Chemical and isotopic systematics of the Caledonian intrusions of Scotland and Northern England: a guide to magma source region and magma-crust interaction

1984 ◽  
Vol 310 (1514) ◽  
pp. 709-742 ◽  
Keyword(s):  
Source Region ◽  
Thermal Conditions ◽  
Magma Source ◽  
Substantial Part ◽  
Upper Crust ◽  
Scottish Highlands ◽  
Late Proterozoic ◽  
Source Regions ◽  
Subducted Oceanic Crust ◽  
Lower Palaeozoic

Chemical and O-, Sr-, Nd-, and Pb-isotope relations for the British Caledonian granitoids exhibit systematic variations that are attributed to derivation from both mantle and crustal sources. The ‘older’ (more than ca . 470 Ma) pre- and syn-tectonic granites were the product of local anatectic melting of Late Proterozoic metasedimentary upper crust (8 18 O æ 8 to 14% 0 , 87 S r/ 86 Sr > 0.710, 206 Pb / 204 Pb « 18.1-19.2) during the peak thermal conditions of the Grampian Orogeny. The ‘younger’ (less than ca . 440 Ma) post-tectonic granitoids have a complex origin which, in individual cases, involved at least four different source regions: (i) the upper mantle or subducted oceanic crust (8 18 O « 5.7 to 7.0%o, 87 Sr/ 86 Sr « 0.7035-0.7040, 206 Pb/ 204 Pb = 17.9 to 18.1) and (ii) Lower Palaeozoic geosynclinal sedimentary upper crust (8 18 O « 11 to 14% 0 , 87 Sr/ 86 Sr « 705-0.711, 206 Pb/ 204 Pb « 18.4) within the paratectonic Caledonides in the Scottish Midland Valley and Southern Uplands and in Northern England or (iii) Middle Proterozoic (?) mafic to intermediate granulitic lower crust (8 18 O « 8 to 10% 0 , 87 Sr/ 86 Sr « 0.705-0.707, 206 Pb / 204 Pb « 16.5-17.0) and (iv) Middle to Late Proterozoic metasedimentary upper crust (8 18 0 « 8 to 14% 0 , 87 Sr/ 86 Sr > 0.710, 206 Pb/ 207 Pb » 18.1-19.2) in the Scottish Highlands. Mantle-derived magmas or their direct derivatives were likely involved in the development of all of the ‘younger’ granitoids, either as end-member components or as the source for a substantial part of the heat required for crustal melting and assimilation. Although the Lower Palaeozoic was a time during which a large amount of igneous material was introduced into the upper crust in Britain, it was not a major crust-forming period because the Caledonian granitoids are dominated by recycled continental crust.

scholarly journals The Fate of Accessory Minerals and Key Trace Elements During Anatexis and Magma Extraction

2020 ◽  
Vol 61 (2) ◽  
Author(s):  
Martin Schwindinger ◽  
Roberto F Weinberg ◽  
Richard W White
Keyword(s):  
Trace Elements ◽  
Partial Melting ◽  
Source Region ◽  
Source Rocks ◽  
Magma Source ◽  
Crustal Evolution ◽  
Upper Crust ◽  
Host Reaction ◽  
Accessory Minerals ◽  
Field Evidence

Abstract Granite genesis and crustal evolution are closely associated with partial melting in the lower or middle crust and extraction of granite magmas to upper crustal levels. This is generally thought to be the leading mechanism by which the upper continental crust became enriched in incompatible components such as the heat-producing elements U and Th through time. However, field evidence from anatectic terrains, the source rocks of granite magmas, raises doubt about the efficiency of this process. Leucosomes and associated leucogranites, representative of melts in such terrains, are often depleted in U, Th and REE compared to their source and therefore unable to enrich the upper crust in these elements. This paper demonstrates using anatectic turbidites exposed on Kangaroo Island that accessory minerals, the main hosts of U, Th and REE, become preferentially concentrated in the melanosomes, effectively removing these elements from the melt. Whole rock geochemistry and detailed petrography suggests that (1) peraluminous melts dissolve only small fractions of monazite and xenotime, because efficient apatite dissolution saturates melt early in phosphorous; and (2) local melt–host reaction emerging from melt migration may cause melt to crystallize in the magma extraction channelways in or close to the magma source region. Crystallization causes oversaturation of the magma triggering crystallization and capture of accessory minerals in the growing biotite-rich selvedge rather than in the melt channel itself. Crystallization of accessory minerals away from the leucosome explains the apparent under-saturation of elements hosted by these accessory minerals in the leucosome and leucogranites. While intense reworking of thick piles of turbidites, common in accretionary orogens, reflect important processes of crustal formation, the fate of accessory phases and the key elements they control, such as the heat producing elements U and Th, are strongly dependent on the interaction between melt and surrounding solids during segregation and extraction.

