Petrology and geochemistry of post-obduction dykes of the Ballantrae complex, SW Scotland

1984 ◽  
Vol 75 (2) ◽  
pp. 211-223 ◽  
Author(s):  
F. V. Holub ◽  
H. Klápová ◽  
B. J. Bluck ◽  
D. R. Bowes
Keyword(s):  
Source Region ◽  
Parental Magma ◽  
Virtual Absence ◽  
Ti Oxides ◽  
Depleted Mantle ◽  
Show Evidence ◽  
Petrology And Geochemistry ◽  
Original Magma ◽  
Metamorphic Facies ◽  
Plate Type

ABSTRACTDoleritic intrusions known to post-date the obduction of the Ballantrae complex during Arenig times record changing magma provenance during the cooling and serpentinisation of obducted peridotite. There are two groups of dolerites with different petrographical and geochemical characteristics.The earlier emplaced group, which is subordinate, is characterised by amphibole formed under low metamorphic facies conditions and the virtual absence of Fe–Ti oxides. Chemically these rocks are of primitive tholeiitic character and are similar to modern island-arc basalts. They were derived from a strongly depleted mantle source region. The source region of the later emplaced group, which is predominant, was much less depleted. Clinopyroxene and plagioclase, much of it albitised, are the dominant minerals. Fe–Ti oxides also are common and there are pronounced chilled margins and well-preserved ophitic textures. Although showing mildly alkaline tendencies, these rocks originated from a tholeiitic parental magma of “within-plate” type.Both groups show evidence of rodingitisation and associated alteration related to serpentinisation of the peridotite. During the metasomatic activity, only some elements were mobile, while Al2O3, total Fe, MgO, TiO2, Cr, Ni, Nb, Y and Zr remained almost constant. Assessment of original magma type and geotectonic environment, and demonstration that both groups of doleritic rocks show the products of fractionation, has relied heavily on data for the apparently immobile elements and on petrographical study which identified those rocks least affected by alteration.

scholarly journals Geochemistry and Sr, Nd isotopic composition of the Hronic Upper Paleozoic basic rocks (Western Carpathians, Slovakia)

2015 ◽  
Vol 66 (1) ◽  
pp. 3-17 ◽  
Author(s):  
Jozef Vozár ◽  
Ján Spišiak ◽  
Anna Vozárová ◽  
Jakub Bazarnik ◽  
Ján Krái
Keyword(s):  
Basaltic Andesite ◽  
Parental Magma ◽  
Crustal Material ◽  
Nd Isotope ◽  
Upper Paleozoic ◽  
Three Samples ◽  
Original Magma ◽  
Basic Rocks ◽  
Nd Isotopic Composition ◽  
Heterogeneous Source

Abstract The paper presents new major and trace element and first Sr-Nd isotope data from selected lavas among the Permian basaltic andesite and basalts of the Hronicum Unit and the dolerite dykes cutting mainly the Pennsylvanian strata. The basic rocks are characterized by small to moderate mg# numbers (30 to 54) and high SiO2 contents (51-57 wt. %). Low values of TiO2 (1.07-1.76 wt. %) span the low-Ti basalts. Ti/Y ratios in the dolerite dykes as well as the basaltic andesite and basalt of the 1st eruption phase are close to the recommended boundary 500 between high-Ti and low-Ti basalts. Ti/Y value from the 2nd eruption phase basalt is higher and inclined to the high-Ti basalts. In spite of this fact, in all studied Hronicum basic rocks Fe2O3* is lower than 12 wt. % and Nb/La ratios (0.3-0.6) are low, which is more characteristic of low-Ti basalts. The basic rocks are characterized by Nb/La ratios (0.56 to 0.33), and negative correlations between Nb/La and SiO2, which point to crustal assimilation and fraction crystallization. The intercept for Sr evolution lines of the 1st intrusive phase basalt is closest to the expected extrusions age (about 290 Ma) with an initial 87Sr/86Sr ratio of about 0.7054. Small differences in calculated values ISr document a partial Sr isotopic heterogeneity source (0.70435-0.70566), or possible contamination of the original magma by crustal material. For Nd analyses of the three samples, the calculated values εCHUR (285 Ma) are positive (from 1.75 to 3.97) for all samples with only subtle variation. Chemical and isotopic data permit us to assume that the parental magma for the Hronicum basic rocks was generated from an enriched heterogeneous source in the subcontinental lithospheric mantle.

