R-3 Repository :: Browsing by Author "Lee, Cin-Ty"

Browsing by Author "Lee, Cin-Ty"

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Diagenetic controls on fault zone structure along the Sestola-Vidiciatico unit, as an analogue to the shallow subduction megathrust
(2023-12-01) Mckenzie, Emory Isaac; French, Melodie; Morgan, Juli; Lee, Cin-Ty
Along the subduction megathrust, the up-dip limit of the seismogenic zone is thought to occur at 100 to 150 °C and the shallower region hosts diverse modes of fault slip. The transition to the seismogenic zone is thought to occur due to evolving material properties that promote seismicity; however, which properties are responsible and how they evolve is poorly understood. The Sestola-Vidiciatico Unit (SVU) has been interpreted as an analog of the sedimentary component of active subduction megathrusts, near the up-dip transition to seismicity. The SVU accommodated Miocene convergence between the subducting Adriatic plate and the overriding accretionary prisms of the European plate. Deformation was dominantly accommodated within a 500 m thick shear zone along a well-exposed basal decollement and inaccessible roof decollement. Here we evaluate the role that diagenesis of sedimentary rocks plays in controlling fault zone architecture and strain partitioning. We use HAWK pyrolysis to determine new temperature constraints for deformation at multiple outcrops along the basal decollement and show that deformation occurred at temperatures between ~180 to 190 °C at our four field sites. We characterize the macroscopic fault architecture through field measurements and rock composition and microfabrics of the basal decollement using scanning electron microscopy and electron probe microanalysis. Diagenetic reactions such as silicification, chloritization, and pyritization occur in samples from each outcrop. We show that fault architecture is variable even at similar deformation conditions. We quantify the abundance and occurrence of diagenetic reactions and discuss their correlations with variations in fault architecture and deformation textures.
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Differentiation of a CO2-rich, hydrous alkalic basalt and the genesis of carbonatites
(2024-03-20) Rodriguez, Maria Raquel; Dasgupta, Rajdeep; Lee, Cin-Ty; Torres, Mark
Intraplate settings almost uniquely host alkaline magmas and carbonatites. Although these magmas are spatially connected, the petrogenetic link between alkali magmas such as ocean island basalts (OIBs) and carbonatites is not well established. While previous studies have sought to identify the source origin of these magmas, the mechanisms behind their differentiation remain poorly understood. To constrain the evolution of alkalic magmas at mid-lithospheric depths, we performed high pressure-temperature, phase equilibria experiments on a hydrous, CO2 rich mantle-derived partial melt composition. The experiments were conducted at 1.5-2.0 GPa and 1200-1500 °C. The experimentally generated samples were studied using electron probe micro-analysis, where phase assemblage consisted of olivine + clinopyroxene + spinel + carbonated-silicate melt ± calcite ± vapor. As the melt composition undergoes evolution, the initial stages of crystallization generate alkalic OIB-like compositions, which subsequently transition towards natural calcio-magnesio carbonatite compositions. Our findings suggest that a single volatile-rich parental melt composition can give rise to OIBs and carbonatites at varying conditions.
Experimental investigation of crust-mantle hybridization in the Earth’s shallow upper mantle
(2014-11-13) Mallik, Ananya; Dasgupta, Rajdeep; Lee, Cin-Ty; Lenardic, Adrian; Brooks, Philip R
Chemical heterogeneities in the Earth’s mantle, such as subducted sediments and oceanic crust, along with volatiles such as H2O and CO2 affect melting processes, hence, chemical differentiation of the Earth and their presence in the source of erupted magma has been unequivocally established through isotope and trace element geochemistry. Yet, the nature of major element contribution of recycled crustal lithologies to the erupted basalts on the Earth’s surface is poorly understood because direct partial melting of crustal lithologies at mantle depths produces siliceous melts that are unlike surface basalts or their estimated parental melts. In case of oceanic crust and sediments, partial melting initiates at lower temperatures and at deeper depths than the surrounding mantle, hence, an andesitic partial melt (±CO2) from recycled oceanic crust and a rhyolitic partial melt (±H2O) from subducted sediments, being out of equilibrium with the surrounding peridotitic mantle with a hotter solidus temperature, must undergo reactive crystallization. However, the impact of crustal melt impregnation into mantle peridotite on the potential formation of hybrid melts and lithologies remained largely uninvestigated. The phase equilibria of reaction of siliceous partial melts (derived from crustal heterogeneities) with the mantle has been investigated in this thesis with the aid of high pressure-temperature laboratory experiments that simulated conditions at depths of 80 – 100 km inside the Earth. Andesite evolves to a basanite