Deformational history of an outlier of metasedimentary rocks, Coast Plutonic Complex, British Columbia, Canada

1986 ◽  
Vol 23 (6) ◽  
pp. 813-826 ◽  
Author(s):  
Bruce J. Douglas
Keyword(s):  
Shear Zones ◽  
Metasedimentary Rocks ◽  
Thrust Faulting ◽  
Deformational History ◽  
Plutonic Complex ◽  
Coast Plutonic Complex ◽  
History Of ◽  
Peak Metamorphism ◽  
Differential Uplift ◽  
Penetrative Foliation

The Khutzeymateen assemblage records a portion of the polyphase deformation experienced by rocks within the core of the Coast Plutonic Complex. This series of deformational events probably took place during Late Cretaceous to Early Eocene regional orogenic activity. The Khutzeymateen assemblage is dominated by metamorphosed graywackes and volcaniclastic material. The earliest recognizable deformation involves thrust faulting that juxtaposed rocks of the Khutzeymateen assemblage and Central Gneiss Complex. The next deformational event produced isoclinal folds (F1), a penetrative foliation (S1), and a strong mineral lineation (L1). Both F1 and L1 have a 340°, 15 °orientation. Peak metamorphism (P = 450 ± 50 MPa, T = 650° ± 50 °C) was synchronous with this isoclinal folding event. F1 folding was followed by a brittle chevron folding event (F2) with a 335°, 20° orientation. There is a strong lithologic control on the development of F2 minor folds, which are developed predominantly within regularly layered quartzo-feldspathic lithologies. Open F3 folds (065°, 35°) may have developed by buckling related to differential uplift on the Larch Creek Fault. Post-F3 faults and minor shear zones are developed mostly in the eastern half of the area. The different deformational styles associated with the different deformational events probably reflect variations in the position of this group of rocks with respect to the surface during a single orogenic episode.

Metasedimentary rocks, intrusions and deformation history in the south-east part of the c. 1800 Ma Ketilidian orogen, South Greenland: Project SUPRASYD 1996

1997 ◽  
pp. 60-65
Author(s):  
Adam A. Garde ◽  
Brian Chadwick ◽  
John Grocott ◽  
Cees Swager
Keyword(s):  
Field Work ◽  
Deformation History ◽  
The South ◽  
Present Contribution ◽  
East Part ◽  
Metasedimentary Rocks ◽  
Deformational History ◽  
Base Camp ◽  
History Of ◽  
Geological Map

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Garde, A. A., Chadwick, B., Grocott, J., & Swager, C. (1997). Metasedimentary rocks, intrusions and deformation history in the south-east part of the c. 1800 Ma Ketilidian orogen, South Greenland: Project SUPRASYD 1996. Geology of Greenland Survey Bulletin, 176, 60-65. https://doi.org/10.34194/ggub.v176.5063 _______________ The south-east part of the c. 1800 Ma Ketilidian orogen in South Greenland (Allaart, 1976) is dominated by strongly deformed and variably migmatised metasedimentary rocks known as the ‘Psammite and Pelite Zones’ (Chadwick & Garde, 1996); the sediments were mainly derived from the evolving Julianehåb batholith which dominates the central part of the orogen. The main purpose of the present contribution is to outline the deformational history of the Psammite Zone in the region between Lindenow Fjord and Kangerluluk (Fig. 2), investigated in 1994 and 1996 as part of the SUPRASYD project (Garde & Schønwandt, 1995 and references therein; Chadwick et al., in press). The Lindenow Fjord region has high alpine relief and extensive ice and glacier cover, and the fjords are regularly blocked by sea ice. Early studies of this part of the orogen were by boat reconnaissance (Andrews et al., 1971, 1973); extensive helicopter support in the summers of 1992 and 1994 made access to the inner fjord regions and nunataks possible for the first time.A preliminary geological map covering part of the area between Lindenow Fjord and Kangerluluk was published by Swager et al. (1995). Hamilton et al. (1996) have addressed the timing of sedimentation and deformation in the Psammite Zone by means of precise zircon U-Pb geochronology. However, major problems regarding the correlation of individual deformational events and their relationship with the evolution of the Julianehåb batholith were not resolved until the field work in 1996. The SUPRASYD field party in 1996 (Fig. 1) was based at the telestation of Prins Christian Sund some 50 km south of the working area (Fig. 2). In addition to base camp personnel, helicopter crew and the four authors, the party consisted of five geologists and M.Sc. students studying mafic igneous rocks and their mineralisation in selected areas (Stendal et al., 1997), and a geologist investigating rust zones and areas with known gold anomalies.

