W. S. Burbank
R. G. Luedke
1966
<p><span>Three major cycles of </span>volcanism<span> during the Miocene and Pliocene formed a layered succession of calc-alkaline eruptive materials </span>in<span> the </span>western<span> </span>San<span> </span>Juan<span> </span>Mountains<span> nearly 1.5 miles thick and having a volume greater than 1,000 cubic miles. Each cycle was characterised by major eruptions followed by subsidence </span>in<span> the vent areas, and the resulting structure was a great volcanic plateau surrounding a complex of nested cauldrons. </span>In<span> the first cycle, cruption of several hundred cubic miles of tuff breccia and subordinate lavas was followed by subsidence that created the </span>San<span> </span>Juan<span> volcanic depression, about 15 miles wide and 30 miles long. During the second cycle, pyroclastic rocks and lava flows accumulated within this depression and on its borders, and the depression subsided further. During the third cycle, ash flows spead widely from centres within the depression, and their eruption resulted </span>in<span> formation and subsidence of the nearly circular comagmatic Silverton and Lake City cauldrons, each about 10 miles across, within the earlier depression. Cauldron subsidence </span>in<span> the second and third cycles was followed by resurgence and doming of the central blocks. Keystone grabens formed along the distended crests of the domed floors; graben faults formed </span>in<span> the third cycle were </span>in<span> part controlled by those formed </span>in<span> the second cycle. The distribution of post-cauldron radial and concentric fractures, dikes, and intrusive plutons, particularly around the Silverton cauldron, suggests that the underlying magma chamber must have been appreciably larger than the associated cauldrons. </span></p>
application/pdf
10.1007/BF02597162
en
Springer
Volcanism in the western San Juan Mountains, Colorado
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