Structure, petrology, and tectonic history of the Leech River complex northwest of Victoria, Vancouver Island

1982 ◽  
Vol 19 (9) ◽  
pp. 1817-1835 ◽  
Author(s):  
Lee H. Fairchild ◽  
Darrel S. Cowan
Keyword(s):  
Volcanic Rocks ◽  
Low Pressure ◽  
Vancouver Island ◽  
Southern Boundary ◽  
Late Mesozoic ◽  
The North ◽  
Tectonic History ◽  
Early Tertiary ◽  
History Of ◽  
Pelitic Rocks

The Leech River complex 45 km northwest of Victoria consists of metamorphosed pelitic rocks, sandstone, and minor volcanic rocks, chert, and conglomerate of probable Late Jurassic to Cretaceous age. The assemblage experienced two similar deformational events during which regional shortening induced macroscopic east-plunging folds and related coaxial, mesoscopic linear structures, parasitic folds, and axial-plane cleavages. Fragmentation along the developing cleavages disrupted layering and eventually led to transposition during both events. Regional, progressive, low-pressure greenschist- to amphibolite-facies (andalusite–staurolite–biotite) metamorphism began during the first deformation and extended into the waning stages of the second. Intrusion of composite felsic sills was synchronous with deformation and metamorphism, which concluded about 39–41 Ma, according to K–Ar data. The Leech River fault, which forms the southern boundary of the complex, is a zone of two to four subparallel faults. All are relatively straight, narrow faults that appear to dip steeply. This structure is interpreted to be a left-lateral strike-slip fault, active exclusively after the 39–41 Ma conclusion of metamorphism and deformation.The Leech River complex originally may have accumulated somewhere along a late Mesozoic convergent margin, but there is no evidence that it either constitutes a subduction complex per se or was metamorphosed in such a setting in early Tertiary time. The Leech River complex is interpreted to be allochthonous with respect to the bulk of Vancouver Island, since neither older rocks of the Insular Belt (Wrangellia) to the north nor coeval rocks in northwestern Washington record the early Tertiary deformations and synkinematic low-pressure metamorphism. The complex apparently was derived from a cryptic terrane to the west and emplaced against Vancouver Island by left-lateral slip on the San Juan fault after 39–41 Ma.

Implication of dating of Early Tertiary volcanic rocks from the north-Chilean Precordillera

1992 ◽  
Vol 202 (1) ◽  
pp. 55-81 ◽  
Author(s):  
K. Hammerschmidt ◽  
R. Döbel ◽  
H. Friedrichsen
Keyword(s):  
Volcanic Rocks ◽  
The North ◽  
Early Tertiary

Late Mesozoic and Cenozoic tectonic history of south central California

Tectonics ◽  
1984 ◽  
Vol 3 (6) ◽  
pp. 659-675 ◽  
Author(s):  
A. E. J. Engel ◽  
P. A. Schultejann
Keyword(s):  
Central California ◽  
Late Mesozoic ◽  
Tectonic History ◽  
South Central ◽  
History Of

scholarly journals IV.—The Volcanic History of Ireland

1874 ◽  
Vol 1 (5) ◽  
pp. 205-210
Author(s):  
Edward Hull
Keyword(s):  
Volcanic Rocks ◽  
Central Valley ◽  
Short Description ◽  
Lower Carboniferous ◽  
Volcanic History ◽  
The North ◽  
History Of ◽  
Similar Materials ◽  
Considerable Intensity

Carboniferous Period.—The Lower Carboniferous rocks, both of the North of England, of Scotland, and of Ireland, afford examples of contemporaneous volcanic action of considerable intensity. The so-called “toad-stones” of Derbyshire, and the great sheets of melaphyre, porphyrite, and ashes of the central valley of Scotland, forming the Kilpatrick, Campsie, and Dairy Hills, appear to have been erupted over the bed of the same sea as that in which were poured out similar materials in County Limerick, forming the well-known Carboniferous volcanic rocks of “the Limerick Basin.” These rocks have been already so fully described by several observers, that I shall confine myself to a very short description, such as is essential to the brief history of volcanic action which I am here endeavouring to draw up.

scholarly journals Cenozoic tectonic history of the North America-Caribbean plate boundary zone in western Cuba

1997 ◽  
Vol 102 (B5) ◽  
pp. 10055-10082 ◽  
Author(s):  
Mark B. Gordon ◽  
Paul Mann ◽  
Dámaso Cáceres ◽  
Raúl Flores
Keyword(s):  
North America ◽  
Plate Boundary ◽  
Boundary Zone ◽  
Caribbean Plate ◽  
The North ◽  
Tectonic History ◽  
History Of ◽  
Plate Boundary Zone