Obducted nappe sequence in the San Juan Islands – northwest Cascades thrust system, Washington and British Columbia

2012 ◽  
Vol 49 (7) ◽  
pp. 796-817 ◽  
Author(s):  
E.H. Brown
Keyword(s):  
British Columbia ◽  
Detrital Zircons ◽  
San Juan ◽  
San Juan Islands ◽  
Tectonic History ◽  
Plutonic Complex ◽  
Coast Plutonic Complex ◽  
History Of ◽  
Accreted Terranes ◽  
Thrust System

The San Juan Islands – northwest Cascades thrust system in Washington and British Columbia is composed of previously accreted terranes now assembled as four broadly defined composite nappes stacked on a continental footwall of Wrangellia and the Coast Plutonic Complex. Emplacement ages of the nappe sequence are interpreted from zircon ages, field relations, and lithlogies, to young upward. The basal nappe was emplaced prior to early Turonian time (∼93 Ma), indicated by the occurrence of age-distinctive zircons from this nappe in the Sidney Island Formation of the Nanaimo Group. The emplacement age of the highest nappe in the thrust system postdates 87 Ma detrital zircons within the nappe. The nappes bear high-pressure – low-temperature (HP–LT) mineral assemblages indicative of deep burial in a thrust wedge; however, several features indicate that metamorphism occurred prior to nappe assembly: metamorphic discontinuities at nappe boundaries, absence of HP–LT assemblages in the footwall to the nappe pile, and absence of significant unroofing detritus in the Nanaimo Group. A synorogenic relationship of the thrust system to the Nanaimo Group is evident from mutually overlapping ages and by conglomerates of Nanaimo affinity that lie within the nappe pile. From the foregoing relations, and broader Cordilleran geology, the tectonic history of the nappe terranes is interpreted to involve initial accretion and subduction-zone metamorphism south of the present locality, uplift and exhumation, orogen-parallel northward transport of the nappes as part of a forearc sliver, and finally obduction at the present site over the truncated south end of Wrangellia and the Coast Plutonic Complex.

First in-situ Rb-Sr dating of metasedimentary rocks from the Pontiac subprovince, Superior Craton, Canada. Implications towards the regional metamorphic evolution of the sequence.

2020 ◽  
Author(s):  
Nicholas Leventis ◽  
Thomas Zack ◽  
Iain Pitcairn ◽  
Johan Högmalm
Keyword(s):  
Accretionary Prism ◽  
Metasedimentary Rocks ◽  
Metamorphic History ◽  
Accuracy And Precision ◽  
Icp Ms ◽  
Age Variations ◽  
History Of ◽  
Peak Metamorphism ◽  
Superior Craton

