Geodynamic Domains Research Articles

Constraints on the Structure of the Shallow Crust in Central Italy from Geophysical Log Data

To better define the seismic velocities of the shallow crust in central Italy, in the area affected by the 1997 Colfiorito, 2009 L’Aquila and 2016–2018 Amatrice–Norcia seismic sequences, we selected all deep wells with available sonic logs from the Apennine belt to the related Adriatic foredeep. Sonic logs are among the most important in situ measurements of rock properties and provide a reliable image of physical conditions at depth. By analysing the wave train transit times, we inferred the P-wave velocity within depth intervals displaying homogeneous sonic log properties, and estimated the rock density by applying an empirical relationship between the sonic velocity and density in sedimentary rocks. We compared these results with the main litho-stratigraphic units in stratigraphic profiles of the wells. From the density estimates, we inferred the trends of the vertical stress magnitude in the belt, eastern front and foredeep geodynamic domains. This work is a contribution to better interpretation of physical conditions at depth and provides data that can be applied to define more complete seismological, gravity and magnetic models. We provide data uncertainties that must be considered to ensure proper use of data and to evaluate the spatial resolution of the models derived from those data.

The Early Jurassic Fe–Sn metallogenic event and its geodynamic setting in South China: Evidence from Re–Os, U–Pb geochronology and geochemistry of the Dading magnesian skarn Fe–Sn deposit

The South China Block (SCB) is one of the largest W-Sn-polymetallic metallogenic district over the world, with most of the deposits formed during the Mesozoic. The Early Jurassic of SCB was considered as a magmatic and metallogenic quiescence stage, as response to the tectonic transition from the paleo-Tethyan to the paleo-Pacific geodynamic domains. The Dading Fe-Sn deposit is a quite rare Early Jurassic deposit recognized in SCB. SIMS Zircon U–Pb and molybdenite Re-Os dating indicate that the Dading Fe–Sn deposit (185.9 ± 4.9 Ma) and related Shibei granite (189.0 ± 1.5 Ma) formed at the Early Jurassic, which provides convincing evidence for a previously unrecognized Early Jurassic Fe–Sn metallogenic event in SCB. Geochemical data show that the Shibei granite has high SiO2, Nb, Zr + Nb + Ce + Y concentrations and high Ga/Al ratio, but low Y/Nb ratio, which are similar to those of A1-type granite. The large range of zircon εHf(t) values (−2.4 to +3.4), negative correlation between zircon εHf(t) and δ18O values, and unique whole-rock Sr–Nd isotopic compositions (εNd(t) = −3.3 to −3.7; ISr = 0.7063 – 0.7085) suggest that the Shibei granite is likely to originate from a mixed source of pre-existing crust and juvenile material with OIB-like isotopic composition. Combining with the spatial distribution of the volcanic–intrusive rocks, sedimentary basins, and tectonic deformation styles, we suggest that the Early Jurassic Fe–Sn mineralization occurred in an extensional environment, which was probably linked to the post-orogenic collapse of the Indosinian orogeny between the SCB and Indochina Block.

Geodetic implications on block formation and geodynamic domains in the South Shetland Islands, Antarctic Peninsula

The South Shetland Islands archipelago is dynamically complex due to its tectonic surroundings. Most islands are part of a formerly active volcanic arc, although Deception, Penguin and Bridgeman Islands, as well as several submarine volcanoes, are characterized by active back-arc volcanism. Geodetic benchmarks were deployed and the movement of the lithosphere to which they were fixed measured to provide geodynamic insight for the South Shetland Islands, Bransfield Basin and Antarctic Peninsula area based on surface deformation. These benchmarks' data add spatial and temporal coverage to previous results. The results reveal two different geodynamic patterns, each confined to a distinct part of the South Shetland Islands archipelago. The inferred absolute horizontal velocity vectors for the benchmarks in the northeastern part of the archipelago are consistent with the opening of the Bransfield Basin, while benchmark vectors in the southwestern part of the archipelago are similar to those of the benchmarks on the Antarctic Peninsula. In between, Snow, Deception and Livingston Islands represent a transition zone. In this area, the horizontal velocity vectors relative to the Antarctic plate shift northeastwards from N to NW. Furthermore, the South Shetland Islands benchmarks, except for that at Gibbs (Elephant) Islands, indicate subsidence, which might be a consequence of the slab roll-back at the South Shetland Trench. In contrast, the uplift revealed by the Antarctic Peninsula benchmarks suggests glacial isostatic adjustment after the Larson B ice-shelf breakup.

