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To the best of our knowledge, this is the first study using 3D seismic reflection data to document the morphology of a shallow mafic laccolith and its relationship to its erupted products, whilst the HHL is notable for possessing characteristics of both classic laccoliths and shallowly emplaced, multi-lobate mafic sills. Dikes can occur alone or in sets and may be comprised of light (high-silica) or dark (low-silica) rocks, or any composition in between. Keywords: Northeastern South China Sea Continental slope Sills Laccolith Fault zone; Citation: Li, B., Q. Tang, P. Yan, J. Yu, and X. Wang, 2021: Characteristics of a laccolith along the LRTPB fault zone between Pearl River Mouth Basin and Southwest Taiwan Basin. [31], Dolerite intrusion laccolith in Sydney, Australia, Laccolith exposed by erosion of overlying strata in Montana, Pink monzonite laccolith intrudes within the grey Cambrian and Ordovician strata near Notch Peak, Utah[32], The eroded laccolith on the top of Vitosha[33] - the domed mountain next to Sofia, Bulgaria. 1:24,000", 10.1130/0016-7606(1988)100<0117:TLSCNR>2.3.CO;2, "Dynamics of magmatic intrusions in the upper crust: Theory and applications to laccoliths on Earth and the Moon", "Laccolith Complexes of Southeastern Utah: Time of Emplacement and Tectonic Setting Workshop Proceedings", https://en.wikipedia.org/w/index.php?title=Laccolith&oldid=1140554490, Short description is different from Wikidata, Creative Commons Attribution-ShareAlike License 3.0, This page was last edited on 20 February 2023, at 16:34. Named for its resemblance to the silhouette of a sailing ship, Ship Rock is a volcanic neck located where the main feeder pipe for a larger volcano was once located. In Big Bend Ranch State Park, at the southwesternmost visible extent of the Ouachita orogeny, lies the Solitario. The intrusion takes place when the pressure of magma is high enough to move the strata of sedimentary rock in an upward position or to make them fold. The locations where volcanic eruptions have occurred are usually acidic which makes it difficult to harbor any plants or animals. In the diagram above, the dike and the volcanic neckdespite the latter's nameare both intrusive features, whereas the fissure, lava flows, and volcanic cone are all extrusive. Its like a teacher waved a magic wand and did the work for me. {\displaystyle \tau } Lava Flow Composition & Types | What is Lava Flow? - Definition & Explanation, What is a Map Key/Legend? The main conduit through which magma rises in a volcano is called a volcanic pipe. Both sills and laccoliths have blunt rather than wedgelike edges, and sills of the Henry Mountains are typically up to 10 meters (33ft) thick while laccoliths are up to 200 meters (660ft) thick. A laccolith is a rock that appears as a sheet-like intrusion and is intruded between the layers of sedimentary rock. For example, in the Henry Mountains of Utah, US, the geologist Grove Karl Gilbert found in 1877 that sills were always less than 1 square kilometer (0.4sqmi) in area while laccoliths were always greater than 1 square kilometer in area. . Some of the most common igneous features include: An aerial view of a low-silica lava flow seen erupting from Hawaii's Mauna Loa in 1984. This stone constitutes the basis for a new batholith. A batholith is a large mass of intrusive igneous rock that forms and cools deep in the Earth's crust. Igneous rocks form from the solidification of once-molten rock material. However, eld . All rights reserved. Updates? This article was most recently revised and updated by, https://www.britannica.com/science/laccolith, Academia - Two-Stage Growth of Laccoliths at Elba Island, Italy. "Geomythology: geological origins of myths and legends" in, "Progressive Growth of the Cerro Bayo Cryptodome, Chachahun Volcano, ArgentinaImplications for Viscous Magma Emplacement", 10.1130/0016-7606(1975)86<351:TFAGOF>2.0.CO;2, "Rapid laccolith intrusion driven by explosive volcanic eruption", "Syn-Emplacement Fracturing in the Sandfell Laccolith, Eastern IcelandImplications for Rhyolite Intrusion Growth and Volcanic Hazards", "Laccoliths of the Ortiz porphyry belt, Santa Fe County, New Mexico", "Petrological constraints on the recycling of mafic crystal mushes and intrusion of braided sills in the Torres del Paine Mafic Complex (Patagonia)", 10.1130/0091-7613(2002)030<0983:TSGOLA>2.0.CO;2, "Noe, D. C., and Alexander T. Klink. As a result, the magma cools in place and forms new stone. Terri is also the author or co-author of five books, including Hiking the Grand Canyons Geology, Geology Underfoot in Northern Arizona, and Geology Underfoot Along Colorados Front Range. This pressure gives the laccolith a dome or mushroom-like