<p>The Pontiac subprovince consists of metaturbidites, plutons and thin ultramafic rock layers of Archean age and lies south of the Cadillac-Larder Lake (C-LL) fault zone which is the boundary between the Pontiac and the extensively mineralized Abitibi Greenstone Belt. The sediments show a Barrovian metamorphic gradient which increases southwards, away from the C-LL fault. The most likely tectonic provenance for the Pontiac sedimentary rocks is that they represent a relic accretionary prism with material derived from both the Abitibi and an older terrane. Zircon U-Pb dating shows that deposition occurred not later than 2685±3 Ma ago and recent, robust Lu-Hf dating of garnets bracketed Pontiac's peak metamorphic conditions at 2658±4 Ma. For this study we used a recently developed LA-ICP-MS/MS method for in-situ Rb-Sr dating of biotite and plagioclase in samples ranging in metamorphic grade (biotite to sillimanite zones) from the Pontiac subprovince. Calibration of the instrument was achieved by repeated ablations on several reference materials (see Hogmalm et al. 2017) which also provided the monitoring of accuracy and precision throughout the analyses. Results show a range in dates between 2550 Ma and 2200 Ma with an average of 2440±50 Ma (2σ). Samples from the staurolite and kyanite zones have a larger range with respect to the other zones, but no significant differences are observed in the data with any method of data handing. These dates are ≈300Ma younger than the peak metamorphism in the area and this is attributed to either overgrowth and re-setting of the Rb-Sr system by a second metamorphic/hydrothermal event, or diffusional resetting with core-rim age variations. Possible influence from the adjacent late syntectonic to post-tectonic monzodiorite-monzonite-granodiorite-syenite (MMGS) plutons dated 2671±4 Ma and the garnet-muscovite-granite series (GMG) dated ≈2650 Ma cannot be ruled out. This study provides insights about the metamorphic history of the sequence and supports previous findings regarding resetting of some isotopic systems with relatively low closure temperatures (≈350-400°C) by later thermal events.</p>

scholarly journals Rhabdophane Th-Pb ages indicate reactivation of Mesoarchean structures in west Pilbara Craton during breakup of Greater India and Australia-Antarctica

Geology ◽  
2021 ◽  
Author(s):  
Birger Rasmussen ◽  
Jian-Wei Zi ◽  
Janet R. Muhling
Keyword(s):  
Fluid Flow ◽  
Shear Zones ◽  
Drill Hole ◽  
Carbonaceous Shale ◽  
Low Grade ◽  
Early Environment ◽  
Metasedimentary Rocks ◽  
Rift Propagation ◽  
History Of ◽  
Pilbara Craton

Uranium-Th-Pb dating of phosphate minerals in very low-grade metasedimentary rocks from the Archean Pilbara Craton, Western Australia, has revealed a long history of deformation and fluid flow during the Paleoproterozoic. However, this technique has not detected evidence for fluid flow along craton margins during Phanerozoic rifting and breakup. We report the use of in situ Th-Pb geochronology of rhabdophane, a hydrous light rare earth element phosphate, to date fluid flow in shale from the 2.76 Ga Mount Roe Basalt from drill hole number 6 of the Archean Biosphere Drilling Program (ABDP6), northwestern Pilbara Craton. Thorium-Pb dating of rhabdophane in carbonaceous shale yields three main populations with weighted mean 208Pb/232Th ages of 152 ± 6 Ma, 132 ± 4 Ma, and 119 ± 4 Ma, which indicates phosphate growth up to 2.64 b.y. after deposition. The rhabdophane ages are coeval with three major breakup events in eastern Gondwana: separation of Southwest Borneo and Argoland from Australia (ca. 156–152 Ma), breakup of Greater India from Australia (ca. 140–135 Ma), and separation of Greater India/India from Antarctica (ca. 123 Ma). The proximity of drill hole ABDP6 to major Mesoarchean faults and shear zones on the craton margin, which are parallel to rift propagation and basin development, points to episodic reactivation of ancient crustal structures >2.8 b.y. after their formation. Our results also highlight the potential of rhabdophane as a U-Th-Pb geochronometer for dating low-temperature (<200 °C) fluid flow and hydrous alteration. The migration of Mesozoic fluids through Archean shales adds weight to questions about the origin of geochemical signals in ancient altered rocks and how to extract information about the early environment and biosphere.

