Rationale

Combined shaded and colored SRTM elevation model of Central America (NASA/JPL/NGA, 2000) and high-resolution bathymetry along the Middle America Trench (MAT) from Ranero et al. (2005).

Authors: Walter Kurz (1), Steffen Kutterolf (2), Jennifer Brandstätter (1,#), Udo Barckhausen (3), Robert Harris (4), Paola Vannucchi (5), Jason P. Morgan (5), César R. Ranero (6), Alan Baxter (7)

(1) University of Graz, Institute of Earth Sciences, Heinrichstrasse 26, 8010 Graz, Austria.
(2) Dynamics of the Ocean Floor, GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany
(3) Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), Hannover, Germany
(4) College of Earth, Oceanic, and Atmospheric Sciences, Oregon State University, USA
(5) Department of Earth Sciences, Royal Holloway, University of London, United Kingdom
(6) Barcelona Center for Subsurface Imaging, Instituto de Ciencias del Mar, Barcelona, Spain.
(7) Department of Earth and Environmental Sciences, University of Ottawa, Canada
(#) early carreer scientist

Main applicant: Walter Kurz (Institute of Earth Sciences, University of Graz, Austria)

Summary

We propose the COSNICA workshop to be held in Graz, Austria, with the overarching objective of integrating several drilling projects offshore Nicaragua and Costa Rica under a general umbrella theme, and to develop and brainstorm two IODP-Pre-Proposals targeting the Cocos Plate and the Nicaraguan fore arc region. The first objective is the result of unsolved questions arising from two CRISP expeditions (Exp. 334 and 344) and the second objective has a potential amphibian component associated to the ICDP workshop proposal that will be held in March 2020 in Nicaragua to drill the terrestrial part of the Nicaragua depression. These two drilling targets will additionally complement a third proposed project at the Nicaraguan section of the incoming Cocos Plate where bend faults will be targeted and where a successful Magellan workshop was held in 2016 in London (Morgan et al. 2016). Scientists from ESSAC member countries have already participated in CRISP expeditions, the proposed NICA-BRIDGE ICDP workshop proposal, and the Magellan workshop: “Bend-Fault Serpentinization (BFS+H-ODIN): Oceanic Crust and Mantle Evolution from Ridge through Trench”.  In addition to the two specific drilling proposals offshore Nicaragua and Costa Rica we intend to integrate the results of the successful Bend-Fault Serpentinization workshop to develop major objectives and challenges for an overarching scientific umbrella proposal integrating all three potential drilling proposals.

Workshop description

During the past decades several international marine expeditions and three IODP expeditions have identified the Central American margin as one of the most active and fascinating margins in the world due to its unique components (subducting Cocos Ridge, young plate, faults, volcanism, tectonic evolution, hazards) and its social and economic implications for the local and international societies. Therefore, we propose the COSNICA workshop to coordinate and integrate multiple research topics under the overarching theme: “The life cycle of oceanic microplates at convergent plate margins”. Our overarching goal is to integrate ideas and coordinate goals for two drilling proposals (“The Cocos Plate enigma” and “Seagoing part of Nica-Bridge”) and how they are related to goals that have been developed during the Magellan workshop: “Bend-Fault Serpentinization: Oceanic Crust and Mantle Evolution from Ridge through Trench” in London 2016. Finally, the workshop will define overarching scientific goals leading to an umbrella proposal combining the three single project proposals.

The Cocos Plate enigma:

The oceanic Cocos Plate offshore the western margin of Costa Rica has a complex tectonic history (e.g., Schindlbeck et al., 2016a-c; Brandstätter et al., 2016; Herbrich et al., 2015; Werner et al., 2003; Barckhausen et al., 2001). The northern part of the Cocos Plate, with generally smooth morphology, is generated by the East Pacific Rise (EPR), whereas the southern part is Cocos Nazca spreading center (CNS) generated crust with rougher morphology (Werner et al. 2003). After the breakup of the Farallon Plate at 23 Ma, Cocos Plate lithosphere was formed at the opened CNS-1 (Barckhausen et al., 2001). A major ridge jump at 19.5 Ma (CNS-2), and multiple southward ridge jumps after ~14.5 Ma resulted in segmentation of the Cocos Plate lithosphere. A further segmentation process is the overprint of the Cocos Plate by the Galapagos hot spot volcanism (Barckhausen et al., 2001). Previous studies showed the tectonic complexity of the Cocos Plate (e.g. Barckhausen et al., 2001) and that Late Miocene to Pliocene magmatic processes overprint the igneous and sedimentary rocks on the Cocos Plate (Brandstätter et al., 2016; 2018). The origin of the ~2 Ma old Cocos Island is discussed in several papers (e.g., Castillo et al., 1988; Schindlbeck et al, 2016a). The aseismic Cocos Ridge (CCR), orientated parallel to the recent movement direction of the underlying Cocos Plate (Walther, 2003), extends more than 1000 km from the CNS to the Cocos Plate - Caribbean Plate boundary at the Middle America Trench. It stands ≥ 2 km higher than the surrounding seafloor is an asymmetric overthickened ridge of oceanic crust and has influenced the entire margin significantly. This crustal thickening reaches ranges from 8-10 km in the northwest to ~ 20 km beneath the center of the Cocos Ridge and is undoubtedly related to the Galapagos hot spot (Hoernle et al., 2002). The sedimentary deposits on the CCR and the surrounding ocean floor are less than 1 km thick (Walther 2003) and drill cores from several deep sea drilling expeditions (Exps. 170. 202, 334, 344) revealed very heterogenous stratigraphic records sometimes only in a few km distance from each other (e.g. Schindlbeck et al. 2016b, Brandstätter et al. 2016, Harris et al. 2013, Kimura et al. 1997). These records comprise hiatuses versus continuous stratigraphy, exclusive Galapagos versus solely arc derived fallout tephras of the same age, and different magmatic basements etc.  Pliocene to Late Miocene sediment hiatuses, for example, occur at Sites U1381 and 1242 although these are located next to Site U1414. The latter has a continuous and homogenous sedimentation with arc-derived tephras. The causes for this discrepancy are subject of ongoing investigations (Schindlbeck et al., 2016b). Possible explanations are sought in the context of temporally and regionally variable interplays of erosion, morphology and biogenic productivity. At the same time, higher Pliocene sediment accumulation at Site U1414, along the western margin of the Cocos Ridge, may be explained by erosional detritus contribution from the Cocos Ridge crest domains. Similar Pliocene sedimentation rates occur at Site 1039, which was located in an open ocean environment at that time. However, the backtracked Pliocene position of Site 1039 was in the equatorial upwelling zone, which may be responsible for higher contents of siliceous microfossils reflecting higher Pliocene/Miocene productivity (e.g., Mix et al., 2003) that may result also in an increase of the sedimentation rate. However, more detailed investigations are required to explain these inconsistencies. Therefore, the main aim of that workshop is to identify drilling locations and possible sites to reveal the internal Cocos Plate structure and the boundary between hiatus-non hiatus sites, and the processes that brought these sites so close together.

