A new thermodynamic model is presented for calculating phase relations in peridotite, from 0.001 to 60kbar and from 800 degree C to liquidus temperatures, in the system NCFMASOCr. This model system ...is large enough to simulate phase relations and melting of natural peridotite and basaltic liquids. Calculations in the program thermocalc illustrate mantle phase relationships and melting conditions, specifically for the peridotite composition KLB-1. The garnet-spinel transition zone intersects the solidus at 21.4-21.7kbar, where both Fe super(3+) and Cr increase spinel stability, expanding the width of the transition. Orthopyroxene is lost at the solidus at 42kbar in KLB-1, although this pressure is very sensitive to bulk composition. Calculated oxidation states are in excellent agreement with measured log fO sub(2) for xenolith suites with mantle Fe sub(2)O sub(3) contents in the range 0.1-0.3wt %. It appears that mantle oxidation state is not just a simple function of P and T, but depends on phase assemblage, and may vary in a complex way within a single assemblage. The liquid model performs well, such that calculated solidus, melt productivity and liquid compositions compare favourably with those of experimental studies, permitting its use in interpolating between, and extrapolating from, experimental P-T conditions. Experimentally challenging but geologically useful regimes can be explored, such as subsolidus samples and very low melt fractions, with application to both mantle xenoliths and the origin of basalt.
Olivine‐phyric shergottites are relatively young Martian meteorites that resemble primitive mantle‐derived melts, so offer insight into the causes of recent magmatism on Mars. The Al‐in‐olivine ...geothermometer offers the potential to examine (near‐)liquidus melt temperatures. However, the ubiquitous shock features in most Martian meteorites, caused by high‐energy impacts, can change the structure and composition of olivine crystals, making the applicability of mineral geothermometry methods uncertain. This study examines microstructure and mineral chemistry in two shocked primitive, depleted olivine‐phyric shergottites, Sayh al Uhaymir (SaU) 005 and Dar al Gani (DaG) 476. DaG 476 is unsuitable for Al‐in‐olivine thermometry because of the presence of difficult‐to‐observe but pervasive networks of undulating veins in olivine down to sub‐micron sizes, caused by melting and providing pathways for cation diffusion. In contrast, SaU 005 can be used for Al‐in‐olivine thermometry despite the presence of conjugate shear and fracture sets and micron‐scale cpx‐spinel exsolution. The average crystallization temperature of Fo>70 olivine in SaU 005, 1380°C, is near‐identical to the average temperature of new and published Fo>70 data from all olivine‐phyric shergottites. When corrected for equilibrium with mantle olivine (Fo80) this corresponds to a mantle temperature of approximately 1500°C, 130°C hotter than ambient Martian mantle when shergottites formed. Shergottites were generated by melting within a moderately hot mantle plume or thermal anomaly, in support of other evidence that the Martian mantle is actively convecting. However, it does not support the extremely high potential temperatures estimated for the shergottite source by a whole‐rock petrological method.
One of the most important physical characteristics driving lifecycle events in lakes is stratification. Already subtle variations in the timing of stratification onset and break-up (phenology) are ...known to have major ecological effects, mainly by determining the availability of light, nutrients, carbon and oxygen to organisms. Despite its ecological importance, historic and future global changes in stratification phenology are unknown. Here, we used a lake-climate model ensemble and long-term observational data, to investigate changes in lake stratification phenology across the Northern Hemisphere from 1901 to 2099. Under the high-greenhouse-gas-emission scenario, stratification will begin 22.0 ± 7.0 days earlier and end 11.3 ± 4.7 days later by the end of this century. It is very likely that this 33.3 ± 11.7 day prolongation in stratification will accelerate lake deoxygenation with subsequent effects on nutrient mineralization and phosphorus release from lake sediments. Further misalignment of lifecycle events, with possible irreversible changes for lake ecosystems, is also likely.
We report the first application of CRISPR‐Cas technology to single species detection from environmental DNA (eDNA). Organisms shed and excrete DNA into their environment such as in skin cells and ...faeces, referred to as environmental DNA (eDNA). Utilising eDNA allows noninvasive monitoring with increased specificity and sensitivity. Current methods primarily employ PCR‐based techniques to detect a given species from eDNA samples, posing a logistical challenge for on‐site monitoring and potential adaptation to biosensor devices. We have developed an alternative method; coupling isothermal amplification to a CRISPR‐Cas12a detection system. This utilises the collateral cleavage activity of Cas12a, a ribonuclease guided by a highly specific single CRISPR RNA. We used the target species Salmo salar as a proof‐of‐concept test of the specificity of the assay among closely related species and to show the assay is successful at a single temperature of 37°C with signal detection at 535 nM. The specific assay, detects at attomolar sensitivity with rapid detection rates (<2.5 hr). This approach simplifies the challenge of building a biosensor device for rapid target species detection in the field and can be easily adapted to detect any species from eDNA samples from a variety of sources enhancing the capabilities of eDNA as a tool for monitoring biodiversity.
