Triple oxygen isotope systematics as a tracer of fluids in the crust: A study from modern geothermal systems of Iceland

The triple oxygen isotope composition of Precambrian chert

“…For instance, through these measurements and associated models we show that changes in the isotopic composition of tions [23,22,21]. We do note that our analysis can allow for some variance in seawater composition, on the scale suggested elsewhere [24,54], despite it not statistically being the lone cause. For our data, the most parsimonious solution calls upon equitable surface temperatures, and secondary fluids that look very meteoric in composition (≈ -15 ) at common subsurface temperatures of a couple hundred degrees.…”

“…The decreasing temperature manifests as a change in the equilibrium isotope fractionation factor (α chert−water ), offset relative to an ice-free ocean of constant composition (calculated as δ 18 O of ≈ -1.2 , ∆' 17 O of ≈ -0.005 ,; and consistent with [23,24]). In this scenario, the median δ 18 O in the Archean corresponds to a temperature of over 120 o C, which subsequently evolves to a 38 o C Phanerozoic ocean.…”

“…Here, iron minerals carry a lesser temperature dependence on oxygen isotope fractionation, whereas shale data represent a composite of multiple oxygen-bearing phases and complexities therein. In parallel, triple oxygen isotope analysis of altered crustal materials, and ensuing models suggest no change in seawater composition, but rather offer a revision to oceanic crust interactions through time [23,24]. With a suite of opposing interpretations derived from similar data, the underlying source of the chert δ 18 O signal is therefore still uncertain.…”

Triple Oxygen Isotope Trend Recorded by Precambrian Cherts: A Perspective from Combined Bulk and in situ Secondary Ion Probe Measurements

“…The triple oxygen and hydrogen isotope analyses were carried out at the University of Oregon Stable Isotope Lab. The methodology was previously described in (Zakharov et al 2019b). Briefl y, small chips of chert (1.5−2 mg) excluding visible quartz veins were placed in a stainless-steel holder inside an oven at 130 °C held under vacuum of a roughing pump for several hours.…”

Triple Oxygen Isotope Paleoaltimetry of Crystalline Rocks

“…4) Extrapolation of a fitted line through this array, using water/rock equations for both δ 17 O and δ 18 O (Taylor, 1978), to the meteoric water line with the added and small water/rock equilibrium fractionation factor. An excellent example of this approach is given in Zakharov et al (2019) who used triple oxygen isotopes to study fluidrock interaction in the well-known hydrothermal systems in Iceland. Through careful analysis of minerals and fluids they were able to demonstrate how triple oxygen can be used assess the complicated processes that occur in hydrothermal systemsthereby setting the stage too apply this approach to ancient hydrothermal systems.…”