Moine Thrust Belt
Encyclopedia
The Moine Thrust Belt is a linear geological feature in the Scottish Highlands
which runs from Loch Eriboll
on the north coast 190 km south-west to the Sleat peninsula on the Isle of Skye. The thrust belt
is a zone between an extensive landscape of rolling hills over a metamorphic rock base to the east and more rugged, terraced mountains with steep sides sculptured from weathered igneous, sedimentary and metamorphic
rocks to the west. Mountains within the belt display complicated layers and the width of the zone varies up to 10 km. Often, summits of hard rock cap softer sedimentary rock layers visible on lower slopes. Ben More Assynt
, in the centre of the belt, is a typical example that rises from a glen
of limestone
cave
s up through sandstone
terraces to a quartzite
summit cap.
as it was one of the first thrust belts discovered. The formation has since been re-interpreted many times. Eventually, the Moine Thrust corroborated tectonic plate
theory in that, during the Caledonian orogeny
of the Silurian
period, Scotland
was compressed as a European plate thrust westwards over a thrust fault
and above the ancient Lewisian Gneiss
on the Laurentian Plate
.
The thrust belt defines the boundary between the Hebridean Terrane
to its northwest and the Northern Highlands Terrane to its southeast. The thrust carried metamorphic material over 200 km across Scotland entirely masking the geology of the previous terrane. However, small windows, such as the Assynt
window and the Glen Achall imbricated thrust system, allow Geologists to estimate what the geology of Scotland was like before the Caledonian orogeny.
Scottish Highlands
The Highlands is an historic region of Scotland. The area is sometimes referred to as the "Scottish Highlands". It was culturally distinguishable from the Lowlands from the later Middle Ages into the modern period, when Lowland Scots replaced Scottish Gaelic throughout most of the Lowlands...
which runs from Loch Eriboll
Loch Eriboll
Loch Eriboll is a long sea loch on the north coast of Scotland, which has been used for centuries as a deep water anchorage as it is safe from the often stormy seas of Cape Wrath and the Pentland Firth...
on the north coast 190 km south-west to the Sleat peninsula on the Isle of Skye. The thrust belt
Thrust fault
A thrust fault is a type of fault, or break in the Earth's crust across which there has been relative movement, in which rocks of lower stratigraphic position are pushed up and over higher strata. They are often recognized because they place older rocks above younger...
is a zone between an extensive landscape of rolling hills over a metamorphic rock base to the east and more rugged, terraced mountains with steep sides sculptured from weathered igneous, sedimentary and metamorphic
Metamorphic rock
Metamorphic rock is the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form". The protolith is subjected to heat and pressure causing profound physical and/or chemical change...
rocks to the west. Mountains within the belt display complicated layers and the width of the zone varies up to 10 km. Often, summits of hard rock cap softer sedimentary rock layers visible on lower slopes. Ben More Assynt
Ben More Assynt
Ben More Assynt is a mountain in Assynt in the far north-west of Scotland, north-north-east of the town of Ullapool...
, in the centre of the belt, is a typical example that rises from a glen
Glen
A glen is a valley, typically one that is long, deep, and often glacially U-shaped; or one with a watercourse running through such a valley. Whittow defines it as a "Scottish term for a deep valley in the Highlands" that is "narrower than a strath."...
of limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
cave
Cave
A cave or cavern is a natural underground space large enough for a human to enter. The term applies to natural cavities some part of which is in total darkness. The word cave also includes smaller spaces like rock shelters, sea caves, and grottos.Speleology is the science of exploration and study...
s up through sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
terraces to a quartzite
Quartzite
Quartzite is a hard metamorphic rock which was originally sandstone. Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts. Pure quartzite is usually white to gray, though quartzites often occur in various shades of pink...
summit cap.
Formation
The discovery of the Moine Thrust in 1907 was a milestone in the history of geologyGeology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
as it was one of the first thrust belts discovered. The formation has since been re-interpreted many times. Eventually, the Moine Thrust corroborated tectonic plate
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
theory in that, during the Caledonian orogeny
Caledonian orogeny
The Caledonian orogeny is a mountain building era recorded in the northern parts of the British Isles, the Scandinavian Mountains, Svalbard, eastern Greenland and parts of north-central Europe. The Caledonian orogeny encompasses events that occurred from the Ordovician to Early Devonian, roughly...
of the Silurian
Silurian
The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...
period, Scotland
Scotland
Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...
was compressed as a European plate thrust westwards over a thrust fault
Thrust fault
A thrust fault is a type of fault, or break in the Earth's crust across which there has been relative movement, in which rocks of lower stratigraphic position are pushed up and over higher strata. They are often recognized because they place older rocks above younger...
and above the ancient Lewisian Gneiss
Lewisian complex
The Lewisian complex or Lewisian Gneiss is a suite of Precambrian metamorphic rocks that outcrop in the northwestern part of Scotland, forming part of the Hebridean Terrane. These rocks are of Archaean and Paleoproterozoic age, ranging from 3.0–1.7 Ga. They form the basement on which the...
on the Laurentian Plate
Laurentia
Laurentia is a large area of continental craton, which forms the ancient geological core of the North American continent...
.
The thrust belt defines the boundary between the Hebridean Terrane
Hebridean Terrane
The Hebridean Terrane is one of the terranes that form part of the Caledonian orogenic belt in northwest Scotland. Its boundary with the neighbouring Northern Highland Terrane is formed by the Moine Thrust Belt...
to its northwest and the Northern Highlands Terrane to its southeast. The thrust carried metamorphic material over 200 km across Scotland entirely masking the geology of the previous terrane. However, small windows, such as the Assynt
Assynt
Assynt is a civil parish in west Sutherland, Highland, Scotland – north of Ullapool.It is famous for its landscape and its remarkable mountains...
window and the Glen Achall imbricated thrust system, allow Geologists to estimate what the geology of Scotland was like before the Caledonian orogeny.