U–Pb geochronology of late Neoarchean tonalites in the Flin Flon Belt, Trans-Hudson Orogen: surprise at surface

1994 ◽  
Vol 31 (12) ◽  
pp. 1785-1790 ◽  
Author(s):  
J. David ◽  
E. C. Syme
Keyword(s):  
Shear Zone ◽  
Tectonic Evolution ◽  
Volcanic Belt ◽  
Lake Area ◽  
Magmatic Rocks ◽  
Flin Flon ◽  
First Time

The Flin Flon volcanic belt of the Trans-Hudson Orogen in northern Manitoba comprises magmatic rocks (1.88 – 1.90 Ga) generated in an intra-oceanic arc and identified as one of the best examples of juvenile Paleoproterozoic crust. In the Flin Flon – Athapapuskow Lake area, the belt consists of a series of fault-bounded blocks, each having distinct stratigraphic and magmatic affinities, juxtaposed to form an accretionary collage. Two tonalitic bodies within the Northeast Arm shear zone, a major deformation corridor separating two of the most important blocks in the area, have been dated by the U–Pb zircon method at [Formula: see text] and [Formula: see text]. These results indicate the presence of fragments of late Neoarchean crust within the Flin Flon belt, possibly related to ca. 2.5 Ga granitic bodies found in terranes beyond the western limit of the belt. The presence of ca. 2.5 Ga tonalites within the Flin Flon Belt, herein reported for the first time, has major implications for basement involvement in the early tectonic evolution of the Flin Flon Belt.

Vorticity analysis of the Palmi shear zone mylonites: new insights for the Alpine tectonic evolution of the Calabria-Peloritani terrane (southern Italy)

2015 ◽  
Vol 51 (4) ◽  
pp. 670-681 ◽  
Author(s):  
Vincenzo Festa ◽  
Giacomo Prosser ◽  
Alfredo Caggianelli ◽  
Antonietta Grande ◽  
Antonio Langone ◽  
...  
Keyword(s):  
Shear Zone ◽  
Tectonic Evolution ◽  
Southern Italy ◽  
Vorticity Analysis

Structure and spatial-temporal relationship of potassic magmatism linked to a continental-scale strike-slip shear zone and post-collisional Cenozoic extension

2021 ◽  
Author(s):  
junyu Li ◽  
shunyun Cao ◽  
Xuemei Cheng ◽  
Haobo Wang ◽  
Wenxuan Li
Keyword(s):  
Partial Melting ◽  
Shear Zone ◽  
Continental Crust ◽  
Red River ◽  
Compositional Variation ◽  
Continental Scale ◽  
Magmatic Rocks ◽  
Western Yunnan ◽  
Potassic Rocks ◽  
Potassic Magmatism

<p>Adakite‐like potassic rocks are widespread in post-collisional settings and provide potential insights into deep crustal or crust-mantle interaction processes including asthenosphere upwelling, partial melting, lower crustal flow, thickening and collapse of the overthickened orogen. However, petrogenesis and compositional variation of these adakite‐like potassic rocks and their implications are still controversial. Potassic magmatic rocks are abundant developed in the Jinshajiang–Ailaoshan tectono-magmatic belt that stretches from eastern Tibet over western Yunnan to Vietnam. Integrated studies of structure, geochronology, mineral compositions and geochemistry indicate adakite-like potassic rocks with different deformation are exposed along the Ailaoshan-Red River shear zone. The potassic felsic rocks formed by mixing and partial melting between enriched mantle-derived ultrapotassic and thickened ancient crust-derived magmas. The mixing of the mafic and felsic melts and their extended fractional crystallization of plagioclase, K-feldspar, hornblende and biotite gave rise to the potassic magmatic rocks. Zircon geochronology provide chronological markers for emplacement at 35–37 Ma of these adakite-like potassic rocks along the shear zone. Temperature and pressure calculated by amphibole-plagioclase thermobarometry range from 3.5 to 5.9 kbar and 650 to 750 ℃, respectively, and average emplacement depths of ca. 18 km for granodiorite within this suite. In combination with the results of the Cenozoic potassic magmatism in the Jinshajiang–Ailaoshan tectono-magmatic belt, we suggest that in addition to partial melting of the thickened ancient continental crust, magma underplating and subsequent crust-mantle mixing beneath the ancient continental crust have also played an important role in crustal reworking and strongly affected the rheological properties and density of rocks. The exhumation underlines the role of lateral motion of the Ailaoshan-Red River shear zone initiation by potassic magma-assisted rheological weakening and exhumation at high ambient temperatures within the shear zone.</p>

scholarly journals Kinematics and Timing Constraints in a Transpressive Tectonic Regime: The Example of the Posada-Asinara Shear Zone (NE Sardinia, Italy)

