Geology Reference
In-Depth Information
pyroxene pair in the lherzolite nodules is 1,300
125 km.
Chemical analyses of K-rich rocks from Sierra Nevada are given in Table
4.10
.
Absarokite and minette magmas (43
°
C at a depth of 100
-
57 wt% SiO
2
) erupted along the western
slope of Sierra Nevada, California, within the Kings River Valley during the Late
Pliocene (3.4
-
3.6 Ma, Van Kooten 1981). The absarokites contain phenocrysts of
-
olivine
±
augite in a groundmass of predominantly augite and feldspar (plagio-
clase
±
alkali feldspar
±
anorthoclase
±
hyalophane) along with leucite
±
nephe-
line
pseudobrookite.
The second most abundant lava type found in this area is minette containing
phenocrysts of phlogopite, augite and/or olivine
±
analcite
±
olivine
±
apatite
±
titano-magnetite
±
phlogopite
±
chromite. The groundmass phases
are same as those found in the absarokite. The K
2
O content of absarokites ranges
between 2 and 6 wt% and the MgO content varies between 9 and 15 wt%. The K
2
O
content for the minette varies between 3.6 and 8.1 wt%. The MgO content of the
minettes is usually less (7.54 and 7.82 wt%). Absarokites are typical rock types found
in the Absaroka Range near Yellowstone Park, U.S.A. (Meen and Eggler 1987)
±
4.5.10 Pliocene Potassic Volcanic Rocks from Deep Springs
Valley, California
Potassic Rocks from Deep Springs Valley, California (Fig.
4.16
) consist of lava
flow remnants that lie upon Jurassic granitoids (Beard and Glazner 1998). The lava
flows are essentially olivine leucitites, basanites and trachybasalts having K
2
O
content varying between 5.4 and 3.2 wt%. The whole-rock K
Ar method yielded an
-
age of 2.6
±
0.1 Ma. These lavas show positive correlations between such
118
0
Long
Valloy
Caldora
6
Mammoth
Lakes
Devils
Postpile
395
Bishop
Deep Springs
Valley leucitites
168
Big Pine
North
North Palisade
4341m
Big Pine
Volcanic
Field
37
0
Ubehebe
Crater
395
0
20
40
km
Independence
Fig. 4.16 Sketch map of Deep Spring valley leucitites (after Beard and Glazner 1998)
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