The Highland Boundary Fault is a major fault zone [1] that traverses Scotland from Arran and Helensburgh on the west coast to Stonehaven in the east. It separates two different geological terranes which give rise to two distinct physiographic terrains: the Highlands and the Lowlands, and in most places it is recognisable as a change in topography. Where rivers cross the fault, they often pass through gorges, and the associated waterfalls can be a barrier to salmon migration. [2]
The fault is believed to have formed in conjunction with the Strathmore syncline to the south-east during the Acadian orogeny in a transpressive regime that caused the uplift of the Grampian block and a small sinistral movement on the Highland Boundary Fault. [3] [4]
One of the earliest and most prominent references to the Highland Boundary Fault was by George Barrow in 1912 ʻOn the Geology of Lower Dee-side and the Southern Highland Borderʼ, which highlights the nature of the rocks accompanying the Highland Border and describes the mineral zones associated with metamorphism. [5] In the same publication, Barrow also outlines the ʻHighland Faultʼ and the areas where he believes there are planes of overthrust. Barrowʼs description of the structural nature of the rocks along the Highland Border suggests that rocks along both ends of the fault plane are indistinguishable from one another, with no brecciation.
Aligned southwest to northeast from Lochranza on Arran, the Highland Boundary Fault bisects Bute and crosses the southeastern parts of the Cowal and Rosneath peninsulas, as it passes up the Firth of Clyde. It comes ashore near Helensburgh, then continues through Loch Lomond. The loch islands of Inchmurrin, Creinch, Torrinch, and Inchcailloch all lie on the Highland Boundary Fault. [6] From Loch Lomond the Highland Boundary Fault continues to Aberfoyle, then Callander, Comrie and Crieff. It then forms the northern boundary of Strathmore and reaches the North Sea immediately north of Stonehaven near the ruined Chapel of St. Mary and St. Nathalan. [4] [7] Aeromagnetic maps of Great Britain and Northern Ireland show that the Highland Boundary Fault can be traced from Ireland to the region of Greenock. In these areas, the Highland Boundary Fault is seen to be dividing a northerly low area from a southerly high area. [8] The fault is often considered a terrane boundary: the Midland Valley terrane lies to the south whilst the Southern Highlands or Grampian terrane lies to the north [9] In 1970, Hall and Dagley identified the Highland Boundary Fault as coincident with a regional magnetic feature dividing a string of negative anomalies in the north from positive ones in the south. [8] On discovering this, Hall and Dagley concluded that the observed trend, which followed the length of the Dalradian trough, transition from positive to negative anomalies. This linear feature of magnetic anomalies has since been referred to as the Fair Head–Clew Bay line. [10]
At present, it is believed that the Highland Boundary Fault was active during two main orogenic events associated with the Caledonian orogeny: the Grampian orogeny in the Early Ordovician and the Acadian orogeny in the Middle Devonian. [3] The fault allowed the Midland Valley to descend as a major rift by up to 4,000 m (13,000 ft) and there was subsequent vertical movement. This earlier vertical movement was later replaced by a horizontal shear. A complementary fault, the Southern Uplands Fault, forms the southern boundary for the Central Lowlands. [3] [4] The age of the Highland Boundary Fault has been inferred to be between Ordovician to middle Devonian and through several generations it has been interpreted as a graben-bounding normal fault, a major sinistral strike-slip fault, a northwest-dipping reverse fault or terrane boundary. [3] The reason the precise nature of the fault is still unknown is because there is little evidence of a continuous fault plane on the surface. More recently, seismic activities marking the fault line have been analysed to show that the 2003 Aberfoyle earthquake had a hypocentre at 4 km (2+1⁄2 mi) depth and was caused by an oblique sinistral strike-slip fault with normal movement. The fault plane was estimated to be dipping at 65° NW. [3]
To the north and west of the Highland Boundary Fault lie hard Precambrian and Cambrian metamorphic rocks: marine deposits metamorphosed to schists, phyllites and slates, namely the Dalradian Supergroup and the Highland Border Ophiolite suite. [3] To the south and east are Old Red Sandstone conglomerates and sandstones: softer, sedimentary rocks of the Devonian and Carboniferous periods. [4] Between these areas lie the quite different rocks of the Highland Border Complex (at one time called the Highland Boundary Complex [11] ), a weakly metamorphosed sedimentary sequence of sandstones, lavas, limestones, mudstones and conglomerates. These make up a zone which is found discontinuously along the line of the fault and which is up to 1.2 kilometres (3⁄4 mi) in width. [12]
The Dalradian Supergroup consists of metasedimentary rocks which underwent polyphase deformation and metamorphism during the Precambrian and early Paleozoic. [3] [4] The oldest Dalradian rocks (the Grampian Group) were deformed and metamorphosed around 750 Ma. The deposition of younger Dalradian sediments continued until 590 Ma, when the sediments underwent transformation to the greenschist facies during the Proterozoic and Ordovician. [3]