scholarly journals Melt segregation from partially molten source regions: The importance of melt density and source region size

1981 ◽  
Vol 86 (B7) ◽  
pp. 6261-6271 ◽  
Author(s):  
Edward Stolper ◽  
David Walker ◽  
Bradford H. Hager ◽  
James F. Hays
Keyword(s):  
Source Region ◽  
Source Regions ◽  
Melt Density ◽  
Melt Segregation ◽  
Region Size

scholarly journals Precambrian metamorphic complexes in the East Greenland Caledonices (72°–74°N) – their relationship to the Eleonore Bay Group, and Caledonian orogenesis

1981 ◽  
Vol 104 ◽  
pp. 5-46
Author(s):  
A.K Higgins ◽  
J.D Friderichsen ◽  
T Thyrsted
Keyword(s):  
Metamorphic Complex ◽  
East Greenland ◽  
Late Proterozoic ◽  
Isotopic Studies ◽  
Lower Palaeozoic ◽  
Caledonian Orogeny ◽  
Proterozoic Basement ◽  
Basement Gneiss ◽  
Metamorphic Complexes ◽  
Middle Proterozoic

Results are presented of regional geological reconnaissance and local detailed studies. The new fjeld work, together with isotopic studies, has made possibie a provisional reassignment of metamorphic, plutonic and deformational events recorded in the different rock units to Archaean and Proterozoic, as well as Caledonian, orogenic episodes. The infracrustal elements of the 'central metamorphic complex' are considered to be essentiaIly Archaean - early Proterozoic basement gneiss complexes, and are overlain by middle Proterozoic metasedimentary sequences. The late Proterozoic and Lower Palaeozoic sediments have arestricted outcrop at present levels of exposure. During the Caledonian orogeny the late Proterozoic cover sequences appear to have become detatched from their older metamorphic 'basernent' along a decollement surface, but the nature of this contact is usually obscured by Caledonian metamorphic effects. The main characteristics of the different rock units are described. Detailed relationships are illustrated by studies of four areas: Nunatakgletscher-Eremitdal, Knækdalen and adjacent areas, Kap Hediund, and Tærskeldal-Forsblads Fjord-Randenæs.

scholarly journals Annual variation in event-scale precipitation <i>δ</i><sup>2</sup>H at Barrow, AK, reflects vapor source region

2017 ◽  
Vol 17 (7) ◽  
pp. 4627-4639 ◽  
Author(s):  
Annie L. Putman ◽  
Xiahong Feng ◽  
Leslie J. Sonder ◽  
Eric S. Posmentier
Keyword(s):  
Source Region ◽  
Arctic Sea Ice ◽  
Dew Point ◽  
Precipitation Event ◽  
Boolean Variable ◽  
Deuterium Excess ◽  
Vapor Source ◽  
Source Regions ◽  
Circulation Cell ◽  
Transport Path