Rb–Sr geochronology and metamorphic history of Proterozoic to early Archean rocks north of the Cape Smith Fold Belt, Quebec

1987 ◽  
Vol 24 (4) ◽  
pp. 813-825 ◽  
Author(s):  
Ronald Doig
Keyword(s):  
Volcanic Rocks ◽  
Granitic Rocks ◽  
Iron Formation ◽  
Fold Belt ◽  
Metasedimentary Rocks ◽  
Metamorphic History ◽  
The North ◽  
Basement Rocks ◽  
History Of ◽  
Wide Zone

The Churchill Province north of the Proterozoic Cape Smith volcanic fold belt of Quebec may be divided into two parts. The first is a broad antiform of migmatitic gneisses (Deception gneisses) extending north from the fold belt ~50 km to Sugluk Inlet. The second is a 20 km wide zone of high-grade metasedimentary rocks northwest of Sugluk Inlet. The Deception gneisses yield Rb–Sr isochron ages of 2600–2900 Ma and initial ratios of 0.701–0.703, showing that they are Archean basement to the Cape Smith Belt. The evidence that the basement rocks have been isoclinally refolded in the Proterozoic is clear at the contact with the fold belt. However, the gneisses also contain ubiquitous synclinal keels of metasiltstone with minor metapelite and marble that give isochron ages less than 2150 Ma. These ages, combined with low initial ratios of 0.7036, show that they are not part of the basement, as the average 87Sr/86Sr ratio for the basement rocks was about 0.718 at that time.The rocks west of Sugluk Inlet consist mainly of quartzo-feldspathic sediments, quartzites, para-amphibolites, marbles, and some pelite and iron formation. In contrast to the Proterozoic sediments in the Deception gneisses, these rocks yield dates of 3000–3200 Ma, with high initial ratios of 0.707–0.714. These initial ratios point to an age (or a provenance) much greater than that of the Archean Deception gneisses. The rocks of the Sugluk terrain are intruded by highly deformed sills of granitic rocks with ages of about 1830 Ma, demonstrating again the extent and severity of the Proterozoic overprint. The eastern margin of this possibly early Archean Sugluk block is a discontinuity in age, lithology, and geophysical character that could be a suture between two Archean cratons. It is not known if such a suturing event is of Archean age, or if it is related to the deformation of the Cape Smith Fold Belt.Models of evolution incorporating both the Cape Smith Belt and the Archean rocks to the north need to account for the internal structure of the fold belt, the continental affinity of many of the volcanic rocks, the continuity of basement around the eastern end of the belt, and the increase in metamorphism through the northern part of the belt into a broad area to the north. The Cape Smith volcanic rocks may have been extruded along a continental rift, parallel to a continental margin at Sugluk. Continental collison at Sugluk would have thrust the older and higher grade Sugluk rocks over the Deception gneisses, produced the broad Deception antiform, and displaced the Cape Smith rocks to the south in a series of north-dipping thrust slices.

On the nature of the crust in the vicinity of the southeast Newfoundland Ridge

1978 ◽  
Vol 15 (9) ◽  
pp. 1462-1471 ◽  
Author(s):  
K. D. Sullivan ◽  
C. E. Keen
Keyword(s):  
Focal Point ◽  
Magnetic Data ◽  
Seismic Structure ◽  
Grand Banks ◽  
The North ◽  
Tectonic History ◽  
History Of ◽  
Continental Origin ◽  
Magnetic Lineations ◽  
Gravity And Magnetic Data

This paper presents new seismic reflection, refraction, gravity, and magnetic data bearing on the nature of the crust in the vicinity of the Newfoundland Ridge and the J-anomaly Ridge, immediately south of the Grand Banks. This area experienced a complicated plate tectonic history being the focal point for interactions of the North American, African, and Iberian plates. New data have recently been published for this region and conflicting interpretations have been offered in relation to the oceanic or continental origin of the crust there. The data presented here show that the seismic structure and the most reasonable models for the magnetic anomalies are more consistent with an oceanic origin. The trends and offsets in the magnetic lineations and possible differences in subsidence, north and south of the Newfoundland Ridge, are discussed in relation to possible modes of formation of this feature. It is proposed that similar subsidence histories since mid-Cretaceous time on the Grand Banks and J-anomaly Ridge are related to a similarity in the thermal history of the lithosphere beneath these areas, as the ridge crest migrated eastwards, and do not require the same type of crust to underlie both areas.