scholarly journals What lies beneath? Reconstructing the primitive magmas fueling voluminous silicic volcanism using olivine-hosted melt inclusions

Geology ◽  
2020 ◽  
Vol 48 (5) ◽  
pp. 504-508 ◽  
Author(s):  
Simon J. Barker ◽  
Michael C. Rowe ◽  
Colin J.N. Wilson ◽  
John A. Gamble ◽  
Shane M. Rooyakkers ◽  
...  
Keyword(s):  
Melt Inclusions ◽  
Melt Inclusion ◽  
Taupo Volcanic Zone ◽  
Mantle Dynamics ◽  
Silicic Volcanism ◽  
Depleted Mantle ◽  
Basaltic Magmas ◽  
Show Evidence ◽  
Basaltic Melts ◽  
Eruptive Centers

Abstract Understanding the origins of the mantle melts that drive voluminous silicic volcanism is challenging because primitive magmas are generally trapped at depth. The central Taupō Volcanic Zone (TVZ; New Zealand) hosts an extraordinarily productive region of rhyolitic caldera volcanism. Accompanying and interspersed with the rhyolitic products, there are traces of basalt to andesite preserved as enclaves or pyroclasts in caldera eruption products and occurring as small monogenetic eruptive centers between calderas. These mafic materials contain MgO-rich olivines (Fo79–86) that host melt inclusions capturing the most primitive basaltic melts fueling the central TVZ. Olivine-hosted melt inclusion compositions associated with the caldera volcanoes (intracaldera samples) contrast with those from the nearby, mafic intercaldera monogenetic centers. Intracaldera melt inclusions from the modern caldera volcanoes of Taupō and Okataina have lower abundances of incompatible elements, reflecting distinct mantle melts. There is a direct link showing that caldera-related silicic volcanism is fueled by basaltic magmas that have resulted from higher degrees of partial melting of a more depleted mantle source, along with distinct subduction signatures. The locations and vigor of Taupō and Okataina are fundamentally related to the degree of melting and flux of basalt from the mantle, and intercaldera mafic eruptive products are thus not representative of the feeder magmas for the caldera volcanoes. Inherited olivines and their melt inclusions provide a unique “window” into the mantle dynamics that drive the active TVZ silicic magmatic systems and may present a useful approach at other volcanoes that show evidence for mafic recharge.

A Cretaceous back-arc basin in the Coast Belt of the northern Canadian Cordillera: evidence from geochemical and neodymium isotope characteristics of the Kluane metamorphic assemblage, southwest Yukon

2001 ◽  
Vol 38 (1) ◽  
pp. 91-103 ◽  
Author(s):  
Jochen E Mezger ◽  
Robert A Creaser ◽  
Philippe Erdmer ◽  
Stephen T Johnston
Keyword(s):  
Late Jurassic ◽  
Metamorphic Rock ◽  
Tectonic Setting ◽  
Source Region ◽  
Canadian Cordillera ◽  
Metasedimentary Rocks ◽  
Depleted Mantle ◽  
Metamorphic Assemblage ◽  
Continental Source ◽  
Back Arc

The Coast Belt of the northern Cordillera in Canada is the locus of the boundary between accreted and ancient North American margin rocks. The largest exposure of metasedimentary rocks in the Coast Belt is the Kluane metamorphic assemblage (KMA), a northwest-striking belt 160 km long of graphitic mica–quartz schist and gneiss with minor interfoliated olivine serpentinite. The KMA does not appear to correlate with other sedimentary or metamorphic rock assemblages in the Canadian Cordillera. To determine its tectonic setting and protolith provenance, we analyzed trace element, rare earth elements, and neodymium isotope compositions of the KMA, of the adjacent pericratonic Aishihik metamorphic suite (AMS) of the Yukon–Tanana terrane, and of adjacent slates of the Dezadeash Formation (DF), filling a Late Jurassic – Early Cretaceous flysch basin. The εNd(0) values of analyzed KMA samples range from –1.4 to –5.6 and depleted mantle model ages (TDM) range from 1.16 to 1.45 Ga. KMA samples are intermediate between more evolved AMS samples (average εNd(0) –25, TDM = 2.6 Ga) and more juvenile DF samples (εNd(0) = +1.9, TDM = 0.95 Ga). The intermediate characteristics of the KMA samples cannot be linked to a known source region and are interpreted to reflect homogeneous mixing from predominantly juvenile and minor evolved sedimentary sources. A compatible tectonic setting is a back-arc basin within influence of a continental source. Eastward subduction of the KMA beneath ancient North America collapsed the back-arc basin by latest Cretaceous time.