upon partial reactive crystallization in a peridotite matrix (Chapter 2), and with increasing amount of CO2 in the system, the residual melt evolves even to a nephelinite (Chapter 3 and 4). This is the effect of reaction of the silica component in the melt with olivine in the peridotite to crystallize orthopyroxene, with the orthopyroxene stability field being enhanced under the influence of CO2, therefore, drawing down the SiO2 content of the reacted melt even further. Major element characteristics of alkalic ocean island basalts can be reproduced by the reacted melts from these studies by a two-stage hybridization process: Firstly, partial melt from recycled oceanic crust reacts with surrounding sub-solidus peridotite and undergoes partial reactive crystallization and secondly, the reacted, residual melt from the first step subsequently mixes with peridotite-derived partial melt. An empirical model has been proposed to estimate the source characteristics of alkalic ocean island basalts. The model predicts that 15 – 45 wt.% oceanic-crust derived melt and 0.2 – 2 wt.% CO2 are required, followed by mixing with 25 – 55 wt.% peridotite partial melt to reproduce major element characteristics of alkalic lavas from Canary Islands, Cape Verde and Cook Australs (Chapter 4). The results from the studies obviate the need for the presence of silica-undersaturated exotic lithologies in the source of alkalic ocean island basalts. Also, the studies demonstrate that high MgO (>15 wt.%) alkalic basalts from the mantle can be produced by a potential temperature of 1350 °C and do not require potential temperatures exceeding 1430 °C, as predicted by current thermometers. This is owing to the effect of CO2 dissolution in the melt in the form of MgCO3 complexes, which enhances the MgO content of melts at a given pressure and temperature. Flux of hydrous rhyolitic, sediment-derived melts, to the mantle wedge fertile peridotite leads rhyolites to evolve to ultrapotassic nepheline normative basalts similar in composition to ultrapotassic lavas from active and inactive arcs (Chapter 5). This evolution in melt composition from a highly siliceous rhyolite to a nepheline-normative ultrapotassic basalt is due to the formation of orthopyroxene at the expense of olivine as well as the dominance of phlogopite in the melting systematics, buffering the K2O content of the melt to produce ultrapotassic compositions. Thermal stability of phlogopite to the core of hot mantle wedge is established in conjunction with previous studies, which suggests that recycling of phlogopite to the deeper mantle may be important in deep flux of large ion lithophile elements and volatile elements such as fluorine and nitrogen. Potential long-term survival of phlogopite can potentially create Sr-isotopically enriched zones in the mantle, as evident in the source of several arc and intraplate lavas.
Extra-terrestrial mantle samples: Rare Earth Element variations and evidence for melt metasomatism in ureilite meteorites
(Elsevier, 2024) Downes, Hilary; Mittlefehldt, David W.; Ross, Aidan J.; Lee, Cin-Ty
Ureilites are meteorites derived from the mantle of a reduced differentiated asteroid, the “Ureilite Parent Body” (UPB), which was later disrupted by impact with another Solar System body. They have ultramafic compositions dominated mostly by olivine and pigeonite with rare orthopyroxene and augite; aluminous phases are generally absent. Ureilites vary from abundant peridotites to much rarer pyroxenites, and their core olivine compositions range from Fo74 to Fo97 across different samples. The UPB experienced sufficiently high temperatures to undergo silicate partial melting, as shown by depletion in the Light Rare Earth Elements (LREE) in bulk restitic ureilites. Plagioclase and merrillite were probably present in the UPB mantle but have been completely removed during silicate partial melting. Partial melts of the UPB mantle are represented by glassy melt inclusions, igneous clasts in ureilite breccias, cumulus augite in some ureilites, and rare trachyandesitic fragments. These melts are generally intermediate and sub-alkaline in composition, although a few are alkaline. They have more enriched and flatter bulk REE patterns than the restitic ureilites and often show positive Eu anomalies. Glasses (representing melts) in ureilites from this study range from 57 to 79 wt% SiO2. One sample (AhS 22) shows petrographic and geochemical evidence for interaction between magma and the solid UPB mantle by forming metasomatic augite. Silicate minerals in ureilites analysed by LA-ICP-MS are generally LREE-depleted, with negative Eu anomalies. Ureilitic olivines have the lowest REE contents and the smallest negative Eu anomalies. Low-Ca pyroxenes have similar patterns with slightly stronger Eu anomalies. Augites have the highest REE contents and the most negative Eu anomalies. Augites show REE disequilibrium with olivine and low-Ca pyroxene, suggesting that they were not part of the restitic assemblage but were added by silicate melts passing through the UPB mantle, i.e. they are metasomatic in origin. We also discuss the size of the original UPB, using silicate minerals as evidence for it being a typical asteroid rather than a planet-sized object.
