Scoria Cone Construction Mechanism, Lathrop Wells Volcano, Southern Nevada

Valentine, G. ; Krier, D. ; Perry, F. ; Heiken, G.

United States. Department of Energy. Yucca Mountain Project Office.

关键词: Cones;    Fallout Deposits;    Welding;    Magma;    Construction;   

DOI  :  10.2172/838906
RP-ID  :  LA-UR-04-8750
RP-ID  :  NONE
RP-ID  :  838906

美国|英语

来源: UNT Digital Library

【 摘 要 】

Scoria cones are commonly assumed to have been constructed by the accumulation of ballistically-ejected clasts from discrete and relatively coarse-grained Strombolian bursts and subsequent avalanching such that the cone slopes are at or near the angle of repose for loose scoria. The cone at the hawaiitic Lathrop Wells volcano, southern Nevada, contains deposits that are consistent with the above processes during early cone-building phases; these early deposits are composed mainly of coarse lapilli and fluidal bombs and are partially welded, indicating relatively little cooling during flight. However, the bulk of the cone is comprised of relatively fine-grained (ash and lapilli), planar beds with no welding, even within a few tens of meters of the vent. This facies is consistent with deposition by direct fallout from sustained eruption columns of relatively well-fragmented material, primarily mantling cone slopes and with a lesser degree of avalanching than is commonly assumed. A laterally extensive fallout deposit (up to 20 km from the vent) is inferred to have formed contemporaneously with these later cone deposits. This additional mechanism for construction of scoria cones may also be important at other locations, particularly where the magmas are relatively high in volatile content and where conditions promote the formation of abundant microlites in the rising mafic magma.