Working Hypotheses:

• Bending of oceanic plate and the marginal area of the Cocos Ridge due to arrival at trench cause large erosional events → No evidence for reworking in the core above; bending a ridge is difficult.
• Uplifting of Cocos Ridge due to increased magmatism (intrusions) probably ~2 Ma ago cause larger erosional events → No evidence for reworked matter in the core above; timing around about 2 Ma ago does not fit to a necessary nearby position to Galapagos Hot Spot.
• Closing the Central American Seaway (CAS) at the Isthmus of Panama between 3.8 and 1.6 Ma caused changes in the bottom currents strengths and directions (Stone, 2013) and caused enhanced abrasion removed 11–2 Myr old sediments from Site U1381. → Strength of ocean bottom currents and position at an elevated position due to the Cocos Ridge?
• Cocos-Nazca spreading center ridge jump resulting in uplift of ridge flanks.
• Extinct plate boundary at the northwestern flank of the Cocos Ridge, extinct spreading center.

The seagoing part of NICA-BRIDGE:

In March 2020, a workshop has taken place to develop a scientific drilling project in Lakes Nicaragua and Managua, Nicaragua. Both are located and originated in a half graben that developed at least since the Pliocene due to tectonic changes at the margin and the subducting Cocos Plate. The lakes are uniquely suited for multidisciplinary, globally important scientific investigation of long, continuous sediment profiles because of its:

1. long tectonic record (>3 Myr) of terrestrial and connected marine basin development at the Southern Central American margin,
2. alternating lacustrine and marine environments,
3. proximity to two (older and younger) volcanic arcs,
4. significance as an endemic hot spot,
5. strategic location to study the great American biotic interchange, and
6. the interactive combination of seismological, volcanological, paleoclimatological, paleoecological, and paleoenvironmental studies in both the ocean and on land.

The Sandino basin offshore Nicaragua is the oceanic continuation of this depression and complements the lake drilling to understand the evolution of the complex margin. The COSNICA workshop will serve to define, complement, and compare scientific objectives of the lake drilling project proposal in the ocean. It will address topics such as

1. development of a Neotropical environmental and paleoclimate record that will extend presently available late Pleistocene-Holocene records back to Miocene times,
2. determination of the times and rates of marine transgressions and regressions, their tectonic and climatic controls and ecological consequences,
3. investigation of recurrence rates and magnitudes of natural hazards such as explosive volcanic eruptions,
4. basin evolution of a tectonic influenced multi stage forearc, and
5. linkages between long-term terrestrial and marine environmental records.

Targeted audience/expected impact.

The main aim of that workshop is to identify drilling locations and possible sites to reveal the internal Cocos Plate structure and the boundary between hiatus-non hiatus sites, and the processes that brought these sites so close together. Additionally, complementary scientific objectives for the seagoing phase of the Nica-Bridge project will be developed and targets for pre-site surveys will be indicated. The final day will be used to develop overarching scientific topics that should be addressed in an umbrella proposal. Therefore, a selection of scientists involved in all three proposed drilling targets will be invited to work together on a common umbrella structure. But the main focus here will be on scientists involved in the “Cocos Plate enigma” and “seagoing Nica Bridge” objectives since the bend-fault and serpentinization objectives have been covered already by a separate Magellan workshop. Students and early-career scientists will be encouraged to attend; Jennifer Brandstätter, as an early career scientist co-author of this proposal, will be encouraged to act as workshop session convener. We will also aim to promote equal gender diversity. The workshop in general will provide a is a good opportunity to involve a new generation of scientists for Central American studies, including colleagues from Costa Rica and Nicaragua that will be invited to attend.