Geology, Mining, and Manufacturing: A Guide to Critical Minerals
(2023-04-20) Perez, Julie Diane; Lee, Cin-Ty; Morgan , Julia
This thesis is a compilation of data and research on the geology, mining, and manufacturing of critical minerals and how they are contributing to the energy transition. This research follows the elements from their respective deposits, refinement facilities, and the final product production through the supply chain. The geology and formation of the minerals is prioritized to have a better understanding of the physical and chemical properties that these minerals possess and why they are considered critical. The history of energy production is included in the research to better emphasize the importance of critical minerals and to better predict how they may contribute in the future. Along with compiling data on the various steps of the life cycle of a mineral, the reserves and future resources are also taken into consideration. All gathered data is formatted into a field guide for easier accessibility.
Igneous life cycles: geochemistry of magma from mantle to surface and back again
(2023-08-11) Allen, Sydney Marie; Lee, Cin-Ty
Material from within the Earth is cycled and recycled from the interior of the Earth to the surface in igneous rocks. The chemistry of igneous rocks record snapshots of this complex history. Here, we use three major projects to assess important processes in this life cycle. Continental arc volcanism generates a wide diversity of magma compositions, but the tempos of compositional variation are unclear. Here, we investigate a 7-million year record of volcanic ash layers in the Cretaceous Eagle Ford Group to investigate temporal changes in ash composition on <100 kyr timescales. We apply an empirical Ti/Zr-SiO2 relationship to Ti/Zr measurements of 52 Eagle Ford bentonites to reconstruct of ash protolith SiO2 of altered bentonites. Ash compositions fluctuate between periods of high and low silica volcanism over ~100 kyr timescales. If the temporal variability of these ashes represents broad snapshots of the Cordilleran continental arc, these results suggest that continental arc systems may undergo episodic changes in the extent of magmatic differentiation or the nature of eruption on rapid (<100 kyr) timescales. Slow-slip megathrust events in the Hikurangi forearc region, New Zealand, may be related to seamount subduction. We examine differences in the clast origins, depositional settings, and diagenetic histories of volcaniclastic units to highlight the heterogeneity of volcanic systems on the Hikurangi Plateau. The presence of voluminous hydrous clays within thick, altered volcaniclastic units provides a ready source for excess pore fluids that may enable slow-slip events along the Hikurangi subduction zone. Alkaline magmatism at Mountain Pass, CA has attracted attention due to its spatial and temporal association with a REE-rich, economically important carbonatite. However, questions remain about the origins of magma here. We present geochemical data for 121 primitive alkaline igneous rocks to allow a more complete picture of these uncommon igneous compositions. Examining primitive magma composition affords a glimpse into the early stages of magma generation to understand the origins and early histories of alkaline magmatism here. We argue for the importance of pyroxenite melting and suggest that metasomatism related to earlier subduction in this region were significant influences on mama compositions.
Large-scale tectonic cycles in Europe revealed by distinct Pb isotope provinces
(American Geophysical Union, 2016) Blichert-Toft, Janne; Delile, Hugo; Lee, Cin-Ty; Stos-Gale, Zofia; Billstrӧm, Kjell; Andersen, Tom; Hannu, Huhma; Albarède, Francis
Lead isotopic systematics of U-poor minerals, such as sulfides and feldspars, can provide unique insights into the origin and evolution of continents because these minerals “freeze in” the Pb isotopic composition of the crust during major tectonothermal events, allowing the history of a continent to be told through Pb isotopes. Lead model ages constrain the timing of crust formation while time-integrated U/Pb, Th/Pb, and Th/U ratios shed light onto key geochemical processes associated with continent formation. Using ∼6800 Pb isotope measurements of primarily lead ores and minor K-feldspar, we mapped out the Pb isotope systematics across Europe and the Mediterranean. Lead model ages define spatially distinct age provinces, consistent with major tectonic events ranging from the Paleozoic to the Proterozoic and latest Archean. However, the regions defined by time-integrated U/Pb and Th/Pb ratios cut across the boundaries of age provinces, with high U/Pb systematics characterizing most of southern Europe. Magmatic influx, followed by segregation of dense sulfide-rich mafic cumulates, resulted in foundering of U- and Th-poor lower crust, thereby changing the bulk composition of the continental crust and leading to distinct time-integrated U-Th/Pb provinces. We show that the tectonic assembly of small crustal fragments leaves the crust largely undifferentiated, whereas the formation of supercontinents results in fundamental changes in the composition of the crust, identifiable in time and space by means of Pb isotope systematics. Observations based on Pb isotopes open up a new perspective on possible relationships between crustal thickness and geodynamic processes, in particular the role of crustal foundering into the mantle and the mechanisms responsible for the existence of cratons.
