Central American Volcanic Arc Research Articles

Planning for the Lake Izabal Basin Research Endeavor (LIBRE) continental scientific drilling project in eastern Guatemala

Abstract. As Earth's atmospheric temperatures and human populations increase, more people are becoming vulnerable to natural and human-induced disasters. This is particularly true in Central America, where the growing human population is experiencing climate extremes (droughts and floods), and the region is susceptible to geological hazards, such as earthquakes and volcanic eruptions, and environmental deterioration in many forms (soil erosion, lake eutrophication, heavy metal contamination, etc.). Instrumental and historical data from the region are insufficient to understand and document past hazards, a necessary first step for mitigating future risks. Long, continuous, well-resolved geological records can, however, provide a window into past climate and environmental changes that can be used to better predict future conditions in the region. The Lake Izabal Basin (LIB), in eastern Guatemala, contains the longest known continental records of tectonics, climate, and environmental change in the northern Neotropics. The basin is a pull-apart depression that developed along the North American and Caribbean plate boundary ∼ 12 Myr ago and contains > 4 km of sediment. The sedimentological archive in the LIB records the interplay among several Earth System processes. Consequently, exploration of sediments in the basin can provide key information concerning: (1) tectonic deformation and earthquake history along the plate boundary; (2) the timing and causes of volcanism from the Central American Volcanic Arc; and (3) hydroclimatic, ecologic, and geomicrobiological responses to different climate and environmental states. To evaluate the LIB as a potential site for scientific drilling, 65 scientists from 13 countries and 33 institutions met in Antigua, Guatemala, in August 2022 under the auspices of the International Continental Scientific Drilling Program (ICDP) and the US National Science Foundation (NSF). Several working groups developed scientific questions and overarching hypotheses that could be addressed by drilling the LIB and identified optimal coring sites and instrumentation needed to achieve the project goals. The group also discussed logistical challenges and outreach opportunities. The project is not only an outstanding opportunity to improve our scientific understanding of seismotectonic, volcanic, paleoclimatic, paleoecologic, and paleobiologic processes that operate in the tropics of Central America, but it is also an opportunity to improve understanding of multiple geological hazards and communicate that knowledge to help increase the resilience of at-risk Central American communities.

Arc adakitic-like signatures caused by amphibole fractionation: An example from 20 Ma granitoids, Charco Rico district, Panama

The Charco Rico prospective comprises a segment of the Sierra de Majé massif in Central Panama, an intrusive complex constructed during a lull in volcanic activity between 40 and 16 Ma at the 75–0 Ma Central American Volcanic arc system (CAVAS). Charco Rico represents an intermediate suite (55–65 wt% SiO2) but with inclusion of related Majé intrusives, range from gabbro to granodiorite. Zircon UPb dating of Charco Rico granitoids yield LA-ICP-MS ages of 20.2 ± 0.9 to 19.1 ± 1.5 Ma. Their formation is consistent with maximum partial melting of ∼10% of a Sr-enriched (i.e., amphibolite) N-MORB like source followed by fractional crystallization of hornblende at about 0.8 GPa (∼29 km depth). Zirconium saturation thermometry shows a temperature of magma crystallization of 700–800 °C which essentially is a record of amphibole crystallization temperature. Whole rock chemistry of the Charco Rico and Majé intrusives and other 32–20 Ma arc-related suites in Panama record chemical parameters similar to adakite, e.g., Sr/Y that ranges to 80, high LREE/HREE ratios, and depletion in HREE (Yb, Lu). A fundamental chemical attribute of these suites, however, is depletion of MREE, and particularly Ho, relative to LREE and HREE, and the absence of Eu-anomalies. These features, together with positive and negative correlations of La/Yb and Dy/Yb with SiO2, respectively, infer a dominant role of amphibole fractionation from basaltic magma and/or residue during partial melting of older calc-alkaline bodies in the lower crust. 176Hf/177Hf ratios in zircon grains range from 0.282925 to 0.283192 and record εHft between +5.8 and + 15.3, which are indicative of a depleted mantle (juvenile) source and/or recycling (partial melting) of older juvenile crust. TDM incubation ages range to higher than 300 Ma, which may reflect old basement recycling. Partial melting of the depleted mantle ± lower crust may have been facilitated by a combination of hot asthenospheric upwelling during slab rollback, slab tear or lithospheric delamination, and simultaneous thinning of the continental crust under extension. Whole rock chemistry and reported cumulate hornblende in host granites with adakitic-like signatures, infer that hornblende differentiation controlled the magma chemistry and migration to high-SiO2 rocks with ‘adakite’ signatures.

