2006 Keck Project: Petrologic Research
Figure 1. Map of Mongolia showing the
study area in the Khangay Mountains (Nuruu)
In the summer of 2006 Bob Carson, Brennan Jordan, and A. Bayasgalan
(Bayasaa) will conduct a Keck
Geology Consortium undergraduate student research project in the
Khangay Mountains of central Mongolia (Fig. 1). The project will
involve eight American students and eight Mongolian students working on
research projects in petrology and volcanology (Jordan); geomorphology
and Quaternary geology (Carson); and structure and neotectonics
(Bayasaa). The 2006 project follows Keck projects directed by
Carson and Bayasaa in Mongolia in 2003 and 2004 (Carson Mongolia pages:
This page introduces the petrologic problems that will be addressed.
Cenozoic volcanism in Mongolia
is part of a diffuse volcanic province in central Asia including
northern China and Siberia,
south of the Baikal Rift. This province is
predominantly basaltic and commonly
alkaline including trachybasalts, basanites, tephrites, and hawaiites. Most of the volcanic fields are low volume
centers with cinder cones and lava sequences tens of meters thick. In a belt across central Mongolia, this province can be divided
three areas: the Khovsgol Nuur area in the north, the Khangay Nuruu in
and the Gobi Altai in the south. The
origin of this diffuse volcanic province
is equivocal. The province traverses
areas of diverse Cenozoic tectonism including transpression in the Gobi
and rifting in Khangay Nuruu and Khovsgol Nuur area.
This suggests that magmatism is driven by
sublithospheric processes. A mantle
plume has been invoked to explain the province. Barry
et al. (2002) provide several lines of
evidence against a plume and develop a model for magmatism driven by a
thermal anomaly heating metasomatized lithosphere.
Figure 2. Volcanic rocks of
the Khangay Mountains region (after Whitford-Stark, 1987)
Cenozoic volcanic rocks are found on both the
southern flanks of the Khangay Nuruu (Fig. 2).
On the north side of the range are four Miocene to Recent
fields which are generally confined to river valleys and half grabens. The
largest and most extensive of these volcanic fields lies in the Tariat
depression. Some Tariat lavas have abundant crustal and mantle
Shavryn Tsaram site has produced diamond-bearing xenoliths.
On the southern flank of the Khangay Nuruu is a
series of plateau basalts that within an Oligocene to Miocene
sequence. The Oligocene lavas are
interbedded with red-beds of the Shand-Gol Suite and have K-Ar ages of
31 and 24 Ma. Miocene lavas make up the
upper stratigraphy of the plateau of the southern Khangay.
These lavas have K-Ar
ages of 20 to 17 Ma. The south Khangay
basalts are of diverse
composition including trachybasalts, limburgites, analcime “andesite
and sanidine- and biotite-bearing basalts, clearly reflecting extremely
potassic compositions. These Tertiary
lavas will be the focus of the
petrology portion of this project.
Problems and questions we hope to address are:
-Map and characterize Tertiary volcanic rocks of the southern
-What mantle sources of these potassic magmas?
-Characterize crustal evolution of these magmas
-If there are xenoliths do they differ from the Quaternary
xenoliths? What do they tell us?
-Do these rocks help us resolve the plume vs. non-plume origin
of central Asian magmatism?