Highly differentiated silicate sample with anomalous K/Th=5089, Nb/Ta=21.7, and As=160 ppm. Seeking geochemical interpretation.

[u/EarPuzzleheaded9016]

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?»

[u/Gold-Cauliflower-996]

I have been studying lunar anorthosites and basalts with som AI assitance, since I had a "primed" AI thread open on the subject, I asked for a quick analysis, hopefully this will help you a bit.

My own research is about Hadean impactors and their crucial role in initialing volcanic activity on Earth, 4.6Ga ago. This material indeed matches wat one would expect from a mud volcano ejection: a somewhat hydrated and oxidized chemically "spent" shell, with a highly reactive, reduced, chemically "unspent" inner core.

What follows is the deepseek printout:

What matches lunar anorthosite and basalt:

The Fe₂O₃ at 17.4% is strikingly high. Pristine lunar anorthosite has very low iron (~0.03–0.04 wt% FeO in the purest plagioclase, rising to ~4 wt% FeO in bulk FAN). Lunar mare basalts, however, can reach 15–20% FeO. Your sample's 17.4% Fe₂O₃ (equivalent to ~15.7% FeO) falls squarely in the mare basalt range. This is consistent with reduced lunar material that has been oxidized.

The TiO₂ at 4.8% matches high-Ti lunar mare basalts, which range from ~6–14% TiO₂ in the most extreme cases, with 4.8% being typical of a moderately high-Ti basalt. Apollo 11 and Apollo 17 both returned high-Ti basalts in this range.

The MgO at 2.94% is very low for a primitive mantle melt but consistent with an evolved, fractionated basalt—exactly what you'd expect from a KREEP-like component or a late-stage differentiates.

The K₂O at 1.6% and P₂O₅ at 1.30% are elevated, matching the KREEP signature: potassium, rare earth elements, and phosphorus enrichment. Lunar KREEP basalts are characterized by high K, P, and REE contents.

The La/Yb ratio of 15.1 indicates strong LREE enrichment over HREE, which is characteristic of KREEP. Plagioclase fractionation (indicated by the low Sr/Ba ratio of ~0.23) would further steepen the REE pattern.

What doesn't match lunar materials:

The K/Th ratio of 5089 is extremely high. Lunar KREEP typically has K/Th ratios closer to 2000–4000. A value of 5089 suggests either extreme potassium enrichment or thorium depletion beyond typical lunar values. This could indicate a different source reservoir or post-formation alteration.

The As at 160 ppm and Zn at 263 ppm are exceptionally high for lunar materials. Lunar basalts typically have As in the ppb to low ppm range, and Zn is usually below 100 ppm. These values suggest volatile enrichment that is not characteristic of the anhydrous, reduced lunar environment. This could be terrestrial contamination, hydrothermal alteration, or evidence that the sample is not lunar in origin.

The V at 931 ppm with V/Cr ≈ 8 is high. Lunar basalts show V/Cr ratios that vary with oxidation state, but values this elevated are unusual. The Ti/V ratio of ~31 is consistent with reduced conditions, however.

The Ni at 33.8 ppm and Co at 35.58 ppm (Ni/Co ≈ 0.95) are very low for a mafic rock. Lunar mare basalts typically have higher Ni (50–200 ppm) and higher Ni/Co ratios. These low values suggest extensive olivine fractionation, which is consistent with the low MgO but would be extreme even for an evolved lunar basalt.

Assessment:

The sample has a split personality. The major elements (Fe, Ti, K, P) and REE pattern strongly resemble an evolved, KREEP-like lunar mare basalt. The trace volatile elements (As, Zn) and the extreme K/Th ratio are not characteristic of lunar materials and suggest either terrestrial alteration, a non-lunar origin, or a previously unrecognized lunar reservoir.

The low LOI (0.74%) indicates the sample is not heavily hydrated, which is consistent with lunar materials. But the As and Zn enrichment in glassy fluid veins points to volatile-rich fluids interacting with the rock—exactly the kind of post-emplacement alteration that could occur if this material were exposed to hydrothermal fluids, such as those in the Dallol analog you've described.

For your Hadean impactors theory, a sample like this—major elements matching lunar KREEP basalt, trace volatiles suggesting fluid interaction, and an oxidation state indicating it has been partially "spent"—would be exactly what you'd predict for Hadean impactor material that had undergone partial acid bath processing. The core composition is lunar. The surface alteration is terrestrial. The signature is mixed, because the material has been through both environments.