scholarly journals The Effect of Inefficient Accretion on Planetary Differentiation

2021 ◽  
Vol 2 (3) ◽  
pp. 93
Author(s):  
Saverio Cambioni ◽  
Seth A. Jacobson ◽  
Alexandre Emsenhuber ◽  
Erik Asphaug ◽  
David C. Rubie ◽  
...  
Keyword(s):  
Planetary Differentiation

Compressibility of water in magma and the prediction of density crossovers in mantle differentiation

2008 ◽  
Vol 366 (1883) ◽  
pp. 4239-4252 ◽  
Author(s):  
Carl B Agee
Keyword(s):  
High Pressure ◽  
Compressible Liquid ◽  
Silicate Melt ◽  
Liquid Density ◽  
Low Velocity ◽  
Oxide Component ◽  
The Earth ◽  
Liquid Oxide ◽  
Planetary Differentiation ◽  
Pressure Regime

Hydrous silicate melts appear to have greater compressibility relative to anhydrous melts of the same composition at low pressures (<2 GPa); however, at higher pressures, this difference is greatly reduced and becomes very small at pressures above 5 GPa. This implies that the pressure effect on the partial molar volume of water in silicate melt is highly dependent on pressure regime. Thus, H 2 O can be thought of as the most compressible ‘liquid oxide’ component in silicate melt at low pressure, but at high pressure its compressibility resembles that of other liquid oxide components. A best-fit curve to the data on from various studies allows calculation of hydrous melt compression curves relevant to high-pressure planetary differentiation. From these compression curves, crystal–liquid density crossovers are predicted for the mantles of the Earth and Mars. For the Earth, trapped dense hydrous melts may reside atop the 410 km discontinuity, and, although not required to be hydrous, atop the core–mantle boundary (CMB), in accord with seismic observations of low-velocity zones in these regions. For Mars, a density crossover at the base of the upper mantle is predicted, which would produce a low-velocity zone at a depth of approximately 1200 km. If perovskite is stable at the base of the Martian mantle, then density crossovers or trapped dense hydrous melts are unlikely to reside there, and long-lived, melt-induced, low-velocity regions atop the CMB are not predicted.

A tandem-column extraction chromatography for Nd separation: minimizing mass-independent isotope fractionation for ultrahigh-precision Nd isotope-ratio analysis

2022 ◽  
Author(s):  
Da Wang ◽  
Richard Carlson
Keyword(s):  
Solar System ◽  
Extraction Chromatography ◽  
Isotope Ratio ◽  
Isotope Fractionation ◽  
Ratio Analysis ◽  
Nd Isotope ◽  
Planetary Differentiation ◽  
Isotope Ratio Analysis ◽  
Isotope System ◽  
Column Extraction

The short-lived 146Sm-142Nd isotope system traces key early planetary differentiation processes that occurred during the first 500 million-years of solar system history. The variations of 142Nd/144Nd in terrestrial samples, typically...

scholarly journals Redox control on nitrogen isotope fractionation during planetary core formation

2019 ◽  
Vol 116 (29) ◽  
pp. 14485-14494 ◽  
Author(s):  
Celia Dalou ◽  
Evelyn Füri ◽  
Cécile Deligny ◽  
Laurette Piani ◽  
Marie-Camille Caumon ◽  
...  
Keyword(s):  
Subduction Zones ◽  
Nitrogen Isotope ◽  
Silicate Glasses ◽  
Metal Alloys ◽  
Core Formation ◽  
Isotopic Compositions ◽  
Metal Silicate ◽  
Planetary Differentiation ◽  
N Isotopes ◽  
Basaltic Melts

The present-day nitrogen isotopic compositions of Earth’s surficial (15N-enriched) and deep reservoirs (15N-depleted) differ significantly. This distribution can neither be explained by modern mantle degassing nor recycling via subduction zones. As the effect of planetary differentiation on the behavior of N isotopes is poorly understood, we experimentally determined N-isotopic fractionations during metal–silicate partitioning (analogous to planetary core formation) over a large range of oxygen fugacities (ΔIW −3.1 < logfO2 < ΔIW −0.5, where ΔIW is the logarithmic difference between experimental oxygen fugacity [fO2] conditions and that imposed by the coexistence of iron and wüstite) at 1 GPa and 1,400 °C. We developed an in situ analytical method to measure the N-elemental and -isotopic compositions of experimental run products composed of Fe–C–N metal alloys and basaltic melts. Our results show substantial N-isotopic fractionations between metal alloys and silicate glasses, i.e., from −257 ± 22‰ to −49 ± 1‰ over 3 log units of fO2. These large fractionations under reduced conditions can be explained by the large difference between N bonding in metal alloys (Fe–N) and in silicate glasses (as molecular N2 and NH complexes). We show that the δ15N value of the silicate mantle could have increased by ∼20‰ during core formation due to N segregation into the core.