Present-day geodynamics of the northern North American Cordillera

Diffuse continental deformation results from interactions at plate boundaries, buoyancy forces generated by gradients in gravitational potential energy, and loads applied to the base of the lithosphere. Using finite element models, we calculate a deviatoric stress field associated with buoyancy forces, and then perform an iterative inversion to calculate deviatoric stress fields associated with boundary forces in the northern North American Cordillera. Our results reveal the presence of two distinct geodynamic domains. In the outboard domain, approximately equal magnitudes of boundary and buoyancy forces can account for the observed deformation along the Aleutian megathrust. In contrast, large boundary forces related to subduction of the Pacific and Yakutat slabs dominate the force-balance in south-central Alaska and combine with relatively small buoyancy forces to reproduce the observed kinematic indicators. In the inboard domain, encompassed by interior and northern Alaska and western Canada, boundary and buoyancy forces alone cannot reproduce the observed deformation. Therefore, we infer that deviatoric stresses due to basal tractions from a deeper mantle convection cell contribute to surface deformation in the inboard domain. Low effective lithospheric viscosity in south-central Alaska and the balancing effect of an independent geodynamic system driven by basal tractions in northern Alaska combine to confine the anomalously large Yakutat-related boundary deviatoric stresses to south-central Alaska. Deviatoric stresses associated with flat-slab subduction of the Yakutat microplate are a factor of two greater than boundary force estimates for the Andean and Indian–Eurasian convergent margins, where buoyancy and boundary forces are roughly equal in magnitude and dominate the force-balance.

A geological synthesis of the Precambrian shield in Madagascar

Available U–Pb geochronology of the Precambrian shield of Madagascar is summarized and integrated into a synthesis of the region’s geological history. The shield is described in terms of six geodynamic domains, from northeast to southwest, the Bemarivo, Antongil–Masora, Antananarivo, Ikalamavony, Androyan–Anosyan, and Vohibory domains. Each domain is defined by distinctive suites of metaigneous rocks and metasedimentary groups, and a unique history of Archean (∼2.5Ga) and Proterozoic (∼1.0Ga, ∼0.80Ga, and ∼0.55Ga) reworking. Superimposed within and across these domains are scores of Neoproterozoic granitic stocks and batholiths as well as kilometer long zones of steeply dipping, highly strained rocks that record the effects of Gondwana’s amalgamation and shortening in latest Neoproterozoic time (0.560–0.520Ga).The present-day shield of Madagascar is best viewed as part of the Greater Dharwar Craton, of Archean age, to which three exotic terranes were added in Proterozoic time. The domains in Madagascar representing the Greater Dharwar Craton include the Antongil–Masora domain, a fragment of the Western Dharwar of India, and the Neoarchean Antananarivo domain (with its Tsaratanana Complex) which is broadly analogous to the Eastern Dharwar of India. In its reconstructed position, the Greater Dharwar Craton consists of a central nucleus of Paleo-Mesoarchean age (>3.1Ga), the combined Western Dharwar and Antongil–Masora domain, flanked by mostly juvenile “granite–greenstone belts” of Neoarchean age (2.70–2.56Ga). The age of the accretionary event that formed this craton is approximately 2.5–2.45Ga. The three domains in Madagascar exotic to the Greater Dharwar Craton are the Androyan–Anosyan, Vohibory, and Bemarivo. The basement to the Androyan–Anosyan domain is a continental terrane of Paleoproterozoic age (2.0–1.78Ga) that was accreted to the southern margin (present-day direction) of the Greater Dharwar Craton in pre-Stratherian time (>1.6Ga), and rejuvenated at 1.03–0.93Ga with the creation of the Ikalamavony domain. The Vohibory domain, an oceanic terrane of Neoproterozoic age was accreted to the Androyan–Anosyan domain in Cryogenian time (∼0.63–0.60Ga). The Bemarivo domain of north Madagascar is a terrane of Cryogenian igneous rocks, with a cryptic Paleoproterozoic basement, that was accreted to the Greater Dharwar Craton in latest Ediacaran to earliest Cambrian time (0.53–0.51Ga).

How much confidence can be conferred on tectonic maps of continental shelves? The Cantabrian-Fault case

The Cantabrian Fault is a long-lived crustal fault, 320 km long on land and extending more than 150 km seawards within the Bay of Biscay, which separates different geodynamic domains. Due to its sub-vertical dip and late strike slip movement is poorly evidenced in the shelf and it has been traditionally mapped following the strike of the deepest submarine canyon in the north Atlantic (~4.600 m drop). Based on multichannel reflection data, seismicity from a thirty year period, a GIS model, and the support of detailed field mapping onshore, the fault has been traced more accurately. Surprisingly, it presents a much more E-W strike than mapped before, and shows a splay fault termination never previously assessed. Moreover, the fault acts as a seismic barrier within the actual stress field of Iberia. Collaterally, a large submarine landslide (2000 km2) associated with its seismicity has been discovered, providing a further argument to support the newly proposed trace of the fault.

