Migration Of Volcanic Activity Research Articles

The complex construction of a glaciovolcanic ridge with insights from the 2021 Fagradalsfjall Eruption (Iceland)

Glaciovolcanic landforms provide global-scale records of paleoenvironmental conditions and yield insights into subglacial eruption processes. Models for the formation of glaciovolcanic ridges, or tindars, are relatively simple, proposing a monogenetic eruption and a fairly uniform stratigraphy with or without a single transition from effusive pillow lavas to explosive fragmental deposits. Others have suggested that tindars are more complicated. To build a more robust model for tindar formation, we conducted a field and geochemical study of Undirhlíðar ridge on the Reykjanes Peninsula in southwestern Iceland. We show that the ridge was built through a complex sequence of eruptive and intrusive events under dynamically changing ice conditions. Quarry walls expose a continuous cross-section of the ridge, revealing multiple pillow and fragmental units. Pillow lava orientations record the emplacement of discrete pillow-dominated lobes and the migration of volcanic activity between eruptive vents. Volatile contents in glassy pillow rinds show repeated pulses of pillow lava emplacement under glaciostatic conditions, with periods of fragmentation caused by depressurization. Variations in major elements, incompatible trace element ratios, and Pb-isotopes demonstrate that the eruption was fed from separate crustal melt reservoirs containing melts from a compositionally heterogeneous mantle source. A shift in mantle source signature of pillow lavas suggests that the primary ridge-building phase was triggered by the injection of magma into the crust. Within the growing edifice, magma was transported through dykes and irregularly shaped intrusions, which are up to 20% by area of exposed stratigraphy sequences. The model for tindar construction should consider the significant role of intrusions in the growth of the ridge, a detail that would be difficult to identify in natural erosional exposures. The 2021–22 eruptions from the adjacent Fagradalsfjall vents allow us to draw parallels between fissure-fed eruptions in subaerial and ice-confined environments and test hypotheses about the composition of the mantle underlying the Reykjanes Peninsula. Both Fagradalsfjall and Undirhlíðar ridge eruptions may have occurred over similar spatial and temporal scales, been triggered by mixing events, erupted lavas with varying mantle source signatures, and focused volcanic activity along migrating vents. Differences in composition between the two locations are not related to systematic lateral variations in the underlying mantle. Rather, the Undirhlíðar ridge and Fagradalsfjall eruptions capture complex interactions among the crustal magma plumbing system, mantle source heterogeneity, and melting conditions for a moment in time.

Geological record of flat slab–induced extension in the southern Peruvian forearc

The long-lived Andean subduction zone underwent several flat slab episodes and is therefore ideal to study the consequences of a complete cycle of slab flattening and steepening on the upper plate deformation pattern. In the modern Peruvian forearc (15°–17°S), slab flattening caused a Paleogene (52–30 Ma) landward migration of volcanic activity. Combining structural geology and a source-to-sink thermochronological study, we show that the flat slab period is contemporaneous with uplift accommodated by large-scale crustal extension in the forearc. In this light, we argue that the study area is an ancient analog to the modern Mexican and northern Peruvian forearcs located above modern flat slab segments and currently undergoing widespread extension.

Geodynamics as wave dynamics of the medium composed of rotating blocks

The geomedium block concept envisages that stresses in the medium composed of rotating blocks have torque and thus predetermine the medium's energy capacity (in terms of [Ponomarev, 2008]). The present paper describes the wave nature of the global geodynamic process taking place in the medium characterized by the existence of slow and fast rotation strain waves that are classified as a new type of waves. Movements may also occur as rheid, superplastic and/or superfluid motions and facilitate the formation of vortex geological structures in the geomedium. Our analysis of data on almost 800 strong volcanic eruptions shows that the magma chamber’s thickness is generally small, about 0.5 km, and this value is constant, independent of the volcanic process and predetermined by properties of the crust. A new magma chamber model is based on the idea of 'thermal explosion’/‘self-acceleration' manifested by intensive plastic movements along boundaries between the blocks in conditions of the low thermal conductivity of the geomedium. It is shown that if the solid rock in the magma chamber is overheated above its melting point, high stresses may occur in the surrounding area, and their elastic energy may amount to 1015 joules per 1 km3 of the overheated solid rock. In view of such stresses, it is possible to consider the interaction between volcano’s magma chambers as the migration of volcanic activity along the volcanic arc and provide an explanation of the interaction between volcanic activity and seismicity within the adjacent parallel arcs. The thin overheated interlayer/magma chamber concept may be valid for the entire Earth's crust. In our hypothesis, properties of the Moho are determined by the phase transition from the block structure of the crust to the nonblock structure of the upper mantle.

