Question

Unlike volcanically driven hydrothermal systems along mid-ocean ridge axes, which are characterized by acidic, black-smoker fluids reaching temperatures in excess of 350°C, hydrothermal systems situated on mantle peridotite detachments—such as the off-axis Lost City field—are powered by the serpentinization reaction. In this process, seawater circulating through exposed mantle peridotite reacts exothermically with the magnesium- and iron-rich mineral olivine at moderate temperatures (100°C–250°C). This low-temperature hydration oxidizes ferrous iron ($Fe^{2+}$) to ferric iron ($Fe^{3+}$), precipitating magnetite and releasing large quantities of molecular hydrogen ($H_2$). This abundant dissolved $H_2$ drives the hyperalkaline pH (9 to 11) of the emergent fluids and reduces dissolved inorganic carbon through Fischer-Tropsch–type reactions, generating abiotic methane ($CH_4$) and short-chain alkanes without biological mediation. Because these ultramafic systems do not rely on magmatic heat sources, their vent chimneys are composed not of polymetallic sulfides, but of calcium carbonate and magnesium hydroxide minerals precipitated when high-pH, calcium-rich hydrothermal fluids mix with cold, carbonate-rich deep ocean water. Moreover, radiometric dating of these carbonate structures demonstrates that serpentinization-driven fields can remain continuously active for tens of thousands of years—more than two orders of magnitude longer than individual magmatic black-smoker vents, which are routinely extinguished when local magma chambers cool or migrate.

Based on the passage, which of the following statements regarding hydrothermal systems are logically supported? (Select all that apply.)