Jurassic and Cretaceous plutonic and structural styles of the Eagle Plutonic Complex, southwestern British Columbia, and their regional significance

1992 ◽  
Vol 29 (4) ◽  
pp. 793-811 ◽  
Author(s):  
Charles J. Greig
Keyword(s):  
Late Jurassic ◽  
High Strain ◽  
Middle Eocene ◽  
Ductile Deformation ◽  
Brittle Deformation ◽  
East Side ◽  
The West ◽  
The North ◽  
Plutonic Complex ◽  
Southwestern Margin

The Eagle Plutonic Complex is an elongate north-northwest-trending body of deformed Middle to Late Jurassic and middle Cretaceous rocks which underlies the southwestern margin of the Intermontane terrane. New mapping of the complex and its country rocks, in concert with geochronometry, has defined episodes of contractional, ductile deformation in the Middle to Late Jurassic and middle Cretaceous, as well as brittle deformation in Tertiary time. Synkinematic Middle to Late Jurassic Eagle tonalite at the eastern margin of the Eagle Complex intrudes mylonitic Nicola Group rocks and structurally overlies them along a southwest-dipping belt of high strain (Eagle shear zone) with a structural thickness of > 1 km and a strike length of > 100 km. In the central and western Eagle Complex, Eagle tonalite grades into tonalite orthogneiss (Eagle gneiss), and both are crosscut by mid-Cretaceous, muscovite-bearing plutons of the Fallslake Plutonic Suite. Fallslake Suite rocks are themselves ductilely deformed along the Pasayten fault, which bounds the Eagle Complex on the west and was active mainly in the mid-Cretaceous (ductile deformation with sinistral, east-side-up, reverse displacement). The Jurassic and Cretaceous episodes of deformation may reflect the respective initial and final stages of the accretion of the Insular terrane to the North American margin. West of the Pasayten fault, Middle to Late Jurassic and older(?) rocks of the Zoa Complex are structurally overlain, in part, by deformed Middle Eocene and middle Cretaceous sedimentary rocks. In the north, the Middle Eocene rocks are intruded on their west side by the Middle Eocene Needle Peak pluton.

Geochronometry of the Eagle Plutonic Complex and the Coquihalla area, southwestern British Columbia

1992 ◽  
Vol 29 (4) ◽  
pp. 812-829 ◽  
Author(s):  
C. J. Greig ◽  
R. L. Armstrong ◽  
J. E. Harakal ◽  
D. Runkle ◽  
P. van der Heyden
Keyword(s):  
British Columbia ◽  
Late Jurassic ◽  
Middle Eocene ◽  
Timing Constraints ◽  
Early Eocene ◽  
East Side ◽  
Eastern Margin ◽  
Plutonic Complex ◽  
Southwestern Margin

New U–Pb, K–Ar, and Rb–Sr dates from the Eagle Plutonic Complex and adjacent map units place timing constraints on intrusive and deformational events along the southwestern margin of the Intermontane Belt. U–Pb zircon minimum dates for Eagle tonalite and gneiss (148 ± 6, 156 ± 4, and 157 ± 4 Ma) document previously unrecognized Middle to Late Jurassic magmatism and syn-intrusive deformation along the eastern margin of the Eagle Plutonic Complex and the southwestern margin of the Intermontane terrane. Widespread mid-Cretaceous (Albian–Cenomanian) resetting of K–Ar and Rb–Sr isotopic systematics in Jurassic and older rocks is coeval and cogenetic with emplacement of plutons of the Fallslake Plutonic Suite (110.5 ± 2 Ma, U–Pb) which crosscut Jurassic plutons and structures but were themselves ductilely deformed along the Pasayten fault during sinistral, east-side-up, reverse displacement. K–Ar and Rb–Sr cooling dates for the Fallslake Suite of ca. 100 Ma, including dates from mylonites along the Pasayten fault, suggest that uplift, cooling, and unroofing of the Eagle Plutonic Complex occurred in mid-Cretaceous time along the Pasayten fault. Regional geologic evidence suggests that this thermal and unroofing event affected much of the southwest margin of the Intermontane Belt. Initial 87Sr/86Sr ratios and U–Pb geochronometry for the Fallslake Plutonic Suite suggest that it was derived, in part, from preexisting and relatively nonradiogenic Paleozoic to Mesozoic crust. K–Ar dating of several stocks demonstrates widespread Early Eocene plutonism in the Coquihalla area, and dating of the Needle Peak pluton indicates plutonism continued into Middle Eocene time.