Geosciences ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 288
Author(s):  
Rodolfo Carosi ◽  
Alessandro Petroccia ◽  
Salvatore Iaccarino ◽  
Matteo Simonetti ◽  
Antonio Langone ◽  
...  
Keyword(s):  
Shear Zone ◽  
Finite Strain ◽  
Pure Shear ◽  
Deformation Gradient ◽  
Shear Zones ◽  
Temperature Deformation ◽  
Timing Constraints ◽  
Important Variation ◽  
Deformation Phase ◽  
First Time

Detailed geological field mapping, integrated with meso- and microstructural investigations, kinematic of the flow and finite strain analyses, combined with geochronology, are fundamental tools to obtain information on the temperature–deformation–timing path of crystalline rocks and shear zone. The Posada-Asinara shear zone (PASZ) in northern Sardinia (Italy) is a steeply dipping km-thick transpressive shear zone. In the study area, located in the Baronie region (NE Sardinia), the presence of mylonites within the PASZ, affecting high- and medium-grade metamorphic rocks, provides an opportunity to quantify finite strain and kinematic vorticity. The main structures of the study area are controlled by a D2 deformation phase, linked to the PASZ activity, in which the strain is partitioned into folds and shear zone domains. Applying two independent vorticity methods, we detected an important variation in the percentage of pure shear and simple shear along the deformation gradient, that increases from south to north. We constrained, for the first time in this sector, the timing of the transpressive deformation by U–(Th)–Pb analysis on monazite. Results indicate that the shear zone has been active at ~325–300 Ma in a transpressive setting, in agreement with the ages of the other dextral transpressive shear zones in the southern Variscan belt.

U–Pb zircon ages from the eastern Savant Lake – Crow Lake metavolcanic–metasedimentary belt, northwest Ontario

1982 ◽  
Vol 19 (4) ◽  
pp. 868-877 ◽  
Author(s):  
D. W. Davis ◽  
N. F. Trowell
Keyword(s):  
Volcanic Belt ◽  
Time Span ◽  
Lake Area ◽  
The South ◽  
Air Abrasion ◽  
Angular Unconformity ◽  
Volcanic Sequence ◽  
Northwest Ontario ◽  
Lake Sample ◽  
Volcanic Cycles

Five rocks from three areas in the eastern part of the Savant Lake – Crow Lake metavolcanic–metasedimentary belt have been dated by U–Pb analysis of zircons.The Sioux Lookout area is composed of a sequence of generally fault-bounded metavolcanic and metasedimentary belts. The age of a felsic tuff in the Central volcanic belt is [Formula: see text]. This is possibly the youngest sequence in the area.The Savant Lake volcanic belt comprises the Jutten volcanic unit at its base separated by an angular unconformity from the Handy Lake volcanic sequence. The age of a dacitic tuff near the base of the Handy Lake volcanic sequence is [Formula: see text].The South Sturgeon Lake volcanic belt is composed of four volcanic cycles. The age of a felsic tuff from the top of the uppermost cycle is [Formula: see text]. The felsic Beidelman Bay pluton and the mafic Pike Lake pluton, which both intruded the lower part of the sequence, give ages of [Formula: see text] and [Formula: see text], respectively. This establishes a minimum time span of [Formula: see text] for deposition of the sequence. This interval, along with the 27 Ma span between the ages of the Handy Lake sample and the volcanic sample from the South Sturgeon Lake area, suggests that the sequences were laid down by a series of discrete volcanic episodes.For samples subjected to multistage lead loss, the reliability of ages has been greatly enhanced by air abrasion of zircons. Several cases of suspected biasing of analyses by the air abrasion process have been encountered. It appears that this biasing problem can be overcome by selection and abrasion of low uranium grains that are free of imperfections.

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