scholarly journals Organic matter matters for ice nuclei of agricultural soil origin

2014 ◽  
Vol 14 (16) ◽  
pp. 8521-8531 ◽  
Author(s):  
Y. Tobo ◽  
P. J. DeMott ◽  
T. C. J. Hill ◽  
A. J. Prenni ◽  
N. G. Swoboda-Colberg ◽  
...  
Keyword(s):  
Organic Matter ◽  
Agricultural Soil ◽  
Source Region ◽  
Ice Nucleation ◽  
Desert Soil ◽  
Composition Analysis ◽  
Ice Nuclei ◽  
Show Evidence ◽  
Dry Heating

Abstract. Heterogeneous ice nucleation is a crucial process for forming ice-containing clouds and subsequent ice-induced precipitation. The importance for ice nucleation by airborne desert soil dusts composed predominantly of minerals is widely acknowledged. However, the potential influence of agricultural soil dusts on ice nucleation has been poorly recognized, despite recent estimates that they may account for up to 20–25% of the global atmospheric dust load. We have conducted freezing experiments with various dusts, including agricultural soil dusts derived from the largest dust-source region in North America. Here we show evidence for the significant role of soil organic matter (SOM) in particles acting as ice nuclei (IN) under mixed-phase cloud conditions. We find that the ice-nucleating ability of the agricultural soil dusts is similar to that of desert soil dusts, but is clearly reduced after either H2O2 digestion or dry heating to 300 °C. In addition, based on chemical composition analysis, we demonstrate that organic-rich particles are more important than mineral particles for the ice-nucleating ability of the agricultural soil dusts at temperatures warmer than about −36 °C. Finally, we suggest that such organic-rich particles of agricultural origin (namely, SOM particles) may contribute significantly to the ubiquity of organic-rich IN in the global atmosphere.

Geochemistry of Cretaceous subduction initiation related cumulate gabbros in a forearc setting from Chaldoran ophiolite, NW Iran

2020 ◽  
Author(s):  
Mahleqa Rezaei ◽  
Mohssen Moazzen ◽  
Tian-Nan Yang
Keyword(s):  
Source Region ◽  
Mineral Chemistry ◽  
Ultramafic Rocks ◽  
Nw Iran ◽  
Subduction Initiation ◽  
Rock Types ◽  
Original Magma ◽  
Ree Patterns ◽  
Ree Pattern ◽  
Cretaceous Subduction

<p>The Neo-Tethys-related Chaldoran ophiolite in NW Iran and at the Turkish border is a part of the larger Khoy ophiolite. Cumulate and isotropic gabbro along with serpentinized peridotite, pillow basalt, pelagic limestone, rare radiolarites, and volcano-sedimentary units are the main rock types in the area. The gabbros occur as lenses with ultramafic rocks, or as relatively large exposures with fault contact with ultramafic rocks. In this study, we provide new whole-rock geochemistry, mineral chemistry and zircon U/Pb age for the cumulate gabbros from the Chaldoran area. Gabbros have tholeiitic composition and are highly depleted. Chondrite normalized rare earth elements (REE) pattern for gabbros are comparative with REE patterns for N-MORB, but overall with more depleted features. The N-MORB normalized multi-elements pattern shows high depletion in HREE and HFSE and enrichment in some LREE and LILEs. Negative anomaly for some HFSE relative to N-MORB, along with enrichment in LILE for the samples indicates the source region as subduction influenced mantle. The cumulated gabbro whole rock and Clinopyroxenes geochemistry indicate an intra-oceanic forearc setting for the studied samples. They also have many similarities to boninite in mineral and whole rock geochemistry. U-Pb zircon dating of the gabbro samples indicates 95.3-114.1 Ma ages for the generation of the gabbros parent magma. The original magma was related to the later stages of the forearc setting in the subduction initiation (SI) stage. This ‘SI’ related Albian-Cenomanian the Chaldoran depleted gabbro likely are the continuation of Taurus SI related late Cretaceous ophiolite complexes in Turkey.</p>

scholarly journals Petrology and geochemistry of a peridotite body in Central- Carpathian Paleogene sediments (Sedlice, eastern Slovakia)