Geochemical characterization of volcanic gas emissions at Santa Ana and San Miguel volcanoes, El Salvador, using remote-sensing and in situ measurements

Volcanic degassing provides important information for the assessment of volcanic hazards. Santa Ana and San Miguel are open vent volcanoes along the Central American Volcanic Arc–CAVA, where the magmatism, basaltic to dacitic, is related to the near-orthogonal convergence of the Caribbean Plate and the subducting Cocos Plate. Both volcanoes are the most active ones in El Salvador with recent eruptive events in October 2005 (Santa Ana) and December 2013 (San Miguel), but still not much data on gas composition and emission are available today. At each volcano, SO2 emissions are regularly monitored using ground-based scanning Differential Optical Absorption Spectrometer (Scan-DOAS) instruments that are part of the global “Network for Observation of Volcanic and Atmospheric Change” (NOVAC). We used the data series from these NOVAC stations in order to retrieve SO2 and minimum bromine emissions, which can be retrieved from the same spectral data for the period 2006–2020 at Santa Ana and 2008–2019 at San Miguel. However, BrO was not detected above the detection limit. SO2 emission ranged from 10 to 7,760 t/d, and from 10 to 5,870 t/d for Santa Ana and San Miguel, respectively. In addition, the SO2 emissions are complemented with in situ plume data collected during regular monitoring surveys (2018–2020) and two field campaigns in El Salvador (2019 and 2020). MultiGAS instruments recorded CO2, SO2, H2S and H2 concentrations. We determined an average CO2/SO2 ratio of 2.9 ± 0.6 when peak SO2 concentration exceeded 15 ppmv at Santa Ana, while at San Miguel the CO2/SO2 ratio was 7.4 ± 1.8, but SO2 levels reached only up to 6.1 ppmv. Taking into account these ratios and the SO2 emissions determined in this study, the resulting CO2 emissions are about one order of magnitude higher than those determined so far for the two volcanoes. During the two field campaigns Raschig tubes (active alkaline trap) were used to collect plume samples which were analyzed with IC and ICP-MS to identify and quantify CO2, SO2, HCl, HF, and HBr. Additionally, also 1,3,5-trimethoxybenzene (TMB)-coated denuders were applied and subsequently analyzed by GC-MS to determine the sum of the reactive halogen species (RHS: including Cl2, Br2, interhalogens, hypohalous acids). The RHS to sulfur ratios at Santa Ana and San Miguel lie in the range of 10−5. Although no new insights could be gained regarding changes with volcanic activity, we present the most comprehensive gas geochemical data set of Santa Ana and San Miguel volcanoes, leading to a solid data baseline for future monitoring purposes at both volcanoes and their improved estimate of CO2, SO2 and halogens emissions. Determining the reactive fraction of halogens is a first step towards a better understanding of their effects on the atmosphere.

Timing and recurrence intervals for voluminous silicic eruptions from Amatitlán caldera (Guatemala)

Defining a precise timeline for past eruptions from explosive volcanoes in continental arcs is imperative to forecast future hazards and mitigate volcanic disasters in these often densely populated regions. However, establishing reliable ages for Quaternary eruptions in the Central American Volcanic Arc has been challenging due to the common lack or alteration of suitable K-rich phases for 40Ar/39Ar geochronology, but also from their position in time beyond the reach of 14C dating. This especially holds for the active Amatitlán caldera in Guatemala, from which at least six explosive silicic eruptions have produced tephra blanketing neighboring regions that are today inhabited by millions of people. Zircon, a common datable accessory mineral in Amatitlán caldera magmas, is used here to retrieve eruption ages by applying the novel zircon double-dating method (ZDD) that integrates 238U–230Th disequilibrium dating and (U–Th)/He thermochronology. This approach yielded the first-ever radioisotopic ages of 24 ± 3 ka and 48 ± 6 ka (1σ), respectively, of two of Amatitlán caldera's most recent eruptions (J-tephra and E-tephra). Remarkably, both zircon crystallization and ZDD eruption ages for the older and voluminous T-tephra and L-tephra units significantly post-date existing plagioclase 40Ar/39Ar dates by ca. 26 and 70 kyr, respectively. The ZDD eruption age for T-tephra is 93 ± 4 ka, whereas zircon crystallization ages for L-tephra yield a maximum model eruption age of ca. 124 ka. The strong eruption age divergence between ZDD and plagioclase 40Ar/39Ar dating argues for the presence of inherited or xenocrystic plagioclase in Amatitlán caldera eruptive products. Statistical analysis based on the updated eruptive history suggests a recurrence interval of ca. 17 kyr, which is significantly shorter than previously estimated. The new age data, thus, suggest a more frequent eruptive activity of Amatitlán caldera than formerly thought and underscores the necessity to better understand the current underlying magmatic system and to constrain its past eruptive history more precisely.

