Source contamination and mantle heterogeneity in the genesis of Italian potassic and ultrapotassic volcanic rocks: Sr-Nd-Pb isotope data from Roman Province and Southern Tuscany

2002 ◽  
Vol 74 (2-4) ◽  
pp. 189-222 ◽  
Author(s):  
S. Conticelli ◽  
M. D'Antonio ◽  
L. Pinarelli ◽  
L. Civetta
Keyword(s):  
Volcanic Rocks ◽  
Mantle Heterogeneity ◽  
Pb Isotope ◽  
Isotope Data ◽  
Source Contamination ◽  
Roman Province

Metallogenic significance of trace element and U–Pb isotope data for uraninite-rich mineral separates from the Labrador Central Mineral Belt

1993 ◽  
Vol 30 (12) ◽  
pp. 2352-2365 ◽  
Author(s):  
Derek H. C. Wilton ◽  
Henry P. Longerich
Keyword(s):  
Inductively Coupled Plasma ◽  
Genetic Relationships ◽  
Volcanic Rocks ◽  
Analytical Techniques ◽  
Geochronological Data ◽  
Pb Isotope ◽  
Isotope Data ◽  
Mineral Belt ◽  
Felsic Volcanic ◽  
Host Rocks

Thirteen concentrates of uraniferous material were prepared from uranium occurrences in the Central Mineral Belt of Labrador. Host rocks to these occurrences include granitoid rocks of the Archean basement, ca. 2000 Ma metasedimentary rocks of the Lower Aillik Group, and 1860 Ma felsic volcanic rocks of the Upper Aillik Group. Common lead corrected Pb isotope data from inductively coupled plasma mass spectrometry analyses define 207Pb/206Pb ages ranging from 1805 to 1697 Ma for all but one sample, with a mean age of 1752 ± 27 Ma (1 σ). Ages calculated for individual samples are similar to those derived by previous workers using standard analytical techniques. Eleven of these samples define linear trends that intersect the U–Pb concordia at 1741 ± 23 Ma and a Tera-Wasserburg curve at 1740 ± 21 Ma, respectively. These data suggest that the occurrences are epigenetic with respect to host rocks and possibly related to a common metallogenic event, therefore resolving a long-standing controversy about the timing and mode of occurrence of the widespread uranium mineralization in this part of the belt. These ages broadly correlate with a period of migmatization, metamorphism, and granitoid plutonism, as defined by U–Pb zircon geochronological data for regional units. Rare earth element data for uraninite from all concentrates resemble those of uraninite in granite-related deposits. One sample has a distinctly different calculated 207Pb/206Pb age of 495 Ma, indicative of a later remobilization of the ca. 1741 Ma mineralization. The geochemical and geochronological data collectively suggest that the Central Mineral Belt uranium occurrences were related to posttectonic granite magmatism and have no direct genetic relationships with nongranitoid host rocks.

Shoshonite and sub-alkaline magmas from an ultrapotassic volcano: Sr–Nd–Pb isotope data on the Roccamonfina volcanic rocks, Roman Magmatic Province, Southern Italy

2008 ◽  
Vol 157 (1) ◽  
pp. 41-63 ◽  
Author(s):  
Sandro Conticelli ◽  
Sara Marchionni ◽  
Davide Rosa ◽  
Guido Giordano ◽  
Elena Boari ◽  
...  
Keyword(s):  
Southern Italy ◽  
Volcanic Rocks ◽  
Pb Isotope ◽  
Isotope Data ◽  
Alkaline Magmas

Tracing Crustal Evolution in the Southern Central Andes from Late Precambrian to Permian with Geochemical and Nd and Pb Isotope Data

2000 ◽  
Vol 108 (5) ◽  
pp. 515-535 ◽  
Author(s):  
B. Bock ◽  
H. Bahlburg ◽  
G. Wörner ◽  
U. Zimmermann
Keyword(s):  
Central Andes ◽  
Crustal Evolution ◽  
Pb Isotope ◽  
Late Precambrian ◽  
Isotope Data ◽  
Southern Central

