Melt-assisted deformation in the lower crust of an active plate boundary, Baja California

Bernard, Rachel E.; Chin, Emily; Murphy, Craig M.

doi:10.1016/j.lithos.2022.106975

Cited by 4 publications

(5 citation statements)

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“…We anticipate that this fabric-cut effect is a significant source of bias in systems with weak fabric (e.g., magmatic fabric), or in seemingly strong fabrics at low sample size (Figure 5), but is present in all EBSD orientational data. If meaningful interpretations of dynamic processes are to be made from EBSD derived orientations (Bernard et al 2023;Casale et al 2023;Forman et al 2023;Goudy et al 2023;Jenkins et al 2022;Koyama et al 2023;Levy et al 2023;Li et al 2023;Rehman et al 2023;Vukmanovic et al 2018;Wiesman et al 2023), then the fabric-cut effect needs to be corrected for. However, when we apply this method to natural samples, we find that the fabric-cut effect is likely not fully decoupled in a multiplicative manner (i.e., Eq.…”

Section: ) Discussionmentioning

confidence: 99%

“…magmatic sense of shear: Vukmanovic et al 2018;compaction: Bertolett et al 2019;Jenkins et al 2022; grain clustering mechanisms: Wieser et al 2019;Holness et al 2023). Similar applications can be extended into metamorphic systems with rock fabric encoding the deformation history and behavior (Bernard et al 2023;Bestmann et al 2006;Casale et al 2023;Cross et al 2017b, Haertel andHerwegh 2014;Fossen and Cavalcante 2017;Koyama et al 2023;Levy et al 2023;Li et al 2023;Rehman et al 2023;Taylor et al 2023;Wiesman et al 2023), impact dynamics recorded in meteorites (Goudy et al 2023;Forman et al 2023), fluid reactivity with primary minerals (Andreani et al 2009;Etschmann et al 2014;Kang et al 2010), sedimentary processes (McLaren 1981), as well as biosphere/geosphere interaction (Hemkemeyer et al 2018).…”

Section: ) Introductionmentioning

confidence: 99%

“…In particular, this paper focuses on the following question: What are the (if any) stereological biases that can be present when analyzing the crystal orientation datasets from EBSD? An increasing number of studies are using EBSD for rock textural analysis (Bernard et al 2023;Bertolett et al 2019;Casale et al 2023;Cheadle and Gee 2017;Cross et al 2017a;Cross et al 2017b;Forman et al 2023;Goudy et al 2023;Henry et al 2021;Holness et al 2023;Jenkins et al 2022;Koyama et al 2023;Levy et al 2023;Li et al 2023;Rehman et al 2023;Wieser et al 2019;Wiesman et al 2023;Vukmanovic et al 2018;Zavada et al 2009). However, in contrast to 2D thin section size-shape analysis, the need for stereological corrections with EBSD orientation datasets hasn't been thoroughly scrutinized.…”

Section: ) Introductionmentioning

confidence: 99%

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Towards an Integrated Texture Toolkit, 1: Unveiling the Complex Relationship Between Crystal Size, Shape, and Fabric in EBSD Data

Currier,

Mittal,

Hidalgo

2023

Preprint

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Rock textures observed via thin section are skewed from their true 3D nature. This is due to a variety of cut effects—artifacts that are introduced due to the lower dimensional nature of the thin section relative to the rock. Typically, these methods invert crystal shape and crystal size, but with each process performed separately and in sequence. With the ongoing adoption of electron backscatter diffraction (EBSD) by petrologists, an additional data stream has now become available: the 3D orientation of 2D grain sections. For EBSD analysis, no stereological corrections are typically applied for interpreting the data. In this study, we test whether this orientational information is also skewed due to a fabric cut effect. We test this by numerically generating synthetic crystal datasets representative of a number of crystal shapes and population sizes. We find that EBSD orientational data does have a fabric cut effect since crystals oriented with long axes perpendicular to the thin section are more likely to be sampled compared to those with long axes oriented parallel to it. This effect needs to be accounted for to accurately interpret the true 3D fabric. Towards this end, we develop a method of inverting cut fabrics which provides robust error estimations and show its accuracy using a range of synthetic examples. When applied to natural samples, which are inherently more complex than the simplified, synthetic samples, we find that the inversion process does not always produce geologically plausible results. To more faithfully correct for the different cut effects, we argue that the stereological inversion process should not be performed separately or sequentially, as is commonly done at present. Instead, we need a new textural toolkit framework to correct for crystal shape, size, and orientation simultaneously with accurate uncertainty estimates.

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Section: ) Discussionmentioning

confidence: 99%

Section: ) Introductionmentioning

confidence: 99%

Section: ) Introductionmentioning

confidence: 99%

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Towards an Integrated Texture Toolkit, 1: Unveiling the Complex Relationship Between Crystal Size, Shape, and Fabric in EBSD Data

Currier,

Mittal,

Hidalgo

2023

Preprint

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“…Valuable insights into the formation process of marine phosphate deposits can be gleaned from sedimentary structural features [20]. In situ microanalysis techniques allow for the comprehensive examination of elemental behavior within microstructural components [21][22][23], while stepwise chemical extraction experiments provide the quantitative characterization of element occurrence states [24][25][26][27]. Hence, this study primarily employs LA-ICP-MS and sequential chemical extraction experiments.…”

Section: Introductionmentioning

confidence: 99%

Microdistribution and Mode of Rare Earth Element Occurrence in the Zhijin Rare Earth Element-Bearing Phosphate Deposit, Guizhou, China