Subsurface geometry and structural evolution of La Gomera island based on gravity data

We hereby present a new Bouguer gravity map of the La Gomera island (Canarian Archipelago), which is analysed and interpreted by means of a 3-dimensional inversion, in order to contribute to the knowledge of the structural setting of this volcanic island and its evolutionary history. A land gravity data set covering the whole island of La Gomera is used in combination with offshore measurements to achieve a better determination of the gravity field in areas near the coasts. The study of this map let us to shed some light on the hypothesis established about the volcanism of this island. Moreover, it shows the information that is hidden from a geological surface exploration, modelling deep sections of the crust in La Gomera, which have been unknown until now. A first interpretation of the Bouguer gravity anomaly is achieved from 1) the residual gravity map calculated by removing a regional component and 2) the total horizontal gradient of the gravity. These residual and derivative maps allow us to identify the horizontal location and borders of the shallowest gravity sources. This provides a useful tool to study the structures associated to the latest periods of the volcanism in the area. Moreover, the information so obtained supports the hypothesis about the migration of volcanic activity towards the south of the island. Subsequently, an inversion process is carried out looking for the 3D-modelisation of the sources of the observed gravity field, which provides a comprehensive view of the structures in volcanic environments. The inversion technique used is based on a genetic algorithm (GA) applied upon a prismatic partition of the subsoil volume, and adopting a priori values of density contrast (positive and negative). The main advantage of this method is that let us to model deep and shallow bodies which exhibit very different geometries and density contrasts. So, results indicate that this inversion strategy can be very effective for characterization of volcanic structures, improving the information from previous geologic and volcanologic studies. The inversion model obtained shows correlation between several sources of the gravity field and the volcanic units associated with the growth of La Gomera Island. The main gravity source of this model is associated with the oldest unit, called the Basal Complex. This unit corresponds to the first submarine growth stage and it is modelled as the most important and deepest high density structure. According to previous geological studies, the following edifice (Old Edifice) was also submarine in its initial phases, later being represented by a wide basaltic shield volcano. The original location and morphology of this Old Edifice is deduced from the distribution of positive density contrasts that appears in the model. Moreover, other gravity field sources are identified and associated to several feeding systems of this stage of the volcanism in La Gomera. The shallowest sections of the model let us recognise the distribution of light material inside the Vallehermoso caldera, surrounded by high density structures. This gives us some insight into the internal structure and morphology of the caldera, pointing to a vertical collapse origin followed by erosion and other destructive processes. Finally, other conclusions are obtained from the correlation found between the sources of the gravity field and the migration of the volcanic activity towards the southern area of the island.

Geochronology of Pliocene volcanism in the Dzhavakheti Highland (the Lesser Caucasus). Part 2: Eastern part of the Dzhavakheti Highland. Regional geological correlation