Deformation timing and strain in Neoproterozoic strata, Jebel Akhdar, northern Oman

2020 ◽  
Author(s):  
Christopher Bailey ◽  
Claire Rae
Keyword(s):  
Strain Analysis ◽  
Low Grade ◽  
Depositional History ◽  
Fine Grained ◽  
Metasedimentary Rocks ◽  
Aspect Ratios ◽  
Deformation Kinematics ◽  
History Of ◽  
Penetrative Foliation ◽  
Ar Geochronology

<p>Neoproterozoic rocks exposed in the Jebel Akhdar massif of northern Oman preserve glaciogenic deposits associated with multiple Cryogenian glaciations. Although the depositional history of these rocks is well understood, the significance of post-depositional deformation is poorly constrained. In this study, we examine low-grade metasedimentary rocks exposed in the Ghubrah Bowl, an erosional window in the Jebel Akhdar massif, in order to quantify the 3D finite strain, understand deformation kinematics, and determine the timing of deformation/metamorphism.</p><p>In the Jebel Akhdar massif, the older Ghubrah (Sturtian glaciation) and younger Fiq (Marinoan glaciation) formations comprise a >1 km thick sequence of diamictite interbedded with sandstone, siltstone, conglomerate, volcanic rock, and minor carbonate. Diamictites contain abundant clasts of siltstone and sandstone, with lesser amounts of granite and metavolcanic rock in a fine-grained quartz + sericite ± chlorite matrix. Clasts range from granules to boulders. Harder clasts tend to be subangular and poorly aligned with low aspect ratios, whereas fine-grained rock clasts are well-aligned with large aspect ratios. Bedding generally dips to the NW, but is gently folded in accord with the overall structure of the Jebel Akhdar massif. A penetrative foliation strikes E-W and dips to the S. At some locations, a prominent elongation lineation/pencil structure occurs and plunges gently to moderately to the S.</p><p>R<sub>f</sub>/phi strain analysis in the diamictites reveals a range of 3D strain geometries (apparent flattening to apparent constriction) with strain ratios up to 2.8 in XZ sections. Strain is strongly partitioned, as clasts of igneous rock have low aspect ratios and are only weakly aligned. Penetrative strain in clast-supported sandstones is negligible (XZ ratios of <1.2). Outsized clasts of granite and sandstone are mantled by distinctive symmetric pressure shadows (double-duckbill structures) that include more recrystallized minerals than elsewhere in the diamictite. <sup>40</sup>Ar/<sup>39</sup>Ar geochronology of sericite in pressure shadows yields ages as young as 90 Ma, which are interpreted as mixed ages containing an older detrital component and a younger fraction formed during growth. Deformation is associated with southward emplacement and loading by the Oman ophiolite & Hawasina Group sediments over the autochthonous sequence in the late Cretaceous.</p>

Deformational History of Archean Metasedimentary Rocks of the Beartooth Mountains in the Vicinity of the Mineral Hill Mine, Jardine, Montana

1992 ◽  
Vol 100 (5) ◽  
pp. 561-578 ◽  
Author(s):  
Joseph D. Jablinski ◽  
Timothy B. Holst
Keyword(s):  
Metasedimentary Rocks ◽  
Deformational History ◽  
History Of

Metamorphism of the Kisseynew gneisses and related rocks of the Reindeer Zone, Trans-Hudson Orogen, northern Saskatchewan

1991 ◽  
Vol 28 (10) ◽  
pp. 1664-1676 ◽  
Author(s):  
Dexter Perkins
Keyword(s):  
Shear Zones ◽  
Granulite Facies ◽  
Metamorphic Grade ◽  
Heat Sources ◽  
Metasedimentary Rocks ◽  
Precambrian Geology ◽  
Thrust Sheets ◽  
Peak Metamorphism ◽  
The Common ◽  
Flin Flon

