Geology 1210
Homework #6
#15 When and what sequence of events led to the origin of the Himalayas in Asia?
During the late Cretaceous India’s plate and the Eurasian plate began to collide approximately 70 million years ago. The Indian plate destroyed a chain of volcanoes as it collided with southern Asia, near present day Tibet. As India’s landmass subducted into southern Asia during the Miocene, the Himalayan Orogeny was born from the continent to continent collision. This ended the ocean to continent subduction in that area. The exposed mountain rocks are limestones that were uplifted after the collision. Still currently, the Indian plate is moving northward into southern Asia, along a thrust fault, that allows the Himalayas to grow bigger still every year (at 5-6 mm a year). This area is seismically active, and earthquakes happen periodically.
#16 Explain how plate interactions were responsible for the origin of the San Andreas Fault.
The North American plate and its collision with the Pacific Farallon plate created the Pacific-Farallon ridge during the Eocene. This created two triple junctions, one at the where the Juan de Fuca (remnant of the Farallon) intersected the NA/Pacific plates along the northern Pacific coastline of NA, and another where the Cocos (remnant of the Farallon) intersected the two plates as well along the southern Pacific coastline of NA. The continued westward movement of the North American Plate over the Pacific Plate caused aforementioned triple junctions to migrate, and as the plates moved northward and southward, causing crustal shearing, it created the San-Andreas Fault. (a Transform fault)
#17 What and where is the Basin and Range Province? Any speculation on what caused the structures typical of this region?
The Basin and Range Province is located in Nevada, and its surrounding areas into Northwestern Mexico. Prior to faulting, the area was deformed by prior orogenies, but during the early Miocene, eruptions of rhyolitic lava flows and pyroclastic materials covered the erosion riddled highlands. During the late Miocene, large-scale faulting began forming the basins and ranges. This created alluvial fans as sediment was transported from the ranges into basins. The ranges and their intervening basins trend north to south. Each range is bounded on one or both sides by a normal fault. The basin and range is the result of extension and thinning of the lithosphere. Geologists have not reached a consensus, but ideas to have caused this include back-arc spreading, spreading at the East Pacific Rise, and deformation caused by the San Andreas Fault.
#20 What happened as the African plate moved northward against Europe and Asia?
Northward movements of the African and Arabian Plates against Eurasia caused compression and deformation, as several small plates created the Alps Mountains during the Alpine Orogeny. The compressional forces generated by the two plates colliding with Eurasia resulted in complex thrust faults in southern Europe. The collision of the African plate with Eurasia created the Atlas Mountains in Northern Africa and closed off the Mediterranean Sea as the Tethys Sea closed.