U-Pb sphene dating of metamorphism: the importance of sphene growth in the contact aureole of the Red Mountain pluton, Laramie Mountains, Wyoming

1996 ◽  
Vol 125 (2-3) ◽  
pp. 186-199 ◽  
Author(s):  
L. A. Verts ◽  
Kevin R. Chamberlain ◽  
C. D. Frost
Keyword(s):  
Contact Aureole ◽  
Laramie Mountains

scholarly journals Archaeopetrological approximation to the lithic procurement of the neolithic axes and adzes from Can Sadurní’s cave (Begues, NE Iberian Peninsula)

2016 ◽  
Vol 3 (2) ◽  
Author(s):  
Mar Rey-Solé ◽  
Gemma Alías ◽  
Mireia Ache ◽  
Elicinia Fierro ◽  
Manel Edo ◽  
...  
Keyword(s):  
Iberian Peninsula ◽  
Raw Materials ◽  
Source Area ◽  
Archaeological Site ◽  
Igneous Rocks ◽  
Contact Aureole ◽  
Stratigraphic Sequence ◽  
Materials Used ◽  
Granodiorite Porphyry ◽  
Ne Iberian Peninsula

Can Sadurní’s cave, located in Begues (NE Iberian Peninsula), in the Baix Llobregat region, is an archaeological site with a wide stratigraphic sequence covering from the Epipaleolithic hunter-gatherers societies at the beginning of the Holocene to Roman times. During the excavations of the last years a large number of different raw materials used for the manufacture of axes have been recovered.The present study is focused on the Neolithic sequence. 31 axes and adzes have been characterised petrographically with the aid of a binocular microscope and transmission microscope. A great variety of rocks constitute the raw materials of these stone tools, ranging from contact and regional metamorphic rocks to plutonic and porphyric igneous rocks. The formers are the most abundant (up to 78%) and include hornfels, spotted phyllites, marbles, quartzites, slates and phyllites. The igneous rocks consist of granodiorite, porphyry and aplites. Such a great assemblage of rocks matches in a geological context representative of a plutonic intrusion and its metamorphic contact aureole. Following that scenario we suggest that the most likely source area for all these materials occur at the Collserola hills, at 27 km far to the east from the cave, at the other side of the Llobregat River, where an Hercynian granodiorite and related igneous rocks intruding Ordovician metasedimentary materials are presented. 

Molecular Identification of Sceloporus Lizards in the Laramie Mountains, Wyoming

2021 ◽  
Vol 81 (4) ◽  
Author(s):  
Kiara W. Milcoff ◽  
Wendy A. Estes-Zumpf ◽  
Adam D. Leaché
Keyword(s):  
Molecular Identification ◽  
Laramie Mountains

Double dating (U–Pb and (U–Th)/He) of detrital zircon from the Gonfolite Group (European Alps) and implications for the lag-time approach to detrital thermochronology

2021 ◽  
Author(s):  
Marco G. Malusà ◽  
Owen A. Anfinson ◽  
Daniel F. Stockli
Keyword(s):  
Detrital Zircon ◽  
Country Rock ◽  
Lag Time ◽  
Source Rocks ◽  
Magmatic Zircon ◽  
Contact Aureole ◽  
European Alps ◽  
Earth Planet ◽  
Shallow Level ◽  
Plutonic Rocks