Sulfur from the subducted slab dominates the sulfur budget of the mantle wedge under volcanic arcs

Sulfur is of a crucial importance in the Earth system influencing biological, climate, ore-forming, and redox processes. Subduction zones play a key role in the global sulfur cycle. Arc magmas have higher sulfur contents and are more oxidised than mid-ocean ridge basalts (MORBs) due to either an oxidised mantle source or magma differentiation. Melt oxidation state and sulfur content may interrelate, as sulfur is a potential oxidising agent during slab-mantle interaction. Here, we use melt inclusions (MIs) to determine the sulfur isotopic composition (δ34S) of primary arc magmas from three volcanic centres along the Central American Volcanic Arc (CAVA): Fuego (Guatemala), Cerro Negro (Nicaragua), and Turrialba (Costa Rica). These three locations sample much of the global arc magma trace element variability: Ba/La ratios range from 22 (Turrialba) to 118 (Cerro Negro). Melt δ34S values are between -0.5‰ and +4.9‰. Sulfur contents and δ34S values of homogenised and naturally quenched MIs overlap, indicating post-entrapment processes do not affect sulfur contents and sulfur isotope ratios in the studied MIs. Degassing causes limited sulfur isotope fractionation; calculated gas-melt isotope fractionation factors are between 0.998-1.001. Our model calculations predict that most volcanic gases along the CAVA have δ34S between -1‰ and +6‰, becoming enriched in 34S as degassing progresses. We estimate initial melt δ34S values for Fuego, Cerro Negro, and Turrialba to be +0.7±1.4‰, +2.2±1.0‰, and +1.6±0.8‰ (two standard errors), respectively. All these values are elevated compared to MORBs (-0.9‰). Addition of oxidised slab material enriched in 34S to the mantle wedge can explain elevated arc primary melt δ34S and the oxidising conditions observed in arc magmas globally. Based on mass balance, a slab component with δ34S between +2‰ to +5‰ is present in the mantle wedge under the CAVA, elevating local arc mantle S contents to 360±30 ppm at Fuego, 462±11 ppm at Cerro Negro. Modelling suggests that 40-70% of sulfur in the mantle wedge originates from a slab-derived component. Slab subduction is expected to have major control on the evolution of Earth's sulfur cycle and mantle oxidation state over its geological history.

Magmatic and Tectonic Domains of Central Costa Rica and the Irazú‐Turrialba Volcanic Complex Revealed by Ambient Noise Tomography

AbstractThe Central America Volcanic Arc runs from Guatemala to Panama, locally interrupted in Costa Rica after the twin‐system Irazú‐Turrialba Volcanic Complex, at the onset of the Talamanca Cordillera. A marked geological discontinuity characterizes the transition between the volcanic arc and this continental mountain range. To shed light on the spatial and structural relationships between active tectonics and volcanism, we deployed a temporary network consisting of 20 broadband seismic stations around the Irazú‐Turrialba Volcanic Complex that integrated the national seismic networks maintained by Costa Rican institutes. From the seismic records, we extract cross‐correlation functions and Rayleigh wave group‐velocity dispersion curves to perform two ambient noise tomographies at a regional and local scale. From this, we derive two models that point out the magmatic and tectonic features of the southern part of the Central American Volcanic Arc and of the Irazú‐Turrialba Volcanic Complex. The regional‐scale tomographic inversion suggests that such a volcanic complex shares a common reservoir at about 5–7 km depth that is fed by a sub‐vertical region, departing from at least 12 km depth. From here magmas appear to be transported upwards and stored in separate reservoirs below each volcanic edifice. Our study establishes an improved understanding of the spatial relationship between tectonic features and distribution of magmatic reservoirs underpinning the plumbing system of the Irazú‐Turrialba volcanic complex.

Active Triclinic Transtension in a Volcanic Arc: A Case of the El Salvador Fault Zone in Central America

The El Salvador Fault Zone (ESFZ) is part of the Central American Volcanic Arc and accommodates the oblique separation movement between the forearc sliver and the Chortis block (Caribbean Plate). In this work, a triclinic transtension model was applied to geological (fault-slip inversion, shape of volcanic calderas), seismic (focal mechanisms) and geodetic (GPS displacements) data to evaluate the characteristics of the last stages of the kinematic evolution of the arc. The El Salvador Fault Zone constitutes a large band of transtensional deformation whose direction varies between N90° E and N110° E. Its dip is about 70° S because it comes from the reactivation of a previous extensional stage. A protocol consisting of three successive steps was followed to compare the predictions of the model with the natural data. The results show a simple shear direction plunging between 20° and 50° W (triclinic flow) and a kinematic vorticity number that is mostly higher than 0.81 (simple-shearing-dominated flow). The direction of shortening of the coaxial component would be located according to the dip of the deformation band. It was concluded that this type of analytical model could be very useful in the kinematic study of active volcanic arcs, even though only information on small deformation increments is available.