appearance Generally, the base of the laccolith is planar. This type of volcanic activity is called a 'fissure eruption'. Jonathan M. Castro, Benoit Cordonnier, C. Ian Schipper, Hugh Tuffen, Tobias S. Baumann &. [18], Sheet intrusions tend to form perpendicular to the direction of least stress in the country rock they intrude. Ocean. Characteristics of a Laccolith Along the LRTPB Fault Zone 445 A NW directional fault zone, named as Luzon-Ryukyu Transform Plate Boundary (LRTPB) goes along the Taiwan Canyon (or Formosa. The largest laccolith in the United States is Pine Valley Mountain in the Pine Valley Mountain Wilderness area near St. George Utah. The laccolith is a framework of igneous rock intruded between layers of sedimentary rock n resulting in uplifting, The batholith is referred to as individual igneous rock, The laccolith is referred to as intrusion in sedimentary rock. DOI: 10.3319/tao.2021.09.07.01 Corpus ID: 245609638; Characteristics of a laccolith along the LRTPB fault zone between Pearl River Mouth Basin and Southwest Taiwan Basin @article{Li2021CharacteristicsOA, title={Characteristics of a laccolith along the LRTPB fault zone between Pearl River Mouth Basin and Southwest Taiwan Basin}, author={Bo-wen Li and Qunshu Tang and Pin Yan and Junhui Yu and . A tabular igneous intrusion that crosses through other (layered or non-layered) rocks at a steep angle. Silicate Minerals Types & Examples | What are Silicate Minerals? The batholith is the large mass of an intrusive igneous rock form found below the Earths surface by the intrusion and solidification of magma. is the horizontal distance from the center of the laccolith, and There are several batholiths found in the United States. The laccolith forms when the magma pressure is high enough to move the strata of the sedimentary rock upward or to make them folded. A volcanic pipe is a vertical conduit beneath a volcano through which magma once passed on its journey from the magma chamber to the eruption site. These structures are also known as plutonic formation or an igneous intrusion which are similar to the sills. A batholith represents a pluton which is great than 100km in exposed surface area. For example, the laccoliths of the Ortiz porphyry belt in New Mexico likely formed during Laramide compression of the region 33 to 36 million years ago. [24], The original shape of intrusions can be difficult to reconstruct. Shield volcanoes quietly produce broad, massive structures through lava flows. 32 and 15Ma (magnetic anomaly C11 to C5c). Image copyright iStockphoto / GISBA. Our editors will review what youve submitted and determine whether to revise the article. A relatively large igneous intrusion that forms when magma crystallizes underground and is later partially exposed following uplift and/or erosion. These structures form when tectonic plates move towards each other or when magma rises to the Earth's surface and cools. Laccoliths are intrusive igneous rock formations distinguished by their characteristic lens shapes. Semantic Scholar is a free, AI-powered research tool for scientific literature, based at the Allen Institute for AI. Yves Feisel. Various igneous features such as sills, volcanic edifices and stocks were identified by the, The northeastern part of the South China Sea is a special region in many aspects of its tectonics. The laccolith formation can take quite a few months to go when related with a single magma injection event or up to hundreds or thousands of years when varied by varied magmatic pulses stacking sills on the top of each other and deforming the host rock incrementally. Magmatic activities occurred after the cessation of seafloor spreading were founded mainly over the Continent-Ocean Transition (COT) zone. (a) The Laccolith is imaged in two intersecting seismic profiles, and (b) the detailed view of the red box in (a). New magnetic data acquired in the northernmost SCS, Igneous rocks in the northern margin of the South China Sea (SCS) have been identified via high resolution multi-channel seismic data in addition to other geophysical and drilling well data. The intrusive layers are 50 700 m thick, with diameters between 1.6 and 10 km. Non-silicate Minerals: Chemical Classifications & Examples, Oceanic Ridge System: Formation & Distribution. Intrusive rocks are observed in the Luzon-Ryukyu Transform Plate Boundary (LRTPB) dividing Southwest Taiwan Basin (SWTB) and Pearl River Mouth Basin (PRMB) north of the COT and their evolution mechanisms are not very well-studied. is the shear strength of the overlying rock. The pressure of the magma is high enough that the overlying strata are forced upward, giving the laccolith its dome-like form. Due to the intense pressure of the magma, the overlying