scholarly journals Zur Tal- und Reliefgeschichte des Churfirsten-Alvier-Gebietes (Kanton St. Gallen)

1987 ◽  
Vol 42 (2) ◽  
pp. 159-168
Author(s):  
R. Hantke
Keyword(s):  
Southern Slope ◽  
The South ◽  
Helvetic Nappes ◽  
Early Stages ◽  
Tectonic History ◽  
Early Tertiary ◽  
History Of

Abstract. The valley and relief history of the Churfirsten-Alvier ränge (Ct. St. Gallen): Valley formation in the Churfirsten-Alvier range, between the Linth and Rhine rivers. began at the end of the Miocene with the tectonic history of the Helvetic nappes. In early stages. the Cretaceaous sequences became independent of their Jurassic substratums and these from their Verrucano-Tnassic basement. The valley of Lake Walenstadt in the south was initiated between this basement and north-moving younger sequences. The Thur valley, north of the Churfirsten range, which follows a syncline in the highest Helvetic nappe. was filled with early Tertiary Sediments and Pennine Flysch. The Valleys in the Alvier area are formed along synclmes and faults in the Cretaceous sequence; these structures dip towards the Rhme valley. The Churfirsten range forms a limestone shield in the Helvetic nappe. It broke up foUowing ±N/S-onented joints. There inbetween, excavation of kars (cirques) began already during pre-Ouaternary glaciation; they are still intact at the ends of the ränge, but in the middle the kar-walls broke down along the steeper southern slope. During the Mindel and Riss glaciations. no Rhine ice flowed through the saddles between the Churfirsten peaks into the Thur valley; however, this could have been possible in pre- Mindelian cold periods at high ice levels and still lower moun¬ tain relief.

scholarly journals Mesozoic Paleo-Pacific Subduction Beneath SW Borneo: U-Pb Geochronology of the Schwaner Granitoids and the Pinoh Metamorphic Group

2020 ◽  
Vol 8 ◽  
Author(s):  
H. Tim Breitfeld ◽  
Lorin Davies ◽  
Robert Hall ◽  
Richard Armstrong ◽  
Marnie Forster ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Large Igneous Province ◽  
Metamorphic Rocks ◽  
Volcanic Arc ◽  
The North ◽  
Tectonic History ◽  
Igneous Province ◽  
Magmatic History ◽  
Nw Australia ◽  
C 78

The Schwaner Mountains in southwestern Borneo form a large igneous province with a complex magmatic history and poorly known tectonic history. Previously it was known that Cretaceous granitoids intruded metamorphic rocks of the Pinoh Metamorphic Group assumed to be of Paleozoic age. Jurassic granitoids had been reported from the southern Schwaner Mountains. Most ages were based on K-Ar dating. We present new geochemistry, zircon U-Pb and 40Ar/39Ar age data from igneous and metamorphic rocks from the Schwaner Mountains to investigate their tectono-magmatic histories. We subdivide the Schwaner Mountains into three different zones which record rifting, subduction-related and post-collisional magmatism. The Northwest Schwaner Zone (NWSZ) is part of the West Borneo Block which in the Triassic was within the Sundaland margin. It records Triassic to Jurassic magmatism during early Paleo-Pacific subduction. In contrast, the North Schwaner Zone (NSZ) and South Schwaner Zone (SSZ) are part of the SW Borneo (Banda) Block that separated from NW Australia in the Jurassic. Jurassic granitoids in the SSZ are within-plate (A-type) granites interpreted to have formed during rifting. The SW Borneo (Banda) Block collided with eastern Sundaland at c. 135 Ma. Following this, large I-type granitoid plutons and arc volcanics formed in the NWSZ and NSZ between c. 90 and 132 Ma, associated with Cretaceous Paleo-Pacific subduction. The largest intrusion is the c. 110 to 120 Ma Sepauk Tonalite. After collision of the East Java-West Sulawesi (Argo) Block, subduction ceased and post-collisional magmatism produced the c. 78 to 85 Ma Sukadana Granite and the A-type 72 Ma Sangiyang Granite in the SSZ. Rocks of the Pinoh Metamorphic Group mainly exposed in the NSZ, previously assumed to represent Paleozoic basement, contain abundant Early Cretaceous (110 to 135 Ma) zircons. They are interpreted as volcaniclastic sediments that formed contemporaneously with subduction-related volcanic rocks of the NSZ subsequently metamorphosed during intrusion of Cretaceous granitoids. There are no igneous rocks older than Cretaceous in the NSZ and older than Jurassic in the SSZ and there is no evidence for a continuation of a Triassic volcanic arc crossing Borneo from Sundaland to the east.

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