Resurgent uplift at large calderas and relationship to caldera-forming faults and the magma reservoir: new insights from the Neapolitan Yellow Tuff caldera (Italy)

<p>Resurgence uplift is the rising of the caldera floor, mainly due to pressure or volume changes in the magma reservoir. Identifying resurgence structures and understanding their relationship to the magmatic reservoir is challenging. We investigate the resurgence structures of the Neapolitan Yellow Tuff (NYT) caldera (Italy) by integrating bathymetric data, high-resolution seismic profiles and Differential Synthetic-Aperture Radar Interferometry data. Our results show that the resurgent area is manifested as 1) a central dome constituted by two main blocks bounded by NNE-SSW trending faults, 2) an apical graben developed on top of the most uplifted block, 3) a peripheral zone including several uplifted and tilted blocks, bounded by inward-dipping faults. The onset of the uplift of the central dome occurred through re-activation, in reverse motion, of normal faults formed during the caldera collapse, and located in the peripheral zone. During periods of unrests, the blocks of the central dome move independently at different velocities, and the peripheral zone accommodates the deformation. The restless behaviour of the NYT caldera is the result of a shallow magmatic reservoir located at 3.5 ± 0.7 km, and characterised by a width that roughly corresponds to the extension of the overlaying resurgent area. Defining the caldera-forming fault system and identifying the area involved by the resurgence is crucial for estimating depth and width of the magma reservoir, and predicting the caldera behaviour during periods of unrest by localising possible vents and sectors that will deform. This knowledge contributes to the evaluation of the volcanic hazard.</p>

Zirconology of syenites of the Northern Timan

Northern Timan is an uplifted block of the Upper Precambrian basement of the Timan Ridge, where intrusive rocks of various compositions cut Neoproterozoic metaterrigenous rocks of the Barmin Group and are overlain by Lower Silurian limestone. Syenites are widespread in the Cape Bolshoy Rumyanichny pluton and compose the Krayny Kameshek and Malyi Kameshek plutons. To determine the age of the syenites, U—Pb dating of zircons was carried out using secondary ion mass spectrometry (SIMS). The age of zircons from syenite of the Cape Bolshoy Rumyanichny pluton is 613 ± 7 Ma, Krayny Kameshek pluton — 602 ± 5 Ma, and Malyi Kameshek pluton — 598 ± 17 Ma. Similar zircon ages are known for other alkaline igneous rocks that occur within the Cape Bolshoy Rumyanichny pluton: olivine-kersutite gabbro — 614 ± 2 Ma, granites — 614 ± 11 Ma. Zircons from subalkaline granites of the Bolshoy Kameshek pluton are of the same age — 613 ± 6 Ma. The location of the plutons in the area of the Late Riphean passive margin of Baltica, the close association of subalkaline and alkaline granites, syenites, and alkaline gabbros indicate the anorogenic nature of these magmatic rocks and possible relationship with mantle plume activity. Ediacaran magmatic rocks of 614—600 Ma located in the Northern Timan could be associated with the final stages of Rodinia breakup, accompanied by plume-related magmatism, the products of which are also known in the eastern part of Laurentia and in the Scandinavia.

Paleoenvironmental reconstructions and a sedimentological evidence of paleoseismic activity ca 9000 yr BP in Karelia, NW Russia, based on lake sediment studies on Mount Vottovaara

Karelia, like the entire Fennoscandian Shield, is a region with a low seismic activity. An example of the best-studied locality is a paleoseismic dislocation on Mount Vottovaara, which bears traces of disastrous Holocene geological events following the degradation of the last ice sheet. The evolution of the study area falls into three stages. At pre-Quaternary stage I, an uplifted block broken by numerous fractures and faults was formed. At glacial stage II, coarse clastic moraine was formed, the moving ice polished the crystalline basement surface and glacial scars were formed. At final deglaciation stages, the mountain top remained a nunatak. As Salpausselkä II marginal sediments retreated by about 70 km from the mountain, a postglacial stage in the region’s evolution, at which an earthquake occurred, began. It could have been triggered mainly by the consequences of the degradation of the Late Weischelian glaciations such as the rapid removal of the glacial load that contributed to the rejuvenation of various old faults. Changes in paleoecological conditions for the Mount Vottovaara area were reconstructed based on the results of lithological, palynological, diatom and radiocarbon studies of bottom sediments from a small lake on the mountain top. Vegetation dynamics from the Younger Dryas to the Subboreal period is presented. Small lake evolution stages were distinguished based on analysis of diatom complexes and the pollen and spores of aquatic and aquatic-subaquatic plants and Pediastrum algae. The data obtained show that minerogenic sediments were abruptly succeeded by organic in the late Preboreal-early Boreal period. The thickness of Boreal sediments and changes in the composition of diatom complexes and spore-and-pollen spectra suggest a depositional hiatus triggered by a strong earthquake which changed the water level of the pond and its basin structure. The earthquake is also indicated by numerous dismembered, displaced, thrown-away and shifted rock blocks and seismogravity downfalls. Deflation and other types of weathering are responsible for the formation of seide-shaped piles of blocks and boulders on the mountain top.