2014 ◽  
Vol 65 (5) ◽  
pp. 390-402 ◽  
Author(s):  
Matúš Koppa ◽  
Friedrich Koller ◽  
Marián Putiš
Keyword(s):  
Western Carpathians ◽  
Primitive Mantle ◽  
Metamorphic Overprint ◽  
Orogenic Wedge ◽  
Depleted Mantle ◽  
Petrology And Geochemistry ◽  
Central Western Carpathians ◽  
Rock Suite ◽  
Relationship Of ◽  
Ree Patterns

Abstract We studied representative samples from a peridotite body situated NE of Sedlice village within the Central- Carpathian Paleogene sediments in the Central Western Carpathians. The relationship of the peridotite to the surrounding Paleogene sediments is not clear. The fractures of the brecciated peridotite margin are healed with secondary magnesite and calcite. On the basis of the presented bulk-rock and electron microprobe data, the wt. % amounts of mineral phases were calculated. Most of calculated “modal” compositions of this peridotite corresponds to harzburgites composed of olivine (∼70-80 wt. %), orthopyroxene (∼17-24 wt. %), clinopyroxene ( < 5 wt. %) and minor spinel ( < 1 wt. %). Harzburgites could originate from lherzolitic protoliths due to a higher degree of partial melting. Rare lherzolites contain porphyroclastic 1-2 mm across orthopyroxene (up to 25 wt. %), clinopyroxene (∼ 5-8 wt. %) and minor spinel ( < 0.75 wt. %). On the other hand, rare, olivine-rich dunites with scarce orthopyroxene porphyroclasts are associated with harzburgites. Metamorphic mineral assemblage of low-Al clinopyroxene (3), tremolite, chrysotile, andradite, Cr-spinel to chromite and magnetite, and an increase of fayalite component in part of olivine, indicate low-temperature metamorphic overprint. The Primitive Mantle normalized whole-rock REE patterns suggest a depleted mantle rock-suite. An increase in LREE and a positive Eu anomaly may be consequence of interactive metamorphic fluids during serpentinization. Similar rocks have been reported from the Meliatic Bôrka Nappe overlying the Central Western Carpathians orogenic wedge since the Late Cretaceous, and they could be a potential source of these peridotite blocks in the Paleogene sediments.

Geochemistry of the Little Dal basalts: continental tholeiites from the Mackenzie Mountains, Northwest Territories, Canada

1997 ◽  
Vol 34 (1) ◽  
pp. 50-58 ◽  
Author(s):  
Francis Ö. Dudás ◽  
Rigel L. Lustwerk
Keyword(s):  
Northwest Territories ◽  
Fractional Crystallization ◽  
Source Region ◽  
Sedimentary Rocks ◽  
Crustal Component ◽  
Lava Sequence ◽  
Original Magma ◽  
Geochemical Variation ◽  
Mackenzie Mountains ◽  
Nd Isotopic Composition

Analyses of the Little Dal lavas and the 779 Ma Tsezotene sills, both of the Mackenzie Mountains Supergroup, Northwest Territories, Canada, show them to be continental tholeiites that are geochemically related. The plagioclase- and clinopyroxene-phyric lavas are geochemically evolved and enriched in iron (up to 20.2 wt.% as Fe2O3). Two magmatic lineages are identifiable and may represent different degrees of partial melting in the same source region, but cannot be related by fractional crystallization. Within each lineage, geochemical variation can be explained by fractional crystallization involving up to 60% crystallization of the original magma. The most evolved lavas occur at the base of the pile; less fractionated lavas occur toward the top of the sequence. The Nd isotopic composition of the Little Dal lavas averages ε = 1.4 at 780 Ma. Trace element and isotopic compositions are permissive of contamination by continental crust, but do not require a crustal component. The preserved volume of the Little Dal basalts is anomalously low (−100 km3) compared with other Proterozoic continental tholeiites. There is considerable basaltic detritus in the sedimentary rocks of the overlying Coates Lake and Rapitan groups, and much of the original lava sequence may have been eroded. The Little Dal magmatic event is interpreted to be an early manifestation of rifting of North America from Australia.

