An example of in situ granite formation in the northern boundary of the Proterozoic Sergipano fold belt, NE Brazil: the Xingó Complex

1995 ◽  
Vol 8 (3-4) ◽  
pp. 341-354 ◽  
Author(s):  
I.P. Guimarães ◽  
A.F. Da Silva Filho
Keyword(s):  
Fold Belt ◽  
Northern Boundary ◽  
Granite Formation

The mistletoe flora of southern Western Australia, with a particular reference to host relationships and fire

2015 ◽  
Vol 63 (8) ◽  
pp. 636 ◽  
Author(s):  
A. N. Start
Keyword(s):  
Western Australia ◽  
Urban Areas ◽  
Fire Management ◽  
Seed Storage ◽  
The South ◽  
Northern Boundary ◽  
South West ◽  
Sclerophyll Forest ◽  
Host Relationships

The mistletoe flora of southern Western Australia was studied over a 30-year period with a particular emphasis on distributions, host relationships and fire. The study area encompassed Western Australia south of ~26° S. It included all the South-west Botanical Province and southern components of the Eremaean Botanical Province, with the northern boundary corresponding with bioregional boundaries. Vegetation ranges from wet and dry sclerophyll forest through woodlands and heaths to deserts. The mistletoe flora comprises 21 taxa, 19 in the Loranthaceae and two in the Santalaceae. They infect 153 species in 25 genera and 15 families. The Fabaceae provides hosts to more taxa than any other family; however, the genus with most host species, Eucalyptus (Myrtaceae), supports only two mistletoe species, one of which barely enters the study area. Melaleuca (also Myrtaceae) is host to seven species. The number of mistletoe species per bioregion ranges from 0 to 18, with 12 species in the seven bioregions of the South-west Botanical Province and 20 in the six bioregions of Eremaean Botanical Province that are within the study area. In both provinces, diversity is lower in coastal areas and higher in more arid, inland areas. Most mistletoe habitats in the study area are fire-prone. One species is probably capable of resprouting whereas all other taxa are obligate seeders. With no means of in situ seed storage, post-fire recovery depends on seed importation. Fire is the most pervasive (but not the only) threatening process operating today. However, fire management in more populous agricultural and urban areas safeguards many populations in the South-west Province.

In situ U–Pb dating and geochemical constraints on UHT metamorphism in the Brasilia fold belt

2006 ◽  
Vol 70 (18) ◽  
pp. A425
Author(s):  
A. Möller ◽  
R. Moraes ◽  
E. Hellebrand ◽  
A. Kennedy ◽  
R.A. Fuck
Keyword(s):  
Fold Belt ◽  
Uht Metamorphism ◽  
Geochemical Constraints

Metamorphic evolution of Palaeoproterozoic anatectic migmatites in the eastern part of the Aravalli–Delhi Fold Belt, India: constraints from thermodynamic modelling and monazite dating

2017 ◽  
Vol 155 (4) ◽  
pp. 955-978 ◽  
Author(s):  
A. PRAKASH ◽  
L. SAHA ◽  
I. PETRIK ◽  
M. JANAK ◽  
A. BHATTACHARYA
Keyword(s):  
Chemical Analyses ◽  
Fold Belt ◽  
Monazite Dating ◽  
The North ◽  
Facies Metamorphism ◽  
Aravalli Supergroup ◽  
Type Granite ◽  
Granite Magmatism ◽  
The One

AbstractGarnetiferous pelitic to psammopelitic migmatites widespread across the central and eastern part of the Aravalli–Delhi Fold Belt in NW India record two distinct orogenies, e.g. the Aravalli Orogeny (1.7–1.6 Ga) and the Delhi Orogeny (1.0 Ga). In this study, we integrate field geological studies with textural and mineral–chemical analyses,P–Tpseudosection modelling andin situmonazite dating in anatectic migmatites in the Aravalli Supergroup occurring along the Deoli–Shahpura segment. The study reveals formation of peak assemblages of garnet + sillimanite + biotite + K-feldspar + melt and garnet + muscovite + K-feldspar + melt in two anatectic migmatite samples.P–Tpseudosection modelling suggests that anatexis in the gneisses occurred at ~8 kbar and 700–800°C along a tight-loop clockwiseP–Tpath. Monazite ages from the migmatites indicate that the anatexis occurred at ~1.73–1.74 Ga. This age is similar to the Palaeoproterozoic anatexis (at 7–8 kbar) and charnockite emplacement in the Sandmata and the Mangalwar complexes, the subsolidus amphibolite-facies metamorphism in the Rajpura–Dariba and Pur–Banera supracrustal belts, and the A-type granite magmatism in the North Delhi Fold Belt. We propose that the Palaeoproterozoic migmatites in central and eastern Rajasthan are part of the one crustal unit that underwent anatexis during an accretion event along the NE–SW-trending Aravalli orogenic belt.