A new Middle–Upper Jurassic succession on Hold with Hope, North-East Greenland

A succession of marine, Jurassic sediments was recently discovered on Hold with Hope, NorthEast Greenland. The discovery shows that the area was covered by the sea during Middle–Late Jurassic transgressive events and thus adds to the understanding of the palaeogeography of the area. The Jurassic succession on northern Hold with Hope is exposed in the hangingwalls of small fault blocks formed by rifting in Late Jurassic – Early Cretaceous times. It unconformably overlies Lower Triassic siltstones and sandstones and is overlain by Lower Cretaceous coarsegrained sandstones with an angular unconformity. The succession is up to 360 m thick and includes sandstones of the Lower–Upper Callovian Pelion and Middle–Upper Oxfordian Payer Dal Formations (Vardekløft Group) and heteroliths and mudstones of the Upper Oxfordian – Lower Kimmeridgian Bernbjerg Formation (Hall Bredning Group). The Pelion Formation includes the new Spath Plateau Member (defined herein). The palaeogeographic setting was a narrow rift-controlled embayment along the western margin of the rifted Jurassic seaway between Greenland and Norway. It was open to marine circulation to the south as indicated by the distribution and lateral facies variations and a dominant south-westwards marine palaeocurrent direction. The Pelion and Payer Dal Formations represent upper shoreface and tidally influenced delta deposits formed by the migration of dunes in distributary channels and mouthbars over the delta front. The boundary between the two formations is unconformable and represents a Late Callovian – Middle Oxfordian hiatus. It is interpreted to have formed by subaerial erosion related to a sea-level fall combined with minor tilting of fault blocks and erosion of uplifted block crests. In Late Jurassic time, the sand-rich depositional systems of the Pelion and Payer Dal Formations drowned and offshore transition – lower shoreface heteroliths and offshore mudstones of the Bernbjerg Formation accumulated. The fault block crest forming the eastern basin margin was inundated by a rise in relative sea level. Major fault activity probably occurred in latest Jurassic – Early Cretaceous times when the major fault block originally defining the Hold with Hope basin was split into smaller blocks.

The effect of Quaternary uplift on the stability of slopes in the central part the Skorusinske Vrchy mountains in the west Carpathians

The Skorušinské vrchy mountains are part of the West Carpathians in northwest Slovakia near the Polish border. They consist of four Palaeogene sedimentary complexes and comprise a 1500 to 2000 m thick sequence of conglomerates, claystones, flyschoid rocks and sandstones. The older complexes erop out on the margins of the mountains and are covered by relatively thin clayey soils. The central part, the most highly uplifted block, consists of Eocene calcareous sandstone which are disturbed by joints and deep-seated faults. The difference in elevation between the mountain summits and the valley floors is more than 400 m.A detailed investigation of mass movement has been carried out using aerial photographs,air borne radar and satellite imagery foliowed by a field survey.Three main types of slope deformation were identified - rock block slides along bedding surfaces, rock siumps across bedding surfaces and landslides in slope debris. The occurrence of the largest and most deep-seated slides are controlled by faults. The presence of these mass deformations indicate the existence of tilted fault blocks which are the result of neotectonic arch uplift. About 15–17% of the area covered by sandstones is affected by mass movements. This paper describes the methodology of the investigation, the mechanism and genesis of slope deformations, the occurrence and parameters of slides and the role of the Quaternary uplift in the slope instability component of regional geomorphological evolution.