scholarly journals The two-stage Aegean extension, from localized to distributed, a result of slab rollback acceleration

2016 ◽  
Vol 53 (11) ◽  
pp. 1142-1157 ◽  
Author(s):  
Jean-Pierre Brun ◽  
Claudio Faccenna ◽  
Frédéric Gueydan ◽  
Dimitrios Sokoutis ◽  
Mélody Philippon ◽  
...  
Keyword(s):  
Middle Miocene ◽  
Middle Eocene ◽  
Sedimentary Basins ◽  
Ductile Deformation ◽  
Metamorphic Rocks ◽  
Western Anatolia ◽  
Two Stage ◽  
The North ◽  
Slab Rollback ◽  
Slab Tearing

Back-arc extension in the Aegean, which was driven by slab rollback since 45 Ma, is described here for the first time in two stages. From Middle Eocene to Middle Miocene, deformation was localized leading to (i) the exhumation of high-pressure metamorphic rocks to crustal depths, (ii) the exhumation of high-temperature metamorphic rocks in core complexes, and (iii) the deposition of sedimentary basins. Since Middle Miocene, extension distributed over the whole Aegean domain controlled the deposition of onshore and offshore Neogene sedimentary basins. We reconstructed this two-stage evolution in 3D and four steps at Aegean scale by using available ages of metamorphic and sedimentary processes, geometry, and kinematics of ductile deformation, paleomagnetic data, and available tomographic models. The restoration model shows that the rate of trench retreat was around 0.6 cm/year during the first 30 My and then accelerated up to 3.2 cm/year during the last 15 My. The sharp transition observed in the mode of extension, localized versus distributed, in Middle Miocene correlates with the acceleration of trench retreat and is likely a consequence of the Hellenic slab tearing documented by mantle tomography. The development of large dextral northeast–southwest strike-slip faults, since Middle Miocene, is illustrated by the 450 km long fault zone, offshore from Myrthes to Ikaria and onshore from Izmir to Balikeshir, in Western Anatolia. Therefore, the interaction between the Hellenic trench retreat and the westward displacement of Anatolia started in Middle Miocene, almost 10 Ma before the propagation of the North Anatolian Fault in the North Aegean.

Adapting to Life Without the Legions

2005 ◽  
Author(s):  
David A. Hinton
Keyword(s):  
High Order ◽  
East Side ◽  
The West ◽  
Roman Britain ◽  
Imperial Authority ◽  
The North ◽  
Hadrian's Wall ◽  
Gold Coins ◽  
Subsequent Failure ◽  
Late Roman

If gold and silver are a measure of wealth, late Roman Britain was very rich. Hoards of coins, jewellery, and plate buried in the late fourth and early fifth centuries show that their owners’ lifestyle was coming to an end as central imperial authority broke down, troops were withdrawn from the island, villas fell into disuse, and towns lost their markets and trade. Raiders threatened by land and sea: Irish from the west, Pictish from the north, Frisian, Saxon, and others from the east; and as civic order broke down, the likelihood of robbery by people living south of Hadrian’s Wall grew worse. The hoards’ owners were right to worry, and their subsequent failure to retrieve their valuables must testify to many personal catastrophes. Hoards containing dishes, bowls, and spoons as well as coins and jewellery have been found on the east side of Roman Britain from Canterbury, Kent, in the south to Whorlton, Yorkshire, in the north. Further west, coin-hoards are quite plentiful, although none has any plate. Some contain jewellery, like one found in 1843 at Amesbury, Wiltshire, that included three silver finger-rings; in the same area, another hoard with eight gold coins and one of silver was found in 1990, apparently concealed in a pot around the year 405, to judge from the date of the latest coin. But as with plate so with jewellery, the contrast with the east is still considerable; Thetford, Norfolk, has gold finger-rings as well as ornamental chains, bracelets, and a buckle; Hoxne, Suffolk, has gold bracelets, and again chains, these with elaborate mounts. Some of the craftsmanship shown in these pieces is of a high order, that only well-off patrons could have afforded. The plate suggests displays of tableware by a society that set great store on being able to offer lavish feasts and entertainment. These late Roman treasures may be giving a slightly false impression of Britain’s prosperity. Silver was probably extracted from the same native deposits that yielded lead, so would have been more available than in most parts of the Empire. Some may also have entered Britain from Ireland, where evidence of Roman intervention is accumulating.