Ongoing lithospheric removal in the western Mediterranean: Evidence from Ps receiver functions and thermobarometry of Neogene basalts (PICASSO project)
(American Geophysical Union, 2014) Thurner, Sally; Palomeras, Imma; Levander, Alan; Carbonell, Ramon; Lee, Cin-Ty
The western Mediterranean tectonic system consists of the Betic Mountains in southern Spain and the Rif Mountains in northern Morocco curved around the back-arc extensional Alboran basin. Multiple tectonic models have been developed to explain the coeval compressional and extensional tectonic processes that have affected the western Mediterranean since the Oligocene. In order to provide constraints on these evolutionary models, we use Ps teleseismic receiver functions (RF), thermobarometric analyses of post-Oligocene basalts, and previous teleseismic tomography images to investigate the lithospheric structure of the region. Ps RFs were calculated using seismic data from 239 broadband seismic stations in southern Iberia and northern Morocco and thermobarometric analysis was performed on 19 volcanic samples distributed throughout the region. The RF images reveal a highly variable Moho depth (∼25 to ∼55 km), as well as a strong positive, sub-Moho horizon between ∼45 and ∼80 km depth beneath the central Betic and Rif Mountains, which we interpret to be the top of the previously imaged Alboran Sea slab. Thermobarometric constraints from magmas in the eastern Betics and Rif indicate mantle melting depths between 40 and 60 km, typical of melting depths beneath mid-oceanic ridges where little to no lithosphere exists. Together, the RF and thermobarometric data suggest ongoing and recent slab detachment resulting from delamination of the continental lithosphere.
Petrologic Controls on the Temperature and Volatile Evolution of Magmas
(2023-08-29) Borchardt, Jackson Stone; Lee, Cin-Ty
Scientists cannot directly observe deep into our Earth. To better understand the processes that control Earth's evolution, petrologists use the chemistry of magmas to infer properties of the mantle. This thesis centers on using magma chemistry to investigate the thermal variations throughout the mantle and the role of volatiles in both magma evolution and ore formation. Chapter two reevaluates the assumptions behind olivine-liquid thermometry. Novel methods were devised to identify primitive magmas unaffected by olivine addition. Additionally, new constraints linking melt fraction to olivine forsterite content enabled a more precise determination of the amount of olivine addition required to correct the primitive magma for fractional crystallization. Applying these new methods, we reassessed the formation temperature of the North Atlantic Igneous Province, revealing that its temperature does not align with a plume origin. Chapter three examines the evolution of volatiles in arc magmas by using a compilation of arc amphiboles to recreate the chlorine evolution of arc magmas. Amphibole-reconstructed chlorine contents indicate magmatic differentiation leads to an increase in chlorine concentration due to its incompatible behavior. The amphibole-reconstructed chlorine contents of arc magmas are significantly higher than values reported from melt inclusions, suggesting that melt inclusions may have trapped melts that had already lost volatiles. This observation implies that the crust might act as a filter for magma volatile contents, likely influencing the formation of ore deposits. In Chapter four, amphiboles are once again employed, but this time to reconstruct the evolution of fluorine in arc magmas. The melts reconstructed from amphibole data indicate that fluorine is a compatible element, sequestered within arc cumulates. Compiled experimental data suggests amphibole crystallization controls the bulk fluorine evolution in arc magmas, creating fluorine poor, but water rich arc melts. We hypothesize that the subsequent melting of these arc cumulates gives rise to fluorine-rich yet water-poor melts, which serve as hosts for rare earth element deposits.
