OREGON STATE UNIVERSITY

Stop 17: Chillahuita Dome

Chillahuita

22°8.356'S, 68°01.766'W

     Chillahuita

Just over the pass near Linsor dome and to the east of the Chao complex and Cerro Lean, we come across Chillahuita, yet another large silicic lava dome.  Like Chanka and many of the domes yet to come, Chillahuita has the “torta” shape often exhibited by these large domes - flat tops and steep sides with some talus around the flanks.  

Along with close proximity, Chillahuita has many similar characteristics to Chao, it is thought to be nearly contemporaneous in age and contains similar texture and mineralogy.  It does, however, differ to Chao in that it was build on a much more gentle slope, and thus is smaller in size – 5km3 in volume.   

 Chillahuita - Click for High Resolution

Click for a high resolution image


Petrographic and Mineralogic details

 

Like most of the domes we have seen, and will see, Chillahuita is dacitic in composition and extremely rich in crystals (50%+).  Mineralogically, the phenocrysts consist of plagioclase, quartz, hornblende, and sphene. The texture, like Chao, is friable due to microvesiculation of the matrix.   

Chillahuita Wind ErosionAs an interesting note, many boulders that have fallen down the steep sides of Chillahuita show evidence of the primary wind direction through the products of wind erosion. Saltating sand grains hit these large boulders and overtime have formed many small holes that almost resemble a honeycomb texture.