Xiong,

Xie,

Wang

et al. 2024

Minerals

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Rare-earth elements (REEs) are often highly concentrated in sedimentary phosphate deposits, and the microdistribution characteristics and occurrence state of rare earth in these deposits play a crucial role in the overall development and utilization of mineral resources. This study aims to analyze the microdistribution of REEs in REE-bearing phosphate deposits in the Zhijin region of Guizhou at the microstructural level and investigate their occurrence modes. Specifically, rock and mineral identification, X-ray diffraction (XRD), scanning electron microscopy–energy-dispersive X-ray spectroscopy (SEM-EDS), and laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) were utilized to analyze the samples. The correlation between the distribution of REEs and phosphorus was examined. In addition, the microdistribution of REEs in specific mineral phases and the locations of their occurrence were investigated. The analysis revealed that no REEs existed independently in the deposit. Instead, the distribution of REEs was highly consistent and significantly positively correlated with that of phosphorus. In the microarea structure, REEs were predominantly found both in particles, such as bioclasts, sand debris, and agglomerates, and in phosphate cement, where the main mineral components were collophane and apatite. Conversely, the content of REEs in dolomitized sand debris edges, sparry dolomitic cement, and siliceous cement was considerably lower. Based on these findings, it is speculated that REEs primarily occur within the lattice defects of apatite or on the surface of collophanite. There is a notable contrast in the REE content between the unaltered sand debris at the periphery and the dolomitized sand debris, indicating that the dolomitization in the diagenetic stage resulted in a depletion of REE abundance in the ore. Obviously, the dominant gangue mineral, dolomite, does not serve as the primary host for REEs. Furthermore, the highest concentration of REEs was inside organisms. This finding suggests that the high content of REEs in biological soft tissue may remain under the influence of waves and tides, and REE-bearing apatite may be preferentially separated and fill the cavities of deceased organisms. The second highest content of REEs was found in the shells of organisms, indicating that small shelly organisms absorb phosphorus materials through their life activities to construct their shells, resulting in REE enrichment. Quantitative analysis through sequential extraction procedures displayed that most REEs were present in the residual state, with a smaller portion combined with organic matter. These results confirm that REEs in the Zhijin phosphate deposits primarily exist as isomorphic substitutions in the lattice defects of apatite, with a secondary occurrence as organic matter-bound REEs.

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“…As examples: (a) partial melting may dry out residuum as water preferentially partitions into the melt phase (Aubaud et al., 2004; Hirth & Kohlstedt, 1996; Karato, 1986); and (b) melt percolation can introduce fluids and/or crystallize phases that contain relatively high fluid concentrations (e.g., pyroxenes—Smyth et al., 1991). In addition to the effects of melt and water, the deep roots of faults may be affected by shear heating and may undergo microstructural transformations due to intrinsic strain localization processes (Bernard et al., 2023; Chatzaras et al., 2021; Hartz & Podladchikov, 2008; Regenauer‐Lieb et al., 2006; Warren & Hirth, 2006).…”

Section: Introductionmentioning

confidence: 99%

Hydration State and Rheologic Stratification of the Lithospheric Mantle Beneath the North Anatolian Fault, Turkey

Lusk,

Chatzaras,

Aldanmaz

et al. 2023

Geochem Geophys Geosyst

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We present constraints on the hydration state and rheology of the lithospheric mantle beneath the North Anatolian fault zone (NAFZ). Peridotite xenoliths from the Biyikali and Çorlu volcanic centers record deformational microstructures consistent with shearing in a lithosphere‐scale transcurrent fault system. Analysis by Fourier transform infrared spectroscopy indicates that nominally anhydrous phases retain some OH−, but bulk rock concentrations are generally restricted to <50 ppm H2O by weight. From the rock microstructure, we determined differential stress magnitude and active deformation mechanism(s); combined with estimates of hydration state, we constrained the rheology. Recrystallized grain size piezometry shows that the mantle beneath the NAFZ sustained differential stresses of 10–20 MPa, largely independent of depth. The dominant deformation mechanism(s) change with depth; xenoliths extracted from shallower depths record evidence for grain size‐sensitive creep possibly in the presence of melt. At intermediate depths, both dislocation creep and grain size‐sensitive mechanisms were active, and we did not observe evidence for deformation in the presence of melt. The deepest samples were dominated by dislocation creep. The strong temperature sensitivity of creep mechanisms, combined with the low variability in differential stress, contributes to a stratified viscosity profile ranging from 1018 Pa s for the deepest samples to >1022 Pa s at shallower depths (assuming a melt‐free rheology). Although difficult to quantify from the rock record, melt likely reduced the viscosity of the shallow lithospheric mantle. Vertical stratification in viscosity beneath the NAFZ, the result of melt‐present deformation and/or transitions in the dominant deformation mechanism, has important consequences for the seismic cycle of strike‐slip fault systems.

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Melt-assisted deformation in the lower crust of an active plate boundary, Baja California

Cited by 4 publications

References 51 publications

Towards an Integrated Texture Toolkit, 1: Unveiling the Complex Relationship Between Crystal Size, Shape, and Fabric in EBSD Data

Towards an Integrated Texture Toolkit, 1: Unveiling the Complex Relationship Between Crystal Size, Shape, and Fabric in EBSD Data

Microdistribution and Mode of Rare Earth Element Occurrence in the Zhijin Rare Earth Element-Bearing Phosphate Deposit, Guizhou, China

Hydration State and Rheologic Stratification of the Lithospheric Mantle Beneath the North Anatolian Fault, Turkey

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