3He/4He Signature of Magmatic Fluids from Telica (Nicaragua) and Baru (Panama) Volcanoes, Central American Volcanic Arc

Constraining the magmatic 3He/4He signature of fluids degassed from a magmatic system is crucial for making inferences on its mantle source. This is especially important in arc volcanism, where variations in the composition of the wedge potentially induced by slab sediment fluids must be distinguished from the effects of magma differentiation, degassing, and crustal contamination. The study of fluid inclusions (FIs) trapped in minerals of volcanic rocks is becoming an increasingly used methodology in geochemical studies that integrates the classical study of volcanic and geothermal fluids. Here, we report on the first noble gas (He, Ne, Ar) concentrations and isotopic ratios of FI in olivine (Ol) and pyroxene (Px) crystals separated from eruptive products of the Telica and Baru volcanoes, belonging to the Nicaraguan and Panamanian arc-segments of Central America Volcanic arc (CAVA). FIs from Telica yield air corrected 3He/4He (Rc/Ra) of 7.2–7.4 Ra in Ol and 6.1–7.3 in Px, while those from Baru give 7.1–8.0 Ra in Ol and 4.2–5.8 Ra in Px. After a data quality check and a comparison with previous 3He/4He measurements carried out on the same volcanoes and along CAVA, we constrained a magmatic Rc/Ra signature of 7.5 Ra for Telica and of 8.0 Ra for Baru, both within the MORB range (8 ± 1 Ra). These 3He/4He differences also reflect variations in the respective arc-segments, which cannot be explained by radiogenic 4He addition due to variable crust thickness, as the mantle beneath Nicaragua and Panama is at about 35 and 30 km, respectively. We instead highlight that the lowest 3He/4He signature observed in the Nicaraguan arc segment reflects a contamination of the underlying wedge by slab sediment fluids. Rc/Ra values up to 9.0 Ra are found at Pacaya volcano in Guatemala, where the crust is 45 km thick, while a 3He/4He signature of about 8.0 Ra was measured at Turrialba volcano in Costa Rica, which is similar to that of Baru, and reflects possible influence of slab melting, triggered by a change in subduction conditions and the contemporary subduction of the Galapagos hot-spot track below southern Costa Rica and western Panama.

Chlorine isotope behavior in subduction zone settings revealed by olivine-hosted melt inclusions from the Central America Volcanic Arc

The isotopic composition of Cl, a highly hydrophilic and incompatible element, can provide new insights into the processes of element recycling in subduction zone settings. Samples from 13 localities in Guatemala, El Salvador, Nicaragua and Costa Rica, representing a ca. 1000 km long NW-SE segment along the Central American Volcanic Arc (CAVA), were selected. Ninety-seven melt inclusions, hosted by olivine Fo90−70, were measured for Cl isotope ratios and trace element concentrations. Melt inclusions from samples from Guatemala to northwest Nicaragua have a restricted range of δ37Cl values (range < 1‰ within a sample) with values decreasing from Santa Maria (Guatemala) to San Miguel (El Salvador), whereas melt inclusions from Nicaragua and Costa Rica display larger variation within a sample (δ37Cl value range >1‰, up to 3.8‰) and do not show any systematic variation along the arc. For some samples, the δ37Cl in the melt inclusions is shifted by up to 2‰ to higher values compared to bulk rock data from the same volcanic center, for which the extent of Cl degassing is not known. The combination of δ37Cl values in melt inclusions with trace elements and the existing knowledge about the slab contributions along the arc allows us to elucidate the Cl isotope composition of different endmembers in this subduction zone. From Guatemala to northwest Nicaragua, a fluid component, originating from serpentinite, has a δ37Cl value close to +0.6‰. This value, similar to lithospheric serpentinites, confirms that despite the aqueous fluid migration through the entire slab, Cl isotopes do not fractionate significantly during transport. A melt-like component, present in the southern part of the arc, has negative δ37Cl, possibly down to −2.5‰. This component has lower δ37Cl than values of the oceanic crust but similar to sediments currently subducting beneath CAVA. Finally, a common component, most likely amphibole-bearing metasomatized mantle, is identified in samples with the highest δ37Cl values (up to +3.0‰). The melting of amphibole, a mineral concentrating 37Cl over 35Cl, could explain the high δ37Cl values. The difference between melt inclusions and bulk rock δ37Cl in some volcanic centers probably results from late-stage processes such as mixing of different batches of magma at shallower levels after melt inclusions entrapment. Melt inclusions thus give a more comprehensive picture of Cl isotope systematics along the CAVA and in primitive subduction-related magmas.

