the K – h relationship

The K (potassium (or potash)) to h (distance from surface to the subducting slab) relationship is an older concept based on a common observation of increasing potassium concentrations with distance into the rear arc of subduction zones. Here is a plot from a Geology paper by William R. Dickinson in 1975 showing the relationship.
K-h relationship

And here is a graph of my new data from southwest Bolivia. (click here for the location map (red circles are the new data)).
output_GWel0l
wt. % K2O vs. distance from arc front (equivalent to 125 km above the slab in the west (left side of graph) to 180 km in the east (right side)).

As is common in the central Andes (but rarely seen with such awesome data), there isn’t much (if at all) of a K-h relationship.

The relationship (when apparent) is often attributed to smaller degrees of partial melting with distance behind the arc front.

data!

After transporting my rocks around three continents, I now have my first geochemical data (thanks to the team at WSU GeoAnalytical Laboratory). The analyses look pretty good (decent totals). They mostly range from basaltic trachyandesites, through trachydacites and even include some proper rhyolites.
Bolivia volcanism
The filled circles are the new data, and the open triangles are from my previous work on Tunupa volcano (also within the study area).

durham library rocks

very rare that an article i am looking for isn’t available online through the Durham Library.
Quite pleased to get this article from Mineralium Deposita about the 14 million year old lava dome of Cerro Rico and its rich mineralization that occurred shortly after the eruption (< 300,000 years).

Screen shot 2013-10-17 at 1.07.36 AM

 

success cooking rocks in pullman

I spent a week at the Geoanalytical sample prep lab in pullman, washington.
crushing, weighing, and cooking 50 lava samples from Bolivia. Prep for XRF + ICPMS, whole-rock major and trace element analysis.

here are some videos of the process.

part 1: from pea-sized rocks to powder
part 2: packaging the last of 50 powders
part 3: mixing rock powder with lithium tetraborate
part 4: adding rock powders (within carbon crucible) to the furnace
part 5: pulling hot samples out of the oven.  red hot carbon and liquid rock.
Director: Fede        Producer: Silvi

part 6: final product. glass beads. notice the clear yellow bead. started out as pumice.

Screen shot 2013-08-16 at 5.14.16 PM