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113-463: The Fra Mauro formation (or Fra Mauro Highlands ) is a formation on the near side of Earth's Moon that served as the landing site for the American Apollo 14 mission in 1971. It is named after the 80-kilometer-diameter crater Fra Mauro , located within it. The formation, as well as Fra Mauro crater, take their names from a 15th-century Italian monk and mapmaker of the same name. Apollo 13

226-687: A fault that divides the rock into two or more pieces. A fracture will sometimes form a deep fissure or crevice in the rock. Fractures are commonly caused by stress exceeding the rock strength, causing the rock to lose cohesion along its weakest plane. Fractures can provide permeability for fluid movement, such as water or hydrocarbons . Highly fractured rocks can make good aquifers or hydrocarbon reservoirs , since they may possess both significant permeability and fracture porosity . Fractures are forms of brittle deformation. There are two types of primary brittle deformation processes. Tensile fracturing results in joints . Shear fractures are

339-509: A free-return trajectory should the Apollo Service Module engine fail. After Apollo 12 demonstrated the ability to land with some degree of precision at a pre-specified landing site, mission planners considered landings in rough, but geologically interesting areas of the Moon. The aborted Apollo 13 mission was originally scheduled to land at Fra Mauro, with Apollo 14 scheduled to land in

452-731: A 'natural drill hole' to allow the astronauts to obtain Imbrium ejecta, a primary objective of the mission. Geology of the Moon Geological studies of the Moon are based on a combination of Earth-based telescope observations, measurements from orbiting spacecraft , lunar samples , and geophysical data. Six locations were sampled directly during the crewed Apollo program landings from 1969 to 1972, which returned 382 kilograms (842 lb) of lunar rock and lunar soil to Earth In addition, three robotic Soviet Luna spacecraft returned another 301 grams (10.6 oz) of samples, and

565-480: A = half crack length. Fracture mechanics has generalized to that γ represents energy dissipated in fracture not just the energy associated with creation of new surfaces Linear elastic fracture mechanics (LEFM) builds off the energy balance approach taken by Griffith but provides a more generalized approach for many crack problems. LEFM investigates the stress field near the crack tip and bases fracture criteria on stress field parameters. One important contribution of LEFM

678-451: A car windshield or a highly ductile crack like a ripped plastic grocery bag. Rocks are a polycrystalline material so cracks grow through the coalescing of complex microcracks that occur in front of the crack tip. This area of microcracks is called the brittle process zone. Consider a simplified 2D shear crack as shown in the image on the right. The shear crack, shown in blue, propagates when tensile cracks, shown in red, grow perpendicular to

791-524: A compositionally distinct crust and mantle and accounts for the major suites of lunar rocks. As crystallization of the lunar magma ocean proceeded, minerals such as olivine and pyroxene would have precipitated and sank to form the lunar mantle. After crystallization was about three-quarters complete, anorthositic plagioclase would have begun to crystallize, and because of its low density, float, forming an anorthositic crust. Importantly, elements that are incompatible (i.e., those that partition preferentially into

904-445: A constant of proportionality within geology. σ n is the normal stress across the fracture at the instant of failure, σ f represents the pore fluid pressure. It is important to point out that pore fluid pressure has a significant impact on shear stress, especially where pore fluid pressure approaches lithostatic pressure , which is the normal pressure induced by the weight of the overlying rock. This relationship serves to provide

1017-497: A continuum in titanium concentrations, with the highest concentration rocks being the least abundant. The current model of the interior of the Moon was derived using seismometers left behind during the crewed Apollo program missions, as well as investigations of the Moon's gravity field and rotation. The mass of the Moon is sufficient to eliminate any voids within the interior, so it is estimated to be composed of solid rock throughout. Its low bulk density (~3346 kg m ) indicates

1130-483: A core whose size is only about one quarter of its radius. The crust of the Moon is on average about 50 km thick (though this is uncertain by about ±15 km). It is estimated that the far-side crust is on average thicker than the near side by about 15 km. Seismology has constrained the thickness of the crust only near the Apollo 12 and Apollo 14 landing sites. Although the initial Apollo -era analyses suggested

