Chronology of Avalonian events on Presqu'île du Cap Miquelon (Le Cap), Saint-Pierre et Miquelon (France)

1995 ◽  
Vol 32 (7) ◽  
pp. 952-958
Author(s):  
G.R. Dunning ◽  
C. Lepvrier ◽  
S.J. O'brien ◽  
S.P. Colman-Sadd ◽  
H. Maluski
Keyword(s):  
Field Studies ◽  
Ductile Deformation ◽  
Grade Metamorphism ◽  
Younger Age ◽  
Significant Area ◽  
Age Limit ◽  
Metaigneous Rocks ◽  
Thermal Overprint ◽  
Proterozoic Age

U/Pb geochronology and field studies on Presqu'île du Cap Miquelon demonstrate that amphibolite-grade metamorphism, ductile deformation, and subsequent plutonism in this part of the Appalachian Avalon Zone are of Proterozoic age. Clear, crosscutting relationships between a dated granite dyke (part of the Cap Blanc granite) and foliated, amphibolite-grade metasedimentary and metaigneous rocks provide a younger age limit of [Formula: see text] Ma for tectonism. Proterozoic titanite and hornblende ages indicate that no significant younger thermal overprint occurred such as those recorded in nearby southern Newfoundland. Deformation and metamorphism of the country rocks and intrusion of the Cap Blanc granite are at least 30 Ma older than the onset of deposition of the youngest Proterozoic volcano-sedimentary successions in adjacent insular Newfoundland. Possible equivalents of these younger sequences occur near Cap Blanc, and contain what may be interpreted as clasts of granite, dated at 620 ± 3 Ma. The Miquelon metamorphic sequence is unique with respect to the southern Newfoundland Appalachians in representing a significant area of Proterozoic migmatite, not observably affected by tectonothermal events after 580 Ma.

Neoproterozoic extension in the Greater Dharwar Craton: a reevaluation of the “Betsimisaraka suture” in MadagascarThis article is one of a series of papers published in this Special Issue on the theme of Geochronology in honour of Tom Krogh.

2011 ◽  
Vol 48 (2) ◽  
pp. 389-417 ◽  
Author(s):  
R. D. Tucker ◽  
J.-Y. Roig ◽  
C. Delor ◽  
Y. Amelin ◽  
P. Goncalves ◽  
...  
Keyword(s):  
Dharwar Craton ◽  
High Grade ◽  
Grade Metamorphism ◽  
Continental Extension ◽  
Shrimp Geochronology ◽  
Igneous Activity ◽  
High Grade Metamorphism ◽  
Local Inversion ◽  
Metaigneous Rocks ◽  
Eastern Domain

The Precambrian shield of Madagascar is reevaluated with recently compiled geological data and new U–Pb sensitive high-resolution ion microprobe (SHRIMP) geochronology. Two Archean domains are recognized: the eastern Antongil–Masora domain and the central Antananarivo domain, the latter with distinctive belts of metamafic gneiss and schist (Tsaratanana Complex). In the eastern domain, the period of early crust formation is extended to the Paleo–Mesoarchean (3.32–3.15 Ga) and a supracrustal sequence (Fenerivo Group), deposited at 3.18 Ga and metamorphosed at 2.55 Ga, is identified. In the central domain, a Neoarchean period of high-grade metamorphism and anatexis that affected both felsic (Betsiboka Suite) and mafic gneisses (Tsaratanana Complex) is documented. We propose, therefore, that the Antananarivo domain was amalgamated within the Greater Dharwar Craton (India + Madagascar) by a Neoarchean accretion event (2.55–2.48 Ga), involving emplacement of juvenile igneous rocks, high-grade metamorphism, and the juxtaposition of disparate belts of mafic gneiss and schist (metagreenstones). The concept of the “Betsimisaraka suture” is dispelled and the zone is redefined as a domain of Neoproterozoic metasedimentary (Manampotsy Group) and metaigneous rocks (Itsindro–Imorona Suite) formed during a period of continental extension and intrusive igneous activity between 840 and 760 Ma. Younger orogenic convergence (560–520 Ma) resulted in east-directed overthrusting throughout south Madagascar and steepening with local inversion of the domain in central Madagascar. Along part of its length, the Manampotsy Group covers the boundary between the eastern and central Archean domains and is overprinted by the Angavo–Ifanadiana high-strain zone that served as a zone of crustal weakness throughout Cretaceous to Recent times.