In the Reindeer Zone of Saskatchewan, the mostly metasedimentary Kisseynew gneiss crops out in a 300 km wide belt extending from the Tabbernor Fault to the Manitoba border. Metamorphic grade varies from middle amphibolite to granulite facies. Associated with the main Kisseynew gneiss are metasedimentary rocks of the Glennie Domain, Attitti Block, and Hanson Lake Block. Sillimanite is the common aluminosilicate in most parts of the four domains. Andalusite occurs at several places within the southern Glennie Domain, in the southern Hanson Lake Block, and in the northern Flin Flon Belt. Kyanite, appearing relict in many samples, is found in a 10 km × 50 km zone adjacent to the Flin Flon Belt.Most of the regional variation in metamorphic P–T can be explained by postmetamorphic folding and uplift. Peak T varied from less than 600 °C (in the Glennie Domain) to 725 °C. The highest temperatures were recorded near enderbite occurrences at Chicken Lake, 10 km east of Sandy Bay, and along a thermal anticline, extending east-northeast from the Hanson Lake Block, across the Attitti Block. Metamorphic P ranged from less than 4.5 kbar to 10 kbar (1 kbar = 100 MPa). Highest pressures were associated with the uplifted Hanson Lake and Attitti blocks.The Precambrian geology of the Reindeer Zone is characterized by stacked thrust sheets, many of which are separated by originally subhorizontal shear zones. The sheet including the Kisseynew sediments was carried to approximately 20–30 km depth by continental thickening due to the thrusting. Metamorphism did not take place on a normal geotherm: heat for metamorphism was augmented by plutonic heat sources. Late, northeast-plunging folds postdated peak metamorphism and were followed by uplift. If the Kisseynew sediments are metamorphosed equivalents of the Flin Flon Amisk and Missi Groups, a transect from the Flin Flon Belt to the Attitti Block may represent a deformed 20 km section.

Geochronology and thermal history of the Coast Plutonic Complex, near Prince Rupert, British Columbia

1979 ◽  
Vol 16 (3) ◽  
pp. 400-410 ◽  
Author(s):  
T. Mark Harrison ◽  
Richard Lee Armstrong ◽  
C. W. Naeser ◽  
J. E. Harakal
Keyword(s):  
Thermal History ◽  
Land Surface ◽  
Fission Track ◽  
Average Rate ◽  
Closure Temperature ◽  
Plutonic Complex ◽  
Coast Plutonic Complex ◽  
History Of ◽  
Intermediate Cooling ◽  
Temperature Time

Fission track, K–Ar, and Rb–Sr mineral dates for the Ecstall and Quottoon plutons were determined to resolve the different cooling histories indicated by Rb–Sr whole-rock and mineral isochrons and published K–Ar dates.Comparison of mineral dates with previously assigned closure temperatures for the various isotopic chronometers has allowed temperature–time plots for the thermal history of individual samples and sample suites to be constructed.The Quottoon pluton, emplaced approximately 51 Ma ago, cooled rapidly during initial uplift that ended ~46 Ma ago with the present-day land surface at a depth of ~4 km. A second episode of uplift at an average rate of 0.05 cm year−1 (measured in Kasiks pluton that lies immediately to the east) began in the late Miocene. Cooling of the Ecstall pluton, following emplacement approximately 80 Ma ago, was disrupted by a thermal event approximately 65 Ma ago. Biotite in the Ecstall pluton appears to have incorporated extraneous argon during this event so that the calculated K–Ar dates lie between the time of emplacement and time of cooling through the closure temperature for Ar in biotite.The cooling curves and observed dates yield estimates for closure temperatures, at an intermediate cooling rate, for Ar in plagioclase and K-feldspar of ~260 °C and ~160 °C, respectively. For fission tracks in epidote the closure temperature estimate is ~240 °C.

