Bayesian Markov-Chain Monte Carlo Inversion of Low-Temperature Thermochronology Around Two 8 − 10 m Wide Columbia River Flood Basalt Dikes

Abstract

Flood basalt volcanism involves large volumes of magma emplaced into the crust and surface environment on geologically short timescales. The mechanics of flood basalt emplacement, including dynamics of the crustal magma transport system and the tempo of individual eruptions, are not well-constrained. Here we study two exhumed dikes from the Columbia River Flood Basalt province in northeast Oregon, USA, using apatite and zircon (U-Th)/He thermochronology to constrain dike emplacement histories. Sample transects perpendicular to the dike margins document transient heating of granitic host rocks. We model heating as due to dike emplacement, considering a thermal model with distinct melt-fraction temperature relationships for basaltic magma and granitic wallrock, and a parameterization of unsteady flow within the dike. We model partial resetting of thermochronometers by considering He diffusion in spherical grains as a response to dike heating. A Bayesian Markov-Chain Monte Carlo framework is used to jointly invert for six parameters related to dike emplacement and grain-scale He diffusion. We find that the two dikes, despite similar dimensions on an outcrop scale, exhibit different spatial patterns of thermochronometer partial resetting away from the dike. These patterns predict distinct emplacement histories. We extend previous modeling of a presumed feeder dike at Maxwell Lake in the Wallowa Mountains of northeastern Oregon, finding posterior probability distribution functions (PDFs) that predict steady heating from sustained magma flow over 1-6 years and elevated farfield host rock temperatures. This suggests regional-scale heating in the vicinity of Maxwell Lake, which might arise from nearby intrusions. The other dike, within the Cornucopia subswarm, is predicted to have a 1-4 year thermally active lifespan with an unsteady heating rate suggestive of low magma flow rate compared to Maxwell Lake, in a cool near-surface thermal environment. In both cases, misfit of near-dike partial resetting of thermochronometers by models suggests either heat transfer via fluid advection in host rocks or pulsed magma flow in the dikes. Our results highlight the diversity of dike emplacement histories within the Columbia River Flood Basalt province and the power of Bayesian inversion methods for quantifying parameter trade-offs and uncertainty in thermal models.

Deep open storage and shallow closed transport system for a continental flood basalt sequence revealed with Magma Chamber Simulator

“…If values for the parameters that are roughly constant are set, one can determine an approximate value for the initial crustal temperature that delimits the crack-meltback and crack-closing regimes. For example, scaling the solutions in Bruce and Huppert (1990) and adopting the reasonable constant values Δh f,m = 600 kJ/kg, Δh f,wr = 320 kJ/kg, c p = 950 J/kg K, η = 1000 Pa s, κ = 5 × 10 −7 m 2 /s, l = 10 km, Δp = 10 MPa, w i = 1.5 m, T m = 1250 °C, and T w = 1075 °C (Stebbins et al 1984;Lange and Carmichael 1990;Rubin 1995;Lange 1997;Petcovic and Dufek 2005;Giordano et al 2008;Pertermann et al 2008;Hofmeister et al 2009;Tikunoff and Spera 2014;Lesher and Spera 2015;Karlstrom et al 2019; see Online Resource 1 for more details), the transition between crack meltback and crack closing occurs roughly at the initial crustal temperature T ∞ = 280 °C.…”

Using a Paleosurface to Constrain Low‐Temperature Thermochronological Data: Tectonic Evolution of the Cuevas Range, Central Andes

“…Miocene volcanism is the most plausible explanation for the differential Miocene reheating. Several studies have shown how the emplacement of magmatic bodies can create partial resetting aureoles of the low-temperature thermochronological systems in the host rock; the size of these aureols is directly related to the duration of magmatism, the depth of emplacement, and the size of the intrusives (e.g., Karlstrom et al, 2019;Murray et al, 2018).…”

Pervasive Hydrothermal Events Associated with Large Igneous Provinces Documented by the Columbia River Basaltic Province

“…1), which may have played a role in the small climatic impact of the CRB through heating and contact metamorphism of the crust 4,5,8 . While many of the dikes are buried under the thick CRB lavas, recent uplift of the province in the east has exposed inner workings of the crustal dike system (down to ~2 km depth [15][16][17], allowing an insight into dike-crust interactions [18][19][20] . This unique setting shows that dikes intruded into a variety of rock types including earlier erupted CRB lavas, granitic batholiths, and Paleozoic metasedimentary rocks that often contain organic-rich shale and carbonates.…”

“…Dikes range in thickness from 1 to >100 m, although the distribution strongly peaks at ~8 m, and larger structures likely record multiple reoccupations 15,16 . Based on the number of segments exhibiting partial melt in host rocks 16 , an estimated 3% of all known dikes served as feeders for lava flows and long-lived transport was probably highly localized along strike 19 . As they would have been potentially active for much longer, these feeder dikes likely caused larger degrees of thermal metamorphism and contact melting in country rocks than dead-end dikes that did not reach the surface [18][19][20] .…”

“…The Maxwell Lake dike has been geochemically correlated with the WRM and therefore the peak of CRB activity, and cross-cuts tonalitic granites of the Jurassic Wallowa Batholith in Oregon, USA 15,18,19 . Previous studies of the degree of dehydration partial melting of the wall rocks 18 and apatite and zircon thermochronology of those same wall rocks 19 , have demonstrated that country rock was heated to as much Table S1 for chemical and isotopic values. Roman numerals indicate dike groups.…”