Stanner Rocks

Last updated

Stanner Rocks is a rounded hill, steep in parts, which lies close to the Wales border with England between Walton and Kington. A superb collection of wild plants can be found here. Where it faces south, warm sunshine and drying winds create an ideal environment for plants which are more likely to be seen around the Mediterranean. The most famous of Stanner Rocks’ specialties is the pretty and elusive Radnor lily, having small, starry yellow flowers.

The Stanner–Hanter complex is the set of rocks which outcrop at Stanner Hill and the nearby Hanter Hill and Worsel Wood and which have long been considered to be the oldest in Wales, having been dated to around 700 million years BP using the rubidium-strontium dating method. They comprise gabbro, diorite and granite. [1] Little modern research has been undertaken on the Complex. The rocks have been variously described as a hypersthene trap (Murchison 1867); an Archean ridge (Calloway1879); a Carboniferous laccolith (Raw 1904); a Tertiary igneous complex (Watts 1906); and a Carboniferous intrusion (Pocock & Whitehead 1935).

Holgate & Knight-Hallowes (1941) suggested a Precambrian origin based on the occurrence of dolerite clasts associated with Longmyndian sediments in a nearby quarry. Much of the confusion must relate to the fault-bounded nature of the Complex which gives no direct stratigraphic control of its age of formation. In the late 1970s the general acceptance of the theory of plate tectonics resulted in a re-investigation of the Precambrian and Paleozoic igneous rocks of southern Britain. Thorpe et al. (1984) made the earliest developments by identifying the calc-alkaline nature of many of these exposures and interpreting this evidence as the product of Precambrian subduction. The Stanner - Hanter Complex was not part of this study, perhaps because of its considerable alteration or possibly owing to the limited range of rock types. In 1980 the publication of a Rb/Sr isotopic age of 702 ± 4 Ma by Pachett et al. confirmed the Neoproterozoic age of the Complex whilst establishing it as the oldest dated rock sequence in southern Britain. More extensive dating of Avalonian rocks both in southern Britain and Maritime Canada has allowed Avalonian subduction to be refined into several stages. Gibbons & Hõrak (1996) grouped the Stanner-Hanter Complex with the Malverns Complex placing both within Avalonian Event 1, the early arc-construction phase, which has been dated at 677Ma. Implicit in this interpretation, however, is the assumption that the Stanner-Hanter rocks have a calc-alkaline composition. Slightly older dolerites and gabbros in the Avalonian of Newfoundland have a more primitive oceanic affinity related to the rifting and formation of primitive oceanic crust.

Related Research Articles

<span class="mw-page-title-main">Ophiolite</span> Uplifted and exposed oceanic crust

An ophiolite is a section of Earth's oceanic crust and the underlying upper mantle that has been uplifted and exposed, and often emplaced onto continental crustal rocks.

The geology of the county of Shropshire, England is very diverse with a large number of periods being represented at outcrop. The bedrock consists principally of sedimentary rocks of Palaeozoic and Mesozoic age, surrounding restricted areas of Precambrian metasedimentary and metavolcanic rocks. The county hosts in its Quaternary deposits and landforms, a significant record of recent glaciation. The exploitation of the Coal Measures and other Carboniferous age strata in the Ironbridge area made it one of the birthplaces of the Industrial Revolution. There is also a large amount of mineral wealth in the county, including lead and baryte. Quarrying is still active, with limestone for cement manufacture and concrete aggregate, sandstone, greywacke and dolerite for road aggregate, and sand and gravel for aggregate and drainage filters. Groundwater is an equally important economic resource.

<span class="mw-page-title-main">Geology of Australia</span>

The geology of Australia includes virtually all known rock types, spanning a geological time period of over 3.8 billion years, including some of the oldest rocks on earth. Australia is a continent situated on the Indo-Australian Plate.

The calc-alkaline magma series is one of two main subdivisions of the subalkaline magma series, the other subalkaline magma series being the tholeiitic series. A magma series is a series of compositions that describes the evolution of a mafic magma, which is high in magnesium and iron and produces basalt or gabbro, as it fractionally crystallizes to become a felsic magma, which is low in magnesium and iron and produces rhyolite or granite. Calc-alkaline rocks are rich in alkaline earths and alkali metals and make up a major part of the crust of the continents.