U–Pb, Rb–Sr, and K–Ar isotopic constraints for ductile deformation and related metamorphism in the Teslin suture zone, Yukon–Tanana terrane, south-central Yukon

1989 ◽  
Vol 26 (11) ◽  
pp. 2224-2235 ◽  
Author(s):  
Vicki L. Hansen ◽  
James K. Mortensen ◽  
Richard L. Armstrong
Keyword(s):  
Shear Zones ◽  
Suture Zone ◽  
Early Jurassic ◽  
Ductile Deformation ◽  
Peraluminous Granite ◽  
South Central ◽  
Younger Age ◽  
Tectonic Boundary ◽  
Temperature Time ◽  
Dextral Strike Slip

The Teslin suture zone (TSZ) comprises a portion of the Yukon–Tanana terrane (YT), in the Yukon, formed by steeply dipping layering and L–S tectonite foliation. The TSZ forms the fundamental tectonic boundary between rocks deposited along the ancient margin of North America and allochthonous terranes to the west. TSZ tectonites evolved during initial penetrative dip-slip deformation (Dds) and later dextral strike-slip shear (Dss) along steep, 1–3 km wide shear zones. Several workers have speculated that the TSZ and related YT heterogeneous ductile deformation and associated metamorphism are Devonian to Mississippian in age and related to the intrusion of a similar-age orthogneiss throughout the Yukon and Alaska. However, recent structural and metamorphic studies of the TSZ provide evidence contradicting this view. New isotopic evidence, presented herein, indicates that TSZ dynamothermal metamorphism was cooled by Early Jurassic time, that it cannot be related to Devonian–Mississippian and Permian granitic intrusion, and that it predates Cretaceous plutonism.U–Pb zircon dating of peraluminous orthogneiss constrains primary peraluminous granite crystallization at 355 ± 25 Ma. Three Rb–Sr whole rock + muscovite and three K–Ar muscovite cooling dates of rocks containing Dds and Dss fabrics place a younger age limit of 182–213 Ma (latest Triassic to Early Jurassic) on Dds/Dss deformation. In addition, three Rb–Sr whole-rock + muscovite isochrons and one K–Ar date on biotite indicate peraluminous orthogneisses in the eastern portion of the study area were affected by a mid-Cretaceous thermal event. These data, togemer with structural and metamorphic relationships reported elsewhere, are summarized in pressure–temperature–time–displacement diagrams illustrating the evolution of TSZ and adjacent rocks from Devonian to Late Cretaceous time. Tectonites within the TSZ can be differentiated from peraluminous orthogneiss east of the d'Abbadie fault on the basis of their respective cooling histories.

PALAEOZOIC FLOOD BASALTS IN NORTHERN NEWFOUNDLAND AND LABRADOR

1965 ◽  
Vol 2 (3) ◽  
pp. 183-187 ◽  
Author(s):  
Paul M. Clifford
Keyword(s):  
Newfoundland And Labrador ◽  
Lower Cambrian ◽  
Flood Basalt ◽  
Flood Basalts ◽  
Clastic Rocks ◽  
Younger Age ◽  
Age Limit

Columnar basalt of the Cloud Hills in northern Newfoundland, previously regarded as of Keeweenawan age, now is thought to be post-Lower Cambrian, since it lies on coarse clastic rocks correlated with known Lower Cambrian strata nearby. A younger age limit is given by a whole rock K-A date of 334 m.y. Perhaps these and similar basalts in southern Labrador represent a flood basalt province, once much more continuous than now.

Unveiling ductile deformation during fast exhumation of a granitic pluton in a transfer zone

2021 ◽  
Author(s):  
Richard Spiess ◽  
Antonio Langone ◽  
Alfredo Caggianelli ◽  
Finlay M. Stuart ◽  
Martina Zucchi ◽  
...  
Keyword(s):  
Shear Zones ◽  
Integrated Approach ◽  
Field Studies ◽  
Ductile Deformation ◽  
Exhumation Rate ◽  
Pluton Emplacement ◽  
Ductile Shear Zones ◽  
Granitic Intrusion ◽  
Rheological Modeling ◽  
Extensional Setting

<p>Exhumation and cooling of upper crustal plutons is generally assumed to develop in the brittle domain, thus determining an abrupt passage from crystallization to faulting. To challenge this general statement, we have applied an integrated approach involving meso- and micro-structural studies, thermochronology, geochronology and rheological modeling. We have analyzed the Miocene syn-tectonic Porto Azzurro pluton on Elba (Tuscan archipelago – Italy), emplaced in an extensional setting, and have realized that its fast exhumation is accompanied by localized ductile shear zones, developing along dykes and veins, later affected by brittle deformation. This is unequivocally highlighted by field studies and the analysis of microstructures with EBSD. In order to constrain the emplacement and exhumation rate of the Porto Azzurro pluton we performed U-Pb zircon dating and (U+Th)/He apatite thermochronology. It results in a magma emplacement age of 6.4 ± 0.4 Ma and an exhumation rate of 3.4 to 3.9 mm/yr. By thermo-rheological modeling we were able to establish that localized ductile deformation occurred at two different time steps: within felsic dykes when the pluton first entered into the brittle field at 380 kyr, and along quartz-rich hydrothermal veins at c. 550 kyr after pluton emplacement. Hence, the major conclusion of our data is that ductile deformation can affect a granitic intrusion even when it is entered into the brittle domain in a fast exhuming extensional regime.</p>

Evidence for late Precambrian to early Cambrian orogeny in northwest Himalaya, Pakistan

