Geology

Rhyolite

Plagioclase

Silicic

Volcano

Geochemistry

Paleontology

Magma

Volcanic rock

Zircon

Quartz

Caldera

Geochemistry Geophysics Geosystems

Longevity and size of magmatic systems are fundamental factors for assessing the potential of a geothermal field. At Los Humeros volcanic complex (LHVC), the first caldera‐forming event was reported at 460 ± 40 ka. New zircon U/Th and plagioclase 40 Ar/ 39 Ar dates of pre‐, syn‐ and postcaldera volcanics allow a reappraisal of the evolution of the geothermally active LHVC. The age of the voluminous Xaltipan ignimbrite (115 km 3 dense rock equivalent [DRE]) associated with the formation of the Los Humeros caldera is now constrained by two geochronometers (zircon U/Th and plagioclase 40 Ar/ 39 Ar dating) to 164 ± 4.2 ka, which postdates a long episode of precaldera volcanism (rhyolitic domes), the oldest age of which is 693.0 ± 1.9 ka ( 40 Ar/ 39 Ar). The inferred short residence time (around 5 ka) for the paroxysmal Xaltipan ignimbrite is indicative of rapid assembly of a large magma body and rejuvenation of the system due to recurrent recharge magmas, as it has been occurred in some other large magmatic systems. Younger ages than previously believed have been obtained also for the other voluminous explosive phases of the Faby fall tuff at ∼70 ka and the second caldera‐forming Zaragoza ignimbrite with 15 km 3 DRE, which erupted immediately after. Thus, the time interval that separates the two caldera‐forming episodes at Los Humeros is only 94 kyr, which is a much shorter interval than suggested by previous K‐Ar dates (410 kyr). This temporal proximity allows us to propose a caldera stage encompassing the Xaltipan and the Zaragoza ignimbrites, followed by emplacement at 44.8 ± 1.7 ka of rhyolitic magmas interpreted to represent a postcaldera, resurgent stage. Rhyolitic eruptions have also occurred during the Holocene (&lt;7.3 ± 0.1 ka) along with olivine‐rich basalts that suggest recharge of the system. The estimated large volume magmatic reservoir for Los Humeros (&gt;∼1,200 km 3 ) and these new ages indicating much younger caldera‐forming volcanism than previously believed are fundamental factors in the application of classical conductive models of heat resource, enhancing the heat production capacity and favor a higher geothermal potential.

Reappraisal of Los Humeros Volcanic Complex by New U/Th Zircon and <sup>40</sup> Ar/ <sup>39</sup> Ar Dating: Implications for Greater Geothermal Potential

Reappraisal of Los Humeros Volcanic Complex by New U/Th Zircon and 40 Ar/ 39 Ar Dating: Implications for Greater Geothermal Potential

Reappraisal of Los Humeros Volcanic Complex by New U/Th Zircon and ⁴⁰ Ar/ ³⁹ Ar Dating: Implications for Greater Geothermal Potential