Compositional Closure—Its Origin Lies Not in Mathematics but Rather in Nature Itself

Compositional closure, spurious negative correlations in data sets of a fixed sum (e.g., fractions and percent), is often encountered in geostatistical analyses, particularly in mineralogy, petrology, and geochemistry. Techniques to minimize the effects of closure (e.g., log-ratio transformations) can provide consistent geostatistical results. However, such approaches do not remove these effects because closure does not result from mathematical operations but is an inherent property of the physical systems under study. The natural world causes physical closure; mathematics simply describes that closure and cannot alter it by manipulations. Here, we examine the distinct types of geologic systems and samples to determine in which situations closure (physical and mathematical) does or does not ensue and the reasons therefor. We parse compositional systems based on (1) types of components under study, immutable (e.g., elements) or reactive (minerals), and (2) whether the system is open or closed to component transfer. Further, open systems can be (1) displacive in which addition of a component physically crowds out others, or (2) accommodative in which addition or subtraction of components does not affect the others. Only displacive systems are subject to compositional closure. Accommodative systems, even with components expressed as percent or fractions, are not closed physically or, therefore, mathematically.

Petrology and geochemistry of metapelites from Asenitsa unit, Central Rhodope massif

Asenitsa unit metapelites (Central Rhodope massif) have a high variability in mineral, bulk chemical and trace element composition. Kyanite, staurolite and garnet are the major minerals in schists and show intensive retrograde change. Discrimination diagrams based on immobile trace elements indicate continental island arc or active margin setting of deposition.

Editorial for Special Issue “Mineralogy, Petrology, and Geochemistry of Evaporites”

In his excellent and complete compendium “Evaporites” [...]

Petrology and Geochemistry of Rocks of Ishiagu and Environs Southeastern Nigeria Using Ed-Xrf Method

Geochemistry of rocks of Ishiagu area was carried out using Energy Dispersive X-Ray fluorescence (ED-XRF) method. Twelve samples were analyzed and their geochemical properties determined using Excel-Software. Geological mapping reveals that basalts, dolerites and diorites emplaced in shale and mudrock country hosts are the main lithological units occurring in the area. They have silica content of 40.4–49.2wt.%, indicating they are basic-ultrabasic in character. The dolerite and diorite contain average plagioclase (An70-17.4vol.%), hematite 26.29vol.%, showing enrichment in ferromagnesian minerals and depletion in quartz. The Na2O and K2O averaged 1.22wt.% and 1.46wt.% respectively, indicating depletion in alkali, thus corroborating their basic–ultrabasic property. The TiO2 value is 3.6wt. %, indicating oceanic magma derivation. The industrial metals Pb, Cu, Ni and Zn were relatively similar with average values of 37.13, 23.96, 23.69, and 20.08ppm respectively, showing common protolith. The diorite and dolerite are enriched in trace elements Zr, Sr, with average concentration of 172.49, 109.73ppm, and relatively depleted in As and Au with values of 0.04 and 0.03ppm respectively. Petrogenetic analyses using ternary diagram TiO2–K2O–P2O5 for discriminating magma type, the dolerites and diorites all plot in continental basaltic field. In the AFM, and P2O5 versus Zr plots all the dolerites and diorites fall in the tholeiitic field, corroborating that they originated from tholeiitic basaltic magma, probably derived from lower crust/upper mantle. In the Na2O/Al2O3 versus K2O/Al2O3 diagram the dolerites and diorites all plot in the igneous field, the shale plot in metasedimentary field, while the ironstone fall on the boundary between igneous and metasedimentary fields indicating hybrid provenance.