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1. Corinth Active Rift Development

   https://doi.org/10.14379/iodp.proc.381.2019  

   McNeill, L.C.; Shillington, D.J.; Carter, G.D.O. (February 2019, Proceedings of the International Ocean Discovery Program)

   null (Ed.)

   The primary objective of International Ocean Discovery Program Expedition 381 was to retrieve a record of early continental rifting and basin evolution from the Corinth rift, central Greece. Continental rifting is fundamental for the formation of ocean basins, and active rift zones are dynamic regions of high geohazard potential. However, the detailed spatial and temporal evolution of a complete rift system needed to understand rift development from the fault to plate scale is poorly resolved. In the active Corinth rift, deformation rates are high, the recent synrift succession is preserved and complete offshore, and earlier rift phases are preserved onshore. Additionally, a dense seismic database provides high-resolution imaging of the fault network and seismic stratigraphy around the basin. As the basin has subsided, its depositional environment has been affected by fluctuating global sea level and its absolute position relative to sea level, and the basin sediments record this changing environment through time. In Corinth, we can therefore achieve an unprecedented precision of timing and spatial complexity of rift-fault system development, rift-controlled drainage system evolution, and basin fill in the first few million years of rift history. The following are the expedition themes: 1. High-resolution fault slip and rift evolution history, 2. Surface processes in active rifts, 3. High-resolution late Quaternary Eastern Mediterranean paleoclimate and paleoenvironment of a developing rift basin, and 4. Geohazard assessment in an active rift. These objectives were and will be accomplished as a result of successful drilling, coring, and logging at three sites in the Gulf of Corinth, which collectively yielded 1645 m of recovered core over a 1905 m cored interval. Together, these cores provide (1) a long rift history (Sites M0078 and M0080), (2) a high-resolution record of the most recent phase of rifting (Site M0079), and (3) the spatial variation of rift evolution (comparison of sites in the central and eastern rift). The sediments contain a rich and complex record of changing sedimentation, sediment and pore water geochemistry, and environmental conditions from micropaleontological assemblages. The preliminary chronology developed by shipboard analyses will be refined and improved during postexpedition research, providing a high-resolution chronostratigraphy down to the orbital timescale for a range of tectonic, sedimentological, and paleoenvironmental studies. This chronology will provide absolute timing of key rift events, rates of fault movement, rift extension and subsidence, and the spatial variations of these parameters. The core data will also allow us to investigate the relative roles of and feedbacks between tectonics, climate, and eustasy in sediment flux, basin evolution, and basin environment. Finally, the Corinth rift boreholes will provide the first long Quaternary record of Mediterranean-type climate in the region. The potential range of scientific applications for this unique data set is very large, encompassing tectonics, sedimentary processes, paleoenvironment, paleoclimate, paleoecology, geochemistry, and geohazards. 

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2. Expedition 381 Scientific Prospectus: Corinth Active Rift Development

   https://doi.org/10.14379/iodp.sp.381.2017  

   McNeill, L.; Shillington, D.; Carter, G. (October 2017, Scientific prospectus)

   null (Ed.)

   Continental rifting is fundamental for the formation of ocean basins, and active rift zones are dynamic regions of high geohazard potential. However, much of what we know from the fault to plate scale is poorly constrained and is not resolved at any level of spatial or temporal detail over a complete rift system. For International Ocean Discovery Program Expedition 381, we propose drilling within the active Corinth rift, Greece, where deformation rates are high, the synrift succession is preserved and accessible, and a dense, seismic database provides high-resolution imaging, with limited chronology, of the fault network and of seismic stratigraphy for the recent rift history. In Corinth, we can therefore achieve an unprecedented precision of timing and spatial complexity of rift-fault system development and rift-controlled drainage system evolution in the first 1–2 My of rift history. We propose to determine at a high temporal and spatial resolution how faults evolve, how strain is distributed, and how the landscape responds within the first few million years in a nonvolcanic continental rift, as modulated by Quaternary changes in sea level and climate. High horizontal spatial resolution (1–3 km) is provided by a dense grid of seismic profiles offshore that have been recently fully integrated and are complemented by extensive outcrops onshore. High temporal resolution (~20–50 ky) will be provided by seismic stratigraphy tied to new core and log data from three carefully located boreholes to sample the recent synrift sequence. Two primary themes are addressed by the proposed drilling integrated with the seismic database and onshore data. First, we will examine fault and rift evolutionary history (including fault growth, strain localization, and rift propagation) and deformation rates. The spatial scales and relative timing can already be determined within the seismic data offshore, and dating of drill core will provide the absolute timing offshore, the temporal correlation to the onshore data, and the ability to quantify strain rates. Second, we will study the response of drainage evolution and sediment supply to rift and fault evolution. Core data will define lithologies, depositional systems and paleoenvironment (including catchment paleoclimate), basin paleobathymetry, and relative sea level. Integrated with seismic data, onshore stratigraphy, and catchment data, we will investigate the relative roles and feedbacks between tectonics, climate, and eustasy in sediment flux and basin evolution. A multidisciplinary approach to core sampling integrated with log and seismic data will generate a Quaternary chronology for the synrift stratigraphy down to orbital timescale resolutions and will resolve the paleoenvironmental history of the basin in order to address our objectives. 

