Potential secondary events caused by early Holocene paleoearthquakes in Fennoscandia – a climate-related review

During the last deglaciation of Fennoscandia, large earthquakes may have induced secondary effects on the high-latitude coastal regions and continental margins primarily from surface rock avalanches, large and small submarine slides, local and regional flooding, and tsunamis. In this overview, we show that the climate-earthquake-slide-tsunami causal sequence is particularly important, as is structural inheritance and rejuvenation. However, there are potential earthquake-generating early Holocene faults also beyond the previously defined Lapland Fault Province. Thus, we introduce the term the Greater Lapland Fault Province. Earthquakes in the expanded fault province are candidates for triggering the 8.1 ka Storegga Megaslide and/or its predecessors and coeval tsunamis. The events might have released other submarine slides, gas hydrate expulsion leaving large pockmark fields, rock avalanches and submarine mass wasting in fjord and lake settings. Moreover, the seismic events may also have triggered local and regional flooding by breakup of ice and sediment barriers.publishedVersio

Environmental impact of volcanic margin formation

ABSTRACT Late rift stage uplift and subsequent massive, transient volcanism during breakup of rifted volcanic continental margins constrain paleoenvironments by modifying basin geometry and the composition of the atmosphere, hydrosphere and thus biosphere on regional and global scales. The early Tertiary North Atlantic breakup history shows that lava emplacement was accompanied by regional ashfalls, and that extrusive complexes influenced Paleogene oceanic and continental margin circulation and sedimentation. Temporal correspondence with the terminal Paleocene deep-sea extinction event and the earliest Eocene greenhouse suggests a global impact, possibly by enhanced atmospheric CO 2 levels, leading to polar warming and thereby changing patterns of deep-water formation. In this context, transient subaerial volcanism at continental margins should be considered with the much discussed continental flood basalt provinces and oceanic plateaus

Malvinas (Falkland) Plateau structure versus Mjølnir crater: Templatefor marine impact craters.

A diagnostic geophysical-based template, supported by modelling, is suggested to be used prior to, or in combination with geological/drilling data, when proposing a marine impact crater. The latter refers to impacts occurring in a marine setting and resulting in structures that are currently partially or totally underwater. The methodology is based on the well-documented Mjølnir crater in the Barents Sea. The template has been developed in conjunction with the recently proposed and debated impact crater on the Malvinas (Falkland) Plateau in the South Atlantic. Despite their different sizes, their comparison adds to the ambiguous nature of the Malvinas structure and shows that the integrated analysis of seismic and potential field data and modelling is crucial for any interpretation of a marine impact crater without relevant geological information. The proposed workflow template utilizes all available geophysical data and is composed of a series of iterative steps, including a range of alternative nonimpact interpretations that must be discussed and accounted for. Subsequently, further iterative geophysical modelling is required to support and decipher the impact related processes. A more complex impact crater model and additional impact crater features can be resolved by physical property modelling. In all cases, a close spatial correspondence of the defined impact structure with potential field anomalies is a necessity to establish a causal relationship. We suggest that the diagnostic workflow template provides a methodology to be applied to future studies of the Malvinas structure, as well as to proposed marine (and, with minor adaptions, to nonmarine) impact craters in general

Potential secondary events caused by early Holocene paleoearthquakes in Fennoscandia – a climate-related review

During the last deglaciation of Fennoscandia, large earthquakes may have induced secondary effects on the high-latitude coastal regions and continental margins primarily from surface rock avalanches, large and small submarine slides, local and regional flooding, and tsunamis. In this overview, we show that the climate-earthquake-slide-tsunami causal sequence is particularly important, as is structural inheritance and rejuvenation. However, there are potential earthquake-generating early Holocene faults also beyond the previously defined Lapland Fault Province. Thus, we introduce the term the Greater Lapland Fault Province. Earthquakes in the expanded fault province are candidates for triggering the 8.1 ka Storegga Megaslide and/or its predecessors and coeval tsunamis. The events might have released other submarine slides, gas hydrate expulsion leaving large pockmark fields, rock avalanches and submarine mass wasting in fjord and lake settings. Moreover, the seismic events may also have triggered local and regional flooding by breakup of ice and sediment barriers

North Atlantic volcanic margins: Dimensions and production rates

Early Tertiary lithospheric breakup between Eurasia and Greenland was accompanied by a transient (∼3 m.y.) igneous event emplacing both the onshore flood basalts of the North Atlantic Volcanic Province (NAVP) and huge extrusive complexes along the continent‐ocean transition on the rifted continental margins. Seismic data show that volcanic margins extend >2600 km along the early Eocene plate boundary, in places underlain by high‐velocity (7.2–7.7 km/s) lower crustal bodies. Quantitative calculations of NAVP dimensions, considered minimum estimates, reveal an areal extent of 1.3×106 km2 and a volume of flood basalts of 1.8×106 km3, yielding a mean eruption rate of 0.6 km3/yr or 2.4 km3/yr if two‐thirds of the basalts were emplaced within 0.5 m.y. The total crustal volume is 6.6×106 km3, resulting in a mean crustal accretion rate of 2.2 km3/yr. Thus NAVP ranks among the world's larger igneous provinces if the volcanic margins are considered. The velocity structure of the expanded crust seaward of the continent‐ocean boundary differs from standard oceanic and continental crustal models. Based on seismic velocities this “volcanic margin” crust can be divided into three units of which the upper unit corresponds to basaltic extrusives. The regionally consistent velocity structure and geometry of the crustal units suggest that the expanded crust, including the high‐velocity lower crust which extends some distance landward of the continent‐ocean boundary, was emplaced during and subsequent to breakup. The volcanic margin crust was formed by excess melting within a wide zone of asthenospheric upwelling, probably reflecting the interaction of a mantle plume and a lithosphere already extending

Large igneous provinces: progenitors of some ophiolites?

Mesozoic and Cenozoic continental flood-basalt provinces, oceanic plateaus, oceanic basin flood basalts, and volcanic passive margins share geologic and geophysical characteristics that indicate an origin distinct from igneous rocks formed at mid-ocean ridges. Such characteristics of mafic large igneous provinces (LIPs) include (1) broad areal extent (>10^5 km^2) of basalts of similar age erupted over ~10^6 yr; (2) lower-crustal bodies characterized by Vp = 7.0–7.6 km·s^–1; (3) some component of intermediate and silicic volcanic rocks; (4) trace element, rare earth element, and isotopic signatures in flood basalts that are distinct from mid-oceanic-ridge basalts (MORBs); (5) thick (10s–100s of meters) individual basalt flows; and (6) long (?750 km) individual basalt flows. In addition, basaltic and gabbroic crustal sections of oceanic LIPs are two to five times thicker than those of “normal” oceanic crust, implying larger magma chambers than at typical mid-ocean ridges and, in the case of some continental flood basalts, resulting in layered intrusive complexes containing chromite. Lastly, some flood-basalt provinces are associated with kimberlites and other ultramafic volcanism. LIPs have formed, on average, every 10 m.y. since 250 Ma. However, despite the lower energy required to obduct relatively high standing oceanic LIPs in contrast to normal oceanic crust, only five obducted oceanic LIPs have been well documented in the Mesozoic and Cenozoic continental and island-arc geologic record. More ophiolite fragments may be obducted sections of volcanic passive margins and oceanic plateaus than we now suppose