Modeling of gravity and magnetic data along the fault has confirmed the presence of an extensive ophiolite suite. The Dalradian metasedimentary rocks are overlain by an obducted ophiolite that is continuous for at least several kilometres on either side of the Highland Boundary Fault. The models generated from magnetic data suggest that the ophiolite is only slightly displaced vertically by the fault. [3]
The Old Red Sandstone is a magnafacies of red beds and lacustrine deposits from the Late Silurian to the Carboniferous. The NE segment of the Highland Boundary Fault is marked by an abrupt change in the dip of the Old Red Sandstone from around 20° to near-vertical and subsequently exposes the Old Red Sandstone basement. [3]
It is currently believed that there were two main displacement events along the Highland Boundary Fault: the Acadian, and the post-Acadian. [3] [13] [14]
Evidence for the Acadian displacement event is based on the geochemical study of detrital garnets in the Lower Old Red Sandstone on the Northern limb of the Strathmore Basin. These garnets were linked to those in isolated Dalradian sediments in the northwest, providing evidence for post-Early Devonian (Acadian) movement to be only few tens of kilometers. [13] [14]
In addition, the Lintrathen ignimbrite, which is present at the base of the Lower Devonian sequence was traced along the fault and it was found that the displacement was both short and lateral. [3] [13]
The post-Acadian movements are highlighted in the stratigraphy of the region. The Lower Old Red Sandstone is unconformably overlain by Upper Old Red Sandstone, where the Upper Old Red Sandstone is tilted close to the Highland Boundary Fault. [3]
The boundary is used as a natural barrier to prevent northwards movement of grey squirrels, thus protecting the only red squirrel population in the Highlands. [15]
Victoria is an Australian state, situated at the southern end of the Great Dividing Range. The Great Dividing Range stretches along the east coast of the continent and terminates near the Victorian city of Ballarat west of the capital Melbourne, though the nearby Grampians may be considered to be the final part of the range. The highest mountains in Victoria are the Victorian Alps, located in the northeast of the state.
Cape Breton Highlands National Park is a Canadian national park on northern Cape Breton Island in Nova Scotia. The park was the first national park in the Atlantic provinces of Canada and covers an area of 948 square kilometres (366 sq mi). It is one of 42 in Canada's system of national parks.
The Old Red Sandstone is an assemblage of rocks in the North Atlantic region largely of Devonian age. It extends in the east across Great Britain, Ireland and Norway, and in the west along the northeastern seaboard of North America. It also extends northwards into Greenland and Svalbard. These areas were a part of the ancient continent of Euramerica/Laurussia. In Britain it is a lithostratigraphic unit to which stratigraphers accord supergroup status and which is of considerable importance to early paleontology. For convenience the short version of the term, ORS is often used in literature on the subject. The term was coined to distinguish the sequence from the younger New Red Sandstone which also occurs widely throughout Britain.
The Acadian orogeny is a long-lasting mountain building event which began in the Middle Devonian, reaching a climax in the early Late Devonian. It was active for approximately 50 million years, beginning roughly around 375 million years ago, with deformational, plutonic, and metamorphic events extending into the Early Mississippian. The Acadian orogeny is the third of the four orogenies that created the Appalachian orogen and subsequent basin. The preceding orogenies consisted of the Potomac and Taconic orogeny, which followed a rift/drift stage in the Late Neoproterozoic. The Acadian orogeny involved the collision of a series of Avalonian continental fragments with the Laurasian continent. Geographically, the Acadian orogeny extended from the Canadian Maritime provinces migrating in a southwesterly direction toward Alabama. However, the Northern Appalachian region, from New England northeastward into Gaspé region of Canada, was the most greatly affected region by the collision.
The Taconic orogeny was a mountain building period that ended 440 million years ago and affected most of modern-day New England. A great mountain chain formed from eastern Canada down through what is now the Piedmont of the East coast of the United States. As the mountain chain eroded in the Silurian and Devonian periods, sediments from the mountain chain spread throughout the present-day Appalachians and midcontinental North America.
The Moine Thrust Belt or Moine Thrust Zone is a linear tectonic feature in the Scottish Highlands which runs from Loch Eriboll on the north coast 190 kilometres (120 mi) south-west to the Sleat peninsula on the Isle of Skye. The thrust belt consists of a series of thrust faults that branch off the Moine Thrust itself. Topographically, the belt marks a change from rugged, terraced mountains with steep sides sculptured from weathered igneous, sedimentary and metamorphic rocks in the west to an extensive landscape of rolling hills over a metamorphic rock base to the east. Mountains within the belt display complexly folded and faulted layers and the width of the main part of the zone varies up to 10 kilometres (6.2 mi), although it is significantly wider on Skye.