Constraints on the sulfur subduction cycle in Central America from sulfur isotope compositions of volcanic gases

The sulfur cycle at convergent margins remains poorly constrained yet is fundamentally important for understanding the redox state of Earth's reservoirs and the formation of ore deposits. In this study we investigate the sulfur isotope composition of high temperature volcanic gases emitted from the Nicaraguan (average of +4.8 ± 1.3‰) and Costa Rican (average of +2.3 ± 1.3‰) arc segments contributing to emissions from the Southern Central American Volcanic Arc (SCAVA; average of +3.8 ± 1.7‰). Along-arc variations in geochemical tracers at SCAVA are widely accepted to reflect variations in subduction parameters and deep fluid sources and correlations between these parameters and gas S isotope compositions are observed. These correlations suggest that gas emissions are sourced from a mixture of mantle S with δ34S ~ 0‰ and isotopically heavy slab-derived sulfur with δ34S ≥ ~ +8‰. We employ Monte Carlo mass balance modeling to constrain S inputs to the subduction zone and relative contributions from mantle and slab to arc sulfur emissions. The models indicate that bulk subduction input in Nicaragua has a S isotope composition of +1.4 ± 0.5‰ compared to −0.2 ± 0.4‰ in Costa Rica, requiring preferential release of isotopically heavy oxidized S from the slab to explain the relatively high δ34S observed in arc outputs. We show that the flux of S from the slab is sufficient to oxidize the entire mantle wedge within the lifetime of the arc, indicating that S is a primary oxidizing agent in subduction zones. Furthermore, the preferential removal of heavy S from the slab requires retention of isotopically light S in the residual slab. Subduction-scale fractionation of S isotopes is fundamentally important in explaining why Earth's bulk surface reservoirs are isotopically positive.

Mineral Geochemistry of Basaltic Rocks from IODP Expeditions 334 and 344: Implications for Magmatic Processes of Cocos Ridge Segment Being Subducted Beneath the Middle America Trench

The Cocos Ridge, which is subducted beneath the Central American Volcanic Arc, has a complex tectonic evolution history due to plume-ridge interaction between the Galápagos plume and the Cocos—Nazca spreading center. This study presents major and trace element analyses of plagioclase and clinopyroxenes hosted by Cocos Ridge basaltic rocks that were drilled in three holes (U1381A, U1381C and U1414A) of Sites U1381 and U1414 on the Cocos Ridge close to the Middle America Trench during the Integrated Ocean Drilling Program (IODP) Expeditions 334 and 344. The results show that (1) plagioclases are mainly bytownite and labradorite with subordinate andesine, which are enriched in light rare earth elements (LREE) and some large-ion lithophile elements (LILE) and exhibit marked positive Eu anomalies; and (2) that clinopyroxenes are augites, which are depleted in highly incompatible elements such as LREE and LILE, have nearly flat heavy rare earth elements patterns (HREE) and lack Eu anomalies in chondrite-normalized rare earth element (REE) diagrams. During the ascent to the surface, the primary magmas experienced fractional crystallization of plagioclase, clinopyroxene, Ti-Fe oxides and possibly olivine (complete replacement of olivine by secondary minerals). The crystallization temperatures of plagioclase phenocrysts and microlites are 1050 to 1269 °C, and 866 to 1038 °C, respectively, and the pressures of plagioclase phenocrysts are 0.3–0.7 GPa. The crystallization temperatures of clinopyroxene phenocrysts/micro-phenocrysts is 1174–1268 °C, similar to those of plagioclase phenocrysts, suggesting some of clinopyroxene and plagioclase phenocrysts cotectic crystallized during early stage of magmatic evolution. In addition, the equilibrium pressures of clinopyroxene phenocrysts/micro phenocrysts are 0.02–0.97 GPa, implying that the clinopyroxene started to crystallize within the mantle, and magma evolution has undergone an early crystallization stage with clinopyroxene and no plagioclase.

Using GIS to Create Hazard Maps and Assess Evacuation Routes around “The Gate to Hell”; Masaya Volcano, Nicaragua

Volcán Masaya in Nicaragua is made of a series of calderas and craters that lies 7 km from the city of Masaya with a population of over 100,000. Masaya is part of the Central American Volcanic Arc (CAVA) which contains hundreds of volcanoes. While many of the volcanoes of the arc produce small, quiescent eruptions, some are capable of large explosive events. The recent cycle of volcanism at Masaya began 7000 years ago. Initial eruptions were primarily lava, small ash flows, ashfalls, and degassing events which eventually gave way to climactic Vulcanian eruptions. The hazards presented from this system affect not only larger cities, but many underdeveloped communities surrounding Volcán Masaya. These communities require a simple map and action plan to use during an evacuation. While government-issued routes are in place, there are no known secondary options. The communities surrounding Masaya lack the education they need for having such a fierce geologic feature right in their backyard to base their own opinions on when and if to evacuate the area on their own accord. We visited the study area to gather data for the creation of an evacuation route and hazard map to help prepare the surrounding communities. By consolidating our research and field data, the maps we created give the communities surrounding Masaya more insight as to the behavior of the eruptions. This research gives the local population options for evacuation and more knowledge about their environment.