1243-479: A crustal thickness of about 60 km at this site, recent reanalyses of this data suggest that it is thinner, somewhere between about 30 and 45 km. Compared with Earth, the Moon has a weak external magnetic field. Other significant differences are that the Moon does not currently have a dipolar magnetic field (as would be generated by a geodynamo in its core), and the magnetizations that are present are almost entirely crustal in origin. One hypothesis holds that

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1356-431: A depth of about 500 km or greater. The first minerals to form in this ocean were the iron and magnesium silicates olivine and pyroxene . Because these minerals were denser than the molten material around them, they sank. After crystallization was about 75% complete, less dense anorthositic plagioclase feldspar crystallized and floated, forming an anorthositic crust about 50 km in thickness. The majority of

1469-500: A direct affiliation with the landing site, as it is located in a valley between ridges, and there exists the possibility that the basalts were merely deposited there as a result of other impact events. The Apollo 14 crew members sampled boulders in the ejecta of Cone crater. These boulders appeared to be layered and fractured breccias , contrasting from the appearance of the surrounding area because of their older age. As these boulders increase in size and number closer to Cone crater, it

1582-419: A down-dropped block between them. Most grabens are found within the lunar maria near the edges of large impact basins. The origin of the Moon's craters as impact features became widely accepted only in the 1960s. This realization allowed the impact history of the Moon to be gradually worked out by means of the geologic principle of superposition . That is, if a crater (or its ejecta) overlaid another, it must be

1695-473: A fixed function of θ {\displaystyle \theta } . With knowledge of the geometry of the crack and applied far field stresses, it is possible to predict the crack tip stresses, displacement, and growth. Energy release rate is defined to relate K to the Griffith energy balance as previously defined. In both LEFM and energy balance approaches, the crack is assumed to be cohesionless behind

1808-437: A fracture forms a discontinuity that may have a large influence on the mechanical behavior (strength, deformation, etc.) of soil and rock masses in, for example, tunnel , foundation , or slope construction. Fractures also play a significant role in minerals exploitation. One aspect of the upstream energy sector is the production from naturally fractured reservoirs. There are a good number of naturally fractured reservoirs in

1921-472: A kilometer. Examples of such impact melt can be seen in the northeastern part of the Mare Orientale impact basin. The surface of the Moon has been subject to billions of years of collisions with both small and large asteroidal and cometary materials. Over time, these impact processes have pulverized and "gardened" the surface materials, forming a fine-grained layer termed regolith . The thickness of

2034-416: A low metal abundance. Mass and moment of inertia constraints indicate that the Moon likely has an iron core that is less than about 450 km in radius. Studies of the Moon's physical librations (small perturbations to its rotation) furthermore indicate that the core is still molten. Most planetary bodies and moons have iron cores that are about half the size of the body. The Moon is thus anomalous in having

2147-403: A much longer time, and that younger plutonic rocks exist deep below the surface. Analysis of the samples from the Moon seems to show that a lot of the Moon's impact basins formed in a short amount of time between about 4 and 3.85 Ga ago. This hypothesis is referred to as the lunar cataclysm or late heavy bombardment . However, it is now recognized that ejecta from the Imbrium impact basin (one of

2260-413: A remote tensile stress, σ n , is applied, allowing microcracks to open slightly throughout the tensile region. As these cracks open up, the stresses at the crack tips intensify, eventually exceeding the rock strength and allowing the fracture to propagate. This can occur at times of rapid overburden erosion. Folding also can provide tension, such as along the top of an anticlinal fold axis. In this scenario

2373-403: A result from shear or tensile stress. Some of the primary mechanisms are discussed below. First, there are three modes of fractures that occur (regardless of mechanism): For more information on this, see fracture mechanics . Rocks contain many pre-existing cracks where development of tensile fracture, or Mode I fracture, may be examined. The first form is in axial stretching. In this case

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2486-418: A result, any differences in hydrostatic balance down the well can result in well control issues. If a higher pressured natural fracture system is encountered, the rapid rate at which formation fluid can flow into the wellbore can cause the situation to rapidly escalate into a blowout, either at surface or in a higher subsurface formation. Conversely, if a lower pressured fracture network is encountered, fluid from

