scholarly journals Interaction of B-rich supercritical magmatic fluids with granite: first report of dumortierite in Larderello, Italy

2019 ◽  
Vol 98 ◽  
pp. 01042
Author(s):  
Mariano Puxeddu
Keyword(s):  
Fluid Inclusions ◽  
Lower Crust ◽  
Extensional Tectonics ◽  
The West ◽  
Average Composition ◽  
Lithosphere Thinning ◽  
Synthetic Fluid Inclusions ◽  
Magmatic Fluids ◽  
Western Side ◽  
Roll Back

In a peraluminous two-mica monzogranite cored at 4.5 km depth in well Radicondoli 29, dumortierite occurs together with andalusite, Li-rich tourmaline, fluorite and fluorapatite. The average composition is SiO2: 30.9, Al2O3: 58.6, FeO: 0.44, MgO: 0.47, CaO: 0.02, F: 0.15. Dumortierite crystallized from supercritical magmatic fluids at T =520-620°C, P = 100 ± 30 MPa. Synthetic fluid inclusions yielded T = 510 ± 10°C, P = 42 ±3 MPa at 2.9 km depth in well Venelle 2. All data suggest present-day T = 450-550°C, P = 40-80 MPa. The supercritical magmatic fluids were hypersaline brines with ~ 30 wt % LiCl and up to 2.4 wt % F, extreme contents that can be found only in pegmatites, aplites and leucogranites. Larderello granites derived from partial melting of a lower crust made up of interlayered metasediments and amphibolites. Extensive melting took place in the lower crust during the last 10 Ma owing to extensional tectonics, lithosphere thinning, roll back or break down of the west merging Adria plate and swelling of the asthenosphere below the western side of the Apennines.

Dynamics of the extension in the Fonualei Rift in the northern Lau Basin at 16 °S

2021 ◽  
Author(s):  
Anna Jegen ◽  
Anke Dannowski ◽  
Heidrun Kopp ◽  
Udo Barckhausen ◽  
Ingo Heyde ◽  
...  
Keyword(s):  
Velocity Gradient ◽  
Lower Crust ◽  
Pacific Plate ◽  
P Wave ◽  
Upper Crust ◽  
Lau Basin ◽  
Australian Plate ◽  
The Pacific ◽  
Refraction Seismic ◽  
Roll Back

<p>The Lau Basin is a young back-arc basin steadily forming at the Indo-Australian-Pacific plate boundary, where the Pacific plate is subducting underneath the Australian plate along the Tonga-Kermadec island arc. Roughly 25 Ma ago, roll-back of the Kermadec-Tonga subduction zone commenced, which lead to break up of the overriding plate and thus the formation of the western Lau Ridge and the eastern Tonga Ridge separated by the emerging Lau Basin.</p><p>As an analogue to the asymmetric roll back of the Pacific plate, the divergence rates decline southwards hence dictating an asymmetric, V-shaped basin opening. Further, the decentralisation of the extensional motion over 11 distinct spreading centres and zones of active rifting has led to the formation of a composite crust formed of a microplate mosaic. A simplified three plate model of the Lau Basin comprises the Tonga plate, the Australian plate and the Niuafo'ou microplate. The northeastern boundary of the Niuafo'ou microplate is given by two overlapping spreading centres (OLSC), the southern tip of the eastern axis of the Mangatolu Triple Junction (MTJ-S) and the northern tip of the Fonualei Rift spreading centre (FRSC) on the eastern side. Slow to ultraslow divergence rates were identified along the FRSC (8-32 mm/a) and slow divergence at the MTJ (27-32 mm/a), both decreasing southwards. However, the manner of divergence has not yet been identified. Additional regional geophysical data are necessary to overcome this gap of knowledge.</p><p>Research vessel RV Sonne (cruise SO267) set out to conduct seismic refraction and wide-angle reflection data along a 185 km long transect crossing the Lau Basin at ~16 °S from the Tonga arc in the east, the overlapping spreading centres, FRSC1 and MTJ-S2, and extending as far as a volcanic ridge in the west. The refraction seismic profile consisted of 30 ocean bottom seismometers. Additionally, 2D MCS reflection seismic data as well as magnetic and gravimetric data were acquired.</p><p>The results of our P-wave traveltime tomography show a crust that varies between 4.5-6 km in thickness. Underneath the OLSC the upper crust is 2-2.5 km thick and the lower crust 2-2.5 km thick. The velocity gradients of the upper and lower crust differ significantly from tomographic models of magmatically dominated oceanic ridges. Compared to such magmatically dominated ridges, our final P-wave velocity model displays a decreased velocity gradient in the upper crust and an increased velocity gradient in the lower crust more comparable to tectonically dominated rifts with a sparse magmatic budget.</p><p>The dominance of crustal stretching in the regional rifting process leads to a tectonical stretching, thus thinning of the crust under the OLSC and therefore increasing the lower crust’s velocity gradient. Due to the limited magmatic budget of the area, neither the magnetic anomaly nor the gravity data indicate a magmatically dominated spreading centre. We conclude that extension in the Lau Basin at the OLSC at 16 °S is dominated by extensional processes with little magmatism, which is supported by the distribution of seismic events concentrated at the northern tip of the FRSC.</p>

Metastability at cryometry of sulfate-containing synthetic fluid inclusions

2008 ◽  
Vol 420 (1) ◽  
pp. 697-699 ◽  
Author(s):  
Z. A. Kotel’nikova ◽  
A. R. Kotel’nikov
Keyword(s):  
Fluid Inclusions ◽  
Synthetic Fluid Inclusions

