Metastable prograde mineral reactions in contact aureoles

Geology ◽  
2004 ◽  
Vol 32 (9) ◽  
pp. 821 ◽  
Author(s):  
Thomas Müller ◽  
Lukas P. Baumgartner ◽  
C.T. Foster ◽  
Torsten W. Vennemann
Keyword(s):  
Contact Aureoles

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.

scholarly journals Thermogenic carbon release from the Central Atlantic magmatic province caused major end-Triassic carbon cycle perturbations

2020 ◽  
Vol 117 (22) ◽  
pp. 11968-11974 ◽  
Author(s):  
Thea H. Heimdal ◽  
Morgan T. Jones ◽  
Henrik. H. Svensen
Keyword(s):  
Carbon Cycle ◽  
Carbon Sources ◽  
Carbon Burial ◽  
Central Atlantic Magmatic Province ◽  
Organic Carbon Burial ◽  
Terrestrial Sediments ◽  
Carbon Release ◽  
Sediment Carbon ◽  
Central Atlantic ◽  
Contact Aureoles

The Central Atlantic magmatic province (CAMP), the end-Triassic mass extinction (ETE), and associated major carbon cycle perturbations occurred synchronously around the Triassic–Jurassic (T–J) boundary (201 Ma). Negative carbon isotope excursions (CIEs) recorded in marine and terrestrial sediments attest to the input of isotopically light carbon, although the carbon sources remain debated. Here, we explore the effects of mantle-derived and thermogenic carbon released from the emplacement of CAMP using the long-term ocean–atmosphere–sediment carbon cycle reservoir (LOSCAR) model. We have tested a detailed emission scenario grounded by numerous complementary boundary conditions, aiming to model the full extent of the carbon cycle perturbations around the T–J boundary. These include three negative CIEs (i.e., Marshi/Precursor, Spelae/Initial, Tilmanni/Main) with sharp positive CIEs in between. We show that a total of ∼24,000 Gt C (including ∼12,000 Gt thermogenic C) replicates the proxy data. These results indicate that thermogenic carbon generated from the contact aureoles around CAMP sills represents a credible source for the negative CIEs. An extremely isotopically depleted carbon source, such as marine methane clathrates, is therefore not required. Furthermore, we also find that significant organic carbon burial, in addition to silicate weathering, is necessary to account for the positive δ13C intervals following the negative CIEs.

Formation and destruction of periclase by fluid flow in two contact aureoles

1997 ◽  
Vol 128 (4) ◽  
pp. 313-334 ◽  
Author(s):  
John M. Ferry ◽  
Douglas Rumble III.
Keyword(s):  
Fluid Flow ◽  
Contact Aureoles

Metamorphic charnockite in contact aureoles around intrusive enderbite from Natal, South Africa

1999 ◽  
Vol 137 (1-2) ◽  
pp. 115-132 ◽  
Author(s):  
Alfons M. van den Kerkhof ◽  
Geoffrey H. Grantham
Keyword(s):  
South Africa ◽  
Contact Aureoles

Structural evolution in the northern part of the Moine thrust belt, NW Scotland

1980 ◽  
Vol 71 (2) ◽  
pp. 69-96 ◽  
Author(s):  
D. Elliott ◽  
M. R. W. Johnson
Keyword(s):  
Cross Sections ◽  
Structural Evolution ◽  
Thrust Belt ◽  
Sequence Diagrams ◽  
Western Margin ◽  
Contour Maps ◽  
Contact Aureoles

ABSTRACTFour balanced cross sections, supported by longitudinal sections, structure contour maps, stratigraphic separation diagrams and hangingwall sequence diagrams are keys to this interpretation of the Moine thrust, which forms the western margin of the Caledonides in NW Scotland. New basement and cover correlations between foreland and thrust belt give new slip estimates for the Moine thrust (∼ 77 km), the Loch More klippe (≥ 43 km), Glencoul sheet (20–25 km), Ben More sheet (∼28 km), Achall and Dundonnell ‘sheet II’ (∼28 km).Like other major thrusts the Moine thrust moved in a smooth or rough fashion at different places and times, and many structures are a footwall response to its passage. Widely developed duplexes vary in thickness so that the roof thrust is folded and occasionally faulted; many late Caledonian folds in the Moine metasediments are of this origin. The presence of igneous bodies with contact aureoles increased the propensity to rough slip and this, by causing thickening in the footwall to the Moine thrust, is partly responsible for the Assynt culmination.The previously accepted sequence of thrusting from foreland to hinterland, which has been deduced from the concept of ‘overstep’ of the Moine thrust across lower thrusts, is considered to be a misconception of thrust geometry. Instead, a ‘piggy-back’ sequence of thrusts, from higher to lower, is proposed.

Conditions et ages 40 Ar/ 39 Ar de mise en place des granitoides de la zone externe sud du Massif central francais; exemple des granodiorites de St-Guiral et du Liron (Cevennes, France)

2000 ◽  
Vol 171 (5) ◽  
pp. 495-510 ◽  
Author(s):  
Khalid Najoui ◽  
Andre Francois Leyreloup ◽  
Patrick Monie
Keyword(s):  
Gravitational Collapse ◽  
Regional Metamorphism ◽  
Low Grade ◽  
French Massif Central ◽  
The South ◽  
Massif Central ◽  
Laser Probe ◽  
Thermal Structures ◽  
Minimum Age ◽  
Contact Aureoles

Abstract The St-Guiral and the Liron laccolithic granodiorites outcropping in the southeastern area of the French Massif Central intrude the Cambro-Ordovician low grade series of the western Cevennes. The petrological study of their contact aureoles shows that these plutons emplaced at low depth (1-2 kb; 690-700 degrees C). The laser probe 40 Ar/ 39 Ar allows us to suggest a minimum age of 324 Ma for the emplacement of the St-Guiral granodiorite. This emplacement seems synchronous with the LP-HT regional metamorphism in the western Cevennes for which the cooling ages are identical. The Liron granodiorite (310 Ma) is younger and crosscuts the thermal structures of the LP-HT regional metamorphism. Accordingly these plutons emplaced at the Namurian-early Westphalian during the extensional phases related to the generalised gravitational collapse of the previously thickened Hercynian belt. The detachment of the subducted lithosphere (slab detachment) could be related to these phenomena and could explain the granitization of the south external area of the Hercynian belt as well as the migration of the magmatism towards the south of the belt.

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