Search

An international, multidisciplinary research group is proposing the "NICA-BRIDGE" drilling project, within the framework of the International Continental Scientific Drilling Program (ICDP). The project goal is to conduct scientific drilling in Lake Nicaragua and Lake Managua (Nicaragua, Central America) to obtain long lacustrine sediment records to (a) extend the neotropical paleoclimate record back to the Pliocene, making it one of the longest continental tropical climate archives in the world, and to (b) provide geological data on the long-term complex interplay among tectonics, volcanism, sea-level dynamics, climate change, and biosphere. The lakes are the two largest in Central America, and they are located in a trench-parallel half graben that hosts the volcanic front, which developed during or prior to the Pliocene, as a consequence of subduction-related tectonic activity. The lakes are uniquely suited for multidisciplinary scientific investigation as their long, continuous sediment records (several Myr) will facilitate the study of (1) terrestrial and marine basin development at the southern Central American margin, (2) alternating lacustrine and marine environments in response to tectonic and climatic changes, (3) the longest record of tropical climate proxies, (4) the evolution of (and transition between) the Miocene to Pliocene/Pleistocene and Pleistocene to present volcanic arcs, which were separated by slab rollback, (5) the significance of the lakes as hot spots for endemism, and (6) the Great American Biotic Interchange at this strategic location, i.e., the N–S and reverse migration of fauna after the land bridge between the Americas was established. The planned ICDP project offers an opportunity to explore these topics through continent-based seismological, volcanological, paleoclimatological, paleoecological, and paleoenvironmental studies, combined with an International Ocean Discovery Program (IODP) drill project to explore its oceanic continuation. In preparation of this drilling project, an ICDP workshop was held in Montelimar, Nicaragua, on 2–5 March 2020 to develop drilling strategies and refine scientific questions, objectives, and hypotheses. The workshop was organized and hosted by the principal investigators and the Instituto Nicaragüense de Estudios Territoriales (INETER), with funding from the ICDP. Forty-five researchers from 12 countries participated in the workshop, including representatives from ICDP. During the workshop, previous research data on the study lakes, including new recent surveys, were reviewed, and a three-phase strategy for the proposed research was developed. The aim of Phase 0 is to complement the pre-site surveys where we identified the need for further data. In Phase I, with ICDP support, we will obtain sediment cores ∼ 100 m long, which will allow us to investigate many of the scientific questions. Based on the data from those drill cores, coring locations will be identified for a future Phase II, which we envisage as a combined ICDP/IODP project to collect deep drill cores in the lakes and the offshore Sandino Basin in order to extend Phase I results to much deeper time. The Sandino Basin is the oceanic continuation of the depression in which the studied lakes are located, and complementary marine drilling will improve the understanding of the evolution of this complex margin. [ABSTRACT FROM AUTHOR] more...

Despite the strong theoretical basis for the importance of magma decompression rate in modulating the dynamics of explosive basaltic eruptions, few measurements exist. Here, we quantify magma decompression rate using the incomplete diffusive re-equilibration of water through olivine for two contrasting eruptions at Cerro Negro volcano in Nicaragua: the 1992 VEI 3 and 1995 VEI 2 eruptions. Both eruptions have the same basaltic composition (SiO 2 ∼ 50 wt %) and maximum volatile concentrations (H 2 O ∼ 4.7 wt %). SIMS and NanoSIMS measurements of water in olivine-hosted melt inclusions (MIs) from both eruptions show a negative correlation between MI size and water loss, as predicted for diffusive re-equilibration. MIs from the 1995 eruption appear to have experienced more water loss compared to those from the 1992 eruption (up to 80–90 % water loss in MIs < 50 μm), which is consistent with slower magma ascent. Quantifying the timescale for water diffusion during magma decompression requires an accurate constraint on H+ diffusivity through olivine. We perform dehydration experiments on oriented cuboids of olivine from Cerro Negro in a 1 atm. furnace at 800 and 1000 °C and at an oxygen fugacity 0.25 log units above the nickel-nickel oxide buffer (NNO + 0.25) in a sequence of heating steps. Between each heating step we measure the H+ concentration along each crystallographic direction by FTIR and model these profiles to determine the diffusivity. We find the fastest diffusion direction along a ̱ and develop an Arrhenius relationship for the diffusivity along this direction: D a (m 2 / s) = 9.6 × 1 0 − 6 exp − 125 R T , where R is the gas constant 8.314 J/mol K; T is the temperature in K and the activation energy is 125 kJ/mol. These are the fastest rates ever measured for olivine dehydration, which may relate to the low forsterite content of the olivines (Fo ∼ 79). We have developed a 1D model for H+ diffusion along the fast direction since this dominates water loss (D a > 10 × D b or D c). Using our new H+ diffusivity, we model water diffusion from MIs during magma decompression to determine ascent timescales. We find that magma from the VEI 3 eruption of 1992 ascended at a median rate of 0.007 MPa/s, which is ∼5 × faster than the median for the 1995 VEI 2 eruption, although both eruptions show a ∼ two orders of magnitude spread in decompression rate. Assuming linear decompression, this places a minimum bound of ∼6.5 h on magma ascent during the 1992 eruption and ∼35 h for the 1995 eruption. Monte Carlo simulations give a 2 σ uncertainty on log 10(dP / dt) of ∼ 10 % — much smaller than the order of magnitude spread in decompression rate within each eruption, which suggests that there is real variation in decompression rate for a given deposit. Our results support the hypothesis that higher decompression rates are correlated with more explosive eruptions and show that diffusion modelling of MI water loss is a powerful tool that is sensitive to changes in decompression between VEI 2 and 3 eruption intensities. • Fastest H+ diffusivity in olivine on record for dehydration, possibly linked to Fe content • Strongly anisotropic diffusivity of H+ in olivine requires care with crystal orientation. • 1D diffusion models show link between eruption style and magma decompression rate. • No link between eruption style and initial magma water concentration [ABSTRACT FROM AUTHOR] more...