The Pontiac problem, Quebec–Ontario, in the light of gravity data

A belt of Archean quartzose metasedimentary gneisses with minor mafic volcanic rocks (the Pontiac Group) lies south of the Blake River and older Archean mafic volcanic rocks of the Abitibi Greenstone Belt, and is separated from them by the Larder Lake – Cadillac Break. To the west of the Pontiac Group, on strike, is the Archean Larder Lake Group of turbidite conglomerate, argillite, limestone, and iron formation with abundant mafic flows and intrusions. These strata also lie south of the Larder Lake – Cadillac Break and south of the Blake River and older Archean mafic volcanic rocks. The western contact between the Pontiac and Larder Lake groups is covered by a narrow north–south strip of Proterozoic Cobalt sedimentary rocks. On the basis of gravity work that compares the Bouguer gravity anomaly gradient across the Cadillac Break with that across the west margin of the Pontiac Group, it is proposed that the Larder Lake and Pontiac groups are separated by a north–south fault and that the Pontiac Group represents a lithologically distinct uplifted block. The Pontiac block may be an Archean terrane.

THE GEOLOGY OF THE WEST TRYAL ROCKS GAS FIELD

The West Tryal Rocks gas field is located offshore at the western margin of the Barrow Sub- basin, in the Carnarvon Basin of Western Australia. It was discovered by West Australian Petroleum Pty Ltd ( WAPET) in 1973 on a southwesterly extension of the Rankin Platform where, farther north, a number of major gas/condensate discoveries have been made by Burmah Oil Company of Australia Ltd (BOCAL) since 1971.The productive structure at West Tryal Rocks lies at a depth of 3200 m in about 150 m of water. It consists of an elongate north - trending uplifted block of Triassic and possibly Lower Jurassic reservoir rocks called the Mungaroo Beds.The block is unconformably capped by the Lower Cretaceous Muderong Shale which also provides the lateral seal across the bounding faults. The reservoir section dips to the north at a greater rate than does the sealing unconformity so that progressively younger pre-Cretaceous sediments subcrop the unconformity in that direction.Shales of Middle to Late Jurassic age in the Barrow Sub-basin to the east are believed to be the primary source of hydrocarbons, although the overlying Muderong Shale cannot be ruled out.Three main gas-bearing sands have been encountered by the two wells drilled to date. The second well was drilled up-structure from the first and penetrated 144 m of net gas pay of which 133 m is contained in the three sands. The sands are mainly medium to very coarse grained and possess good porosity and permeability.Preliminary reoervvs estimates indicate that the field contains in excess of 28 x 109 m3 (1 x 1012 ft3) of gas (Playford, 1975).The West Tryal Rocks gas field is unique compared to the other Northwest Shelf fields, in that it is slightly overpressured and contains up to 28% of non-combustible gases - predominantly carbon dioxide and nitrogen. Additionally, the field possesses relatively fresh underlying formation waters with high concentrations of bicarbonate ions.

Geology of Belle Isle—northern extremity of the deformed Appalachian miogeosynclinal belt

Belle Isle, situated between northern Newfoundland and the southeast coast of Labrador, consists of an uplifted block of Precambrian plutonic rocks intruded by northeast-trending diabase dikes and uncomformably overlain by Lower Cambrian and earlier (?) sedimentary and volcanic rocks. The Precambrian rocks lie along strike and are similar to Grenville gneisses of the Long Range Complex of western Newfoundland. In the southwest part of Belle Isle, the cover rocks are gently dipping basaltic flows and agglomerates that are succeeded conformably by arkosic sandstones and fossiliferous upper Lower Cambrian shales. In the northeast, the basement rocks are overlain by steeply dipping boulder conglomerates and arkosic sandstones, followed conformably by white quartzites.Diabase dikes are inseparable from overlying flows, but do not penetrate higher sedimentary strata of the southwestern Lower Cambrian succession. Toward the northeast, plutonic boulder conglomerates and quartzites are cut by the dikes.The distribution of supracrustal rocks around the periphery of the island, combined with local steeply inclined surfaces of unconformity between basement and cover rocks, indicate a major anticlinal structure produced by Paleozoic deformation. The study also shows that at Belle Isle the established Lower Cambrian succession of southeast Labrador and western Newfoundland is locally underlain by basalts and conglomerates and quartzites that thicken southeastward and northeastward.