The West Court at Perachora

1967 ◽  
Vol 62 ◽  
pp. 353-371
Author(s):  
J. J. Coulton
Keyword(s):  
Short Distance ◽  
Sixth Century ◽  
East Side ◽  
The South ◽  
The West ◽  
Rock Face ◽  
North East ◽  
The North ◽  
South West ◽  
East And West

About 10 metres south-west of the sixth-century temple of Hera Akraia at Perachora, and nearly due west of the little harbour lies the small courtyard previously known as the ‘Agora’. Since its purpose is not known, it will here be non-committally referred to as the West Court. It was first excavated in 1932, and more fully, under the supervision of J. K. Brock, in 1933, but it was not entirely cleared until 1939, and it was at that time that the Roman house which stood in the middle of the court was demolished. The West Court is discussed briefly (under the name of ‘Agora’) in Perachora 1 and in the preliminary reports of the Perachora excavations. Short supplementary excavations were carried out in 1964 and 1966 to examine certain points of the structure.In shape the West Court is an irregular pentagon, about 24 metres from north to south and the same from east to west (Fig. 1; Plate 91 a, b). It is enclosed on the west, north, and on part, at least, of the east side by a wall of orthostates on an ashlar foundation. For a short distance on either side of the south corner, the court is bounded by a vertically dressed rock face which is extended to the north-east and west by walls of polygonal masonry. At the south-west corner the west orthostate wall butts against the polygonal wall, which continues for about 0·80 m. beyond it and then returns north for about 8 metres behind it.

Stonehenge, Wiltshire, UK: High Resolution Geophysical Surveys in the Surrounding Landscape, 2011

2013 ◽  
Vol 16 (1) ◽  
pp. 63-93 ◽  
Author(s):  
Timothy Darvill ◽  
Friedrich Lüth ◽  
Knut Rassmann ◽  
Andreas Fischer ◽  
Kay Winkelmann
Keyword(s):  
High Resolution ◽  
East Side ◽  
The West ◽  
Additional Information ◽  
The North ◽  
Geophysical Surveys ◽  
Surrounding Landscape ◽  
First Time ◽  
Southern Section ◽  
Management Issues

An extensive high-resolution geophysical survey covering 2 km2was undertaken to the north of Stonehenge in June and October 2011. The survey is important in providing, for the first time, abundant detail on the form and structure of the Stonehenge Cursus, including the recognition of entrances in both of the long sides. Much additional information about the internal form of round barrows in the Cursus Round Barrow Cemetery, the course of the Avenue, the course of the so-called Gate Ditch, and numerous tracks and early roads crossing the landscape was recorded. A series of previously unrecognized features were identified: a pit-arc or cove below a barrow on the west side of King Barrow Ridge, a square-shaped feature surrounded by pits on the east side of Stonehenge Bottom, and a linear ditch on the same solstical axis, and parallel to, the southern section of the Stonehenge Avenue. An extensive scatter of small metallic anomalies marking the position of camping grounds associated with the Stonehenge Free Festival in the late 1970s and early 1980s raise interesting conservation and management issues.

Structural and metamorphic relationships between the Mount Ida and Monashee Groups at Mara Lake, British Columbia

1982 ◽  
Vol 19 (2) ◽  
pp. 288-307 ◽  
Author(s):  
Kent C. Nielsen
Keyword(s):  
British Columbia ◽  
Large Scale ◽  
Ductile Deformation ◽  
Late Triassic ◽  
Second Phase ◽  
The West ◽  
Late Mesozoic ◽  
The North ◽  
Phase Deformation ◽  
Metamorphic Core

