Stanner Rocks is a rounded hill, steep in parts, which lies close to the

Wales Wales ( cy, Cymru ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by England to the Wales–England border, east, the Irish Sea to the north and west, the Celtic Sea to the south west and the ...

border with

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...

between

Walton Walton may refer to: People * Walton (given name) * Walton (surname) * Susana, Lady Walton (1926–2010), Argentine writer Places Canada *Walton, Nova Scotia, a community ** Walton River (Nova Scotia) *Walton, Ontario, a hamlet United Kingdom ...

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 refers to 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 Gabbro () is a phaneritic (coarse-grained), mafic intrusive igneous rock formed from the slow cooling of magnesium-rich and iron-rich magma into a holocrystalline mass deep beneath the Earth's surface. Slow-cooling, coarse-grained gabbro is che ...

diorite Diorite ( ) is an intrusive igneous rock formed by the slow cooling underground of magma (molten rock) that has a moderate content of silica and a relatively low content of alkali metals. It is intermediate in composition between low-silic ...

and

granite Granite () is a coarse-grained (phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies undergro ...

. Little modern research has been undertaken on the Complex. The rocks have been variously described as a

hypersthene Hypersthene is a common rock-forming inosilicate mineral belonging to the group of orthorhombic pyroxenes. Its chemical formula is . It is found in igneous and some metamorphic rocks as well as in stony and iron meteorites. Many references have f ...

trap (Murchison 1867); an

Archean The Archean Eon ( , also spelled Archaean or Archæan) is the second of four geologic eons of Earth's history, representing the time from . The Archean was preceded by the Hadean Eon and followed by the Proterozoic. The Earth Earth ...

ridge (Calloway1879); a

Carboniferous The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonifero ...

laccolith A laccolith is a body of intrusive rock with a dome-shaped upper surface and a level base, fed by a conduit from below. A laccolith forms when magma (molten rock) rising through the Earth's crust begins to spread out horizontally, prying ap ...

(Raw 1904); a

Tertiary Tertiary ( ) is a widely used but obsolete term for the geologic period from 66 million to 2.6 million years ago. The period began with the demise of the non-avian dinosaurs in the Cretaceous–Paleogene extinction event, at the start ...

igneous complex (Watts 1906); and a Carboniferous intrusion (Pocock & Whitehead 1935). Holgate & Knight-Hallowes (1941) suggested a

Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...

origin based on the occurrence of

dolerite Diabase (), also called dolerite () or microgabbro, is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine-grained ...

clasts associated with

Longmyndian The Longmyndian Supergroup is a sequence of Late Precambrian rocks that outcrop between the Pontesford–Linley Fault System and the Church Stretton Fault System in the Welsh Borderland Fault System. The supergroup consists of two major geol ...

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 Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large ...

resulted in a re-investigation of the Precambrian and

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

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 Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...

. 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 The Neoproterozoic Era is the unit of geologic time from 1 billion to 538.8 million years ago. It is the last era of the Precambrian Supereon and the Proterozoic Eon; it is subdivided into the Tonian, Cryogenian, and Ediacaran periods. It is ...

age of the Complex whilst establishing it as the oldest dated rock sequence in southern Britain. More extensive dating of

Avalonia Avalonia was a microcontinent in the Paleozoic era. Crustal fragments of this former microcontinent underlie south-west Great Britain, southern Ireland, and the eastern coast of North America. It is the source of many of the older rocks of Wester ...

n 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 Newfoundland and Labrador (; french: Terre-Neuve-et-Labrador; frequently abbreviated as NL) is the easternmost province of Canada, in the country's Atlantic region. The province comprises the island of Newfoundland and the continental region ...

have a more primitive oceanic affinity related to the rifting and formation of primitive

oceanic crust Oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust, composed of troctolite, gabbro and ultramafic cumu ...

References

2.Gibbons W & Hõrak J, 1996, The evolution of the Neoproterozoic Avalonian subduction system - evidence from the British Isles, Mountains and hills of Powys {{Powys-geo-stub