1988 ◽  
Vol 125 (1) ◽  
pp. 83-86 ◽  
Author(s):  
M. S. Baig ◽  
R. D. Lawrence ◽  
L. W. Snee
Keyword(s):  
Low Grade ◽  
Early Cambrian ◽  
Northwest Himalaya ◽  
Precambrian Rocks ◽  
Grade Metamorphism ◽  
Angular Unconformity ◽  
Late Precambrian ◽  
Younger Age ◽  
Peraluminous Granites ◽  
The Himalaya

AbstractAn angular unconformity below Cambrian rocks is present in the northwest Himalaya in the Hazara district, Pakistan. Low-grade metamorphism and folding with axial planar cleavage present in Precambrian rocks below the unconformity, but not in those above it, confirm orogenic deformation at this time. This is the first clear evidence for such a deformation episode and it may be referred to locally as the Hazaran orogeny. Anatectic peraluminous granites of the Himalaya are of only slightly younger age and may be related to this orogenic episode.

Clinical genetics should not impose a younger age limit on testing

BMJ ◽  
1999 ◽  
Vol 318 (7190) ◽  
Keyword(s):  
Clinical Genetics ◽  
Younger Age ◽  
Age Limit

The Younger Age Limit of Metasedimentary Protolith Formation of the Lower Part of the Udokan Group Rocks (Aldan Shield)

2018 ◽  
Vol 479 (2) ◽  
pp. 415-419 ◽  
Author(s):  
A. B. Kotov ◽  
E. B. Salnikova ◽  
V. P. Kovach ◽  
S. D. Velikoslavinskii ◽  
E. V. Sklyarov ◽  
...  
Keyword(s):  
Aldan Shield ◽  
Younger Age ◽  
Age Limit

A younger age constraint on high‐grade metamorphism near George Sound in Fiordland, New Zealand

2009 ◽  
Vol 52 (2) ◽  
pp. 67-71 ◽  
Author(s):  
J. M. Scott ◽  
J. M. Palin ◽  
A. F. Cooper
Keyword(s):  
New Zealand ◽  
High Grade ◽  
Grade Metamorphism ◽  
Younger Age ◽  
High Grade Metamorphism

The youngest Paleozoic plutonism of the Newfoundland Appalachians: U–Pb ages from the St. Lawrence and François granites

1993 ◽  
Vol 30 (12) ◽  
pp. 2328-2333 ◽  
Author(s):  
A. Kerr ◽  
G. R. Dunning ◽  
R. D. Tucker
Keyword(s):  
Nova Scotia ◽  
South Coast ◽  
Tectonic Activity ◽  
Late Devonian ◽  
Early Paleozoic ◽  
Cape Breton Island ◽  
Cape Breton ◽  
Younger Age ◽  
Age Limit ◽  
Magmatic Event

The posttectonic St. Lawrence and François granites have long been regarded as the youngest Paleozoic plutonic suites of the Newfoundland Appalachians. Their U–Pb ages of 374 ± 2 and 378 ± 2 Ma, respectively, define a Middle to Late Devonian magmatic event. Mid-Carboniferous magmatic and (or) rifting events, suggested on the basis of earlier Rb–Sr dating of the St. Lawrence Granite, are not supported by these new data. Both granites intrude major ductile and brittle structures that were active during the early Paleozoic, and they provide a younger age limit for major tectonic activity in the Avalon Zone and on the south coast of Newfoundland. The granites may correlate with plutons of closely similar age reported from the Aspy and Mira terranes of Cape Breton Island, Nova Scotia.

Application Of Electron Probe Analyses Of Minerals In Discussing The Relationship Between Ductile Deformation And Metamorphism

1990 ◽  
Vol 48 (2) ◽  
pp. 250-251
Author(s):  
Fan Guochuan ◽  
Sun Zhongshi
Keyword(s):  
Chemical Composition ◽  
Shear Deformation ◽  
Electron Probe ◽  
General Rule ◽  
Granulite Facies ◽  
Ductile Deformation ◽  
Higher Temperature ◽  
Ductile Shear ◽  
The Relationship ◽  
Ductile Shear Deformation

Under influence of ductile shear deformation, granulite facies mineral paragenesis underwent metamorphism and changes in chemical composition. The present paper discusses some changes in chemical composition of garnet in hypers thene_absent felsic gnesiss and of hypersthene in rock in early and late granulite facies undergone increasing ductile shear deformation .In garnet fetsic geniss, band structures were formed because of partial melting and resulted in zoning from massive⟶transitional⟶melanocrate zones in increasing deformed sequence. The electron-probe analyses for garnet in these zones are listed in table 1 . The Table shows that Mno, Cao contents in garnet decrease swiftly from slightly to intensely deformed zones.In slightly and moderately deformed zones, Mgo contents keep unchanged and Feo is slightly lower. In intensely deformed zone, Mgo contents increase, indicating a higher temperature. This is in accord with the general rule that Mgo contents in garnet increase with rising temperature.

Sign in / Sign up

Export Citation Format

Share Document