Mara Lake, British Columbia straddles the boundary between the Monashee Group on the east and the Mount Ida Group on the west. Correlation of units across the southern end of Mara Lake indicates lithologic continuity between parts of the groups. Both groups have experienced four phases of deformation. Phases one and two are tight and recumbent, trending to the north and to the west, respectively. Phases three and four are open to closed and upright, trending northwest and northeast, respectively. Second-phase deformation includes large-scale tectonic slides that separate areas of consistent vergence. Slide surfaces are folded by third- and fourth-phase structures and outline domal outcrop patterns. Metamorphic grade increases from north to south along the west side of Mara Lake. Calc-silicate reactions involving the formation of diopside are characteristic. From west to east increasing grade is evident in the reaction of muscovite + quartz producing sillimanite + K-feldspar + water. These prograde reactions are related to relative position in the second-phase structure. The highest grade is located near the lowest slide surface. Greenschist conditions accompanied phase-three deformation. Fourth phase is characterized by hydrothermal alteration, brittle fracturing, and local faulting. First-phase deformation appears to be pre-Late Triassic whereas second and third phases are post-Late Triassic and pre-Cretaceous. The fourth phase is part of a regional Tertiary event. The third folding event is correlated with the development of the Chase antiform and the second-phase folding is related to the pervasive east–west fabric of the Shuswap Complex. The timing of these events indicates that the metamorphic core zone of the eastern Cordillera was relatively rigid during the late Mesozoic foreland thrust development. Ductile deformation significantly preceded thrusting and developed a fabric almost at right angles to the trend of the thrust belt.

scholarly journals EFFECTS OF SLAB ROLLBACK ACCELERATION ON AEGEAN EXTENSION

2017 ◽  
Vol 50 (1) ◽  
pp. 5 ◽  
Author(s):  
J.-P. Brun ◽  
C. Faccenna ◽  
F. Gueydan ◽  
D. Sokoutis ◽  
M. Philippon ◽  
...  
Keyword(s):  
Middle Miocene ◽  
Middle Eocene ◽  
Sedimentary Basins ◽  
Ductile Deformation ◽  
Western Anatolia ◽  
Localized Deformation ◽  
The North ◽  
Dynamic Relationship ◽  
Slab Rollback ◽  
Slab Tearing

Aegean extension is a process driven by slab rollback that, since 45 Ma, shows a twostage evolution. From Middle Eocene to Middle Miocene it is accommodated by localized deformation leading to i) the exhumation of high-pressure metamorphic rocks from mantle to crustal depths, ii) the exhumation of high-temperature rocks in core complexes and iii) the deposition of Paleogene sedimentary basins. Since Middle Miocene, extension is distributed over the whole Aegean domain giving a widespread development of onshore and offshore Neogene sedimentary basins. We reconstructed this two-stage evolution in 3D at Aegean scale by using available ages of metamorphic and sedimentary processes, geometry and kinematics of ductile deformation, paleomagnetic data and available tomographic models. The restorationmodel shows that the rate of trench retreat was around 0.6 cm/y during the first 30 My and then accelerated up to 3.2 cm/y during the last 15 My. The sharp transition observed in the mode of extension, localized versus distributed, which occurred in Middle Miocene correlates with the acceleration of trench retreat and is more likely a consequence of the Hellenic slab tearing documented by mantle tomography. The development of large dextral NE-SW strike-slip faults during the second stage of Aegean extension, since Middle Miocene, is illustrated by the 450 Km-long fault, recently put in evidence, offshore from Myrthes to Ikaria and onshore from Izmir to Balikeshir, in western Anatolia. Therefore, the interaction between the Hellenic trench retreat and the westward displacement of Anatolia started in Middle Miocene,almost 10 Ma before the propagation of the North Anatolian Fault in the North Aegean. This raises a fundamental issue concerning the dynamic relationship between slab tearing and Anatolia displacement.

V.—Two Bronze Age Cairns in South Wales: Simondston and Pond Cairns, Coity Higher Parish, Bridgend

Archaeologia ◽  
1938 ◽  
Vol 87 ◽  
pp. 129-180 ◽  
Author(s):  
Cyril Fox
Keyword(s):  
Bronze Age ◽  
East Side ◽  
The West ◽  
Northern Margin ◽  
The North ◽  
Outstanding Feature ◽  
South Wales ◽  
The Town

In the angle between the rivers Ogwr and Ewenny on the northern margin of the Vale of Glamorgan, east of the town of Bridgend, Brackla Hill (287 ft.) is the outstanding feature. Its pastoral slopes are linked to higher ground on the north by a saddle, on the east side of which there is a gentle fall to a tributary of the Ewenny, and on the west to a rivulet which flows into the Ogwr. Coity village lies at the point where the saddle merges into the upland.