Architectural and Tectonic Control on the Segmentation of the Central American Volcanic Arc

Central America has a rich mix of conditions that allow comparisons of different natural experiments in the generation of arc magmas within the relatively short length of the margin. The shape of the volcanic front and this margin's architecture derive from the assemblage of exotic continental and oceanic crustal slivers, and later modification by volcanism and tectonic activity. Active tectonics of the Cocos-Caribbean plate boundary are strongly influenced by oblique subduction, resulting in a narrow volcanic front segmented by right steps occurring at ∼150-km intervals. The largest volcanic centers are located where depths to the slab are ∼90–110 km. Volcanoes that develop above deeper sections of the subducting slab are less voluminous and better record source geochemical heterogeneity. Extreme variations in isotopic and trace element ratios are derived from different components of thesubducted oceanic lithosphere. However, the extent that volcanoes sample these signatures is also influenced by lithospheric structures that control the arc segmentation. ▪ The architecture of Central America derives from the assemblage of exotic continental and oceanic crustal slivers modified by arc magmatism and tectonic processes. ▪ Active tectonics in Central America are controlled by oblique subduction. ▪ The lithospheric architecture and tectonics define the segmentation of the volcanic front, and thus the depth to the slab below a volcanic center. ▪ The composition of the subducted material is the main control of the along arc geochemical variations observed in Central American volcanoes. ▪ Geochemical heterogeneity in each segment is highlighted by extreme compositions representing the smaller centers with variations up to 65% of the total observed range.

Integrated hazards maps of the Tacaná Volcanic complex, Mexico-Guatemala: Ashfall, block-and-ash flows, and lahars

The Tacaná Volcanic Complex (TVC) is an active volcano, located on the border between Mexico and Guatemala, in the westernmost part of the Central American Volcanic Arc. The TVC has produced effusive and explosive activity during the past 300 ka through the emplacement of lava flows, pyroclastic deposits, debris avalanches and lahars. During the last 10 ka, at least 11 eruptions have occurred, with three small phreatic explosions documented in 1855–1856, 1949 and 1986. This work presents volcanic hazards maps of the TVC that integrate the results of analyzing two eruptive style scenarios: dome-collapses and Plinian-type eruptions and the lahars triggered by both these hazards. The extents and expected distributions for each of these phenomena were assessed using numerical models and the results were calibrated with recent field data. The simulation results were merged to prepare three new volcanic hazards maps, which depict on a color scale the hazard level forecasted for each phenomenon (high – red, moderate – orange, and low – yellow). The maps show that the total extension of block-and-ash flows will be restricted towards the volcano base, reaching a maximum distance towards Guatemala of ~5 km, and ~10 km in Mexico; while lahars could reach up to 50 km downstream along the main rivers that drains the complex (i.e. Coatán, Cahoacán and Suchiate rivers) that would flood important urban centers mostly over Mexican territory. Ashfall would cover an area of ca. 8000 km2, inhabited by ~2 million people in both countries. Hence, renewed eruptive activity of the TVC would be catastrophic not only because of the loss of human life but also for its adverse impact on economic activity based on corn, coffee, and banana plantations, together with the disruption of communication and transportation systems between Mexico and Central America.

Petrology and geochemistry of Alkaline Basalts and Gabbroic xenoliths from Utila Island (Bay Islands, Honduras): Insights into back - Arc processes in the Central American Volcanic Arc

The island of Utila (Bay islands, Honduras), is situated in a back-arc environment, behind the Central American Volcanic Arc (CAVA). The Utila Volcanic Center (UVC) is Quaternary in age, based on geologic and stratigraphic relations with underlying carbonate rocks and is made up of three distinct, volcanic units: palagonite lapilli tuff, main lava flow and vent facies (in stratigraphic order). The UVC contains gabbroic xenoliths up to 5 cm in size embedded in lapilli and ash tuff. Alkaline basaltic (trachybasalt) flows are porphyritic extrusive rocks with phenocrysts composed of olivine, clinopyroxene, plagioclase and rare kaersutite. Gabbros are composed of amphibole, plagioclase, clinopyroxene, olivine, and Fe-Ti oxides. Primitive mantle normalized trace element patterns show enrichment in Ba, Nb, Ta and light rare earth elements (LREEs) similar to ocean island basalts (OIB) and share trace and major element characteristics similar to high-Nb basalt (HNB). Both basalts and gabbros Sr, Nd and Pb isotopes are distinct from OIB mantle sources in the Central American-Southern Caribbean region but similar to the Pacific MORB (Cocos Plate). A combination of OIB-like trace element characteristics and mid-ocean ridge basalt (MORB) -like isotopic ratios suggest that the UVC basalts originate from an enriched mantle source created by the hybridization of a depleted sub-arc mantle wedge in an earlier subduction stage of the CAVA.