Abstract. In this study, precipitation isotopic variations at Barrow, AK, USA, are linked to conditions at the moisture source region, along the transport path, and at the precipitation site. Seventy precipitation events between January 2009 and March 2013 were analyzed for δ2H and deuterium excess. For each precipitation event, vapor source regions were identified with the hybrid single-particle Lagrangian integrated trajectory (HYSPLIT) air parcel tracking program in back-cast mode. The results show that the vapor source region migrated annually, with the most distal (proximal) and southerly (northerly) vapor source regions occurring during the winter (summer). This may be related to equatorial expansion and poleward contraction of the polar circulation cell and the extent of Arctic sea ice cover. Annual cycles of vapor source region latitude and δ2H in precipitation were in phase; depleted (enriched) δ2H values were associated with winter (summer) and distal (proximal) vapor source regions. Precipitation δ2H responded to variation in vapor source region as reflected by significant correlations between δ2H with the following three parameters: (1) total cooling between lifted condensation level (LCL) and precipitating cloud at Barrow, ΔTcool, (2) meteorological conditions at the evaporation site quantified by 2 m dew point, Td, and (3) whether the vapor transport path crossed the Brooks and/or Alaskan ranges, expressed as a Boolean variable, mtn. These three variables explained 54 % of the variance (p<0. 001) in precipitation δ2H with a sensitivity of −3.51 ± 0.55 ‰ °C−1 (p<0. 001) to ΔTcool, 3.23 ± 0.83 ‰ °C−1 (p<0. 001) to Td, and −32.11 ± 11.04 ‰ (p = 0. 0049) depletion when mtn is true. The magnitude of each effect on isotopic composition also varied with vapor source region proximity. For storms with proximal vapor source regions (where ΔTcool <7 °C), ΔTcool explained 3 % of the variance in δ2H, Td alone accounted for 43 %, while mtn explained 2 %. For storms with distal vapor sources (ΔTcool > 7°C), ΔTcool explained 22 %, Td explained only 1 %, and mtn explained 18 %. The deuterium excess annual cycle lagged by 2–3 months during the δ2H cycle, so the direct correlation between the two variables is weak. Vapor source region relative humidity with respect to the sea surface temperature, hss, explained 34 % of variance in deuterium excess, (−0.395 ± 0.067 ‰ %−1, p<0. 001). The patterns in our data suggest that on an annual scale, isotopic ratios of precipitation at Barrow may respond to changes in the southerly extent of the polar circulation cell, a relationship that may be applicable to interpretation of long-term climate change records like ice cores.

Azimuth estimation capabilities of the ARCESS regional seismic array

1993 ◽  
Vol 83 (4) ◽  
pp. 1213-1231
Author(s):  
Dorthe B. Carr
Keyword(s):  
Time Window ◽  
Source Region ◽  
Event Data ◽  
Small Aperture ◽  
Data Set ◽  
Low Frequencies ◽  
Source Regions ◽  
The Mean ◽  
Local Geology ◽  
Regional Arrays

Abstract The effect of local geology and noise conditions on the performance of a small regional array is investigated by comparing the regional Pn backazimuth estimation capabilities of the ARCESS array in northern Norway to the NORESS array. A broadband frequency-wavenumber estimator was used to calculate backazimuths from the Pn arrival for each of 203 regional events recorded at ARCESS while varying element spacing, frequency band, and time window. Most of the errors in backazimuth are less than 20° when appropriate parameter combinations are used, and mean backazimuth errors are close to zero. The best results are obtained using a 13-element configuration that has a 1.4 km aperture and a maximum station spacing of about 600 m. With the 13-element configuration and the data filtered to include frequencies between 3 and 10 Hz, the mean errors for the 203 event data set are less than 0.9°, and S.D. are as small as 16.9°. There are differences seen in the backazimuth estimation capabilities of ARCESS and NORESS with specific parameter combinations. The larger aperture configurations (10- and 17-elements) have smaller means at ARCESS, although the precision is about the same. The estimates using unfiltered data at ARCESS are poor, because of local noise conditions that increase the level of background noise at low frequencies. Overall the precision is better at NORESS, but both regional arrays have the best results using the 13-element configuration and filtering the data in the middle frequency range (3 to 10 Hz). Other factors investigated include SNR and source region. Backazimuth estimation statistics improve if only events with 5 dB of SNR are included in the data set at both ARCESS and NORESS. The mean errors move closer to zero and standard deviations decrease. The differences between the two arrays are not as pronounced. There are some path effects from different source regions around the ARCESS array. However, combinations of small aperture configurations and middle (3 to 10 Hz) frequency bands work well for events over the entire distance range of 30 to 1200 km. ARCESS and NORESS have similar backazimuth estimation capabilities even though there are differences in the local geology and noise conditions. Because a 13-element configuration produces reliable results for both arrays, it would be reasonable to reduce the number of elements in a regional array. This in turn will reduce the costs associated with building and deploying small regional arrays.