Postmagmatic thermal activity in the Abitibi greenstone belt, Noranda and Matagami districts; evidence from whole-rock Pb isotope data

1993 ◽  
Vol 88 (6) ◽  
pp. 1598-1614 ◽  
Author(s):  
J. D. Vervoort ◽  
W. M. White ◽  
R. I. Thorpe ◽  
J. M. Franklin
Keyword(s):  
Greenstone Belt ◽  
Thermal Activity ◽  
Pb Isotope ◽  
Abitibi Greenstone Belt ◽  
Isotope Data

Nd and Pb isotope mapping of crustal domains within the Makkovik Province, Labrador

2018 ◽  
Vol 156 (5) ◽  
pp. 833-848 ◽  
Author(s):  
R. M. MOUMBLOW ◽  
G. A. ARCURI ◽  
A. P. DICKIN ◽  
C. F. GOWER
Keyword(s):  
Early Stage ◽  
Foreland Basin ◽  
Mobile Belt ◽  
South American ◽  
Pb Isotope ◽  
Volcanic Arc ◽  
Nd Isotope ◽  
North American Cordillera ◽  
Tectonic Model ◽  
Isotope Data

AbstractThe Makkovik Province of eastern Labrador represents part of an accretionary orogen active during an early stage in the development of the Palaeoproterozoic southern Laurentian continental margin. New Nd isotope data for the eastern Makkovik Province suggest that accreted juvenile Makkovik crust was generated in the Cape Harrison domain during a single crust-forming event at c. 2.0 Ga. Pb isotope data support this model, and show a strong similarity to radiogenic crustal signatures in the juvenile Palaeoproterozoic crust of the Ketilidian mobile belt of southern Greenland. As previously proposed, an arc accretion event at c. 1.9 Ga triggered subduction-zone reversal and the development of an ensialic arc on the composite margin. After the subduction flip, a temporary release of compressive stress at c. 1.87 Ga led to the development of a retro-arc foreland basin on the downloaded Archean continental edge, forming the Aillik Group. Unlike previous models, a second arc is not envisaged. Instead, a compressive regime at c. 1.82 Ga is attributed to continued ensialic arc plutonism on the existing margin. The tectonic model for the Makkovikian orogeny proposed here is similar to that for the Ketilidian orogeny. Major- and trace-element analyses suggest that much of the magmatism in the Makkovik orogen results from post-accretionary ensialic arc activity, and that few vestiges remain of the original accreted volcanic arc. This pattern of arc accretion and intense post-accretion reworking is common to many accretionary orogens, such as the South American Andes and North American Cordillera.

Pb-isotope evidence on the origin of the West Shropsh orefield, England

1996 ◽  
Vol 133 (5) ◽  
pp. 611-617 ◽  
Author(s):  
R. Haggerty ◽  
B. M. Rohl ◽  
P. D. Budd ◽  
N. H. Gale
Keyword(s):  
Sea Water ◽  
Multiple Sources ◽  
Pb Isotope ◽  
The West ◽  
Minor Variation ◽  
Isotope Data ◽  
Water Origin ◽  
Isotope Evidence ◽  
Significant Spread ◽  
Isotope Variation

AbstractPb-isotope data on ore galenas from the West Shropshire orefield show a significant spread of 20pb/204pb values, with minor variation in 207Pb/204Pb and 208Pb/204Pb ratios. These indicate that lead was derived from multiple sources, some of them uranium-enriched and incompletely mixed prior to ore deposition. Four possible mineralizing agents are considered: circulating sea-water, metamorphic waters, basinal brines and convecting formation waters. Pb-isotope data exclude a circulating sea-water origin for the mineralization, and best support a convecting formation water mineralizing agent. A model involving a single fluid tapping multiple lead sources is proposed to explain the observed Pb-isotope variation.

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