KIsH GEOCHEMICAL STUDIES OF PUMICE 233

 

 

 

50 60 70 50

 

NEVIS

MARTINIQUE

GRENADA
70

Wt% SIO5

Figure 14. Plot of K,O versus SiO, for voleanic rocks from different islands of the Lesser Antilles (from Smith and Roobol
1990). The individual plots are arranged sequentially from the northern portion of the arc (Saba) to the southernmost portion
of the arc (Grenada). Fields of low-K,O (L-K), medium-K,O (—K) and high-K,O (H-K) are from Gill (1981). The relative
field of compositions for high-K / high silica Florida pumice (FP) is shown as heavy rectangle in the field of analyses for the

island of Saba (upper left-hand corner of the figure).

characteristics of volcanics are compatible with a subduction-
telated, continental volcanic arc (Chesley et al. 2002), and in
eastern Mexico, a behind-the-arc setting (Siebert and Carrasco-
Niifiez 2002). The eastern portion of the TMVB includes
several major active stratovolcanoes, including the Citlaltépetl
volcano (Pico de Orizaba), the third highest peak in North
America (5675 meters). Pico de Orizaba rises 2900 meters
above the central interior basin of Mexico and 4300 meters
above the coastal plain on the Gulf of Mexico. Pico de
Orizaba’s recent eruptive activity includes intense effusive and

explosive events during the sixteenth and seventeenth centuries
(Carrasco-Niifiez and Rose 1995). Major volcanic centers in
the easternmost TMVB include the topographically subdued
Las Cumbers Volcanic Complex and Las La Gloria Volcanic
Complex, located 20-40 km north of Pico de Orizaba volcano,
the Cofre de Perote volcanic complex (4200 meters), and the
Los Humeros Caldera located 50-60 km north of Pico de
Orizaba (Rodriguez 2005). The overall age of volcanic activity
in this volcanic chain increases going from south to north.
Most of these volcanic centers occupy the drainage divide