Publication Date

Fall 2011

Degree Type


Degree Name

Master of Science (MS)




Jonathan Miller


Aztec Wash pluton, stoping

Subject Areas

Geology; Geochemistry


The Miocene Aztec Wash pluton, Eldorado Mountains (NV), has been tilted by regional extension and thus provides a vertical cross-section showing 5 km structural depth. Previous work shows that the Aztec Wash pluton was constructed by vertical accumulation of mafic sheets intruded into granite magma with widespread hybridization. Precambrian orthogneiss and Cretaceous granite host rock xenoliths (1 cm to >20 m long dimension) occur at all structural levels but are heterogeneously distributed (locally varying from 0 to 50% of areal exposure). Their origin and relation to the Aztec Wash pluton are poorly known. Mapping at 1:6000 of a xenolith-rich area has shown that 1) xenolith size and integrity of contacts with surrounding plutonic rock are highly variable; 2) sub-solidus fabrics in xenoliths show no preferred orientation compared to host rocks in the pluton roof; 3) xenoliths display evidence of mechanical disaggregation, but geochemistry suggests minimal assimilation; and 4) draping of sheets over xenoliths indicate they are stratabound within the mafic sheet sequences. These observations, together with documented vertical growth of the pluton and the distribution of host rock xenoliths, suggest episodic detachment and stoping of surrounding host rocks (possibly during eruption) to form xenoliths.

Smith_PLATE1.PDF (1022 kB)
Smith_PLATE2.PDF (666 kB)
Smith_PLATE3.PDF (836 kB)