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3. Microcontinent Breakup and Links to Possible Plate Boundary Reorganization in the Northern Gulf of California, México

   https://doi.org/10.1029/2021TC006933  

   Higa, Justin T.; Brown, Nathan D.; Moon, Seulgi; Stock, Joann M.; Sabbeth, Leah; Bennett, Scott E. K.; Martín‐Barajas, Arturo; Argueta, Marina O. (January 2022, Tectonics)

   Abstract Faults on microcontinents record the dynamic evolution of plate boundaries. However, most microcontinents are submarine and difficult to study. Here, we show that the southern part of the Isla Ángel de la Guarda (IAG) microcontinent, in the northern Gulf of California rift, is densely faulted by a late Quaternary‐active normal fault zone. To characterize the onshore kinematics of this Almeja fault zone, we integrated remote fault mapping using high‐resolution satellite‐ and drone‐based topography with neotectonic field‐mapping. We produced 13 luminescence ages from sediment deposits offset or impounded by faults to constrain the timing of fault offsets. We found that north‐striking normal faults in the Almeja fault zone continue offshore to the south and likely into the nascent North Salsipuedes basin southwest of IAG. Late Pleistocene and Holocene luminescence ages indicate that the most recent onshore fault activity occurred in the last ∼50 kyr. These observations suggest that the North Salsipuedes basin is kinematically linked with and continues onshore as the active Almeja fault zone. We suggest that fragmentation of the evolving IAG microcontinent may not yet be complete and that the Pacific‐North America plate boundary is either not fully localized onto the Ballenas transform fault and Lower Delfin pull‐apart basin or is in the initial stage of a plate boundary reorganization. 

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4. Heterogeneous Strain Distribution in the Malawi (Nyasa) Rift, East Africa: Implications for Rifting in Magma‐Poor, Multi‐Segment Rift Systems

   https://doi.org/10.1029/2022TC007486  

   Wright, Lachlan J. M.; Scholz, Christopher A.; Muirhead, James D.; Shillington, Donna J. (September 2023, Tectonics)

   Abstract Half‐graben basins bounded by border faults typify early‐stage continental rifts. Deciphering the role that intra‐rift faults play in rift basin development is challenging as patterns of early‐stage faulting are commonly overprinted by subsequent deformation; yet the characterization of these faults is crucial to understand the fundamental controls on their evolution, their contribution to rift opening, and to assess their seismic hazard. By integrating multiple offshore seismic reflection data sets with age‐dated drill core, late‐Quaternary and cumulative faulting patterns are characterized in the Central and South Basins of the Malawi (Nyasa) Rift, an active, early‐stage rift system. Almost all intra‐rift faults offset a late‐Quaternary lake lowstand surface, suggesting they are active and should be considered in hazard assessments. Fault throw profiles reveal sawtooth patterns indicating segmented slip histories. Observed extension on intra‐rift faults is approximately twice that predicted from hanging wall flexure of the border fault, suggesting that intra‐rift faults accommodate a proportion of the regional extension. Cumulative and late‐Quaternary throws on intra‐rift faults are correlated with throw measured on the border fault in the Central Basin, whereas an anticorrelation is observed in the South Basin. Viewed in a regional context, these differences do not relate solely to the proposed southward younging of the rift. Instead, it is inferred that the distribution of extension is also influenced by variations in lithospheric structure and crustal heterogeneities that are documented along the rift axis. 

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5. Scientific drilling of Lake Chalco, Basin of Mexico (MexiDrill)

   Brown, Erik T. (December 2019, Scientific drilling)

   The primary scientific objective of MexiDrill, the Basin of Mexico Drilling Program, is development of a continuous, high-resolution  400 kyr lacustrine record of tropical North American environmental change. The field location, in the densely populated, water-stressed Mexico City region gives this record particular societal relevance. A detailed paleoclimate reconstruction from central Mexico will enhance our understanding of long-term natural climate variability in the North American tropics and its relationship with changes at higher latitudes. The site lies at the northern margin of the Intertropical Convergence Zone (ITCZ), where modern precipitation amounts are influenced by sea surface temperatures in the Pacific and Atlantic basins. During the Last Glacial Maximum (LGM), more winter precipitation at the site is hypothesized to have been a consequence of a southward displacement of the mid-latitude westerlies. It thus represents a key spatial node for understanding large-scale hydrological variability of tropical and subtropical North America and is at an altitude (2240ma.s.l.), typical of much of western North America. In addition, its sediments contain a rich record of pre-Holocene volcanic history; knowledge of the magnitude and frequency relationships of the area’s explosive volcanic eruptions will improve capacity for risk assessment of future activity. Explosive eruption deposits will also be used to provide the backbone of a robust chronology necessary for full exploitation of the paleoclimate record. Here we report initial results from, and outreach activities of, the 2016 coring campaign. 

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