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1. A REE-in-plagioclase–clinopyroxene thermometer for crustal rocks

   https://doi.org/10.1007/s00410-016-1326-9  

   Sun, Chenguang; Liang, Yan (April 2017, Contributions to Mineralogy and Petrology)
2. Europium anomalies in zircon: A signal of crustal depth?

   https://doi.org/10.1016/j.epsl.2023.118405  

   Yakymchuk, Chris; Holder, Robert M; Kendrick, Jillian; Moyen, Jean-François (November 2023, Earth and Planetary Science Letters)

   Trace element concentrations and ratios in zircon provide important indicators of the petrological processes that operate in igneous and metamorphic systems. In granitoids, the compositions of zircon have been linked to the behaviour of garnet and plagioclase—pressure-sensitive minerals—in the source during partial melting. This has led to the proposal that Europium anomalies in detrital zircon are linked to the depth of crustal melting or magmatic differentiation and are a proxy for average crustal thickness. In addition to the mineral assemblage present during partial melting, Eu anomalies in zircon are also sensitive to redox conditions as well as magma evolution during extraction, ascent, and emplacement. Here we quantitatively model how rock type, mineral assemblages, redox changes, and reaction sequences influence Eu anomalies of zircon in equilibrium with silicate melt. Partial melting of metasedimentary rocks and metabasites yields felsic to intermediate melts with a large range of Eu anomalies, which do not correlate simply with pressure (i.e. depth) of melting. Europium anomalies of zircon associated with partial melting of metasedimentary rocks are most sensitive to temperature whereas Eu anomalies associated with metabasite melting are controlled by plagioclase proportion—a function of pressure, temperature, and rock composition—as well as changes in oxygen fugacity. Furthermore, magmatic crystallization of granitoids can increase or decrease Eu anomalies in zircon from those of the initial (anatectic) melt. Therefore, Eu anomalies in zircon should not be used as a proxy for the crustal thickness or depth of melting but can be used to track the complex processes of metamorphism, partial melting, and magmatic differentiation in modern and ancient systems. Secular changes of Eu/Eu* from the zircon archive may reflect a change in thermal gradients of crustal melting or an increase in the reworking of sedimentary rocks over time. 

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3. Possibility of Lunar Crustal Magmatism Producing Strong Crustal Magnetism

   https://doi.org/10.1029/2023JE008179  

   Liang, Y; Tikoo, S M; Krawczynski, M J (May 2024, Journal of Geophysical Research: Planets)

   Abstract The Moon generated a long‐lived core dynamo magnetic field, with intensities at least episodically reaching ∼10–100 μT during the period prior to ∼3.56 Ga. While magnetic anomalies observed within impact basins are likely attributable to the presence of impactor‐added metal, other anomalies such as those associated with lunar swirls are not as conclusively linked to exogenic materials. This has led to the hypothesis that some anomalies may be related to magmatic features such as dikes, sills, and laccoliths. However, basalts returned from the Apollo missions are magnetized too weakly to produce the required magnetization intensities (>0.5 A/m). Here, we test the hypothesis that subsolidus reduction of ilmenite within or adjacent to slowly cooled mafic intrusive bodies could locally enhance metallic FeNi contents within the lunar crust. We find that reduction within hypabyssal dikes with high‐Ti or low‐Ti mare basalt compositions can produce sufficient FeNi grains to carry the minimum >0.5 A/m magnetization intensity inferred for swirls, especially if ambient fields are >10 μT or if fine‐grained Fe‐Ni metals in the pseudo‐single domain grain size range are formed. Therefore, there exists a possibility that certain magnetic anomalies exhibiting various shapes such as linear, swarms, and elliptical patterns may be magmatic in origin. Our study highlights that the domain state of the magnetic carriers is an under‐appreciated factor in controlling a rock's magnetization intensity. The results of this study will help guide interpretations of lunar crustal field data acquired by future rovers that will traverse lunar magnetic anomalies. 

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4. Tibetan dichotomy exposed in the Canadian Shield: A lower crustal perspective

   https://doi.org/10.1016/j.epsl.2020.116375  

   Dumond, Gregory (August 2020, Earth and Planetary Science Letters)

   null (Ed.)
5. Mid-crustal overpressure in the Tethyan Himalaya

   https://doi.org/10.5194/egusphere-egu25-11961  

   Vlaha, Dominik R; Zuza, Andrew V; Guevara, Victor E; Haproff, Peter J; Webb, A_Alexander G; Reyes, Francisco; Genge, Marie C; Ganbat, Ariuntsetseg; Wilderman, Devynn; Singh, Birendra P (March 2025, European Geosciences Union General Assembly 2025)

   Theory suggests the possibility for significant deviations between total pressure (or dynamic pressure) and lithostatic pressure during crustal metamorphism. If such deviations exist, the implications for orogenic reconstruction would be profound. Whether such non-lithostatic pressure conditions during crustal metamorphism are recorded and preserved in the rock record remains unresolved, as direct field evidence for this phenomenon is limited. Here, we investigate the Paleogene Tethyan Himalaya fold-thrust belt in Himachal Pradesh, northwestern India, which is the structurally highest part of the Himalayan orogen and deforms a ~10–15 km thick Neoproterozoic–Cretaceous passive margin stratigraphic section. Field-based kinematic studies demonstrate relatively moderate shortening strain across the Tethyan Himalaya. However, basal Tethyan strata consistently yield elevated pressure-temperature-time (P-T-t) estimates of 7–8 kbar and ~650°C, indicative of deep burial during Himalayan orogeny (ca. 20–45 Ma, 25–30 km depths). These P-T-t conditions can be reconciled by: (1) deep Cenozoic burial along cryptic structures and/or significant flattening of the Tethyan strata; (2) basal Tethyan strata recording metamorphism and deformation related to pre-Himalayan tectonism; or (3) non-lithostatic pressure conditions (i.e., tectonic overpressure). To test these models, we systematically mapped the Tethyan fold-thrust belt along the Pin Valley transect in northwestern India, a classic site for stratigraphic, paleontological, paleoenvironmental, and structural reconstructions. The Pin Valley region provides an opportunity to study a structurally continuous metamorphic field gradient from the near-surface to structural depths between 10–15 km, which should reflect P conditions ≤4 kbar if lithostatic. We integrate a multi-method approach combining detailed geologic mapping with quantitative analytical techniques (e.g., thermometry, finite strain analyses, thermo/geochronology, and thermobarometry) to quantify the magnitude, kinematics, thermal architecture, and timing of regional deformation, metamorphism, and subsequent exhumation. Results show: (1) throw on shortening structures is moderate to low (≤4 km); (2) temperature-depth relationships record a continuous, but regionally elevated, upper-crustal geothermal gradient of ≥40 °C/km, which is inconsistent with deep burial models (≤25 °C/km); (3) minimal flattening of basal Tethyan strata; (4) upper Tethyan strata yield pre-Himalayan low-temperature thermochronology dates, further refuting deep Cenozoic burial; and (5) basal Tethyan P-T-t estimates confirm elevated mid-crustal conditions of ~7 kbar, 630°C at 10–15 km depths during the Cenozoic. Preliminary volume expansion calculations are minimal; therefore, mechanisms involving non-hydrostatic thermodynamics, deviatoric stresses, rock strength contrasts, and tectonic mode switching are being explored. 

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