Determine the Physical Mechanism and Source Region of Beat Wave Modulation by Changing the Frequency of HF Waves

2021 ◽  
Author(s):  
Zhe Guo ◽  
Hanxian Fang ◽  
Farideh Honary
Keyword(s):  
Physical Mechanism ◽  
Source Region ◽  
Low Frequency ◽  
Signal Amplitude ◽  
New Approach ◽  
Wave Modulation ◽  
F Region ◽  
Source Regions ◽  
High Modulation ◽  
E Region

Abstract This paper introduces a new approach for the determination of the source region of BW (beat wave) modulation. This type of modulation is achieved by transmitting HF continuous waves with a frequency difference of f, where f is the frequency of modulated ELF/VLF (extremely low frequency/very low frequency) waves from two sub-arrays of a high power HF transmitter. Despite the advantages of BW modulation in terms of generating more stable ELF/VLF signal and high modulation efficiency, there exists a controversy on the physical mechanism of BW and its source region. In this paper, the two controversial theories, i.e. BW based on D-E region thermal nonlinearity and BW based on F region ponderomotive nonlinearity are examined for cases where each of these two theories exists exclusively or both of them exist simultaneously. According to the analysis and the simulation results presented in this paper, it is found that the generated VLF signal amplitude exhibits significant variation as a function of HF frequency in different source regions. Therefore, this characteristic can be utilised as a potential new approach to determine the physical mechanism and source location of BW.

scholarly journals Differentiating between Inherited and Autocrystic Zircon in Granitoids

2020 ◽  
Vol 61 (8) ◽  
Author(s):  
Hugo K H Olierook ◽  
Christopher L Kirkland ◽  
Kristoffer Szilas ◽  
Julie A Hollis ◽  
Nicholas J Gardiner ◽  
...  
Keyword(s):  
Trace Element ◽  
Source Region ◽  
Wall Rock ◽  
Magma Source ◽  
Trace Element Data ◽  
Element Data ◽  
Age Constraints ◽  
Erroneous Interpretation ◽  
Zircon Fraction

Abstract Inherited zircon, crystals that did not form in situ from their host magma but were incorporated from either the source region or assimilated from the wall-rock, is common but can be difficult to identify. Age, chemical and/or textural dissimilarity to the youngest zircon fraction are the primary mechanisms of distinguishing such grains. However, in Zr-undersaturated magmas, the entire zircon population may be inherited and, if not identifiable via textural constraints, can lead to erroneous interpretation of magmatic crystallization age and magma source. Here, we present detailed field mapping of cross-cutting relationships, whole-rock geochemistry and zircon textural, U–Pb and trace element data for trondhjemite, granodiorite and granite from two localities in a complex Archean gneiss terrane in SW Greenland, which reveal cryptic zircon inheritance. Zircon textural, U–Pb and trace element data demonstrate that, in both localities, trondhjemite is the oldest rock (3011 ± 5 Ma, 2σ), which is intruded by granodiorite (2978 ± 4 Ma, 2σ). However, granite intrusions, constrained by cross-cutting relationships as the youngest component, contain only inherited zircon derived from trondhjemite and granodiorite based on ages and trace element concentrations. Without age constraints on the older two lithologies, it would be tempting to consider the youngest zircon fraction as recording crystallization of the granite but this would be erroneous. Furthermore, whole-rock geochemistry indicates that the granite contains only 6 µg g–1 Zr, extremely low for a granitoid with ∼77 wt% SiO2. Such low Zr concentration explains the lack of autocrystic zircon in the granite. We expand on a differentiation tool that uses Th/U ratios in zircon versus that in the whole-rock to aid in the identification of inherited zircon. This work emphasizes the need for field observations, geochemistry, grain characterization, and precise geochronology to accurately determine igneous crystallization ages and differentiate between inherited and autocrystic zircon.

scholarly journals Precursory seismicity associated with frequent, large ice avalanches on Iliamna volcano, Alaska, USA

2007 ◽  
Vol 53 (180) ◽  
pp. 128-140 ◽  
Author(s):  
Jacqueline Caplan-Auerbach ◽  
Christian Huggel
Keyword(s):  
Geothermal Energy ◽  
Source Region ◽  
Thermal Conditions ◽  
Seismic Signal ◽  
Seismic Sequence ◽  
Ground Shaking ◽  
Repeating Earthquakes ◽  
Rock Interface ◽  
Precursory Seismicity ◽  
Time Of Failure

