Great Basin History
I.  The Prepaleozoic

	A. Building the Basement
		1.  Earlist events in teh Great Basin are unknown, since the rock record is missing.
		2.  Very few remnants of the Prepaleozoic are were not eroded, and very few are visable
		3.  Earliest evidence is from metamorphic rocks exposed
			a.  Grouse Creek range
			b.  Raft River range
			c.  both located in northwestern Utah near the Nevada-Idaho border
			d.  Oldest rocks (schists) are 2.5 billion years old
		4.  Magmas intruded through oceanic lithosphere are fundamentally different from magmas intruded through continental lithosphere.
			a.  Strontium isotope ratios characterize the rocks that the magma penetrated	
			b.  Mesozoic granites exists in Southern Idaho and northeastern Nevada
			c.  Isotopes suggest that the Mesozoic granites may have intruded through 
			    Prepaleozoic rocks as old as the Grouse Creek and Raft River range 
		5.  Granitic intrusions, widespread calc-alkalic volcanics, metamorphic belts
		6.  2 Billion years ago rifting of supercontinent occured
                    ask Doug,  what is the evidence for a supercontinet?
			a.  split ruptured land a short distance
			b.  Ruptured occured south of Grouse Creek and Raft river range
			c.  Ocean basin formed to the south (splits Nevada, continent to the north
				and ocean basin to the south)
			d.  Grouse Creek and Raft River were sitting on the continent next to the 
                            southern shore line of North America. 
		7.  1.75 Billion years ago the basin that opened up in the south has 
                    switched direction and is now moving back toward the north closing the basin.
			a.  ocean plate begins to move north agains resistant craton
			b.  Oceanic crust remained firmly attacted to craton
			c.  Oceanic crust buckled and subduction zone formed offshore
                        d.  Oceanic crust from the south overrode the sea floor to the north
			e.  Recycled sea floor magma formed from subduction and created a volcanic arc
			f.  the closing basin trapped volcanic sediment from the south and continental
				sediment from the north
		8.  Island arc accrected by 1.748 billon years
			a.  the basement of the Prepaleozoic crystalline rock is now in place
			b.  this is the basement foundation for the Southern Basin and Range in Nevada
			c.  eastern and western exent of this accretionary belt is not known
			d.  later north-south rifting removed evidence of the extent
		9.  Uranium-Lead isotope radioactive clock was used to determine age 
			a.  1.74 +/- .25 are the oldest rocks dated in the southern Great Basin
		10.  At the same time as the volcanic arc-accretion, instrusive rocks were implaced
			a.  intrusives known for extra-large feldspar crystals
			b.  form rapakivi granite
			c.  Can be seen along the Davis Dmn on the Colorado River
			d.  rapakivi granite 1.45 +/- .25 billion years old
		11.  A new subduction zones formed to the south of the arc-accretion
		12.  The subducting oceanic plate dipped below the craton to the north
		13.  at 1 billion yeats ago Another island arc was accreted from the south of
 			the Great Basin
		14.  The edge of the contitenet was now at the Texas border
 		15.  Closure of the basin to the south added eight hundred miles of new crust beyond 
 			the Grouse Creek and Raft River range 

	B.  The Missing Link  (800 million years missing 1.45 Ga basement under 650 Ma sediement)
		1.  Youngest basement in Nevada is 1.45 billion years old
		2.  Oldest paleozoic rocks deposited are 650 million years old
		3.  800 million years of the rock record are missing
		4.  evolution of shelled animals to present or recorded, but any information before
			that is gone
		5.  There is no evidence for the missing rock
  		6.  The rock could have been forced high aboce sea level
 			a.  no land plant existed to hold to soil in place
			b.  erosion would have been very rapid
			what kind of sediment is produced when there is not erosion control?
		7.  1.2 billion basins started to form	
			a.  evidence of early streching and basin filling 
			b.  localities in the mountains of northern Utah and Death Valley region 
				of California
			c. triplet junction similar to Red-Sea, East Afican rift valley, Gulf of Aden
		8.  Rifting continents will form a failed rift arm (aka aulacogens)
		9.  the lower mississippi river is thought to be a failed rift arm after the breakup
			of North and South America
		10.  New England's Connecticut river valley may have formed when North America and
			Europe seperated 
		11.  Between 850 Ma and 1.2 Ga major continental rifting began again
			a.  north-south basin formed along western Nevada
			b.  ocean basin was created
			c.  How much of a continent and where it went is not known, it could be antartica
			d.  Continent left over after this rifting is seen in the strontium isotope ratios
				1.  Everthing to the west is underlain by oceanic lithosphere
				2.  Evidence for oceanic crust is apparent in the younger overlying 
					rocks which suggest an oceanic environment by there sediemtation
					patterns and fossils
			

			



			

II.  The Paleozoic

III. The Mesozoic

IV.  The Cenozoic