If evolved magmas are not typical of planet-sized bodies, what drives their differentiation in planetesimals?

The revelation that evolved magmas are not typical of large, planet-sized bodies (1), is a most crucial aspect of understanding the differentiation of primary magma of whatever composition it may be. If magmatic evolution or differentiation of magmas is not driven by the gravitational force that is typical of astronomical objects, like planets, then there is some other force that can act at a much smaller scale so that evolved magmas occur even with planetesimals. There are two aspects that need our attention here that can explain magmatic evolution in planetesimals:

i) Either the matter that formed the solar system is already recycled in another star.

The faith for such a thought principally arises from the understanding that there were multiple generations of grain aggregations in the presolar dust (2). Such dust, if they were the broken pieces of an already evolved magma in another stellar object, then that may have been responsible for the observed composition of achondrites (1). The chances are that a supernova explosion or, a strong heating resulting from the acoustic waves of black holes may serve as a source for the formation of such evolved presolar dust.

ii) Alternatively, the "evolutionary graph theory" (3) is applicable here.

Here I consider that the evolution of magmas arises from the inter-atomic forces. In order to apply the "evolutionary graph theory" (3), consider that 1) each node in the graph depicts an individual (for example, an atom or molecule for crystal growth studies); 2) each line or edge in the graph depicts the strength of the interaction between the individuals; 3) a certain degree of heterogeneity exists among the individuals that initiate and drives the evolution of the system".

In this case, the interaction between the nodes (atoms, molecules or, phases) can be quantified by 1) the electronegativity of the atoms when atoms represent the nodes, 2) the intra-molecular forces that arise from van-der-Walls and other electronic interactions when molecules represent the nodes) and, 3) the surface free energy (Gibbs' free energy) when the nodes are represented by different phases (as defined in phase diagrams) in the evolutionary graph theory.

References:

1) Silica-rich volcanism in the early solar system dated at 4.565 Ga, https://doi.org/10.1038/s41467-018-05501-0

2) Multiple generations of grain aggregation in different environments preceded solar system body formation, https://doi.org/10.1073/pnas.1720167115

3) Construction of arbitrarily strong amplifiers of natural selection using evolutionary graph theory, https://doi.org/10.1038/s42003-018-0078-7

Why geochemical surveys should focus on low-order streams?

Consider a virgin terrain with highly variable lithology just exposed to the geological agents of weathering. Here, local lithology controls the development of runnel (Dodge-Wan and Nagarajan, 2016) and its progression into a stream and then a river. The weathering pattern guided by local climate, the intensity of weathering, aspect and gradient that drives rainwater to pass towards downhill, are some of the factors that influence the development of the drainage network in a river basin. Thus, highly variable lithology results in the formation of small streams, and that is how we observe considerable geochemical and provenance heterogeneity in Taiwanese rivers (Deng et al., 2019). The presence of a large number of small streams in an area may represent local lithological heterogeneity. For the same reason, in geochemical surveys, it is very much essential to collect sediment samples from low-order streams apart from the river where these streams deliver their water and sediment. If these streams have a distinct isotopic signature of a conservative trace element in its water column, then it might be possible to estimate the contribution of freshwater from each stream into the river. Such a technique might be useful where stream gauges are not available.

References

Dodge-Wan, D., Nagarajan, R., 2016. Runnel development on granitic boulders on the foothills of Mount Kinabalu (Pinosuk Gravel Formation, Sabah, N Borneo). J. Mt. Sci. 13, 46–58. https://doi.org/10.1007/s11629-014-3169-z

Deng, K., Yang, S., Bi, L., Chang, Y.-P., Su, N., Frings, P., Xie, X., 2019. Small dynamic mountainous rivers in Taiwan exhibit large sedimentary geochemical and provenance heterogeneity over multi-spatial scales. Earth and Planetary Science Letters 505, 96–109. https://doi.org/10.1016/j.epsl.2018.10.012

Sea level rise, shallow carbonate deposition, ocean alkalinity and climate change during Cenozoic

During Quaternary,the sea level around Borneo has oscillated, periodically connecting and disconnecting Borneo from continental Asia (Earl of Cranbrook, 2009). The climate of this region has subsequently undergone significant changes. Abrams et al. (2018) proposed that shallow carbonate deposition in flooded shelves of the Sundaland could have resulted in an increase of pCO₂ by 39 ppm during Holocene (since 5000 BP). A thorough understanding of the processes that link the "shallow carbonate deposition" to atmospheric CO₂ needs further examination. Carter et al. (2014) have introduced a composite indicator, Alk^*, primarily determined by calcium carbonate precipitation or dissolution. They have shown that the effect of temperature on CO₂ solubility, freshwater influence and disequilibrium in the air-sea exchange of CO₂ (in their order of decreasing influence) significantly influences the calcite saturation state in the seawater. The calcium carbonate cycling has an almost insignificant role. Thus, changes in the calcite saturation state are mutually adjusted by the cycling of calcium carbonate by attaining an equilibrium for the given temperature and salinity. The calcite saturation state exerts control over CO₂ uptake by the ocean. Saturation leads to calcite precipitation and, undersaturation leads to dissolution. Precipitation of calcite transforms atmospheric CO2 into sediment repository that maybe finally subducted and undergo a long term burial that may outgas during arc magmatism. Calcium carbonate cycling does not have control over calcite saturation state and therefore ocean alkalinity. Then, the conclusion that silicate weathering is not responsible for long term Cenozoic cooling (Moore et al., 2013) may be an artefact of the inability of the calcium carbonate to influence the alkalinity of the ocean significantly.

References:

Abrams, J.F., Hohn, S., Rixen, T., Merico, A., 2018. Sundaland peat carbon dynamics and its contribution to the Holocene atmospheric CO₂ concentration. Global Biogeochemical Cycles 32, 704–719. https://doi.org/10.1002/2017GB005763

Carter, B.R., Toggweiler, J.R., Key, R.M., Sarmiento, J.L., 2014. Processes determining the marine alkalinity and calcium carbonate saturation state distributions. Biogeosciences 11, 7349–7362. https://doi.org/10.5194/bg-11-7349-2014

Earl of Cranbrook, 2010. Late quaternary turnover of mammals in Borneo: the zooarchaeological record. Biodivers Conserv 19, 373–391. https://doi.org/10.1007/s10531-009-9686-3

Moore, J., Jacobson, A.D., Holmden, C., Craw, D., 2013. Tracking the relationship between mountain uplift, silicate weathering, and long-term CO₂ consumption with Ca isotopes: Southern Alps, New Zealand. Chemical Geology 341, 110–127. https://doi.org/10.1016/j.chemgeo.2013.01.005