AbstractSince 1994, at least six major (volume >106m3) ice and rock avalanches have occurred on Iliamna volcano, Alaska, USA. Each of the avalanches was preceded by up to 2 hours of seismicity believed to represent the initial stages of failure. Each seismic sequence begins with a series of repeating earthquakes thought to represent slip on an ice–rock interface, or between layers of ice. This stage is followed by a prolonged period of continuous ground-shaking that reflects constant slip accommodated by deformation at the glacier base. Finally the glacier fails in a large avalanche. Some of the events appear to have entrained large amounts of rock, while others comprise mostly snow and ice. Several avalanches initiated from the same source region, suggesting that this part of the volcano is particularly susceptible to failure, possibly due to the presence of nearby fumaroles. Although thermal conditions at the time of failure are not well constrained, it is likely that geothermal energy causes melting at the glacier base, promoting slip and culminating in failure. The frequent nature and predictable failure sequence of Iliamna avalanches makes the volcano an excellent laboratory for the study of ice avalanches. The prolonged nature of the seismic signal suggests that warning may one day be given for similar events occurring in populated regions.

Geochemistry, zircon ages and whole-rock Nd isotopic systematics for Palaeoproterozoic A-type granitoids in the northern part of the Delhi belt, Rajasthan, NW India: implications for late Palaeoproterozoic crustal evolution of the Aravalli craton

2006 ◽  
Vol 144 (2) ◽  
pp. 361-378 ◽  
Author(s):  
PARAMPREET KAUR ◽  
NAVEEN CHAUDHRI ◽  
INGRID RACZEK ◽  
ALFRED KRÖNER ◽  
ALBRECHT W. HOFMANN
Keyword(s):  
Source Region ◽  
Magma Source ◽  
Crustal Evolution ◽  
Nd Isotope ◽  
Tectonic Environment ◽  
Granulite Metamorphism ◽  
Extensional Tectonic ◽  
Aravalli Craton ◽  
Isotope Systematics

Determination of zircon ages as well as geochemical and Sm–Nd isotope systematics of granitoids in the Khetri Copper Belt of the Aravalli mountains, NW India, constrain the late Palaeoproterozoic crustal evolution of the Aravalli craton. The plutons are typical A-type within-plate granites, derived from melts generated in an extensional tectonic environment. They display REE and multi-element patterns characterized by steep LREE-enriched and almost flat HREE profiles and distinct negative anomalies for Sr, P and Ti. Initial εNd values range from −1.3 to −6.2 and correspond to crustal sources with mean crustal residence ages of 2.5 to 2.1 Ga. A lower mafic crustal anatectic origin is envisaged for these granitoids, and the heterogeneous εNd(t) values are inferred to have been acquired from the magma source region. Zircon Pb–Pb evaporation and U–Pb ages indicate widespread rift-related A-type magmatism at 1711–1660 Ma in the northern Delhi belt and also suggest a discrete older magmatic event at around 1800 Ma. The emplacement ages of the compositionally distinct A-type granitoid plutons, and virtually coeval granulite metamorphism and exhumation in another segment of the Aravalli mountains, further signify that part of the Aravalli crust evolved during a widespread extensional event in late Palaeoproterozoic time.

Measurement and Prediction of Heat Transfer From Compressor Discs With a Radial Inflow of Cooling Air

1991 ◽  
Author(s):  
P. R. Farthing ◽  
C. A. Long ◽  
R. H. Rogers
Keyword(s):  
Heat Transfer ◽  
Source Region ◽  
Thermal Conditions ◽  
Integral Model ◽  
Transfer Rates ◽  
Nusselt Numbers ◽  
Maximum Value ◽  
Cooling Air ◽  
Experimental Rig ◽  
Acceptable Agreement

An integral theory is used to model the flow, and predict heat transfer rates, for corotating compressor discs with a superposed radial inflow of air. Measurements of heat transfer are also made, both in an experimental rig and in an engine. The flow structure comprises source and sink regions, Ekman-type layers and an inviscid central core. Entrainment occurs in the source region, the fluid being distributed into the two nonentraining Ekman-type layers. Fluid leaves the cavity via the sink region. The integral model is validated against the experimental data, although there are some uncertainties in modelling the exact thermal conditions of the experiment. The magnitude of the Nusselt numbers is affected by the rotational Reynolds number and dimensionless flowrate; the maximum value of Nu is found to occur near the edge of the source region. The heat transfer measurements using the engine data show acceptable agreement with theory and experiment. This is very encouraging considering the large levels of uncertainty in the engine data.

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