2599-475: A rod under uniform tension Griffith determined an expression for the critical stress at which a favorably orientated crack will grow. The critical stress at fracture is given by, σ f = ( 2 E γ π a ) 1 / 2 {\displaystyle \sigma _{f}=({2E\gamma \over \pi a})^{1/2}} where γ = surface energy associated with broken bonds, E = Young's modulus , and

2712-404: A solid body, such as an asteroid or comet , collides with the surface at a high velocity (mean impact velocities for the Moon are about 17 km per second). The kinetic energy of the impact creates a compression shock wave that radiates away from the point of entry. This is succeeded by a rarefaction wave, which is responsible for propelling most of the ejecta out of the crater. Finally there

2825-556: A third of the near side. Only a few percent of the farside has been affected by mare volcanism. Even before the Apollo missions confirmed it, most scientists already thought that the maria are lava-filled plains, because they have lava flow patterns and collapses attributed to lava tubes . The ages of the mare basalts have been determined both by direct radiometric dating and by the technique of crater counting . The oldest radiometric ages are about 4.2 Ga (billion years), and ages of most of

2938-507: A weakened section of rock. This weakened section is more susceptible to changes in pore pressure and dilatation or compaction. Note that this description of formation and propagation considers temperatures and pressures near the Earth's surface. Rocks deep within the earth are subject to very high temperatures and pressures. This causes them to behave in the semi-brittle and plastic regimes which result in significantly different fracture mechanisms. In

3051-423: Is a hydrodynamic rebound of the floor that can create a central peak. These craters appear in a continuum of diameters across the surface of the Moon, ranging in size from tiny pits to the immense South Pole–Aitken basin with a diameter of nearly 2,500 km and a depth of 13 km. In a very general sense, the lunar history of impact cratering follows a trend of decreasing crater size with time. In particular,

3164-525: Is believed that they originate from the greatest depth of excavation of Cone crater. These boulders show what is believed to be general characteristics of the Fra Mauro formation: clastic texture , stratification , and jointing or fracturing. As Apollo 14 was an early Apollo mission, consideration for landing sites was restricted to equatorial regions in order to enable the Moon-bound spacecraft to remain on

3277-422: Is called cataclastic flow, which will cause fractures to fail and propagate due to a mixture of brittle-frictional and plastic deformations. Describing joints can be difficult, especially without visuals. The following are descriptions of typical natural fracture joint geometries that might be encountered in field studies: Faults are another form of fracture in a geologic environment. In any type of faulting,

3390-427: Is debatable). The Apollo 17 mission landed in an area in which the material coming from the crater Tycho might have been sampled. The study of these rocks seem to indicate that this crater could have formed 100 million years ago, though this is debatable as well. The surface has also experienced space weathering due to high energy particles, solar wind implantation, and micrometeorite impacts. This process causes

3503-535: Is less than force required to fracture and create new faults as shown by the Mohr-Coulomb diagram . Since the earth is full of existing cracks and this means for any applied stress, many of these cracks are more likely to slip and redistribute stress than a new crack is to initiate. The Mohr's Diagram shown, provides a visual example. For a given stress state in the earth, if an existing fault or crack exists orientated anywhere from −α/4 to +α/4, this fault will slip before

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3616-422: Is observed. To fully understand the effects of applied tensile stress around a crack in a brittle material such a rock, fracture mechanics can be used. The concept of fracture mechanics was initially developed by A. A. Griffith during World War I. Griffith looked at the energy required to create new surfaces by breaking material bonds versus the elastic strain energy of the stretched bonds released. By analyzing

3729-408: Is primarily composed of relatively low ridges and hills, between which exist undulating valleys. Much of the ejecta blanket from the Imbrium impact is covered with debris from younger impacts and material churned up by possible moonquakes . Debris found in the formation may have originated from deep beneath the original crust, and samples collected there could give insight into the geologic history of

3842-428: Is that the nearside crust is thinner than the farside. Although variations in the crustal thickness might act to modulate the amount of magma that ultimately reaches the surface, this hypothesis does not explain why the farside South Pole-Aitken basin , whose crust is thinner than Oceanus Procellarum, was only modestly filled by volcanic products. Another type of deposit associated with the maria, although it also covers