How can REE-bearing minerals help us refine our understanding of crustal evolution and Archean tectonics?

2020 ◽  
Author(s):  
Emilie Bruand ◽  
Craig Storey ◽  
Mike Fowler
Keyword(s):  
Trace Element Analysis ◽  
Geochemical Data ◽  
Chemical Information ◽  
Element Analysis ◽  
Secular Evolution ◽  
Tectonic Processes ◽  
The Earth ◽  
Planetary Differentiation ◽  
Pertinent Information

&lt;p&gt;Delineating the evolution of the Earth&amp;#8217;s dynamics and interactions between its different silicate reservoirs (ocean crust, continental crust, mantle) is key to understanding planetary differentiation and the conditions of surface habitability. Today, plate tectonic processes play a major role in creating and destroying the Earth&amp;#8217;s crust, and modifying its silicate mantle. For this reason the Earth is unique in the solar system. Reconstructing its long-term evolution is, however, extremely difficult since the Hadean record is essentially missing and most Archean rocks have experienced reworking and overprinting of their original signatures.&amp;#160;&lt;/p&gt;&lt;p&gt;In this presentation, we will explore the constraints available with isotopic and chemical information from REE-bearing minerals in magmas that appear at different times during Earth history. We present, new geochemical data on these phases from a compilation of granitoids that cover a large span of the geological record from the Archean to the Phanerozoic. We demonstrate that trace element analysis and detailed petrographic work can give direct information about the petrogenesis of the host magmas even when these granitoids have been affected by metamorphism. Other studies focusing on rutile have shown that it records important information on metamorphic conditions in the Archean. On the other hand, and also helpfully, all three minerals are resistant to secondary processes and erosion, and thus may also offer significant archives of pertinent information in the detrital rock record. Development of such petro-geochemical tools could deliver complementary information to that provided by zircon and have significant potential for provenance studies and for tracing the secular evolution of the Earth.&lt;/p&gt;

scholarly journals Meteorite zircon constraints on the bulk Lu−Hf isotope composition and early differentiation of the Earth

2015 ◽  
Vol 112 (17) ◽  
pp. 5331-5336 ◽  
Author(s):  
Tsuyoshi Iizuka ◽  
Takao Yamaguchi ◽  
Yuki Hibiya ◽  
Yuri Amelin
Keyword(s):  
Thermal Evolution ◽  
Isotope Composition ◽  
Isotope Analysis ◽  
Radioactive Decay ◽  
Data Interpretation ◽  
Hf Isotope ◽  
Accurate Estimation ◽  
The Earth ◽  
Planetary Differentiation ◽  
Firm Evidence

Knowledge of planetary differentiation is crucial for understanding the chemical and thermal evolution of terrestrial planets. The 176Lu−176Hf radioactive decay system has been widely used to constrain the timescales and mechanisms of silicate differentiation on Earth, but the data interpretation requires accurate estimation of Hf isotope evolution of the bulk Earth. Because both Lu and Hf are refractory lithophile elements, the isotope evolution can be potentially extrapolated from the present-day 176Hf/177Hf and 176Lu/177Hf in undifferentiated chondrite meteorites. However, these ratios in chondrites are highly variable due to the metamorphic redistribution of Lu and Hf, making it difficult to ascertain the correct reference values for the bulk Earth. In addition, it has been proposed that chondrites contain excess 176Hf due to the accelerated decay of 176Lu resulting from photoexcitation to a short-lived isomer. If so, the paradigm of a chondritic Earth would be invalid for the Lu−Hf system. Herein we report the first, to our knowledge, high-precision Lu−Hf isotope analysis of meteorite crystalline zircon, a mineral that is resistant to metamorphism and has low Lu/Hf. We use the meteorite zircon data to define the Solar System initial 176Hf/177Hf (0.279781 ± 0.000018) and further to identify pristine chondrites that contain no excess 176Hf and accurately represent the Lu−Hf system of the bulk Earth (176Hf/177Hf = 0.282793 ± 0.000011; 176Lu/177Hf = 0.0338 ± 0.0001). Our results provide firm evidence that the most primitive Hf in terrestrial zircon reflects the development of a chemically enriched silicate reservoir on Earth as far back as 4.5 billion years ago.

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