Multidisciplinary study of the Tindari Fault (Sicily, Italy) separating ongoing contractional and extensional compartments along the active Africa–Eurasia convergent boundary

The Africa–Eurasia convergence in Sicily and southern Calabria is currently expressed by two different tectonic and geodynamic domains: the western region, governed by a roughly N–S compression generated by a continental collision; the eastern one, controlled by a NW–SE extension related to the south-east-directed expansion of the Calabro–Peloritan Arc. The different deformation pattern of these two domains is accommodated by a right-lateral shear zone (Aeolian–Tindari–Letojanni fault system) which, from the Ionian Sea, north of Mt. Etna, extends across the Peloritani chain to the Aeolian Islands.In this work, we study the evidence of active tectonics characterizing this shear zone, through the analysis of seismic and geodetic data acquired by the INGV networks in the last 15years. The study is completed by structural and morphological surveys carried out between Capo Tindari and the watershed of the chain. The results allowed defining a clear structural picture depicting the tectonic interferences between the two different geodynamic domains. The results indicate that, besides the regional ~N130°E horizontal extensional stress field, another one, NE–SW-oriented, is active in the investigated area. Both tension axes are mutually independent and have been active up to the present at different times. The coexistence of these different active horizontal extensions is the result of complex interactions between several induced stresses: 1) the regional extension (NW–SE) related to the slab rollback and back-arc extension; 2) the strong uplift of the chain; 3) the accommodation between compressional and extensional tectonic regimes along the Aeolian–Tindari–Letojanni faults, through a SSE–NNW right-lateral transtensional displacement. In these conditions, the greater and recurring uplift activity is not able to induce a radial extensional dynamics, but, under the “directing” action of the shear system, it can only act on the regional extension (NW–SE) and produce the second system of extension (NE–SW).

Regional and global changes around the Triassic–Jurassic boundary reflected in the late Norian–Hettangian history of the Apennine basins

Palaeogeographic restorations for the Late Triassic and Early Jurassic of the west-Mediterranean area show that significant facies changes occurred in this period. The study of three basinal successions in the Northern, Central and Southern Apennines indicates that changes in ecological conditions occurred at the same time in different palaeogeographic and geodynamic domains. The early Mesozoic evolution of the Apennines is controlled by the opening of two oceans: the Ionian/East-Mediterranean Tethys to the south-east and the Alpine Ocean to the north-west. The Lagonegro basin, in the Southern Apennines, was the northern continental margin of the Ionian Tethys from the Triassic, while the La Spezia basin, in the Northern Apennines, became part of the south-eastern continental margin of the Alpine Ocean in the Middle-Late Jurassic. The third studied basin (Mt. Camicia basin, in the Gran Sasso, Central Apennines) was an intra-platform basin from the early Norian up to the late Hettangian–early Sinemurian. During the Norian–Hettangian period these basins were not directly connected to each other, being separated by wide carbonate platforms, and show different evolutionary trends. Stratigraphic studies in these successions place the Triassic–Jurassic boundary in 6–8 m thick intervals with anoxic facies in the three basins. Relevant facies changes are also recorded in the late Norian: in the Northern Apennines the sedimentation of sulphate evaporites ended, being replaced by the Rhaetavicula contorta facies; whilst in the Southern Apennines (Lagonegro basin) the deposition of radiolarites began. The end of evaporite accumulation can be explained by a climate change from arid to humid conditions, and it is also probably linked to an extensional phase preceding the Jurassic rifting of the Alpine Ocean, and may therefore have a regional significance. Nevertheless, it corresponds to the spread of the R. contorta facies into other parts of southern Europe, from France to Germany and Austria. The beginning of radiolaritic sedimentation in the Lagonegro basin could be related to the rise of atmospheric CO 2 content, linked to volcanic activity in the Ionian ridge. These facies changes reflect changes of environmental conditions, that caused the decline of some fossil associations favoring the development of opportunistic forms, e.g. Triasina hantkeni. The end-Triassic extinction, coupled with an anoxic episode in all the examined basins, immediately preceded a new environmental change, documented by the recovery of the carbonate platforms with oolitic facies and different associations. The evolution of all these basins suggests that geodynamics were probably responsible for regional events and that, at certain moments, development reflected global effects as a response to new connections between formerly different domains. The Central Atlantic Magmatic Province (CAMP) volcanism, considered as one of the possible causes for the end Triassic mass extinction, would have had even greater importance if coupled with the volcanism linked to the rifting of the Ionian Tethys.

