News
Emmanuel is a master thesis student from the University of Philippines, and a guest student at WHOI until March 2016. He is learning to do experiments to decipher how material is transported from subducted slabs to the source of arc lavas. Welcome Emmanuel!
Emma Soucy comes from Northeastern University (Boston), and is working on calculating temperatures of rocks to understand how our planet Earth has cooled over time. Emma has started in July and has already taken the temperatures of many rocks! Welcome Emma!
After a successful summer as a PEP student last year, Marienel Basiga (San Jose State University) is back into the experimental laboratory to figure out how slab melts modify the composition of mantle wedges in subduction environments. She is now a prestigious Summer Student Fellow at WHOI!
The skyscan 1272 has safely arrived in le Roux’s lab. The table-top micro-CT instrument can scan objects in 3-D up to 7 cm in height and up to 7 cm in diameter. For small objects (< few mm), highest resolution is 0.45 um.
Gaining research experience led Marienel Basiga, a junior geology major at San Jose State University, to the Woods Hole PEP. Her research project with mentor Veronique Le Roux at Woods Hole Oceanographic Institution, in a field of geology known as experimental petrology, involved measuring grain-scale permeabilities of calcite and quartz through high-pressure, high-temperature experiments to study seawater recycling in the deep earth. “I expected to work hard and be extremely dedicated to the internship, but it surprised me how much fun I am having as well. I rode a bike the whole summer, something I haven’t done since I was 12.” Born in the Philippines, Basiga moved to the U.S. when she was nine and plans to attend graduate school on her way to a position as an academic researcher in some field of geology.
Her hometown is San Jose, California.
Text and image courtesy of Shelley Dawicki, NOAA Fisheries Service
“Tracking flux melting and melt percolation in supra-subduction peridotites (Josephine Ophiolite, USA)” is now In Press for Contributions to Mineralogy and Petrology.
Abstract
Here, we investigate the scale and nature of melting and melt percolation processes recorded by 17 supra-subduction peridotites collected in a ~70 km2 area in the northern portion of the Josephine ophiolite (Western USA). We present major and trace element variations in whole rocks; major elements in olivine, orthopyroxene, clinopyroxene and spinel; and trace elements [including rare earth element (REE)] in clinopyroxene and orthopyroxene. In the Josephine peridotites, compositional variability occurs at different scales. On the one hand, large systematic changes from depleted to fertile peridotites occur on large kilometer scales. Field, petrological and geochemical data can be consistently explained if the Josephine mantle experienced variable degrees of hydrous flux melting (10 to >20–23 %), and we argue that small fractions of subduction-derived fluids (0.015–0.1 wt%) were pervasive in the ~70 km2 studied area, and continuously supplied during wedge melting. Fluid localization probably led to increased extent of flux melting in the harzburgitic areas. On the other hand, in single outcrops, sharp transitions from dunite to harzburgite to lherzolite and olivine websterite can be found on meter to centimeter scales. Thus, some fertile samples may reflect limited degrees of refertilization at the outcrop scale. In addition, clinopyroxene and orthopyroxene in ultra-depleted harzburgites (Spinel Cr# > 58) show variable degrees of LREE enrichment, which reflect percolation of and partial re-equilibration with, small fractions of boninite melt. Because the enriched samples also show the highest spinel Cr#, we argue that these enrichments are local features connected to the presence of dunite channels nearby. Lastly, trace element concentrations of pyroxenes in Josephine harzburgites show that they are one of the most depleted harzburgites among worldwide ophiolitic peridotites, indicating particularly high degrees of melting, potentially past the exhaustion of clinopyroxene.
Authors: V. Le Roux, H.J.B. Dick, N. Shimizu