<span class="mw-page-title-main">Geology of Guernsey</span>

Guernsey has a geological history stretching further back into the past than most of Europe. The majority of rock exposures on the Island may be found along the coastlines, with inland exposures scarce and usually highly weathered. There is a broad geological division between the north and south of the Island. The Southern Metamorphic Complex is elevated above the geologically younger, lower lying Northern Igneous Complex. Guernsey has experienced a complex geological evolution with multiple phases of intrusion and deformation recognisable.

<span class="mw-page-title-main">Geology of Tasmania</span>

The geology of Tasmania is complex, with the world's biggest exposure of diabase, or dolerite. The rock record contains representatives of each period of the Neoproterozoic, Paleozoic, Mesozoic and Cenozoic eras. It is one of the few southern hemisphere areas that were glaciated during the Pleistocene with glacial landforms in the higher parts. The west coast region hosts significant mineralisation and numerous active and historic mines.

<span class="mw-page-title-main">Igneous rock</span> Rock formed through the cooling and solidification of magma or lava

Igneous rock, or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rocks are formed through the cooling and solidification of magma or lava.

<span class="mw-page-title-main">Wrekin terrane</span> Inferred basement rock terrane of the southern United Kingdom

The Wrekin terrane is one of five inferred fault bounded terranes that make up the basement rocks of the southern United Kingdom. The other notable geological terranes in the region are the Charnwood terrane, Fenland terrane, Cymru terrane and the Monian Composite terrane. The Wrekin terrane is bounded to the west by the Welsh Borderland fault system and to the east by the Malvern lineament. The geological terrane to the west is the Cymru Terrane and to the east is Charnwood Terrane. The majority of rocks in the area are associated with the outcrops that are evident at the faulted boundaries.

The Cymru terrane is one of five inferred fault bounded terranes that make up the basement rocks of the southern United Kingdom. The other notable geological terranes are the Charnwood, Fenland, Wrekin and the Monian Composite terranes. In this article the definition of terrane is that implying rocks associated with the composition of the Precambrian basement. The Cymru terrane is bounded to the northwest by the Menai Strait Fault System and to the southeast by the Pontesford Lineament. The geological terrane to the west is the Monian Composite terrane and to the east is Wrekin terrane. The majority of rocks in the area are associated with the outcrops that are evident at the faulted boundaries.

The Sarn Complex is a group of closely related igneous rocks that intrude and cut through other rock lithologies in the Cymru terrane in Wales. The complex outcrops on the Llyn Peninsula in a variety of places including Mynydd Cefnamlwch and the flanks of Pen y Gopa.

<span class="mw-page-title-main">Geology of the Isle of Skye</span>

The geology of the Isle of Skye in Scotland is highly varied and the island's landscape reflects changes in the underlying nature of the rocks. A wide range of rock types are exposed on the island, sedimentary, metamorphic and igneous, ranging in age from the Archaean through to the Quaternary.

Dedham granite is a light grayish-pink to greenish-gray, equigranular to slightly porphyritic, variably altered, granite south and west of Boston, named for the town of Dedham, Massachusetts.

The geology of Niger comprises very ancient igneous and metamorphic crystalline basement rocks in the west, more than 2.2 billion years old formed in the late Archean and Proterozoic eons of the Precambrian. The Volta Basin, Air Massif and the Iullemeden Basin began to form in the Neoproterozoic and Paleozoic, along with numerous ring complexes, as the region experienced events such as glaciation and the Pan-African orogeny. Today, Niger has extensive mineral resources due to complex mineralization and laterite weathering including uranium, molybdenum, iron, coal, silver, nickel, cobalt and other resources.

<span class="mw-page-title-main">Geology of Zambia</span>

The geological history of Zambia begins in the Proterozoic eon of the Precambrian. The igneous and metamorphic basement rocks tend to be highly metamorphosed and may have formed earlier in the Archean, but heat and pressure has destroyed evidence of earlier conditions. Major sedimentary and metamorphic groups formed in the mid-Proterozoic, followed by a series of glaciations in the Neoproterozoic and much of the Paleozoic which deposited glacial conglomerate as well as other sediments to form the Katanga Supergroup and rift-related Karoo Supergroup. Basalt eruptions blanketed the Karoo Supergroup in the Mesozoic and Zambia shifted to coal and sandstone formation. Geologically recent windblown sands from the Kalahari Desert and alluvial deposits near rivers play an important role in the modern surficial geology of Zambia. The country has extensive natural resources, particularly copper, but also cobalt, emeralds, other gemstones, uranium and coal.

