Solitario
Encyclopedia
The Solitario is a large geologic formation
in Big Bend Ranch State Park
in West Texas
. Viewed from above, it suggests an impact crater
. In fact, it is the eroded remains of a laccolith
. The approximate center of the Solitario is located 56.8 km (35.3 mi) east southeast of Presidio, Texas
, just west of the line dividing Brewster County, Texas
and Presidio County, Texas
. The formation covers a circular area of approximately 135 km² (52.1 sq mi). The geology
of the Solitario is complex. In 1988 the state of Texas purchased the property containing the Solitario and created Big Bend Ranch State Park.
developed in Paleozoic
and Cretaceous
rocks above an Eocene
granite
laccolith intrusion. The dome is associated with radial rhyolite
to trachyte
dikes
and sills
and erupted ash flow
tuff
s. The 16 km diameter dome contains a 6 by 2 km volcanic cauldera filled with collapse breccia
, tuff, and trachyte lava
.
The Paleozoic rocks of the dome consist of a 2.6 km thick section of intensely folded Cambrian
through Early Pennsylvanian
sediments. The Paleozoic rocks were deformed and thrust
into the area from the southeast during the Ouachita orogeny
. Following the Permian
uplift and erosion during most of the Mesozoic
was followed by deposition of Cretaceous
carbonate rocks which correlate with the Cretaceous of the Gulf Coast. The area was uplifted by the Laramide orogeny
during latest Cretaceous. Following the Eocene intrusive and volcanic events of the Solitario, the area was partially covered by volcanic rocks from the adjacent Bofecillos volcanic center to the west of the area during the Oligocene
and early Miocene
. Erosion
and downcutting following the Pleistocene
deepening of the Rio Grande
to the southwest and south have produced the current topographic expression of the area.
Geologic formation
A formation or geological formation is the fundamental unit of lithostratigraphy. A formation consists of a certain number of rock strata that have a comparable lithology, facies or other similar properties...
in Big Bend Ranch State Park
Big Bend Ranch State Park (Texas)
Big Bend Ranch State Park is a state park located on the Rio Grande in Brewster County and Presidio County, Texas. It is the largest state park in Texas. The closest major town is Presidio, Texas, where the state park's head office is located.-Features:...
in West Texas
West Texas
West Texas is a vernacular term applied to a region in the southwestern quadrant of the United States that primarily encompasses the arid and semi-arid lands in the western portion of the state of Texas....
. Viewed from above, it suggests an impact crater
Impact crater
In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...
. In fact, it is the eroded remains of a laccolith
Laccolith
A laccolith is a sheet intrusion that has been injected between two layers of sedimentary rock. The pressure of the magma is high enough that the overlying strata are forced upward, giving the laccolith a dome or mushroom-like form with a generally planar base.Laccoliths tend to form at relatively...
. The approximate center of the Solitario is located 56.8 km (35.3 mi) east southeast of Presidio, Texas
Presidio, Texas
Presidio is a city in Presidio County, Texas, United States. It stands on the Rio Grande , on the opposite side of the U.S.-Mexico border from Ojinaga, Chihuahua. The population was 4,167 at the 2000 census....
, just west of the line dividing Brewster County, Texas
Brewster County, Texas
Brewster County is a county located in western part of the US state of Texas, along the border with Mexico. It is one of the nine counties that comprise the Trans-Pecos region of West Texas. As of the 2000 census, the population is 8,866. In 2009, the population was estimated to be 9,481. Its...
and Presidio County, Texas
Presidio County, Texas
Presidio County is a county located in the U.S. state of Texas. In 2000, its population was 7,304. Its county seat is Marfa. Presidio County is in the Trans-Pecos region of West Texas and is named for the ancient border settlement of Presidio del Norte.-Geography:Presidio County is triangular in...
. The formation covers a circular area of approximately 135 km² (52.1 sq mi). The geology
Geology
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...
of the Solitario is complex. In 1988 the state of Texas purchased the property containing the Solitario and created Big Bend Ranch State Park.