Early central American forearc follows the subduction initiation rule

The “subduction initiation rule” (SIR) (Whattam and Stern, 2011) advocates that proto-arc and forearc complexes preserved in ophiolites and forearcs follow a predictable chemotemporal and/or chemostratigraphic vertical progression. This chemotemporal evolution is defined by a progression from bottom to top, from less to more depleted and slab-metasomatized sources. This progression has been recently documented for other igneous suites associated with subduction initiation. The Sona-Azuero forearc complex of southern Panama represents the earliest magmatic arc activity at the Central American Volcanic Arc system. Comparison of new and existing geochemical data for the circa 82-40 Ma Sona-Azuero Proto-Arc/Arc, its underlying 89-85 Ma “oceanic plateau” of SW Panama and the 72-69 Ma Golfito Proto-Arc of southern Costa Rica with the 70-39 Ma Chagres-Bayano Arc of eastern Panama exhibits a chemotemporal progression as described above and which follows the SIR. Sona-Azuero lavas are predominantly MORB-like, whereas those of the younger Chagres-Bayano complex are mostly VAB-like; lavas of the Golfito Proto-Arc typically show characteristics intermediate to that of the Sona-Azuero and Chagres-Bayano proto-arc/arc complexes. On the basis of isotope evidence as shown in other studies, lava types of all three complexes are clearly derived from a source contaminated by the Caribbean Large Igneous Province plume; we term these “plume-contaminated” forearc basalts and volcanic arc basalts, respectively. Apart from a plume-induced subduction initiation origin for the Panamanian forearc, these insights suggest otherwise similar petrogenetic origins and tectonic setting to lavas comprising earliest-formed forearc crust, and most ophiolites, which follow the SIR.

Millennial to decadal magma evolution in an arc volcano from zircon and tephra of the 2016 Santiaguito eruption (Guatemala)

The Santa María-Santiaguito volcanic complex collectively is one of the most active and dangerous volcanoes in the entire Central American volcanic arc. Within 20 years of the destructive Plinian eruption of the Santa María stratocone (Guatemala) in 1902, the Santiaguito volcanic dome complex started to form by parasitic vent eruptions which have lasted over nearly a century. Because of the frequent eruptions of Santiaguito, it offers unique opportunities to study secular changes in its subvolcanic magma reservoir at high temporal resolution. Ash collected days and hours after eruptions of Santiaguito during an unusually explosive interval in August 2016 represents some of the least evolved compositions (60–62% SiO2) with the lowest 87Sr/86Sr isotope ratios ever reported for the system. This extends the multi-decadal trend of Santiaguito to progressively less evolved magma compositions with time, relative to the 1902 event which erupted overwhelmingly dacitic pumice. Santiaguito's geochemical changes are indicative of increasingly larger contributions of fresh basaltic andesite magma recharge mixing with dacitic magma that remained after the 1902 eruption. High-resolution secondary ion mass spectrometry (SIMS) 238U-230Th disequilibrium dating and geochemistry of zircon from Santiaguito ash and Santa María 1902 pumice reveal the presence of evolved and zircon-saturated melts over the entire ca. 100 kyr interval of basaltic andesite eruptions that constructed the Santa María central cone. Quartz diorite basement xenoliths (~55% SiO2) with Eocene zircons are common in the Santa María 1902 deposits, and a few equally old zircon xenocrysts within Santiaguito ash suggest that vestiges of assimilated Eocene crustal rocks are present in the modern magma system. Zircon crystals in andesitic Santiaguito tephra are identical in age and trace element signature to those in the 1902 pumice. This is direct evidence for the persistence of residual evolved magma with crystals dating back to the Santiaguito cone-forming stage between ca. 100 and 25 ka and the pre-1902 eruptive quiescence which lasted for ca. 25 kyr. It also indicates that residual dacite still contributes to Santiaguito andesitic magmas. Zircon survival in Santiaguito andesite requires comparatively brief timescales of magma mixing between basaltic andesite and resident dacite magmas because otherwise zircon would become resorbed.