<p>Detrital thermochronologic analyses are increasingly employed to develop quantitative models of landscape evolution and constrain rates of exhumation due to erosion. Crucial for this kind of application is a correct discrimination between thermochronologic ages that record cooling due to exhumation, i.e., the motion of parent rocks towards Earth’s surface, and thermochronologic ages that record cooling independent from exhumation, as expected for example in volcanic and shallow-level plutonic rocks. A suitable approach for the identification of magmatic crystallization ages is provided by double dating, which combines for example U–Pb and (U–Th)/He analyses of the same mineral grain. Magmatic zircon crystallized from volcanic or shallow-level plutonic rocks should display identical U–Pb and (U–Th)/He (ZHe) ages within error, because of rapid magma crystallization in the upper crust where country rocks are at temperatures cooler than the partial retention zone of the ZHe system. Conversely, zircon grains crystallized at greater depth and recording cooling during exhumation should display ZHe ages younger than the corresponding U–Pb ages. These latter ZHe ages may constrain the long-term exhumation history of the source rocks according to the lag-time approach, provided that a range of assumptions are properly evaluated (e.g., Malusà and Fitzgerald 2020). Here, we explore the possibility that detrital zircon grains yielding ZHe ages younger than the corresponding U–Pb ages may record country-rock cooling within a contact aureole rather than exhumation. To tackle this issue, we applied a double-dating approach including U-Pb and ZHe analyses to samples of the Gonfolite Group exposed south of the European Alps. The Gonfolite Group largely derives from erosion of the Bergell volcano-plutonic complex and adjacent country rocks, and its mineral-age stratigraphy is extremely well constrained (Malusà et al. 2011, 2016). Analyses were performed in the UTChron Geochronology Facility at University of Texas at Austin. For U-Pb LA-ICPMS depth-profile analysis, all detrital zircon grains were mounted without polishing, which allowed for subsequent ZHe analysis on the same grains. Zircon for ZHe analyses were selected among those not derived from the Bergell complex or other Periadriatic magmatic rocks, as constrained by their U-Pb age. We found that ca 40% of double-dated grains, despite yielding a ZHe age younger than their U-Pb age, likely record cooling within the Bergell contact aureole, not exhumation. These findings have major implications for a correct application of the lag-time approach to detrital thermochronology and underline the importance of a well-constrained mineral-age stratigraphy for a reliable geologic interpretation.</p><p>Malusà MG, Villa IM, Vezzoli G, Garzanti E (2011) Earth Planet Sci Lett 301(1-2), 324-336</p><p>Malusà MG, Anfinson OA, Dafov LN, Stockli DF (2016) Geology 44(2), 155-158</p><p>Malusà MG, Fitzgerald, PG (2020) Earth-Sci Rev 201, 103074</p>

scholarly journals U-Pb monazite ages of the Kabanga mafic-ultramafic intrusions and contact aureoles, central Africa: Geochronological and tectonic implications

2019 ◽  
Vol 131 (11-12) ◽  
pp. 1857-1870 ◽  
Author(s):  
Jian-Wei Zi ◽  
Birger Rasmussen ◽  
Janet R. Muhling ◽  
Wolfgang D. Maier ◽  
Ian R. Fletcher
Keyword(s):  
Central Africa ◽  
Layered Intrusion ◽  
Thermal Anomaly ◽  
Contact Metamorphism ◽  
Contact Aureole ◽  
East African ◽  
Metamorphic History ◽  
History Of ◽  
Rodinia Assembly ◽  
Contact Aureoles

AbstractMafic-ultramafic rocks of the Kabanga-Musongati alignment in the East African nickel belt occur as Bushveld-type layered intrusions emplaced in metasedimentary sequences. The age of the mafic-ultramafic intrusions remains poorly constrained, though they are regarded to be part of ca. 1375 Ma bimodal magmatism dominated by voluminous S-type granites. In this study, we investigated igneous monazite and zircon from a differentiated layered intrusion and metamorphic monazite from the contact aureole. The monazite shows contrasting crystal morphology, chemical composition, and U-Pb ages. Monazite that formed by contact metamorphism in response to emplacement of mafic-ultramafic melts is characterized by extremely high Th and U and yielded a weighted mean 207Pb/206Pb age of 1402 ± 9 Ma, which is in agreement with dates from the igneous monazite and zircon. The ages indicate that the intrusion of ultramafic melts was substantially earlier (by ∼25 m.y., 95% confidence) than the prevailing S-type granites, calling for a reappraisal of the previously suggested model of coeval, bimodal magmatism. Monazite in the metapelitic rocks also records two younger growth events at ca. 1375 Ma and ca. 990 Ma, coeval with metamorphism during emplacement of S-type granites and tin-bearing granites, respectively. In conjunction with available geologic evidence, we propose that the Kabanga-Musongati mafic-ultramafic intrusions likely heralded a structurally controlled thermal anomaly related to Nuna breakup, which culminated during the ca. 1375 Ma Kibaran event, manifested as extensive intracrustal melting in the adjoining Karagwe-Ankole belt, producing voluminous S-type granites. The Grenvillian-aged (ca. 990 Ma) tin-bearing granite and related Sn mineralization appear to be the far-field record of tectonothermal events associated with collision along the Irumide belt during Rodinia assembly. Since monazite is a ubiquitous trace phase in pelitic sedimentary rocks, in contact aureoles of mafic-ultramafic intrusions, and in regional metamorphic belts, our study highlights the potential of using metamorphic monazite to determine ages of mafic-ultramafic intrusions, and to reconstruct postemplacement metamorphic history of the host terranes.

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