Building neural network forecasting models from time series ARIMA models: A procedure and a comparative analysis

A procedure for designing a multilayer perceptron for predicting time series is proposed. It is based on the generation, according to a set of rules emerging from an ARIMA model previously fitted, of a set of nonlinear forecasting models. These rules are extracted from the set of non-zero coefficients in the ARIMA model, so they consider the autocorrelation structure of the time series. The proposed procedure is intended to help the user in the task of specifying as simple models as possible, providing an unambiguous methodology to construct neural networks for time series forecasting. The performance of this procedure is empirically studied by means of a comparative analysis involving time series from three domains. The first part of the experiment is very extensive and works over 33 time series from the Active Population Survey in Andalusia, Spain. The training of the multilayer perceptron is performed by three different learning rules, incorporating multiple repetitions, and the hidden layer size is determined by means of a grid search. The obtained results show a better performance of these neural network models, in comparison with pure classical statistical techniques, namely ARIMA models and exponential smoothing techniques. These results are confirmed over two more concise studies from the tourist and geodynamic domains, where we graphically illustrate the superiority of the constructed neural networks in long-term forecasting, in comparison with ARIMA models.

Boundary, Hetrogeneity and Collision between the Gondwana and Eurasia Lithosphere in the Tibet-Sanjiang Region, Southwest China: Information from Regional Volcanics : Kaihui Yang, Zengqian Hou & Xuanxue Mo, ed A.K. Sinha, F.P. Sassi & D. Papanikolaou, (A.A. Balkema Publishers), Geodynamic domains in the Alpine-Himalayan Tethys, ISBN 9054107057, 1997, (249–274)

Boundary, Hetrogeneity and Collision between the Gondwana and Eurasia Lithosphere in the Tibet-Sanjiang Region, Southwest China: Information from Regional Volcanics : Kaihui Yang, Zengqian Hou & Xuanxue Mo, ed A.K. Sinha, F.P. Sassi & D. Papanikolaou, (A.A. Balkema Publishers), Geodynamic domains in the Alpine-Himalayan Tethys, ISBN 9054107057, 1997, (249–274)

SKS-wave splitting and upper mantle structure: results in the Southern Apennines

Shear wave splitting measures at six temporary stations in the Southern Apennines are computed analyzing fifteen events recorded during the spring and summer 1996, with magnitude greater than 5.8. The splitting parameters were measured using Silver and Chan's (1991) method only on SKS and SKKS phases. Evidence for strong seismic anisotropy was found at all the stations: delay times dt are generally larger than 1.5 s and fast directions Ø are quite variable in different geodynamic domains. NW-SE Ø average directions are found at stations on the mountain belt while at stations on the foredeep and foreland Ø is on average N-S. Changes in splitting parameters may be related to upper mantle structure, and particularly to the geometry of a fragmented lithosphere subducting beneath the Apennines.

Geodynamic setting of the mineral deposits of the Urals

The first-order geodynamic domains of the Uralide orogen constitute a relatively simple pattern across the orogenic belt. Continental rifting along the western margin is expressed by a system of Vendian-early Palaeozoic structures with shale-hosted siderite and magnesite and basalt-hosted base metals. It is superimposed on a Middle Riphean rift system with layered mafic-ultramafic complexes with chromite and ilmenite-titano-magnetite and subordinate ophiolite massifs with gold and magnetite. An oceanic spreading domain, immediately east of the Main Uralian Fault is associated with chromite, titano-magnetite and massive sulphide deposits (Dombarovsky or Cyprus type). Further east, bimodal volcanic associations in island arcs with oceanic crust have formed copper-zinc massive volcanic sulphide deposits (Uralian type). Subsequently, complex volcanic sulphide deposits are associated with belts of andesite-dacite and co-magmatic diorite (Baymak or Kuroko type). The eastern, destructive, margin of the orogen is characterized by magnetite and copper-magnetite skarns and porphyry systems. Relatively small plagiogranite to granodiorite complexes, related to oceanic crust, carry scheelite and gold. Calc-alkaline granitic massifs have formed associations of tungsten, tantalum and beryllium. This pattern was dissected by major thrusts and transcurrent shear zones. Increased fluid activity in the course of deformation, inferred to have been involved in complex multi-phase gold mineralization was most probably controlled by deep-reaching faults and shears. Although the recognition of the first-order domains represents a guideline for exploration, detailed structural geological studies of the kinematics of the major faults and shear zones are required in conjunction with radiometric dating of suitable fault- and ore-associated minerals, in association with on-going deep-reaching geophysical investigations.