Primitive Magmas in the Early Central American Volcanic Arc System Generated by Plume-Induced Subduction Initiation

Primitive lavas with Mg# ≥60 have been identified in the literature from the Sona-Azuero, Golfito and Chagres-Bayano forearc segments of southern Costa Rica and Panama of the early (75-39 Ma) Central American Volcanic Arc system (CAVAS). Primitive CAVAS basalts are remarkably similar in terms of major and many trace elements to primitive MORB and primitive basalts of the Mariana Arc. Significant differences however, are apparent between primitive lavas of Chagres-Bayano relative to those of Sona-Azuero and Golfito. Primitive Chagres-Bayano lavas record much higher degrees of partial melting and higher amounts of shallow and deep subduction additions (e.g., higher Ba/Th, Th/Nb) than those of the older Sona-Azuero and Golfito arc segments which reflects the early petrologic and tectonic evolution of the CAVAS which is similar to other forearc systems. As shown in previous studies, early CAVAS lavas are exceptionally similar in radiogenic isotopic composition to those of the Caribbean Large Igneous Province (CLIP) oceanic plateau at 90 Ma, the approximate timing of onset of the volumetrically dominant phase of CLIP magmatism. This recognition is consistent with subduction initiation models which require plume-subduction interaction. Such models also dictate that an elevated sub-arc thermal anomaly was present at inception of the CAVAS. It is postulated that in addition to providing an anomalously high temperature regime in the sub-arc mantle at inception of the CAVAS, that extrusion of the CLIP also resulted in lithospheric weakening and extension which allowed for production and rapid ascent of a high percentage of primitive lavas.

Using Drones and Miniaturized Instrumentation to Study Degassing at Turrialba and Masaya Volcanoes, Central America

AbstractGas measurements using unmanned aerial vehicles, or drones, were undertaken at Turrialba volcano, Costa Rica, and Masaya volcano, Nicaragua, in 2016 and 2017. These two volcanoes are the largest time‐integrated sources of gas in the Central American Volcanic Arc, and both systems are currently extremely active with potential for sudden destabilization. We employed a series of miniaturized drone‐mounted instrumentation including a mini‐DOAS, two MultiGAS instruments, and an optical particle counter, supplemented by ground‐based measurements. Payloads were typically 1–1.5 kg and flight times were 10–15 min. The measurements were both accurate and precise due to the inherent sensitivity of the instrumentation and the high gas concentrations, which the drones were able to sample. The quality of data obtained by our drones was comparable to that obtained by our ground‐based measurements. At Turrialba in April 2017, we measured an average SO2 flux of 1,380 ± 280 T/day, CO2/SO2 of 6.5, and H2O/SO2 of 27.8. Using these values, we calculated a CO2 flux of 6,170 T/day and an H2O flux of 10,790 T/day. At Masaya in May 2017, the average SO2 flux was 1,560 ± 180 T/day, with CO2/SO2 of 3.9 and H2O/SO2 of 62.3, giving a mean CO2 flux of 4,150 T/day and mean H2O flux of 27,330 T/day. The elevated carbon and water fluxes and ratios are indicative of underlying magmas that are enriched in these components, resulting in the high levels of activity observed.

Petrogenetic and tectonic implications of major and trace element and radiogenic isotope geochemistry of Pliocene to Holocene rocks from the Tacaná Volcanic Complex and Chiapanecan Volcanic Belt, southern Mexico

New major and trace element, and Sr, Nd and Pb isotope data for samples from the Volcán Tacaná, along with the published data from the Tacaná Volcanic Complex (TVC) and Chiapanecan Volcanic Belt (CVB), were used to better constrain the petrogenesis of the Pliocene to Holocene volcanism in southwestern Mexico. The TVC volcanic rocks sampled in this study were andesite, whereas the literature samples included, besides andesites, one subalkali basalt and a few dacites. The CVB housing the prominent El Chichón volcano, on the other hand, showed more alkalic magmatic products (trachyandesite and basaltic trachyandesite) but also included a few basalts and dacites. The enclaves and lithic fragments sampled from both TVC and CVB showed wide SiO2 compositions similar to the volcanic products. The CVB rocks are more enriched in REE, LILE, and HFSE than the TVC. The combined data of volcanic rocks were evaluated through conventional multi-element diagrams as well as subduction- or crust-sensitive parameters. Although the TVC constitutes the northern end of the Central American Volcanic Arc (CAVA), some chemical differences were documented between them such as the TVC rocks have higher LILE, REE, HFSE, and combined ratio parameters. More importantly, the CVB seems to be significantly different from both TVC and CAVA as well as from other continental arcs such as higher LILE, REE, HFSE, and distinct isotopic signature, which may indicate that the origin of the CVB volcanism represents a direct action of the abundant strike-slip faults and extensional system prevalent in this area. Finally, the relationship of basic and evolved rocks from the CVB, especially on isotope-isotope diagrams, also suggests that the lower crust may have contributed to evolved magmas during the ascent of basic magmas through the crust.