Scope of Presentation Tectonic Map of the Gulf

Where in the world are we? Map of Tectonic Plates Satellite photo of Baja Region

Mexico

BAJA Gulf of California Baja The Gulf of California Pacific Ocean From Spreading Center to Transform Fault and Beyond W. Brent Garry 150 km November 25, 2002 East Pacific Rise

Scope of Presentation Tectonic Map of the Gulf North GulfYounger rift segments South Gulf Older rift segments • What’s so special about the Gulf? – young spreading center (< 4 Ma) – along-strike change N. Am. Plate • rift stages • plate boundary style

• I. What are along-strike geologic changes between… – Southern Gulf of California Rivera – Northern Gulf of California Plate – Southern California (Salton Trough) Farallon 6 cm/yr • II. Where will the Baja Peninsula be 15, 30, 60, 90 Ma from now? Pacific Plate

• divergent plate margin • en-echelon rift segments

Tectonic Map SOUTH Gulf of California bathymetry and geology Extensional Basins - Salton Trough - 3 infant rifts

Transition Zone divergent transform - 300 km wide fault zone - no more rift segments

Salton Transform Fault Trough - San Andreas - Mendocino triple junction

1 SOUTH Gulf: bathymetry SOUTH Gulf: geology

Series of isolated Basins Mexico N Rift segments Mexico - well established Deepest basins N - 3600 m Gulf Volcanism Gulf Basalt EPR Baja - oceanic crust EPR - 3.5 Ma Continental Margin - only at the mouth Baja - Mexico = wide EPR - Baja = narrow Green Basalt Yellow Sediment Red Rhyo. & Andes. White Old Plutonic rocks Light blue = Shallow Dark blue = Deep 200 km 200 km

SOUTH Gulf: magnetic anomalies NORTH Gulf bathymetry and geology Only place in Gulf where anomalies are recorded, because oceanic crust present

Baja Gulf

Red N + anomalies

EPR

NORTH Gulf: bathymetry NORTH Gulf: geology

Decrease in depth Mexico Rift segments Mexico N - intermediate stage N Guaymas Basin - covered by seds marks major depth change Guaymas Gulf Gulf - show as depressions Shallow isolated basins Volcanism < 1000 m deep magmatic intrusions Baja Baja - dikes & sills High Sediment input - intermediate crust - Colorado River Green Basalt Yellow Sediment Red Rhyo. & Andes. Light blue = Shallow White Old plutons 200 km Dark blue = Deep 200 km

2 Southern California Southern CA: bathymetry bathymetry and geology

N USA Mexico Colorado River Delta - high sed input Salton Trough - isolates Salton Sea Gulf Salton Trough - 390 km long Baja - 72 m below SL - 5 km of sediment

Light blue = Shallow Dark blue = Deep ~200 km

Volcanism Salton Buttes Southern CA: geology SaltonTrough Rhyolite domes Salton Sea marks transition zone to transform boundary - basaltic inclusions - basaltic dikes Rift segments Mexico - MOR composition - infant rifting N Salton Trough N - hi geothermal activity Salton Buttes Gulf Green Basalt Yellow Sediment I Red Rhyo. & Andes. II White Old plutons III Baja Rift segments I II III - infant rifting - hi geothermal activity

150 km 20 km

Future of Baja-SW CA exotic terrain? Unaddressed Factors

3000 km 3000 km

N. America N. America III Problems I. Change in spread rate IV Assumptions II. Rotation of Pacific plate 1. 6 cm/yr spread rate III. Juan de Fuca / Mendocino 2. NW spreading direction IV. Failed rifting or Jamming 0 Ma II I

3 Summary • South Gulf – Divergent margin – Established rifting – Active formation of oceanic crust

• North Gulf – Divergent margin – Intermediate rifting – Intrusions and rift segments masked by sediment cover

• South CA – Transition to Transform margin – Infant rifting – Rhyolite domes and early MORBs

• Future of Baja- Southwest CA – Exotic terrain moving towards Aleutian Arc