Seismic Array Study of the Western Mediterranean and the United Stats Great Plains: Insight into the Modification and Evolution of Continental Lithosphere
(2014-11-17) Thurner, Sally; Levander, Alan; Niu, Fenglin; Lee, Cin-Ty; Pu, Han
Numerous tectonic processes are responsible for the modification and evolution of continental lithosphere. The continents, however, are generally resilient through geologic time and keep a record of Earth’s tectonic activity, both past and present. The focus of this work is to better understand the modification and evolution of continental lithosphere associated with continent-continent collisions. We do this by studying two orogenic systems: the Alpine Orogeny, associated with the ongoing collision between the African and Eurasian plates, and the Trans-Hudson Orogeny, associated with the initial formation of the North American craton during the Precambrian. This research focuses on the westernmost edge of the Alpine system in the western Mediterranean, where subduction and slab rollback have caused significant extension and Africa-Iberia convergence has caused simultaneous contraction. Here we calculate Pds receiver functions to constrain the discontinuity structure. Additionally, we jointly invert Pds receiver functions and Rayleigh wave phase velocity dispersion data to create a 3-D shear velocity model. These results show a deep Moho around the western portion of the Gibraltar Arc. Below this deep Moho we see the Alboran Slab extending down to ~250 km. In the eastern Gibraltar Arc, there is a very shallow Moho where the slab has detached from the surface and removed continental lithosphere. In the Trans-Hudson Orogen we use receiver functions and gravity data to determine the discontinuity and density structure of the shallow lithosphere. This analysis reveals crustal-scale thrusting associated with the Wyoming-Superior suture zone. We also find a relatively low Moho density contrast throughout the Trans-Hudson and northern Yavapai Province. This low Moho density contrast is associated with a deep Moho (>50 km) and is interpreted to be evidence of a dense lower crustal layer resulting from mafic underplating. Finally, we investigate the contribution that this dense thick crust may have played in the isostatic stabilization of the North American craton as well as other cratons around the world. We find that the lithospheric mantle must provide a negative component to cratonic lithospheric buoyancy in order to account for the low elevations observed along with thick crust in the cratons.
The applications of data science to petrology and geochemistry
(2020-12-04) Zhang, Julin; Lee, Cin-Ty
Data science has been widely applied to a lot of disciplines in recent years. However, few relevant works have been done in the field of geology. Therefore, this thesis aims to discuss the application and potential of data science in petrology and geochemistry. The most common data in petrology and geochemistry are rock images and geochemical compositions of rocks. The color and texture of igneous rocks are closely related to their diagenetic process while geochemical compositions can be used to decipher the source of rocks and the physical and chemical processes they undergo before they solidify. The development of large geochemical databases such as EarthChem and GeoRoc provides the geochemists with convenience for accessing the big data and studying the origin and evolution of Earth. However, the lack of a large rock image database hinders the potential of using data science to better understand the formation of rocks. Therefore, in this thesis, I propose an image processing workflow that allows geologists to easily acquire and report standardized rock images with smartphones, contributing to the buildup of the rock image database. I also use image analysis methods to discuss the origin of orbicular granitoids from Mount Magnet, western Australia. Moreover, I use machine learning tools to explore the relationship between heat-producing elements and major elements of the igneous rocks, providing the implication on the thermal state of the lower crust during the Archean.
The S-reflector detachment from the Galicia margin, offshore Spain: New insights on fault zone thicknesses, fault surface morphology, and mantle serpentinization associated with a large-scale detachment fault
(2019-04-15) Schuba, Cemile Nur; Morgan, Julia K.; Lee, Cin-Ty
The Galicia magma-poor margin is considered an archetypal location to explore detachment faulting in a passive rift margin setting. A new 3-D seismic reflection volume acquired over the Galicia continent-ocean transition zone provides an unprecedented view of the prominent S-reflector detachment fault from the Deep Galicia Margin. This new dataset shows that the interface of the S-reflector detachment fault has heterogenous seismic reflection amplitudes. The seismic reflection amplitudes are analyzed and discussed relative to fault surface morphology and variations in the fault rock layer above and upper mantle layer below the S-reflector. The fault surface map of the S-reflector shows coherent corrugations parallel to the expected paleo-extension directions with an average azimuth of 107o. Locally, the corrugations are continuous beneath multiple fault blocks, spanning crustal fault intersections with the S-reflector, which suggest that during the final stages of the detachment did not demonstrate sequential crustal faulting. A second somewhat discontinuous layer above the detachment fault, here named the S-interval, interpreted