Two-stage Cooling in the Protoplanetary Disk Governs the Chemical and Isotopic Signatures of Carbonaceous Chondrites

Abstract The thermodynamic evolution of the solar protoplanetary disk fundamentally governed the chemical makeup of accreting planetesimals. While the chondrule–matrix complementarity in carbonaceous chondrites has long been used to trace these processes, its origin—whether from a single closed reservoir or the mechanical mixing of independent components—remains highly debated. Here, we combine in situ chemical analyses of matrices across six major carbonaceous chondrite groups with high-precision silicon isotope data for paired chondrules and matrices to resolve this dichotomy. We demonstrate that moderately refractory elements (Mg/Si, δ 30 Si) strictly follow closed-system complementarity, whereas matrices are systematically depleted in moderately volatile elements (MVEs), necessitating open-system gas loss. Furthermore, the subequilibrium chondrule–matrix δ 30 Si offsets point to kinetically suppressed, nonequilibrium condensation rather than pure equilibrium gas–solid exchange. To unify these contradictory constraints, we propose a two-stage cooling model driven by transient heating events in dynamically confined dust-enriched disk regions. An initial rapid cooling stage drives kinetically controlled condensation, locking in the chemical and isotopic complementarity of refractories while accommodating localized alkali recondensation. A subsequent slower cooling stage retains MVEs in the gas, allowing disk turbulence to physically separate and strip away the volatile-rich gas prior to local accretion. This semiopen framework permits inherited dust to mix with locally formed condensates during late-stage cooling, producing a composite matrix reservoir that can reconcile local component-specific complementarity with bulk-scale binary mixing trends. This fractionation mechanism establishes a primordial chemical heterogeneity in the protoplanetary disk that might be further inherited by accreting planetesimals, shaping the bulk volatile depletion of terrestrial planets.