A Saxon treasure hoard found at Chester, 1950

1953 ◽  
Vol 33 (1-2) ◽  
pp. 22-32 ◽  
Author(s):  
Graham Webster ◽  
R. H. Dolley ◽  
G. C. Dunning
Keyword(s):  
The South ◽  
The West ◽  
West Side ◽  
North Wales ◽  
Western Side ◽  
Girls School ◽  
The City

On 29th November 1950 workmen employed by the Merseyside and North Wales Electricity Board were relaying a cable on the west side of Castle Esplanade, Chester. In cleaning up the western side of the trench with a spade, 18 in. below the present pavement level and 29 ft. to the south of St. Martin's Court, one of the men cut through a small earthenware vessel and a shower of coins and silver bullion poured into the bottom of the trench. It is distressing to record that although the Grosvenor Museum is only 100 yards from the site, the discovery was not reported. No significance was attached to the find; one of the men stated later that they thought they were milk checks. Three of the men put handfuls of coins into their pockets; others were distributed to children near, and the rest shovelled back into the trench. The engineer-in-charge took several to his office for thepurpose of identification, but later forgot about them. One of the men sent some of the coins to Hunter Street Girls' School, by his niece, for identification, and the mistress immediately sent them to the Curator of the Grosvenor Museum.This happened on 10th December, and the Curator at once appreciating the significance of the discovery, set to work to recover as much as possible of the hoard, and reported the matter to the City Coroner. As a result he recovered a hundred coins, twelve ingots of silver, and a fragment of the vessel.

Integrated Geophysical Interpretation of Kerio Valley Basin Stratigraphy, Kenya Rift

2016 ◽  
Author(s):  
Godfred Osukuku ◽  
Abiud Masinde ◽  
Bernard Adero ◽  
Edmond Wanjala ◽  
John Ego
Keyword(s):  
Gravity Data ◽  
Gravity Anomalies ◽  
Fault System ◽  
Magnetic Data ◽  
Data Sets ◽  
Seismic Profiles ◽  
The West ◽  
Seismic Reflection Data ◽  
Basement Rocks ◽  
Western Side

Abstract This research work attempts to map out the stratigraphic sequence of the Kerio Valley Basin using magnetic, gravity and seismic data sets. Regional gravity data consisting of isotactic, free-air and Bouguer anomaly grids were obtained from the International Gravity Bureau (BGI). Magnetic data sets were sourced from the Earth Magnetic Anomaly grid (EMAG2). The seismic reflection data was acquired in 1989 using a vibrating source shot into inline geophones. Gravity Isostacy data shows low gravity anomalies that depict a deeper basement. Magnetic tilt and seismic profiles show sediment thickness of 2.5-3.5 Km above the basement. The Kerio Valley Basin towards the western side is underlain by a deeper basement which are overlain by succession of sandstones/shales and volcanoes. At the very top are the mid Miocene phonolites (Uasin Gishu) underlain by mid Miocene sandstones/shales (Tambach Formation). There are high gravity anomalies in the western and southern parts of the basin with the sedimentation being constrained by two normal faults. The Kerio Valley Basin is bounded to the west by the North-South easterly dipping fault system. Gravity data was significantly of help in delineating the basement, scanning the lithosphere and the upper mantle according to the relative densities. The basement rocks as well as the upper cover of volcanoes have distinctively higher densities than the infilled sedimentary sections within the basin. From the seismic profiles, the frequency of the shaley rocks and compact sandstones increases with depths. The western side of the basin is characterized by the absence of reflections and relatively higher frequency content. The termination of reflectors and the westward dip of reflectors represent a fault (Elgeyo fault). The reflectors dip towards the west, marking the basin as an asymmetrical syncline, indicating that the extension was towards the east. The basin floor is characterized by a nearly vertical fault which runs parallel to the Elgeyo fault. The seismic reflectors show marked discontinuities which may be due to lava flows. The deepest reflector shows deep sedimentation in the basin and is in reasonable agreement with basement depths delineated from potential methods (gravity and magnetic). Basement rocks are deeper at the top of the uplift footwall of the Elgeyo Escarpment. The sediments are likely of a thickness of about 800 M which is an interbed of sandstones and shales above the basement.

Grim's Bank, Padworth, Berkshire

Antiquity ◽  
1943 ◽  
Vol 17 (68) ◽  
pp. 188-195
Author(s):  
B. H. St. J. O'Neil
Keyword(s):  
The Other ◽  
Present Writer ◽  
Recent Past ◽  
The West ◽  
The Road ◽  
The North ◽  
Northern Side ◽  
Western Side

The immediate environs of Silchester consist of fields, which are either now under plough or else have been arable for many years in the recent past. Consequently there are few, if any, traces there of the Roman roads which led from the various gates to Dorchester, Speen and Cirencester, Sarum, Winchester, and London. A mile or more to the north and northwest of the Roman town, however, there is a belt of land, which is largely heathland except where trees have been planted. Here there are clear indications of the line of two Roman roads, one from the west gate, west-northwest to Speen and Cirencester, the other from the north gate to Dorchester (Oxon.)The road to Speen (FIG. I) was formerly thought to follow closely the modern road along the northern side of Silchester Common and thence to run along the straight county boundary between Berkshire and Hampshire. In recent years, however, Mr O. G. S. Crawford has shown that the road, instead of following this traditional line, ran west-northwestward to cross the river Kennet near Brimpton Mill. It is traceable as a raised camber or a deep hollow way from Catthaw Lands Copse, about half-a-mile from the west gate of Silchester, to the western side of Hungry Hill. Further west, in Decoy Plantation, and again beyond the road from Padworth Common, i.e. in Keyser's Plantation, it is clearly seen as a broad cambered way (o.s. 641-1. Berkshire XLIV, SE, Hampshire IV, SE). Beyond this point the present writer has not followed it, but Mr Crawford has noted its continuation.

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