3955-462: Is the stress intensity factor , K, which is used to predict the stress at the crack tip. The stress field is given by σ i j ( r , θ ) = K ( 2 π r ) 1 / 2 f i j ( θ ) {\displaystyle \sigma _{ij}(r,\theta )={K \over (2\pi r)^{1/2}}f_{ij}(\theta )} where K {\displaystyle K}

4068-423: Is the stress intensity factor for Mode I, II, or III cracking and f i j {\displaystyle f_{ij}} is a dimensionless quantity that varies with applied load and sample geometry. As the stress field gets close to the crack tip, i.e. r → 0 {\displaystyle r\rightarrow 0} , f i j {\displaystyle f_{ij}} becomes

4181-401: Is unlikely that a causal relationship exists between the impact event and mare volcanism because the impact basins are much older (by about 500 million years) than the mare fill. Furthermore, Oceanus Procellarum , which is the largest expanse of mare volcanism on the Moon, does not correspond to any known impact basin. It is commonly suggested that the reason the mare only erupted on the nearside

4294-562: The Imbrium basin , a unique geologic province that is now known as the Procellarum KREEP Terrane . Quickly after the lunar crust formed, or even as it was forming, different types of magmas that would give rise to the Mg - suite norites and troctolites began to form, although the exact depths at which this occurred are not known precisely. Recent theories suggest that Mg-suite plutonism

4407-562: The Littrow region of Mare Serenitatis . After Apollo 13 failed to land, mission planners decided to re-target Apollo 14 to Fra Mauro, as they regarded Fra Mauro as more interesting scientifically than the Littrow site. There, Apollo 14 had the objective of sampling ejecta from the Imbrium impact to gain insight into the Moon's geologic history . Mission planners chose a landing site near the relatively freshly formed Cone crater, as this crater served as

4520-450: The basaltic rocks with respect to the rocks of the lunar highlands is that the basalts contain higher abundances of olivine and pyroxene , and less plagioclase . They are richer in iron than terrestrial basalts, and also have lower viscosities. Some of them have high abundances of a ferro - titanic oxide called ilmenite . Because the first sampling of rocks contained a high content of ilmenite and other related minerals, they received

4633-568: The coulomb failure envelope within the Mohr-Coulomb Theory . Frictional sliding is one aspect for consideration during shear fracturing and faulting. The shear force parallel to the plane must overcome the frictional force to move the faces of the fracture across each other. In fracturing, frictional sliding typically only has significant effects on the reactivation on existing shear fractures. For more information on frictional forces, see friction . The shear force required to slip fault

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4746-413: The lunar regolith varies between 2 meters (6.6 ft) beneath the younger maria, to up to 20 meters (66 ft) beneath the oldest surfaces of the lunar highlands. The regolith is predominantly composed of materials found in the region, but also contains traces of materials ejected by distant impact craters. The term mega-regolith is often used to describe the heavily fractured bedrock directly beneath

4859-487: The petrogenesis of KREEP . Composite rocks on the lunar surface often appear in the form of breccias . Of these, the subcategories are called fragmental, granulitic , and impact-melt breccias, depending on how they were formed. The mafic impact melt breccias, which are typified by the low-K Fra Mauro composition, have a higher proportion of iron and magnesium than typical upper crust anorthositic rocks, as well as higher abundances of KREEP. The main characteristics of

4972-411: The ray systems associated with young craters to darken until it matches the albedo of the surrounding surface. However, if the composition of the ray is different from the underlying crustal materials (as might occur when a "highland" ray is emplaced on the mare), the ray could be visible for much longer times. After resumption of Lunar exploration in the 1990s, it was discovered there are scarps across

5085-514: The titanium -rich mineral ilmenite . The majority of basaltic eruptions occurred between about 3 and 3.5 Ga ago, though some mare samples have ages as old as 4.2 Ga. The youngest (based on the method of crater counting) was long thought to date to 1 billion years ago, but research in the 2010s has found evidence of eruptions from less than 50 million years in the past. Along with mare volcanism came pyroclastic eruptions , which launched molten basaltic materials hundreds of kilometers away from