strata are forced upward and folded, giving the laccolith a dome or mushroom-like form (or feasibly conically or wedge shape) with a substantially planar base. Although the use of "volcanic" in the name suggests that volcanic necks are extrusive features, they are comprised of intrusive igneous rocks. The laccolith of the Ortiz Porphyry Belt in New Mexico has probably formed during Laramide compression of the region 33 to 36 million years ago. is the pressure of the magma, The sill near the top of Colorados Engineer Mountain displays vertical cracks that Two well-known batholiths in North America include the Idaho Batholith and the Half Dome in Yosemite National Park. Gilbert also determined that larger laccoliths formed at greater depth. g T Suzanne has taught college economics, geography, and statistics, and has master's degrees in agricultural economics and marine affairs (marine resource management). Some are centered in impact craters and may form as part of the post-impact evolution of the crater. Length to thickness relationships for individual laccolith layers show a power-law correlation that does not fit the . Plus, get practice tests, quizzes, and personalized coaching to help you While batholiths represent the largest type of pluton, with areas greater than 100km, stocks are small plutons with areas less than 100km. Discover how they form, their characteristics, and see examples like the Idaho batholith. Laccoliths are distinguished from other igneous intrusions by their dome-shaped upper surface and level base. The central laccolith may initiate though ination of a sill that grew to a radius sufcient to lift the overburden, as hypothesized in traditional growth models. [21], The small Barber Hill syenite-stock laccolith in Charlotte, Vermont, has several volcanic trachyte dikes associated with it. [4] Because of their greater thickness, which slows the cooling rate, the rock of laccoliths is usually coarser-grained than the rock of sills. The extensive intraplate seamounts are obvious features in the northern South China Sea (SCS). Photos used throughout the site by David Jorre, Jean-Philippe Delberghe, JJ Ying, Luca Bravo, Brandi Redd, & Christian Perner from Unsplash. Ans. The extensive intraplate seamounts are obvious features in the northern South China Sea (SCS). Temperature Inversion - Types, Conditions, Effects and FAQs, Jet Stream - Layers, Formation, Types, Facts and FAQs, Forest Fire - Types, Effects, Natural Disaster and Management, Fly Ash - Concrete, Bricks, Sources, Relation and Facts, Rivers - Origin, History, Formation and Uses, Typhoon - Formation, Structure, Differences and FAQs, Relation Between Temperature and Humidity, Find Best Teacher for Online Tuition on Vedantu. The heart of California's Sierra Nevada mountains is carved from a granitic batholith emplaced between about 120 and 85 million years ago. characteristics are shared by many of the magma systems, both old and new: pulsed construction, tabular geometry, and lateral magma transport. Maps of Mesozoic and Cenozoic major faults in the Zhujiang River Mouth Basin are compiled. Please refer to the appropriate style manual or other sources if you have any questions. The rhyolite displays a wide array of unique mineralogical characteristics indicative to rapid emplacement and metastable crystallization conditions, including three-part quartz . Conceptual diagram showing the major forms of igneous rocks, such as batholiths, lopolith, xenolith, laccolith, sill, dyke, stock, volcano, volcanic neck and lava . The length of the laccolith on SO1E profile is significantly longer than the length on SOY profile. [9] An example of a fingered laccolith is the Shonkin Sag laccolith in Montana, US. Batholiths are found all over the world. In other cases, less sticky magma (For example, shonkinite) may form phenocrysts of augite at the bottom, then inserted through a vertical feeder dike that ends in laccolith. How Much Time Does Laccolith Take to Form? The laccolith is the attribute of the region where the crust is being flattened and the direction of the least stress is vertical, whereas the region where the crust is in pressure is more likely to form dikes as the direction of the least stress is parallel. If the intrusion remains limited in size, it forms a sill, in which the strata above and below the intrusion remain parallel to each other and the intrusion remains sheetlike. They are given the name mushroom-like features because their dome-shaped portion of the feature resembles mushrooms. By definition, batholiths have more than 40 square miles (100 square kilometers) of surface exposure. How quickly lava flows move, and how far they go, depends upon the type of magma that's erupting. The cooled magma penetrates