sweeps up disk material creating larger and fewer objects

3. Orion Nebula • One of the brightest in the night sky • Lies south of Orion's Belt • 1344 ly away • Closest huge star formation area to Earth • A stellar nursery where stars are born • Contains ~700 stars in various stages of birth • Hubble Space Telescope (HST) has discovered 150 formations called proplyds or "protoplanetary disks“ • Believed they are solar systems in the very early beginning of their formation

4. Nebula RCW 79 • RCW 79 ~ 70 light-years in diam • 17,000 ly away in southern constellation Centaurus • Blown by winds and radiation from hot young stars • Infrared light from the dust embedded in the nebula is tinted red in this view from the Spitzer Space Telescope • The expanding nebula triggers star formation as it slams into gas & dust surrounding it • New stars are yellowish points scattered along the bubble's edge

5. Protoplanetary or Circumstellar disks • Rotating circumstellar disk of dense gas surrounding a young, newly formed star • Observed around several young stars in our galaxy • Sometimes called the “accretion disk”

6. Development of the Earth (Planets) • Differentiation • The separation of material through differences in density • Atmosphere/Hydrosphere/Biosphere • The outer lightest gases and liquids • Crust - Thin outer layer composed mostly of Si and O (silicate) rocks • Mantle - Thicker layer dominated by silicates but including heavier elements such as Fe and Mg • Layers based not on composition but strength • Lithosphere – crust and upper mantle composing strong, rocky layer • Asthenosphere – heat-softened, slow-flowing layer of still “solid” rock • Core - Small inner-most layer composed of Fe and Ni • Outer core is liquid – responsible for the Earth’s magnetic field • Inner core is solid

7. Planetary Differentiation :the internal layered structure of the Earth (planets) • Can be defined 2 ways • By mechanical properties • Lithosphere, asthenosphere, mesosphere, outer core, and the inner core • By chemical properties • Crust, upper mantle, lower mantle, outer core, and inner core. • Layering is inferred indirectly using the time of travel of refracted and reflected seismic waves • The Outer Core does not allow shear waves to pass through it • The seismic velocity is different in other layers • Changes in seismic velocity between different layers causes refraction • Reflections are caused by a large increase in seismic velocity

8. Plate TectonicsBasic Concepts • Earth’s lithosphere is composed of rigid plates • 7 major plates • Numerous smaller ones • Most plates are composed of both continental & oceanic crust • Plates “float” upon a hot, plastic layer of the upper mantle • Convection cells in mantle best current theory for driving force of plate movement • “Tectonic conveyor belt” • New crustal material created at divergent plate boundaries • Older crustal material consumed at convergent plate boundaries

9. Earth’s Tectonic Plates

10. Basic Concepts(continued) • Plates move relative to each other in three ways • Divergent – tensional stress at mid-ocean ridges • Convergent – compressional stress at subduction zones • Transform – shear stress at strike-slip faults or offsetting mid-ocean ridges • New oceanic crust is formed at divergent plate boundaries • ~6-11km thick • Mostly gabbros and basalts – ophiolite suites • Older ocean crust is consumed at convergent plate boundaries • Oceanic to oceanic subduction (mostly Pacific) • Oceanic to continental subduction (Western S.A.) • Continent to continent collision (Himalayas) • Most seismic activity, volcanism, and mountain building takes place along plate boundaries • Pacific “Rim of Fire” • The centers of plates are mostly geologically stable

11. Divergent • Tensional • Normal Faulting • Sea-floor spreading • Mid-Ocean Ridges • Mid-Atlantic Ridge System • Convergent • Compressional • Reverse faulting • Subduction Zones • Cascade Mtn. Range • Transform • Shear • Strike-slip faults • Ridge offsets • Major Strike-slip faults • San Andreas 3 Types of Plate Boundaries

12. Schematic of plate boundary locations

13. Rifting and the Origin of Ocean Basins • Intercontinental upwelling of a convection cell causes crust to thin – tensional stress- and break creating rift zone • Evolution of Ocean Basins • Red Sea • Gulf of California • Three arm rift zone • Two continue to form mid-ocean ridge system • One fails to form aulacogen • Rio-Grande, Mississippi valley