Geology
The Solitario is a structural domeDome (geology)
In structural geology, a dome is a deformational feature consisting of symmetrically-dipping anticlines; their general outline on a geologic map is circular or oval...
developed in Paleozoic
Paleozoic
The Paleozoic era is the earliest of three geologic eras of the Phanerozoic eon, spanning from roughly...
and Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
rocks above an Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
granite
Granite
Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...
laccolith intrusion. The dome is associated with radial rhyolite
Rhyolite
This page is about a volcanic rock. For the ghost town see Rhyolite, Nevada, and for the satellite system, see Rhyolite/Aquacade.Rhyolite is an igneous, volcanic rock, of felsic composition . It may have any texture from glassy to aphanitic to porphyritic...
to trachyte
Trachyte
Trachyte is an igneous volcanic rock with an aphanitic to porphyritic texture. The mineral assemblage consists of essential alkali feldspar; relatively minor plagioclase and quartz or a feldspathoid such as nepheline may also be present....
dikes
Dike (geology)
A dike or dyke in geology is a type of sheet intrusion referring to any geologic body that cuts discordantly across* planar wall rock structures, such as bedding or foliation...
and sills
Sill (geology)
In geology, a sill is a tabular sheet intrusion that has intruded between older layers of sedimentary rock, beds of volcanic lava or tuff, or even along the direction of foliation in metamorphic rock. The term sill is synonymous with concordant intrusive sheet...
and erupted ash flow
Volcanic ash
Volcanic ash consists of small tephra, which are bits of pulverized rock and glass created by volcanic eruptions, less than in diameter. There are three mechanisms of volcanic ash formation: gas release under decompression causing magmatic eruptions; thermal contraction from chilling on contact...
tuff
Tuff
Tuff is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. Tuff is sometimes called tufa, particularly when used as construction material, although tufa also refers to a quite different rock. Rock that contains greater than 50% tuff is considered...
s. The 16 km diameter dome contains a 6 by 2 km volcanic cauldera filled with collapse breccia
Breccia
Breccia is a rock composed of broken fragments of minerals or rock cemented together by a fine-grained matrix, that can be either similar to or different from the composition of the fragments....
, tuff, and trachyte lava
Lava
Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...
.
The Paleozoic rocks of the dome consist of a 2.6 km thick section of intensely folded Cambrian
Cambrian
The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...
through Early Pennsylvanian
Pennsylvanian
The Pennsylvanian is, in the ICS geologic timescale, the younger of two subperiods of the Carboniferous Period. It lasted from roughly . As with most other geochronologic units, the rock beds that define the Pennsylvanian are well identified, but the exact date of the start and end are uncertain...
sediments. The Paleozoic rocks were deformed and thrust
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...
into the area from the southeast during the Ouachita orogeny
Ouachita orogeny
The Ouachita orogeny was a mountain building event that resulted in the folding and faulting of strata currently exposed in the Ouachita Mountains...
. Following the Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...
uplift and erosion during most of the Mesozoic
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
was followed by deposition of Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
carbonate rocks which correlate with the Cretaceous of the Gulf Coast. The area was uplifted by the Laramide orogeny
Laramide orogeny
The Laramide orogeny was a period of mountain building in western North America, which started in the Late Cretaceous, 70 to 80 million years ago, and ended 35 to 55 million years ago. The exact duration and ages of beginning and end of the orogeny are in dispute, as is the cause. The Laramide...
during latest Cretaceous. Following the Eocene intrusive and volcanic events of the Solitario, the area was partially covered by volcanic rocks from the adjacent Bofecillos volcanic center to the west of the area during the Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
and early Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
. Erosion
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
and downcutting following the Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
deepening of the Rio Grande
Rio Grande
The Rio Grande is a river that flows from southwestern Colorado in the United States to the Gulf of Mexico. Along the way it forms part of the Mexico – United States border. Its length varies as its course changes...
to the southwest and south have produced the current topographic expression of the area.
External links
- Flora and Vegetation of the Solitario Dome, Jean Evans Hardy, Iron Mountain Press - 2009