to be as zone of fault rock above the S-reflector. Overall, the S-interval increases in thickness by tens of meters to the northwest, in the direction of hanging wall transport. There are localized thick accumulations of fault rock near overlying fault intersections, suggesting either non-uniform fault rock production, or redistribution of fault rock during slip. An artificial neural network has been utilized to estimate the P-wave velocities of the upper mantle, 100 ms (~400 m) below the S-reflector detachment. This approach estimates seismic velocity along a target interface, based on geological and geophysical inputs from both the 3-D seismic reflection survey and and additional 2-D wide-angle seismic profile. This non-linear regression technique results in estimated velocities 100 ms above and below the targeted interface, the S-reflector. An ensemble of similarly trained neural networks is used to estimate previously unknown target velocities where the S-reflector is the cust-mantle boundary within the 3-D dataset, where the S-reflector is the crust-mantle boundary. These networks reached minimum achievable error of 2% on the test data, and the low standard deviation (<300 m/s) between different networks demonstrate that the input features were sufficient to capture variations in the velocity above and below the targeted S-reflector. The upper mantle seismic velocities are used to estimate distribution and the degree of serpentinization in the upper mantle and its distribution beneath the S-reflector detachment fault. The degree of serpentinization is heterogeneous, varying between 0 and 90% across the domain. The distribution pattern shows relationships with both the current intersections of crust-cutting faults soles and to paleo-temperatures estimated for ~112 Ma. High degrees of serpentinization are only observed in areas where overburden thickness at the end of rifting was sufficient to provide optimal serpentinization temperatures. The alignment of crust-cutting fault intersections and serpentinized areas suggest the crustal faults were water conduits that hydrated the mantle peridotite. The correspondence between the fault intersections and present-day serpentinite anomalies indicates that the most of the serpentinization postdated slip on the S-reflector detachment. Volumetric expansion caused by the serpentinization process may also lead to undulations on the fault detachment fault surface. High localized reliefs (0.9 km and 1.4 km) on the S-reflector coincide with highly serpentinized (80-90%) areas in the 3-D seismic reflection survey. These observations have important implications for understanding how detachment faults form and evolve during and after rifting. 3-D seismic reflection imaging and amplitude analysis have enabled unique insights into fault slip history, fault rock production and redistribution, and causal mechanisms behind mantle serpentinization in a passive rift margin environment.
Thick crust, hydrous magmas, and the paradox of voluminous cold magmatism
(Presses universitaires de Strasbourg, 2021) Lee, Cin-Ty; Liu, Boda
Andesites are refined and “cold” magmas compared to their basaltic parents, yet large volumes of andesites are generated at continental arcs. We show that large andesitic plutons are favored when arc crust attains a thickness of ~60 km while mafic plutons are small and favored when arc crust is thin. Using simple thermal models, we show that large, long-lived and relatively cold partially molten zones, sustained by recharge of hydrous basaltic magmas, are favored at depth when arc crust is thick due to the reduced efficiency of heat loss with increasing crustal thickness. Thin crust and drier magmas favor hotter and thinner partially molten zones. Our study provides an explanation for the apparent paradox that the most voluminous magmas in continental arc settings are cold. The origin of andesites may be linked to the interplay between magmatic differentiation, the availability of water, and the processes that control crustal thickness.
Widespread phosphorous excess in olivine, rapid crystal growth, and implications for magma dynamics
(Presses universitaires de Strasbourg, 2022) Lee, Cin-Ty; Sun, Chenguang; Sharton-Bierig, Eytan; Phelps, Patrick; Borchardt, Jackson; Liu, Boda; Costin, Gelu; Johnston, A. Dana
Trace element zoning is often used to unravel the crystallization history of phenocrysts in magmatic systems, but interpretation requires quantifying the relative importance of equilibrium versus disequilibrium. Published partition coefficients for phosphorous (P) in olivine vary by more than a factor of ten. After considering kinetic effects, a new equilibrium partition coefficient was extrapolated from a re-examination of natural and experimental systems, indicating that P partition coefficients in olivine are significantly over-estimated. These new partitioning constraints allow us to establish a theoretical P Equilibrium Fractionation Array (PEFA) for mid-ocean ridge basalts (MORBs), revealing that most olivines from MORBs have excess P (2–15 times PEFA) and are thus in disequilibrium. Using an independent case study of natural dendritic olivines, we show that such P enrichments can be explained by diffusion-limited incorporation of P during rapid crystal growth. If growth rate can be related to cooling, the rapid growth rates of olivines have implications for magma system dynamics, such as the size of magma bodies or where crystallization occurs within the body.

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