Internationally, water management is moving from the traditional top-down approach to more integrated initiatives focussing on community-led action. With inadequacies in previous engagement ...initiatives undertaken through the first cycle of River Basin Management Planning for the EU Water Framework Directive (WFD), the Republic of Ireland has only recently embraced this bottom-up approach. The attempted introduction of national charging for domestic water use in 2015 has resulted in significant public disquiet and protest movements against the national government. In April 2015 we undertook a survey of current opinion on water management and community engagement initiatives in the Republic of Ireland and the United Kingdom. A total of 520 survey responses identified that although freshwater bodies are important in peoples' lives, respondents were typically unaware of global initiatives such as Integrated Water Resources Management and Integrated Catchment Management. Overall, 81% of respondents did not feel included in decisions about their water environment despite an overwhelming 95% believing that local communities should have a say in how the water environment is managed. However, only 35.1% of respondents stated that they would be willing to attend local water management engagement initiatives. Rather than supporting individual gain, respondents identified social gains for the local community as avenues for increasing local involvement in water initiatives. In the Republic of Ireland, a water engagement initiative that implements the national framework local delivery model should be developed and implemented. This would 1) contribute to the second round of WFD River Basin Management Planning; 2) facilitate stronger connections between local communities and their water environment; and 3) foster bottom-up initiatives that empower communities regarding local water management issues.
Calculating reliable temperatures of Mg-rich magmas is problematic because melt composition and KD(Fe–Mg)ol–liq, the key parameters of many traditional thermometers, are difficult to constrain ...precisely. The recently developed Al-in-olivine thermometer Coogan, L.A., Saunders, A.D., Wilson, R.N., 2014. Aluminium-in-olivine thermometry of primitive basalts: Evidence of an anomalously hot mantle source for large igneous provinces. Chemical Geology 368, 1–10 circumvents these problems by relying on the temperature-dependent exchange of Al between olivine and spinel crystallising in equilibrium with each other. This thermometer is used to re-evaluate the crystallisation temperatures of most Mg-rich magma type identified from the Karoo large igneous province (LIP), known as the Vestfjella depleted ferropicrite suite. Previous temperature estimates for the suite were based on olivine–melt equilibria and indicated anomalously high crystallisation temperatures in excess of 1600°C. We also present crystallisation temperatures for another Antarctic Karoo magma type, Group 3 dykes from Ahlmannryggen, which are derived from a pyroxene-rich mantle source. Our high-precision analysis of Al in olivine–spinel pairs indicate crystallisation temperatures from 1391±42°C to 1481±35°C for the Vestfjella depleted ferropicrite suite (Fo88–92) and from 1253±64°C to 1303±40°C for the Group 3 dykes (Fo79–82). Although the maximum temperature estimates for the former are over 100°C lower than the previously presented estimates, they are still ~200°C higher than those calculated for mid-ocean ridge basalts using the same method. Although exact mantle potential temperatures are difficult to estimate, the presented results support elevated sub-Gondwanan upper mantle temperatures (generated by a mantle plume or internal mantle heating) during the generation of the Karoo LIP.
•Re-evaluation of the crystallisation temperatures of the most Mg-rich magmas of the Karoo LIP•Most primitive magmas crystallised at temperatures of 1400–1500°C•Sublithospheric sources of the Karoo LIP heated above ambient upper mantle temperatures
The aluminous calcium-ferrite type phase (CF) and new aluminous phase (NAL) are thought to hold the excess alumina produced by the decomposition of garnet in MORB compositions in the lower mantle. ...The respective stabilities of CF and NAL in the nepheline-spinel binary (NaAlSiO
4
–MgAl
2
O
4
) are well established. However with the addition of further components the phase relations at lower mantle conditions remain unclear. Here we investigate a range of compositions around the nepheline apex of the nepheline-kalsilite-spinel compositional join (NaAlSiO
4
–KAlSiO
4
–MgAl
2
O
4
) at 28–78 GPa and 2000 K. Our experiments indicate that even small amounts of a kalsilite (KAlSiO
4
) component dramatically impact phase relations. We find NAL to be stable up to at least 71 GPa in potassium-bearing compositions. This demonstrates the stabilizing effect of potassium on NAL, because NAL is not observed at pressures above 48 GPa on the nepheline-spinel binary. We also observe a broadening of the CF stability field to incorporate larger amounts of potassium with increasing pressure. For pressures below 50 GPa only minor amounts (
<
0.011
(
1
)
K
K
+
N
a
+
M
g
) of potassium are soluble in CF, whereas at 68 GPa, we find a solubility in CF of at least
0.088
(
3
)
K
K
+
N
a
+
M
g
. This indicates that CF and NAL are suitable hosts of the alkali content of MORB compositions at lower mantle conditions. For sedimentary compositions at lower mantle pressures, we expect K-Hollandite to be stable in addition to CF and NAL for pressures of 28–48 GPa, based on our simplified compositions.
Abstract
Complex multiphase reaction rims that form during garnet breakdown are known as kelyphite coronae and are common amongst exhumed mantle xenoliths. It has long been established that a ...reaction of garnet and olivine produces kelyphite corona consisting of spinel and pyroxenes, and that preservation of high-pressure garnet cores requires sufficiently rapid uplift of material through the spinel lherzolite stability field from depths of at least 60 km. We present new high-pressure, high-temperature experiments of garnet breakdown in the spinel–lherzolite stability field demonstrating that a series of cascading reactions can reproduce the multilayer, multiphase kelyphites seen in nature. In all experiments where breakdown occurred, a melt appears to have moderated the reactions towards equilibrium; we believe this to be the first experimental confirmation of the importance of such melts in garnet breakdown reactions. In our experiments at least three distinct zones of concentric kelyphite growth can occur at a single pressure, temperature condition; we suggest, therefore, that such kelyphites seen in natural samples do not have to be caused by a multistage uplift path as is often assumed. Kelyphitic coronae surrounding garnet have previously been used to estimate uplift rates; however, the lack of kinetic data for relevant exhumation reactions has limited their use for PTt pathway estimations and the understanding of emplacement mechanisms. In order to constrain accurate PTt pathways we use reaction rim thickness as a proxy for reaction progress and present preliminary results for the kinetics of garnet breakdown.
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