Geochemical characteristics of the Eden Lake Complex: evidence for anorogenic magmatism in the Trans-Hudson Orogen

1999 ◽  
Vol 36 (1) ◽  
pp. 91-103 ◽  
Author(s):  
Norman M Halden ◽  
Brian J Fryer
Keyword(s):  
Rare Earth ◽  
Rare Earth Element ◽  
Earth Element ◽  
Source Region ◽  
Bulk Composition ◽  
Granitic Rocks ◽  
Depleted Mantle ◽  
High Silica ◽  
Lynn Lake ◽  
Silica Phases

The Eden Lake Complex intrudes granitic rocks located between the Lynn Lake and Leaf Rapids tectonic domains in the Reindeer Zone of the Trans-Hudson orogenic terrane in northern Manitoba. It consists of a number of magmatic phases. Of particular interest are aegirine-bearing monzonites and late rare earth element (REE)- and fluorine-enriched pegmatites. The aegirine monzonite ranges in SiO2 content from 51 to 76 wt.%, showing a continuous fractionation trend from low to high silica. The CaO, Fe2O3T, and MgO contents are low (about 1-6 wt.%), TiO2 contents range from 0.8 to about 0.1 wt.%, and total alkalis range from about 11 to 13 wt.%. The early evolution of the complex was influenced by pyroxene fractionation; during the later stages, K-feldspar fractionation had an increasing effect on the bulk composition of the magma. Accumulation of K-feldspar has obscured the tectonic signature of the complex, but elevated REE, high field strength element, and fluorine contents are consistent with an A-type granitoid association. The complex is associated with REE-bearing pegmatites. Total REE contents in the monzonites range from 1000 ppm in low-silica phases to 20 ppm in high-silica phases, with La/LuCN values ranging from 80 to 25. REE patterns reflect the fractionation of K-feldspar, pyroxene, and minor amounts of titanite, apatite, and zircon. Y/Nb and Yb/Ta values (relatively constant at ~1 and 1.5, respectively) are consistent with derivation from a depleted- mantle source enriched in REE; moreover, positive εNd values of 0.3-1.7 (with an assumed age of 1750 Ma) are consistent with derivation from an initially light rare earth element (LREE)-depleted source. Elevated Σ REE contents and LREE-enriched characteristics of the complex suggest the source region was altered prior to generation of the magma(s).

scholarly journals Organic matter matters for ice nuclei of agricultural soil origin

2014 ◽  
Vol 14 (7) ◽  
pp. 9705-9728 ◽  
Author(s):  
Y. Tobo ◽  
P. J. DeMott ◽  
T. C. J. Hill ◽  
A. J. Prenni ◽  
N. G. Swoboda-Colberg ◽  
...  
Keyword(s):  
Organic Matter ◽  
Agricultural Soil ◽  
Source Region ◽  
Ice Nucleation ◽  
Desert Soil ◽  
Composition Analysis ◽  
Ice Nuclei ◽  
Show Evidence ◽  
Dry Heating

Abstract. Heterogeneous ice nucleation is a~crucial process for forming ice-containing clouds and subsequent ice-induced precipitation. The importance for ice nucleation of airborne desert soil dusts composed predominantly of minerals is relatively well understood. On the other hand, the potential influence of agricultural soil dusts on ice nucleation has been poorly recognized, despite recent estimates that they may account for up to ∼25% of the global atmospheric dust load. We have conducted freezing experiments with various dusts, including agricultural soil dusts derived from the largest dust source region in North America. Here we show evidence for the significant role of soil organic matter (SOM) in particles acting as ice nuclei (IN) under mixed-phase cloud conditions. We find that the ice nucleating ability of the agricultural soil dusts is similar to that of desert soil dusts, but is reduced to almost the same level as that of clay minerals (e.g., kaolinite) after either H2O2 digestion or dry heating to 300 °C. In addition, based on chemical composition analysis, we show that organic-rich particles are more important than mineral particles for the ice nucleating ability of the agricultural soil dusts at temperatures warmer than about −36 °C. Finally, we suggest that such organic-rich particles of agricultural origin (namely, SOM particles) may contribute significantly to the ubiquity of organic-rich IN in the global atmosphere.

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