The Dalradian Supergroup is a stratigraphic unit in the lithostratigraphy of the Grampian Highlands of Scotland and in the north and west of Ireland. The diverse assemblage of rocks which constitute the supergroup extend across Scotland from Islay in the west to Fraserburgh in the east and are confined by the Great Glen Fault to the northwest and the Highland Boundary Fault to the southeast. Much of Shetland east of the Walls Boundary Fault is also formed from Dalradian rocks. Dalradian rocks extend across the north of Ireland from County Antrim in the north east to Clifden on the Atlantic coast, although obscured by later Palaeogene lavas and tuffs or Carboniferous rocks in large sections.
The Central Lowlands, sometimes called the Midland Valley or Central Valley, is a geologically defined area of relatively low-lying land in southern Scotland. It consists of a rift valley between the Highland Boundary Fault to the north and the Southern Uplands Fault to the south. The Central Lowlands are one of the three main geographical sub-divisions of Scotland, the other two being the Highlands and Islands which lie to the north, northwest and the Southern Uplands, which lie south of the associated second fault line. It is the most populated of Scotland’s three geographical regions.
The Orcadian Basin is a sedimentary basin of Devonian age that formed mainly as a result of extensional tectonics in northeastern Scotland after the end of the Caledonian orogeny. During part of its history, the basin was filled by a lake now known as Lake Orcadie. In that lacustrine environment, a sequence of finely bedded sedimentary rocks was deposited, containing well-preserved fish fossils, with alternating layers of mudstone and coarse siltstone to very fine sandstone. These flagstones split easily along the bedding and have been used as building material for thousands of years. The deposits of the Orcadian Basin form part of the Old Red Sandstone (ORS). The lithostratigraphic terms lower, middle and upper ORS, however, do not necessarily match exactly with sediments of lower, middle and upper Devonian age, as the base of the ORS is now known to be in the Silurian and the top in the Carboniferous.
The Lachlan Fold Belt (LFB) or Lachlan Orogen is a geological subdivision of the east part of Australia. It is a zone of folded and faulted rocks of similar age. It dominates New South Wales and Victoria, also extending into Tasmania, the Australian Capital Territory and Queensland. It was formed in the Middle Paleozoic from 450 to 340 Mya. It was earlier known as Lachlan Geosyncline. It covers an area of 200,000 km2.
The Meguma terrane, also known as Megumia, is a terrane exposed in southern Nova Scotia, that became joined to the present North American landmass as part of the Appalachian orogeny.
The Moine Supergroup is a sequence of Neoproterozoic metamorphic rocks that form the dominant outcrop of the Scottish Highlands between the Moine Thrust Belt to the northwest and the Great Glen Fault to the southeast. The sequence is metasedimentary in nature and was metamorphosed and deformed in a series of tectonic events during the Late Proterozoic and Early Paleozoic. It takes its name from A' Mhòine, a peat bog in northern Sutherland.
The main points that are discussed in the geology of Iran include the study of the geological and structural units or zones; stratigraphy; magmatism and igneous rocks; ophiolite series and ultramafic rocks; and orogenic events in Iran.
The Strathmore Group is a Devonian lithostratigraphic group in central Scotland. Its sandstones are interbedded with siltstones which interfinger with conglomerates. It is encountered from Arran in the west across the Midland Valley to Stonehaven in the east. The name is derived from Strathmore, Angus where this sequence occupies the axis of the Strathmore Syncline which runs for many tens of miles parallel to and south of the Highland Boundary Fault. The rocks of the Strathmore Group have also previously been referred to as the Strathmore Beds.
The geology of Maine is part of the broader geology of New England and eastern North America.
This article describes the geology of the Cairngorms National Park, an area in the Highlands of Scotland designated as a national park in 2003 and extended in 2010. The Cairngorms National Park extends across a much wider area than the Cairngorms massif itself and hence displays rather more varied geology.
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 as well as 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.
The geology of national parks in Britain strongly influences the landscape character of each of the fifteen such areas which have been designated. There are ten national parks in England, three in Wales and two in Scotland. Ten of these were established in England and Wales in the 1950s under the provisions of the National Parks and Access to the Countryside Act 1949. With one exception, all of these first ten, together with the two Scottish parks were centred on upland or coastal areas formed from Palaeozoic rocks. The exception is the North York Moors National Park which is formed from sedimentary rocks of Jurassic age.
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 Grampian orogeny was an orogeny mountain building event which affected Scotland in the middle of the Ordovician. At the time, Scotland was part of proto-North American continent Laurentia.