Deep fluid release beneath arcs from delayed breaching of the slab lower crust

<p>Slabs in subduction zones with geotherms of 7 K km<sup>-1</sup> or higher are expected to dehydrate effectively in the forearc. Nevertheless, large amounts of water are released from these slabs at and beyond subarc depth, indicating that H<sub>2</sub>O remains slab-bound to much greater depth than expected. It is possible that this reflects a transient sealing effect exerted by the subducting lower crust—a section of the lithosphere that typically undergoes delayed recation and is effectively impermeable until then. To test this concept, we investigated gabbros that were partially transformed to hydrous eclogite along shear zones during subduction. The rocks were subjected to a textural, petrological and Li-chronometric analysis. The observations characterize the progressive stages of transformation, and provide detailed insight into the governing feedbacks among fluid flow, deformation, and reaction. Lithium chronometry indicates that it took only a few weeks for the shear zone network to develop and for the externally derived fluids to traverse this network and drive eclogitization; the switch in these rocks—going from strong to weak and from impermeable to sustaining long-range fluid flow—thus was essentially instanteneous on subduction time scales. The re-equilibration of the rocks occurred well beyond equilibrium at c. 90 km depth, which is where large fluid-filled channel system typically emanate from warm slabs. Our data suggest that the fluids that are produced in the slab mantle throughout the forearc accumulate beneath the Moho until the lower crust is breached by dynamic fluid vents and commences its delayed transformation. The subducting lower crust may thus be a exert a strong control on H<sub>2</sub>O and element budgets, and the rheology of slabs in warm subduction zones.</p>

ACCURACY OF EXPERT FRAUD DETECTION TECHNOLOGY IN REMOTE TEST EXAMS (PROCTORING)

The purpose (objective) of the empirical study is the measurement of the accuracy of expert-proctors in detecting cheating in online testing. Sample of the study. 35 test takers passed an online test of general knowledge on the basis of 30 multiple choice questions. Half of the subjects (18 persons) were “artificial cheaters” — they used cheat sheets with correct answers. Methods. The video recording of the testing process included a “screen capture” so that expert-proctors could observe all cursor movements, see a recording of the subject’s facial expressions and a visual focus of attention in a separate window (recording from the front camera), and could listen to the subject pronouncing the task conditions and answers (“oral decision”). 14 experts took part in rating of video recordings, of which 8 experts showed satisfactory results in terms of the level of accuracy in detecting cheating (their accuracy that was measured using the Kappa coefficient was higher than 0.5). Conclusions. A high asymmetric validity of expert assessments is revealed. More accurate experts allowed a negligible (about 5 percent) number of errors of the “false alarm” type, but a relatively large number of errors of the “skip” type. Recommendations are made for the practical use of the expert assessment method in combination with automatic chronometric analysis of the degree of atypical protocols and subsequent control of face-to-face offline testing of all suspected subjects (examinees).

CALCINED BONE AS A RELIABLE MEDIUM FOR RADIOCARBON DATING: A TEST USING PAIRED NORTH AMERICAN SAMPLES

Radiocarbon dating using charcoal and bone collagen, two standards of archaeological chronology, can be difficult to impossible in environments where natural burning is common and bone does not preserve well. In such settings, charcoal ages cannot always be trusted and collagen is unavailable. Calcined bone can be a viable alternative medium in these situations but it has rarely been exploited in the Americas. One area that could benefit from its use is the forested Pacific Northwest. We compare calcined bone ages with charcoal and/or collagen dates from individual features or discrete cultural strata in 10 Washington, Oregon, Idaho, and British Columbia sites dating between 9000 and 100 B.P. Resulting radiocarbon age estimates based on calcined bone closely match those based on charcoal and/or collagen in nearly all cases. We obtained calcined bone dates from three additional Holocene-aged sites that had not previously produced accurate results, obtaining findings consistent with estimates based on cross dating. Preserving well where all other organic media of cultural origin are lost or unreliable, calcined bone holds promise for dating sites in conifer forests and other acidic soil settings, and can allow researchers to refine archaeological sequences that have long defied accurate chronometric analysis.

Moche Sociopolitical Dynamics and the Role of Licapa II, Chicama Valley, Peru

Fieldwork at the Moche (A .D. 250–900) site of Licapa II in the Chicama Valley, Peru, has resulted in a more nuanced history of the changing sociopolitical relationships among Moche centers. The distinct archaeological signatures of Moche society, namely ceramics and huacas (monumental structures), have been interpreted as emblematic of an ethnic and political reality and as evidence for a state. Nonetheless, scholars are now disentangling these assumptions, arguing that Moche society was a complex mosaic of interacting settlements. My research at Licapa II combined surface collection, geophysical surveys, excavation, and chronometric analysis to better understand this site within the context of broader Moche sociopolitical dynamics. Ceramic and architectural evidence from Licapa II indicates that a shift in ideological organization occurred around A.D. 650. This shift reflects changes seen throughout the Moche world. Licapa II is located on the border of the northern and southern regions of Moche cultural development, and ceramic styles indicate that many of the interactions between these regions could have occurred here. By comparing these findings to evidence of sociopolitical reorganization seen elsewhere, research from Licapa II contributes to a non-state and decentralized view of the sociopolitical structure of Moche society.

Neural chronometry and coherency across speed–accuracy demands reveal lack of homomorphism between computational and neural mechanisms of evidence accumulation

The stochastic accumulation framework provides a mechanistic, quantitative account of perceptual decision-making and how task performance changes with experimental manipulations. Importantly, it provides an elegant account of the speed–accuracy trade-off (SAT), which has long been the litmus test for decision models, and also mimics the activity of single neurons in several key respects. Recently, we developed a paradigm whereby macaque monkeys trade speed for accuracy on cue during visual search task. Single-unit activity in frontal eye field (FEF) was not homomorphic with the architecture of models, demonstrating that stochastic accumulators are an incomplete description of neural activity under SAT. This paper summarizes and extends this work, further demonstrating that the SAT leads to extensive, widespread changes in brain activity never before predicted. We will begin by reviewing our recently published work that establishes how spiking activity in FEF accomplishes SAT. Next, we provide two important extensions of this work. First, we report a new chronometric analysis suggesting that increases in perceptual gain with speed stress are evident in FEF synaptic input, implicating afferent sensory-processing sources. Second, we report a new analysis demonstrating selective influence of SAT on frequency coupling between FEF neurons and local field potentials. None of these observations correspond to the mechanics of current accumulator models.