14. East African Rift

15. Rifting & the creation of Ocean Basins • Upwelling beneath a continental landmass • Normal faulting • Mafic volcanism • Crustal thinning • Inundation of low rift valleys • Inland seas • Separation of landmasses • Continued motion forces continental segments apart • Creation of a true mid-ocean ridge • Cooling & sinking of dense plate creates deep ocean basins

16. Mid-Ocean Ridges • Production of new oceanic crust • Upwelling of ultra-mafic magma along linear or sinuous ridge systems • Hotter at ridge spreading centers • > cooling at > distance from rift • Topographic high along spreading centers • Ophiolite Suite – • Siliceous or carbonate sediments • Pillow basalts • Gabbros • Ultra-mafic peridotites • Alteration through heated seawater penetration along cracks and fissures

17. Mid-Atlantic Ridge Complex • The Mid-Atlantic Ridge complex is responsible for the volcanic islands of Iceland • Iceland is composed of some of the youngest oceanic crust surfacing the Earth today • One of easiest areas geologists can study in situ how new oceanic crust is formed

18. Mid-Atlantic Ridge Complex Aerial view of the area around Thingvellir, Iceland, showing a fissure zone (in shadow) that is an on-land exposure of the Mid-Atlantic Ridge. Right of the fissure, the North American Plate is pulling westward away from the Eurasian Plate (left of fissure). (Photograph by Oddur Sigurdsson, National Energy Authority, Iceland.)

19. Oceanic Crust Age(all pre-K has been destroyed) * Note symmetrical ages of oceanic crust across MOR’s

20. Transform Boundaries • Offsets perpendicular to ridge complexes • Rocks moving in same direction at distance from ridge complexes • San Andreas Fault system • Zig-zag ocean ridge system • Overridden by subduction zone • Transform boundary extends as subduction zone moves beneath continental plate • Additional motion is taken up in lateral movement

21. San Andreas Fault Zone • The San Andreas fault zone is ~ 1,300 km long • In places tens of kms wide • Cuts two thirds the length of California • As a transform fault it connects spreading centers in the Gulf of California to ones off the NW coast of NA • Pacific Plate is grinding horizontally NW past the North American Plate • 10 million years • Average rate of about 5 cm/yr

22. San Andreas Fault • The Blanco, Mendocino, Murray, and Molokai fracture zones are some of the many fracture zones that scar the ocean floor and offset ridges • The San Andreas is one of the few transform faults exposed on land

23. 3 Types of Subduction Scenarios

24. Subduction Zones • Oceanic Trenches • Deep, narrow depressions as subducting plate bends downward • Marianas Trench (>36,000ft deep) • Accretionary Wedges • Sediments and pieces of oceanic plate plastered against continental plate • California Coast ranges • Highly deformed sandy and shaly matix with blueschist facies interbedded • Volcanic Arcs • Typically on overriding plate • Partial melting of descending plate results in silicic volcanism on overriding plate • Dangerous pyroclastic eruption potential • Benioff zone – concentration of seismic events tracing a subducting plate

25. Convergent Boundaries • Collision zones • Form large complex mountain chains • Alps, Himalayas, Appalachians, Urals • Suture Zone – where the ocean once existed between continents • New theory that partial continental subduction occurs

26. Pacific Ring of Fire • Subduction Zones + coastal population centers = high risk of multiple events

27. Volcanism and Plate Boundaries • Most volcanic activity occurs along plate boundaries • Little to no volcanism associated with transform boundaries • Mafic volcanism rife along MOR’s where new oceanic crust is created • Intermediate volcanism common along convergent plate boundaries • Violent eruptions because of composition • Most often along coastal areas • Heavily populated areas • Create fertile zones that are heavily farmed

28. Divergent • Commonly associated with movement of magma at MOR’s • Remote & lesser Mag’s = little hazard • Convergent • Frequent with varying depth and magnitude • Vertical (dip-slip) movement > prob of tsunami • High pop density > prob of significant event • Transform • Often shallow & large mag’s > risk • High pop > risk • Rarely cause tsunami Earthquakes and Plate Boundaries

29. Cenozoic tectonic settingof the SW U.S.

30. Convection cells as a driving force for plate movement