through layers of sedimentary rocks that are pre-existing and lie horizontally to each other. It can take millions of years to form the numerous pluton diapirs contained within a single batholith. Made of igneous rock, they are only visible once erosion of the overlaying sediment has taken place. Growing up in a home whose cornerstone was a meteorite inspired Terri to become an award-winning travel and science writer. Many batholithic mountains you may have seen are smooth and rounded - this is because the stresses within the rock cause it to erode in sheets, or exfoliate, like the skin of an onion. [4] The critical radius for the sill to laccolith transition is now thought to be affected the viscosity of the magma (being greater for less viscous magma) as well as the strength of the host rock. Holt Science Spectrum - Physical Science with Earth and Space Science: Online Textbook Help, High School Physical Science: Help and Review, FTCE Middle Grades General Science 5-9 (004) Prep, ILTS Science - Physics (116): Test Practice and Study Guide, ILTS Science - Environmental Science (112): Test Practice and Study Guide, SAT Subject Test Chemistry: Practice and Study Guide, ILTS Science - Chemistry (106): Test Practice and Study Guide, NY Regents Exam - Living Environment: Test Prep & Practice, UExcel Anatomy & Physiology: Study Guide & Test Prep, Human Anatomy & Physiology: Help and Review, Create an account to start this course today. The content of silicon dioxide (SiO 2) in any rock is one of the most significant chemical characteristics of igneous rocks. The name batholith is derived from the Greek words batho for deep and litho for stone. They can be the source of both extrusive and intrusive igneous rocks. New magnetic data acquired in the northernmost SCS, Igneous rocks in the northern margin of the South China Sea (SCS) have been identified via high resolution multi-channel seismic data in addition to other geophysical and drilling well data. A variety of geologic processes contribute to the unique landscapes found throughout the world. As the name suggests, these features tend to be conical in shape and can be light- or dark-colored. Characteristics of a laccolith along the LRTPB fault zone between Pearl River Mouth Basin and Southwest Taiwan Basin Bo-wen Li, Q. Tang, +2 authors Xiao Wang Published 2021 Geology Terrestrial, Atmospheric and Oceanic Sciences The northern margin of the South China Sea (SCS) is often regarded as a magmapoor passive continental margin. These features can vary from less than one inch up to hundreds of feet thick and can extend for many miles. is the thickness of the overlying rocks, and If the rising plutons reach the surface, a volcanic eruption starts - but most plutons tend to slow down, cool, and crystallize before that, anywhere from five to thirty kilometers below the surface. In this lesson, the formation of batholiths and other similar intrusive igneous structures will be explored. As a member, you'll also get unlimited access to over 88,000 This, This paper presents results of two-dimensional seismic mapping of the northern East China Sea Shelf Basin. They are formed when magma rises below the Earth's crust and cools in place. For instance, Devils Tower in Wyoming and Needle Rock in Colorado were both thought to be volcanic necks, but further study has suggested they are eroded laccoliths. All maps, graphics, flags, photos and original descriptions 2023 worldatlas.com, The 8 Most Picturesque Small Towns In the Adirondack Mountains, Meet 12 Incredible Conservation Heroes Saving Our Wildlife From Extinction, India's Leopard God, Waghoba, Aids Wildlife Conservation In The Country, India's Bishnoi Community Has Fearlessly Protected Nature For Over 500 Years, Wildfires And Habitat Loss Are Killing Jaguars In The Amazon Rainforest, In India's Sundarbans: Where People Live Face-To-Face With Wild Tigers, Africa's "Thunderbird" Is At Risk Of Extinction. 9. Stocks refer to plutons having a surface area less than 100km, while batholiths represent plutons greater than 100km in area. When Laramide compression was later replaced by extension, emplacement of sills and laccoliths was replaced by emplacement of dikes. In Geology, laccolith is a sheet-like intrusion that has been inserted between the two layers of sedimentary rocks. Terrestrial, Atmospheric and Oceanic Sciences The northern margin of the South China Sea (SCS) is often regarded as a magmapoor passive continental margin. Magmatic activities occurred after the cessation of seafloor spreading were founded mainly over the Continent-Ocean Transition (COT) zone. P igneous rock and further classified as a laccolith. [5], The growth of laccoliths can take as little as a few months when associated with a single