Granite genesis and the mechanics of convergent orogenic belts with application to the southern Adelaide Fold Belt

1992 ◽  
Vol 83 (1-2) ◽  
pp. 83-93 ◽  
Author(s):  
Mike Sandiford ◽  
John Foden ◽  
Shaohua Zhou ◽  
Simon Turner
Keyword(s):  
Numerical Models ◽  
Thin Sheet ◽  
Causative Factor ◽  
Crustal Thickening ◽  
Low Grade ◽  
Strong Temperature Dependence ◽  
Fold Belt ◽  
Lithospheric Deformation ◽  
Granite Formation ◽  
Mechanical Models

ABSTRACTTwo models for the heating responsible for granite generation during convergent deformation may be distinguished on the basis of the length- and time-scales associated with the thermal perturbation, namely: (1) long-lived, lithospheric-scale heating as a conductive response to the deformation, and (2) transient, localised heating as a response to advective heat sources such as mantle-derived melts. The strong temperature dependence of lithospheric rheology implies that the heat advected within rising granites may affect the distribution and rates of deformation within the developing orogen in a way that reflects the thermal regime attendant on granite formation; this contention is supported by numerical models of lithospheric deformation based on the thin-sheet approximation. The model results are compared with geological and isotopic constraints on granite genesis in the southern Adelaide Fold Belt where intrusion spans a 25 Ma convergent deformation cycle, from about 516 to 490 Ma, resulting in crustal thickening to 50–55 km. High-T metamorphism in this belt is spatially restricted to an axis of magmatic activity where the intensity and complexity of deformation is significantly greater, and may have started earlier, than in adjacent low-grade areas. The implication is that granite generation and emplacement is a causative factor in localising deformation, and on the basis of the results of the mechanical models suggests that granite formation occurred in response to localised, transient crustal heating by mantle melts. This is consistent with the Nd- and Sr-isotopic composition of the granites which seems to reflect mixed sources with components derived both from the depleted contemporary mantle and the older crust.

scholarly journals Hydrothermal Fluids and Cold Meteoric Waters along Tectonic-Controlled Open Spaces in Upper Cretaceous Carbonate Rocks, NE-Iraq: Scanning Data from In Situ U-Pb Geochronology and Microthermometry

Water ◽  
2021 ◽  
Vol 13 (24) ◽  
pp. 3559
Author(s):  
Namam Salih ◽  
Howri Mansurbeg ◽  
Philippe Muchez ◽  
Gerdes Axel ◽  
Alain Préat
Keyword(s):  
Fluid Inclusions ◽  
Carbonate Rocks ◽  
Upper Cretaceous ◽  
Age Dating ◽  
Fold Belt ◽  
Open Spaces ◽  
Low Salinity ◽  
Seawater Salinity ◽  
Dating Method

The Upper Cretaceous carbonates along the Zagros thrust-fold belt “Harir-Safin anticlines” experienced extensive hot brine fluids that produced several phases of hydrothermal cements, including saddle dolomites. Detailed fluid inclusion microthermometry data show that saddle dolomites precipitated from hydrothermal (83–160 °C) and saline fluids (up to 25 eq. wt.% NaCl; i.e., seven times higher than the seawater salinity). The fluids interacted with brine/rocks during their circulation before invading the Upper Cretaceous carbonates. Two entrapment episodes (early and late) of FIs from the hydrothermal “HT” cements are recognized. The early episode is linked to fault-related fractures and was contemporaneous with the precipitation of the HT cements. The fluid inclusions leaked and were refilled during a later diagenetic phase. The late episode is consistent with low saline fluids (0.18 and 2.57 eq. wt.% NaCl) which had a meteoric origin. Utilizing the laser ablation U-Pb age dating method, two numerical absolute ages of ~70 Ma and 3.8 Ma are identified from calcrete levels in the Upper Cretaceous carbonates. These two ages obtained in the same level of calcrete indicate that this unit was twice exposed to subaerial conditions. The earlier exposure was associated with alveolar and other diagenetic features, such as dissolution, micritization, cementation, while the second calcrete level is associated with laminae, pisolitic, and microstromatolite features which formed during the regional uplifting of the area in Pliocene times. In conclusion, the hydrothermal-saddle dolomites were precipitated from high temperature saline fluids, while calcrete levels entrapped large monophase with very low salinity fluid inclusions, indicative for a low temperature precipitation from water with a meteoric origin.

Rendez vous with Saturn's rings

1984 ◽  
Vol 75 ◽  
pp. 743-759 ◽  
Author(s):  
Kerry T. Nock
Keyword(s):  
Solar Energy ◽  
Electric Propulsion ◽  
Power Source ◽  
Propulsion System ◽  
Low Thrust ◽  
Ring Plane ◽  
The Earth ◽  
Total Impulse ◽  
Saturn's Rings

ABSTRACTA mission to rendezvous with the rings of Saturn is studied with regard to science rationale and instrumentation and engineering feasibility and design. Future detailedin situexploration of the rings of Saturn will require spacecraft systems with enormous propulsive capability. NASA is currently studying the critical technologies for just such a system, called Nuclear Electric Propulsion (NEP). Electric propulsion is the only technology which can effectively provide the required total impulse for this demanding mission. Furthermore, the power source must be nuclear because the solar energy reaching Saturn is only 1% of that at the Earth. An important aspect of this mission is the ability of the low thrust propulsion system to continuously boost the spacecraft above the ring plane as it spirals in toward Saturn, thus enabling scientific measurements of ring particles from only a few kilometers.

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