<span class="mw-page-title-main">Geology of Morocco</span>

The geology of Morocco formed beginning up to two billion years ago, in the Paleoproterozoic and potentially even earlier. It was affected by the Pan-African orogeny, although the later Hercynian orogeny produced fewer changes and left the Maseta Domain, a large area of remnant Paleozoic massifs. During the Paleozoic, extensive sedimentary deposits preserved marine fossils. Throughout the Mesozoic, the rifting apart of Pangaea to form the Atlantic Ocean created basins and fault blocks, which were blanketed in terrestrial and marine sediments—particularly as a major marine transgression flooded much of the region. In the Cenozoic, a microcontinent covered in sedimentary rocks from the Triassic and Cretaceous collided with northern Morocco, forming the Rif region. Morocco has extensive phosphate and salt reserves, as well as resources such as lead, zinc, copper and silver.

<span class="mw-page-title-main">Geology of Sudan</span>

The geology of Sudan formed primarily in the Precambrian, as igneous and metamorphic crystalline basement rock. Ancient terranes and inliers were intruded with granites, granitoids, and volcanic rocks. Units of all types were deformed, reactivated, intruded, and metamorphosed during the Proterozoic Pan-African orogeny. Dramatic sheet flow erosion prevented almost any sedimentary rocks from forming during the Paleozoic and Mesozoic. From the Mesozoic into the Cenozoic, the formation of the Red Sea depression and complex faulting led to massive sediment deposition in some locations and regional volcanism. Sudan has petroleum, chromite, salt, gold, limestone, and other natural resources.

<span class="mw-page-title-main">Geology of Sweden</span>

The geology of Sweden is the regional study of rocks, minerals, tectonics, natural resources and groundwater in the country. The oldest rocks in Sweden date to more than 2.5 billion years ago in the Precambrian. Complex orogeny mountain building events and other tectonic occurrences built up extensive metamorphic crystalline basement rock that often contains valuable metal deposits throughout much of the country. Metamorphism continued into the Paleozoic after the Snowball Earth glaciation as the continent Baltica collided with an island arc and then the continent Laurentia. Sedimentary rocks are most common in southern Sweden with thick sequences from the last 250 million years underlying Malmö and older marine sedimentary rocks forming the surface of Gotland.

<span class="mw-page-title-main">Geology of Bulgaria</span>

The geology of Bulgaria consists of two major structural features. The Rhodope Massif in southern Bulgaria is made up of Archean, Proterozoic and Cambrian rocks and is a sub-province of the Thracian-Anatolian polymetallic province. It has dropped down, faulted basins filled with Cenozoic sediments and volcanic rocks. The Moesian Platform to the north extends into Romania and has Paleozoic rocks covered by rocks from the Mesozoic, typically buried by thick Danube River valley Quaternary sediments. In places, the Moesian Platform has small oil and gas fields. Bulgaria is a country in southeastern Europe. It is bordered by Romania to the north, Serbia and North Macedonia to the west, Greece and Turkey to the south, and the Black Sea to the east.

The geology of Loch Lomond and The Trossachs National Park in the southwestern part of the Scottish Highlands consists largely of Neoproterozoic and Palaeozoic bedrock faulted and folded and subjected to low grade metamorphism during the Caledonian orogeny. These older rocks, assigned to the Dalradian Supergroup, lie to the northwest of the northeast – southwest aligned Highland Boundary Fault which defines the southern edge of the Highlands. A part of this mountainous park extends south of this major geological divide into an area characterised by younger Devonian rocks which are assigned to the Old Red Sandstone.

The geology of Pembrokeshire in Wales inevitably includes the geology of the Pembrokeshire Coast National Park which extends around the larger part of the county's coastline and where the majority of rock outcrops are to be seen. The park was established as a national park in 1952. Pembrokeshire's bedrock geology is largely formed from a sequence of sedimentary and igneous rocks originating during the late Precambrian and the Palaeozoic era, namely the Ediacaran, Cambrian, Ordovician, Silurian, Devonian and Carboniferous periods, i.e. between 635 and 299 Ma. The older rocks in the north of the county display patterns of faulting and folding associated with the Caledonian Orogeny. On the other hand, the late Palaeozoic rocks to the south owe their fold patterns and deformation to the later Variscan Orogeny.

References

  1. "The oldest rocks in Wales". National Museum Wales. 26 July 2007. Retrieved 17 March 2016.

2. 52°13′16″N3°04′45″W / 52.22111°N 3.07917°W / 52.22111; -3.07917 Gibbons W & Hõrak J, 1996, The evolution of the Neoproterozoic Avalonian subduction system - evidence from the British Isles,