Search for: All records

Our ability to reconstruct the crystallization history of a given accessory mineral (i.e., geochronometers such as zircon, titanite, monazite, etc.)—and thus the geologic processes of its host—has increased severalfold over the past few decades; primarily through advances in precision, concurrent chemical analysis, throughput, and spatial resolution. In this contribution, we present a methodology that takes these advances a step further through the rapid characterization of a large number of accessory minerals at micron-scale resolution via laser-ablation inductively coupled plasma mass spectrometry. Our analytical setup employs an ultrafast washout laser (~1 ms; Element Scientific Laser) that can send individual, <5um ablation pulses to either one or both of two instruments: a Nu Plasma 3D mulitcollector ICP-MS and a Nu Vitesse time-of-flight ICP-MS. Because either ICP-MS can measure at the sub-ms timescale, every pulse can be analyzed at 100’s of Hz; 1D, 2D, or 3D analysis is possible, and data can be processed in a matter of minutes and hours, instead of days or weeks. We highlight the advantages of this methodology through examples of accessory phases in complex plutonic rocks and high-grade metamorphic terranes. 

ABSTRACT Optogenetics has transformed the study of neural circuit function, but limitations in its application to species with large brains, such as non-human primates (NHPs), remain. A major challenge in NHP optogenetics is delivering light to sufficiently large volumes of deep neural tissue with high spatiotemporal precision, without simultaneously affecting superficial tissue. To overcome these limitations, we recently developed and testedin vivoin NHP cortex, the Utah Optrode Array (UOA). This is a 10×10 array of penetrating glass shanks, tiling a 4×4mm²area, bonded to interleaved needle-aligned and interstitial µLED arrays, which allows for independent photostimulation of deep and superficial brain tissue. Here, we investigate the acute biological response to UOA implantation in NHP cortex, with the goal of optimizing device design for reduced insertion trauma and subsequent chronic response. To this goal, we systematically vary UOA shank diameter, surface texture, tip geometry, and insertion pressure, and assess their effects on astrocytes, microglia, and neuronal viability, following acute implantation. We find that UOAs with shanks of smaller diameter, smooth surface texture and round tips cause the least damage. Higher insertion pressures have limited effects on the inflammatory response, but lead to greater tissue compression. Our results highlight the importance of balancing shank diameter, tip geometry, and insertion pressure in UOA design for preserving tissue integrity and improving long-term UOA performance and biocompatibility. 

Abstract Ultrahigh-temperature metamorphism (UHTM) is important for the evolution and long-term stability of continental crust. The Anosyen domain in southeastern Madagascar is a well-preserved UHTM terrane that formed during the amalgamation of Gondwana. The heat source(s) required to reach peak conditions is(are) a matter of debate. One potential cause of extreme crustal heating is the intrusion of mantle-derived melts into the crust. Foundering of the mantle lithosphere can also lead to increased heat flow. To assess the role of these heating mechanisms, we measured zircon δ18O, εHf(t) compositions, and U-Pb dates for plutonic rocks in the midcrustal UHTM domain. Our results indicate that pluton emplacement predated UHTM by as much as 40 m.y. and that all zircons have crustal O and Hf isotopic compositions. We propose that mantle lithosphere foundering caused melting in the lower crust, producing the magmas responsible for plutonism during the early stages of orogenesis. Prolonged conductive heating of the crust—combined with above-average radiogenic heating—may explain why UHTM occurred ∼40 m.y. after foundering. This suggests that foundering of the mantle lithosphere can swiftly lead to partial melting in the lower crust, as well as protracted heating of the middle crust that culminates tens of millions of years later.