Yukon–Tanana terrane in the southern Campbell Range, Finlayson Lake belt, southeastern Yukon: the geological setting of retrogressed eclogite of the Klatsa metamorphic complex

2007 ◽  
Vol 44 (3) ◽  
pp. 317-336 ◽  
Author(s):  
Fionnuala Devine ◽  
Donald C Murphy ◽  
Sharon D Carr
Keyword(s):  
Lower Permian ◽  
Metamorphic Complex ◽  
Early Permian ◽  
Thrust Sheet ◽  
Volcanic Arc ◽  
Metasedimentary Rocks ◽  
Thrust Faulting ◽  
Structural History ◽  
History Of ◽  
Finlayson Lake

Yukon–Tanana terrane in the southern Campbell Range is composed of rocks that have different metamorphic, exhumation, and structural histories, and that have formed in disparate parts of the Paleozoic Yukon–Tanana volcanic arc. The geological relationships in the southern Campbell Range reveal the tectonic and structural history of the Klatsa metamorphic complex, which represents the remnants of an Early Mississippian subduction zone beneath the Yukon–Tanana arc. The Klatsa metamorphic complex is composed of foliated to massive serpentinite, leucogabbro, amphibolite, and retrogressed eclogitic quartz–muscovite schist with lenses of metabasite. It was structurally juxtaposed on Upper Mississippian to Lower Permian metasedimentary rocks of the White Lake, King Arctic, and Money Creek formations. Regional and local structural and stratigraphic relationships suggest that the Klatsa metamorphic complex is part of the Cleaver Lake thrust sheet, the structurally highest thrust sheet in a north- to northeast-vergent thrust belt that deformed the Yukon–Tanana terrane during the Early Permian. Restoration of the displacement on the Cleaver Lake and underlying thrust faults places the Klatsa metamorphic complex on the western margin of Yukon–Tanana terrane. Late Devonian to Early Mississippian subduction is thought to have occurred along this margin based on previous paleogeographic reconstructions. Generally north- to northeast-vergent D1 to D3 folds deformed the Klatsa metamorphic complex and adjacent metasedimentary rocks. Jurassic(?) D4 imbricate thrust faulting has, in part, reactivated the Cleaver Lake thrust fault contacts and imbricated the Klatsa metamorphic complex with metasedimentary rocks in fault panels that are repeated at a scale of 10 to hundreds of metres.

Deformational history of an Archean fold belt, eastern Point Lake area, Slave Structural Province, N.W.T.

1989 ◽  
Vol 26 (1) ◽  
pp. 106-118 ◽  
Author(s):  
J. E. King ◽  
H. Helmstaedt
Keyword(s):  
Lake Area ◽  
Metasedimentary Rocks ◽  
Thermal Peak ◽  
Strain Pattern ◽  
Slave Province ◽  
Deformational History ◽  
Supracrustal Belt ◽  
Two Generations ◽  
History Of ◽  
Granitoid Intrusions

Archean metasedimentary rocks in the eastern Point Lake area of the Slave Structural Province preserve a sequence of Archean structures consisting of two generations of folds (F1 and F2) with little associated penetrative cleavage and two subsequent generations of cleavage (S3 and S4) with little associated folding. Gneissic layering in the high-grade margin of the belt is composed of transposed bedding and the S3 cleavage. Folding occurred prior to the thermal peak of metamorphism, whereas the develoment of subsequent cleavages spanned the thermal peak. The regional orientation of the folds and cleavages appears to be independent of the emplacement of granitoid intrusions, although their orientation is modified adjacent to syn- to late tectonic plutons. The supracrustal belt is interpreted as being part of a pre- to early metamorphic, west-verging fold (thrust?) belt whose strain pattern has been modified by post-folding, synmetamorphic shortening, and syn- to post-tectonic plutons. This deformation sequence is similar to those described in other supracrustal belts of the Slave Province and supports the concept that the Slave Province has undergone regional, horizontally directed compression before and during intrusion of large amounts of granitoids.

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