5198-422: The volcano . A large portion of the mare formed, or flowed into, the low elevations associated with the nearside impact basins. However, Oceanus Procellarum does not correspond to any known impact structure, and the lowest elevations of the Moon within the farside South Pole-Aitken basin are only modestly covered by mare (see lunar mare for a more detailed discussion). Impacts by meteorites and comets are

5311-521: The Apollo 14 landing site within Fra Mauro: the immediate impact blanket of Cone crater, about 25 million years old, and surrounding older terrain. During Apollo 14, astronauts Alan Shepard and Edgar Mitchell recovered ejecta material from the Cone crater impact, which is believed to have excavated Imbrium impact material from a possible depth of about 80 m (260 ft). Most of the samples returned from

5424-506: The Chinese robotic Chang'e 5 returned a sample of 1,731 g (61.1 oz) in 2020. The Moon is the only extraterrestrial body for which we have samples with a known geologic context. A handful of lunar meteorites have been recognized on Earth, though their source craters on the Moon are unknown. A substantial portion of the lunar surface has not been explored, and a number of geological questions remain unanswered. Elements known to be present on

5537-487: The Fra Mauro formation during Apollo 14 suggest that the impact that formed the Imbrium basin is no older than 4.25 billion years. Analysis of Apollo 14 samples suggests that there are five major geologic constituents present in the immediate landing area: regolith breccias , fragmental breccias, igneous lithologies , granulitic lithologies, and impact - melt lithologies. Samples of each of these compositions were recovered in one or both of two major surface units of

5650-604: The Moon could serve as a shelter from the severe environment of the lunar surface, with its frequent meteorite impacts, high-energy ultraviolet radiation and energetic particles, and extreme diurnal temperature variations. Following the launch of the Lunar Reconnaissance Orbiter , many lunar lava tubes have been imaged. These lunar pits are found in several locations across the Moon, including Marius Hills , Mare Ingenii and Mare Tranquillitatis . The first rocks brought back by Apollo 11 were basalts . Although

5763-470: The Moon from Fra Mauro are classified as breccias from the vicinity of Cone crater. Studies conducted upon samples from Apollo 14 have shown that the samples do not support the possibility that the landing site is floored by volcanic rocks, or basalts . Basalts are sparse in samples of Cone crater ejecta, but somewhat abundant in samples recovered farther west, on the opposite side of the immediate landing site. Two explanations have been presented for this: (1)

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5876-502: The Moon is the contrast between its bright and dark zones. Lighter surfaces are the lunar highlands, which receive the name of terrae (singular terra , from the Latin for earth , land ), and the darker plains are called maria (singular mare , from the Latin for sea ), after Johannes Kepler who introduced the names in the 17th century. The highlands are anorthositic in composition, whereas

5989-457: The Moon. Lunar rocks are in large part made of the same common rock forming minerals as found on Earth, such as olivine , pyroxene , and plagioclase feldspar ( anorthite ). Plagioclase feldspar is mostly found in the lunar crust, whereas pyroxene and olivine are typically seen in the lunar mantle. The mineral ilmenite is highly abundant in some mare basalts, and a new mineral named armalcolite (named for Arm strong, Al drin, and Col lins,

6102-431: The Moon. The petrology of the formation, based on data obtained on Apollo 14, indicates a history of impact and ejection possibly spanning over approximately 500 million years. A relatively recent impact created Cone crater, 1,000 feet across and 250 feet deep, near the landing site of Apollo 14. One of the main objectives of that mission was to sample the original Imbrium material located on its rim. Samples obtained of

6215-485: The United States, and over the past century, they have provided a substantial boost to the nation's net hydrocarbon production. The key concept is while low porosity, brittle rocks may have very little natural storage or flow capability, the rock is subjected to stresses that generate fractures, and these fractures can actually store a very large volume of hydrocarbons, capable of being recovered at very high rates. One of

6328-412: The active fracture experiences shear failure, as the faces of the fracture slip relative to each other. As a result, these fractures seem like large scale representations of Mode II and III fractures, however that is not necessarily the case. On such a large scale, once the shear failure occurs, the fracture begins to curve its propagation towards the same direction as the tensile fractures. In other words,