magma injection event,[10][11] or up to hundreds or thousands of years by multiple magmatic pulses stacking sills on top of each other and deforming the host rock incrementally. Each pluton is typically several kilometers in diameter. Geology Underfoot Along Colorados Front Range. Before an eruption of a volcano, there is usually significant deposits of molten magma beneath the surface of the earth ready to erupt. Magmatic activities occurred after the cessation of seafloor spreading were founded, The seafloor spreading of the South China Sea (SCS) was previously believed to take place between ca. They can be contrasted with sills, which are sheetlike intrusions oriented parallel to the bedding of the enclosing rock: a laccoliths ratio of diameter to thickness should be less than 10; a larger ratio would make the body a sill. A laccolith forms when magma (molten rock) rising through the Earth's crust begins to spread out horizontally, prying apart the host rock strata. After velocity estimation, AVO analysis, and geological interpretation for the LSA, we suggest that the LSA is an intrusive igneous rock and further classified as a laccolith. [1] Both laccoliths and sills are classified as concordant intrusions, since the bulk of the intrusion does not cut across host rock strata, but intrudes between strata.[7]. Crystal Shape Types & Overview | Formation Shapes of Crystals. Ans. Laccolith mountains have since been identified in many other parts of the world. Laccoliths formed from sills only when they became large enough for the pressure of the magma to force the overlying strata to dome upwards. Environmental effects of the formation of laccoliths A laccolith is a mushroom-shaped intrusion that develops beneath the surface of the earth when liquid magma surpasses its way between two horizontal layers of preexisting rock to cause the overlying materials to bulge outwards as the feature grows. Image copyright iStockphoto / Emre Corbaci. It is 15,400m in size, stretching 200 miles in one direction and 75 miles in the other. As described above, plutons represent a type of intrusive igneous structure. is the outer radius of the laccolith. Terrestrial, Atmospheric and Oceanic Sciences, The northern margin of the South China Sea (SCS) is often regarded as a magmapoor passive continental margin. Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree. A few are just one big mountain or isolated formation. As the magma ascends through the channel towards the Earth's surface. [23], A system of laccoliths is exposed at Elba, which form a "Christmas tree" laccolith system in which a single igneous plumbing system has produced multiple laccoliths at different levels in the crust. Batholiths can be found all over the planet, from Yosemite National Park to Canada's Coast Range. This, This paper presents results of two-dimensional seismic mapping of the northern East China Sea Shelf Basin. Lava flows are streams of lava that pour out of a volcanic vent or fissure. A laccolith can be classed as a type of tabular pluton. Content on this site is licensed under a Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0) license. Batholith is derived from two Greek words: "batho" meaning deep and "litho" meaning stone. - "Characteristics of a laccolith along the LRTPB fault zone between Pearl River Mouth Basin and Southwest Taiwan Basin" After velocity estimation, AVO analysis, and geological interpretation for the LSA, we suggest that the LSA is an intrusive igneous rock and further classified as a laccolith. [14], The filled and solidified magma chamber of Torres del Paine (Patagonia) is one of the best exposed laccoliths, built up incrementally by horizontal granitic and mafic magma intrusions over 162 11 thousand years. It is larger than 100 square kilometres (40 sq mi) in area. . Evidence, layout, nature, relation with basin development, and geodynamics of these faults are discussed. Learn about batholiths in geology, including the batholith definition. Thus laccoliths are characteristic of regions where the crust is being compressed and the direction of least stress is vertical, while areas where the crust is in tension are more likely to form dikes, since the direction of least stress is then horizontal. [5], A laccolith forms after an initial sheet-like intrusion has been injected between layers of sedimentary rock. Atmos. Create your account, 12 chapters | [13] Because the emplacement of the laccolith domes up the overlying beds, local topographic relief is increased and erosion is accelerated, so that the overlying beds are eroded away to expose the intrusive cores. succeed. Sci., 32, 443-458, doi: 10.3319/TAO.2021.09.07.01, Terrestrial, Atmospheric and Oceanic Sciences (TAO), A large-scale anomaly was