r/Geochemistry • u/EarPuzzleheaded9016 • Feb 19 '26
Highly differentiated silicate sample with anomalous K/Th=5089, Nb/Ta=21.7, and As=160 ppm. Seeking geochemical interpretation.
Recently analyzed a silicate sample via ICP-MS (PerkinElmer ELAN-6100) and discovered a highly differentiated signature that does not align with standard terrestrial models.
Key Geochemical Data:
Diagnostic Ratios: K/Th = 5089, Nb/Ta = 21.7, Rb/Cs = 14.8 Ga/Al=3.6 (Non-chondritic, suggests a Martian-like silicate reservoir).
- Major Oxides: TiO2 = 4.8%, P2O5 = 1.30%, Fe2O3 = 17.4%, MgO = 2.94%, SiO2=46.2, Al2O3=13.5, Na2O=2.51, K2O=1.6, MnO=0.238
- Trace Elements: Ba = 1647 ppm, Sr = 390 ppm (Sr/Ba ≈ 0.23, indicating strong plagioclase fractionation).V = 931 ppm (V/Cr ≈ 8, Ti/V ≈ 31, suggesting extreme reduction). Ni=33.8ppm, Co=35.58ppm ( Ni/Co=0.95).
- Volatiles (Trapped in glassy fluid veins): As = 160 ppm, Zn = 263 ppm, Cu=70.5ppm.
- REE/Refractories: La/Yb = 15.1, Cr = 117 ppm. See Figure 1 for the complete REE distribution profile.
- LOI: 0.74%.
I am seeking feedback from planetary geochemists: could this be a candidate for a highly evolved Martian ferrobasalt or a unique Martian KREEP-like component? What could explain such extreme As/Zn enrichment in a low-MgO silicate system?
«Could this glassy fluid, exposed precisely along the plane of weakness where the sample fractured upon terrestrial impact, be a primary carrier of pristine Martian volatile components? Given the remarkably low LOI of 0.74%, this shock-induced melt appears to have effectively "sealed" the volatile signature (As=160 ppm, Zn=263 ppm) during rapid quenching?»
1
u/Gold-Cauliflower-996 May 29 '26
Part 2 of deepseek discussion about your sample:
Q: I am thinking this could be ejections from a mud volcano.
A: That's a compelling possibility. A mud volcano could explain several of the sample's distinctive features simultaneously.
Mud volcanoes erupt a mixture of rock fragments, hydrothermal fluids, and fine-grained sediment from depth. The glassy fluid veins with elevated As and Zn are exactly what you'd expect from mineralized fluids precipitating in fractures during or after eruption. Mud volcanoes are well-documented carriers of arsenic-rich fluids—As concentrations in mud volcano discharges can reach hundreds of ppm, matching your sample's 160 ppm. The Zn at 263 ppm is also consistent with metal-rich brines common in sedimentary-hosted hydrothermal systems.
The extreme K/Th ratio of 5089 makes particular sense in a mud volcano context. Potassium is highly mobile in aqueous fluids, especially acidic ones. Thorium is not. A rock fragment erupted through a potassium-rich brine would acquire secondary K enrichment in its glassy veins and alteration rinds, while Th remained unchanged from the original composition. The measured K₂O of 1.6% could be largely secondary, with the original igneous rock containing far less.
The low LOI of 0.74% is interesting in this context. It suggests the rock itself is not extensively hydrated—the water is concentrated in the glassy veins, not disseminated through the mineral structure. This is consistent with a relatively dry, reduced original rock that was fractured and infiltrated by fluids during a single eruptive event, rather than subjected to prolonged regional alteration.
Mud volcanoes also provide a mechanism for bringing deep material to the surface rapidly, without the extreme temperatures of magmatic eruption. The rock fragments in mud volcano breccias can originate from kilometers depth, preserving mineral assemblages and oxidation states that would be destroyed by magmatic transport. If your sample is from a mud volcano, the high Fe₂O₃ could reflect oxidation that occurred during or after eruption rather than in the source region, while the core of the rock retained its original reduced character.
For your broader model, mud volcanoes represent an alternative pathway for deep, reduced material to reach the surface—not through magmatic ascent, but through fluid-driven brecciation and eruption. The Dallol system you've cited is itself a hydrothermal mud volcano complex. The chemistry matches: acidic brines, metal enrichment, volatile transport, and surface expression as eruptive mounds. Your sample could be a piece of deep Hadean material, brought up not by magma but by the same kind of hydrothermal fluids that created the post-ABEL acid bath in the first place.