GEOLOGICAL FRAMEWORK OF THE GREAT AUSTRALIAN BIGHT

1969 ◽  
Vol 9 (1) ◽  
pp. 60
Author(s):  
R. Smith ◽  
P. Kamerling
Keyword(s):  
Middle Eocene ◽  
Early Stage ◽  
Upper Jurassic ◽  
The South ◽  
The West ◽  
Offshore Area ◽  
North West ◽  
Carbonate Sedimentation ◽  
The North ◽  
Great Australian Bight

Geophysical exploration carried out in the Great Australian Bight since 1966, combined with geological fieldwork in the adjacent land areas, has made it possible to outline the broad geological framework of the area.The "basement" consists of two major units, an offshore extension of the locally metamorphic Cambrian Kanmantoo Group in the south-east and the extension of the West Australian Archaean shield in the north-west. The boundary is thought to follow a trend extending westerly from the Cygnet-Snelling fault zone on Kangaroo Island.In two areas the basement has been downfaulted, thus creating depositional areas for thick sequences of sediments, namely the Elliston trough to the west of Eyre Peninsula and the Duntroon basin, south of Eyre Peninsula and west of Kangaroo Island.The geological setting of the Duntroon basin appears to be comparable with the Otway basin and a Jurassic- Cretaceous age is assumed for the folded sequence of sediments overlying the basement and underlying the Tertiary with angular unconformity. The basin was possibly partially and temporarily closed to the south and open to marine influences from the west.In the Elliston trough the lower part of the section which has low to medium velocity seismic character, is probably Mesozoic, as is evidenced by the Upper Jurassic encountered in its onshore extension. Proterozoic-Cambrian sediments may overlie the basement in the eastern part of the trough. Deformation of the Mesozoic is limited to the mouth of the trough where there is indication of a base- Tertiary unconformity. This trough was probably also open to marine influences to the west.Along the continental margin between the basins and also south of the Eucla basin a thin Mesozoic section, conformably underlying the Tertiary, is probably present, gradually thickening towards the continental slope.In the onshore area Tertiary sedimentation started with local deposition of clastics during the Middle Eocene, which also may have been the case off the Eucla basin, in the Elliston trough and in the Duntroon basin. Carbonate sedimentation took place from the Middle-Upper Eocene onwards, to reach its widest areal extent during the Lower Miocene. A hiatus during the Oligocene may have occurred in the western part of the Bight as is the case in the Eucla basin.Only weak deformation of the Tertiary in the offshore area has been observed. This generally occurs over Mesozoic structures in the Duntroon basin and as draping over topographic basement highs at the mouth of the Elliston trough.No significant hydrocarbon indications are known from the surrounding land areas, but the well-documented bitumen strandings along the coast point to offshore seepages indicating generation of hydrocarbons in the general area.At this stage prospects must be regarded as speculative.although a folded probable Mesozoic sequence forms an objective in the Duntroon basin while prospective Mesozoic-Tertiary section appears to be present in the Elliston trough, where structural evaluation is still at a relatively early stage.

scholarly journals An Attempt to Correlate the Glacial and Post-Glacial Deposits of the British Isles, and to Determine their Order of Succession

The Geologist ◽  
1863 ◽  
Vol 6 (5) ◽  
pp. 168-178
Author(s):  
William King
Keyword(s):  
North Atlantic ◽  
Glacial Period ◽  
British Isles ◽  
East Side ◽  
The West ◽  
Relative Level ◽  
Entire Area ◽  
The North ◽  
The North Atlantic ◽  
Glacial Periods

The classification given in the sequel is based on the following premises:—1st. The entire area of the British Isles has undergone at different times, during the Glacial and Post-Glacial periods, a succession of secular elevating and subsiding movements.2nd. At the close of the Pliocene period, the relative level of land and sea over the British area was approximately the same as at present.3rd. The edge of the two-hundred-fathoms submarine plateau, on the east side of the North Atlantic, formed the west coast-line of a continent (now represented by Europe) during the earliest time (epoch) of the Glacial period.4th. The climate of the British area was frigid in the extreme during the Glacial period, allowing epochs of amelioration.5th. Rock-surfaces undergo enormous degradation when they are above the sea-level, during the prevalency of glaciation.

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