seismically observed and identified as laccolith, Its elongated shape is accordant to the LRTPB dividing the SWTB and PRMB, The LRTPB may be responsible for the formation of the large-scale anomaly. Copyrights and related rights for article metadata waived via CC0 1.0 Universal (CC0) Public Domain Dedication. These structures are created as magma cools beneath the Earth's surface. When this mushy melt is found underground penetrating other rocks, it's called magma, and the solidified rock is termed intrusive. While they are still molten magma, the plutons are known as plutonic diapirs - a diapir in geology is any intrusive mass of flexible, moving rock that forces its way up through more brittle rock layers. Terrestrial, Atmospheric and Oceanic Sciences, The northern margin of the South China Sea (SCS) is often regarded as a magmapoor passive continental margin. Laccoliths are generally formed at a relatively shallow depth and in few cases are formed by relatively viscous magma such as those crystallized to granite, diorite, and granodiorite. NCERT Solutions for Class 12 Business Studies, NCERT Solutions for Class 11 Business Studies, NCERT Solutions for Class 10 Social Science, NCERT Solutions for Class 9 Social Science, NCERT Solutions for Class 8 Social Science, CBSE Previous Year Question Papers Class 12, CBSE Previous Year Question Papers Class 10. The coexistence of the laccolith and surrounding sills over the LRTPB shows that the north limit of magmatism is further north than the COT zone. A lopolith is a large, layered igneous intrusion that is distinguished by the convex-downward bowl shape of its floor and whose top can either be flat or convex down. Various igneous features such as sills, volcanic edifices and stocks were identified by the, The northeastern part of the South China Sea is a special region in many aspects of its tectonics. Learn more about DOAJs privacy policy. Gully & Rill Overview & Formation | What is a Gully? Plutons represent large intrusive igneous rocks. Alluvial Fan Overview & Formation | What is an Alluvial Fan? lith la-k-lith : a mass of igneous rock that is intruded between sedimentary beds and produces a domical bulging of the overlying strata laccolithic la-k-li-thik adjective Example Sentences Recent Examples on the Web This is the language of Big Sky Country: laccolith, dike, shonkinite, marine shale. Characteristics of a laccolith along the LRTPB fault zone between Pearl River Mouth Basin and Southwest Taiwan Basin, Boan Li, Qunshu Tang, Pin Yan, Junhui Yu, and Xiao Wang, Li, B., Q. Tang, P. Yan, J. Yu, and X. Wang, 2021: Characteristics of a laccolith along the LRTPB fault zone between Pearl River Mouth Basin and Southwest Taiwan Basin. Although from a distance a batholith may just look like a huge lump of rock, it has an internal structure and history that can be very complicated. Other geologic features produced by volcanic and tectonic activity are highly visible, such as mountains and islands. A magma chamber is a pool of molten rock material located beneath the Earth's surface. Here, detailed structural and geophysical features of a large-scale anomaly (LSA) is revealed from high-resolution multi-channel seismic (MCS) profiles over the LRTPB dividing the SWTB and the PRMB. The following table shows the difference between Batholith and Laccolith. A batholith is a very large mass of intrusive igneous rock that forms and cools deep in the Earth's crust. Both recent drilling into the Mesozoic and new reflection seismic surveys in the area provide a huge. Home Rocks Igneous Rocks and Volcanic Landforms. Although all igneous rocks form from the solidification of molten material, they can have very different appearances and characteristics depending upon the composition of the original material and where exactly it cooled. We have grown leaps and bounds to be the best Online Tuition Website in India with immensely talented Vedantu Master Teachers, from the most reputed institutions. Batholiths are formed when magma rises below the Earth's surface and cools in place. Dark host rocks overlie the light-colored, intrusive igneous spires of the Torres del Paine massif, which glaciers sculpted from a 12.6-million-year-old laccolith. [22], One of the largest laccoliths in the United States is Pine Valley Mountain in the Pine Valley Mountain Wilderness area near St. George, Utah. Various igneous features such as sills, volcanic edifices and stocks were identified by the, The northeastern part of the South China Sea is a special region in many aspects of its tectonics. {\displaystyle r} laccolith, in geology, any of a type of igneous intrusion that has split apart two strata, resulting in a domelike structure; the floor of the structure is usually horizontal.