The results of isotopic-geochronological study of the Pliocene volcanic rocks in reference sections and volcanic edifices of eastern part of the Dzhavakheti Highland (the northwestern Lesser Caucasus) are considered. The isotopic-geochronological data obtained here are correlated with data on western part of the Dzhavakheti Highland, which have been considered in previous part of this work. Based on correlation, time spans of principal volcanic events of the Pliocene in the study region as a whole are determined, and general trends of the young magmatism evolution within the region are established. In sum, the isotopic-geochronological dates evidence that the Pliocene magmatism of the Dzhavakheti Highland developed practically without essential breaks during the period of about 2 Ma long, from 3.75 to 1.75–1.55 Ma ago. The areal basic volcanism that was most widespread at that time is divisible into five discrete phases according to the isotopic dates obtained. Comparatively short pauses, which separated these phases of magmatic activity, were a few hundreds thousand years long, not more. Chemical composition of moderately acidic to silicic volcanics, which are of a limited distribution in the Dzhavakheti Highland, and their age relations with basic lavas of the region suggest that they are most likely the differentiation products of parental basic mantle-derived magmas. The analyzed distribution of volcanic centers, which erupted basic lavas of the Dzhavakheti Highland, evidence that first two phases of basic magmatism were connected here with volcanic activity in southwestern part of the region (northern termination of the Egnakhag Ridge), whereas activity of volcanoes situated on the east, predominantly in water-shed part and on slopes of the submeridional Dzhavakheti Ridge, controlled development of the third and fourth phases. Consequently, magmatic activity of the Pliocene stage in history of the Neogene-Quaternary magmatism of the Dzhavakheti Highland laterally migrated from the west to the east, being controlled by development of regional submeridional extension zones. Volcanic ridges marking the latter are formed by volcanic edifices, which are amalgamated at their bases and have erupted lavas of close age and composition. The migration of volcanic activity can be described in terms of the “domino effect,” when cessation of volcanism in one zone led to formation of the other submeridional zone of extension and magmatic activity displaced from the west eastward in sublatitudinal direction. In general, evolution of the Pliocene magmatism of the Dzhavakheti Highland, was similar, despite the essential regional peculiarities, to the generalized trend of magmatism evolution in the continental rifts and intraplate zones of the “hot-spot” type.

Magnetic Polarity Stratigraphy and K-Ar Dating in the Camargo Volcanic Field, Northern Mexico: Lateral SW-NE Migration of Volcanic Activity

Results of a detailed paleomagnetic study of intraplate mafic alkalic volcanic rocks from the Camargo volcanic field of northern Mexico are presented. The field is formed by >300 eruptive vents and lava flows over an area of 3000 km2, and thus represents an important magmatic episode within the Mexican Basin and Range province. Rock-magnetic properties of the cinder cone field show that remanence is carried in most cases by Ti-poor titanomagnetites, resulting from exsolution and deuteric oxidation of original titanomagnetite during the primary flow cooling. A few units show remanence carried by titanohematite or by secondary titanomaghemite. New radiometric ages and magnetic polarity stratigraphy document a southwest-to-northeast migration of volcanic activity during the Pliocene-Pleistocene (4.7-0.09 Ma). Magnetostratigraphic correlation of dated rocks with the geomagnetic polarity time scale allows improved definition of volcanic stratigraphy. The mean paleomagnetic direction obtained for the Camargo volcanic field is I = 34.7°, D = 351.2°, k = 7, a95 = 16.6°, which deviates about 10° counterclockwise from the expected direction estimated from the North American apparent polar wander path. In the Basin and Range province, extensional faulting is closely related to volcanic activity. The tectonic, structural, and paleomagnetic data for the Camargo field document this association between volcanism and normal faulting, and also indicate the effects of large-scale processes of uplift, extension, block rotation, and regional faults in northern Mexico.

Constructive and destructive episodes in the building of a young Oceanic Island, La Palma, Canary Islands, and genesis of the Caldera de Taburiente

The results of new field observations, 23 new KAr determinations and sixteen previously published determinations provide the basis for the reconstruction of the subaerial volcanic history of the island of La Palma, after the seamount activity represented by the materials of the Basal Complex. An eruptive phase between 2.0 and 1.3 Ma formed a large shield. A period of volcanic quiescence followed, until around 1 Ma, during which a large lateral collapse partly destroyed the former edifice. Between 1.05 and 0.7 Ma, activity was renewed in the shield and a N-S ridge was built in the southern part of the island. Around 0.7 Ma, two new large lateral collapses affected the western part of both edifices, and they were followed by eruptions between 0.71 and 0.65 Ma which built a new edifice that partly filled the depressions thus created. The Caldera de Taburiente constitutes the eroded remnants of the depression formed in the northern shield. From 0.65 Ma to present, activity has been restricted to the N-S ridge, which has continued to grow southwards. There was a general N-S migration of volcanic activity with time, but in the shield the trend was northwest to southeast. Eruptive rates seem to have been fairly constant during the different eruptive phases considered, between 0.15 and 0.37 km 3/ka. A very similar succession of constructive and destructive episodes has been obtained for the neighboring island of Hierro, but in this case the activity started around 0.8 Ma and eruptive rates were about 0.5 km 3/ka.