6441-524: The age of the surface. The most recent impacts are distinguished by well-defined features, including a sharp-edged rim. Small craters tend to form a bowl shape, whereas larger impacts can have a central peak with flat floors. Larger craters generally display slumping features along the inner walls that can form terraces and ledges. The largest impact basins, the multiring basins, can even have secondary concentric rings of raised material. The impact process excavates high albedo materials that initially gives

6554-401: The antipodes of the largest impact basins. Although the Moon does not have a dipolar magnetic field like Earth's, some returned rocks have strong magnetizations. Furthermore, measurements from orbit show that some portions of the lunar surface are associated with strong magnetic fields. Fracture (geology) A fracture is any separation in a geologic formation , such as a joint or

6667-836: The birth of true horizontal drilling in a developmental context. Another example in South Texas is the Georgetown and Buda limestone formations. Furthermore, the recent uprise in prevalence of unconventional reservoirs is actually, in part, a product of natural fractures. In this case, these microfractures are analogous to Griffith Cracks, however they can often be sufficient to supply the necessary productivity, especially after completions, to make what used to be marginally economic zones commercially productive with repeatable success. However, while natural fractures can often be beneficial, they can also act as potential hazards while drilling wells. Natural fractures can have very high permeability , and as

6780-484: The central peak. The ejecta from large impacts can include large blocks of material that reimpact the surface to form secondary impact craters. These craters are sometimes formed in clearly discernible radial patterns, and generally have shallower depths than primary craters of the same size. In some cases an entire line of these blocks can impact to form a valley. These are distinguished from catena , or crater chains, which are linear strings of craters that are formed when

6893-405: The composition of material deep inside the formation. Data from the mission has helped to determine the approximate age of Mare Imbrium, suggesting that it is no more than about 4.25 billion years old. Fra Mauro is a widespread hilly geological area covering large portions of the lunar surface around Mare Imbrium, and is thought to be composed of ejecta from the impact which formed Imbrium. The area

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7006-535: The concentration of titanium that the rock has, with the green particles having the lowest concentrations (about 1%), and red particles having the highest concentrations (up to 14%, much more than the basalts with the highest concentrations). Rilles on the Moon sometimes resulted from the formation of localized lava channels . These generally fall into three categories, consisting of sinuous, arcuate, or linear shapes. By following these meandering rilles back to their source, they often lead to an old volcanic vent. One of

7119-405: The crack tip. This provides a problem for geological applications such a fault, where friction exists all over a fault. Overcoming friction absorbs some of the energy that would otherwise go to crack growth. This means that for Modes II and III crack growth, LEFM and energy balances represent local stress fractures rather than global criteria. Cracks in rock do not form smooth path like a crack in

7232-448: The crater, ejecta, and ray system a bright appearance. The process of space weathering gradually decreases the albedo of this material such that the rays fade with time. Gradually the crater and its ejecta undergo impact erosion from micrometeorites and smaller impacts. This erosional process softens and rounds the features of the crater. The crater can also be covered in ejecta from other impacts, which can submerge features and even bury

7345-426: The crustal magnetizations were acquired early in lunar history when a geodynamo was still operating. However, the lunar core's small size is a potential obstacle to this hypothesis. Alternatively, it is possible that transient magnetic fields could be generated during impact processes on airless bodies such as the Moon. In support of this, it has been noted that the largest crustal magnetizations appear to be located near

7458-417: The direction of the least principal stresses. The tensile cracks propagate a short distance then become stable, allowing the shear crack to propagate. This type of crack propagation should only be considered an example. Fracture in rock is a 3D process with cracks growing in all directions. It is also important to note that once the crack grows, the microcracks in the brittle process zone are left behind leaving

7571-520: The domes contain a small pit at their peak. Wrinkle ridges are features created by compressive tectonic forces within the maria. These features represent buckling of the surface and form long ridges across parts of the maria. Some of these ridges may outline buried craters or other features beneath the maria. A prime example of such an outlined feature is the crater Letronne . Grabens are tectonic features that form under extensional stresses. Structurally, they are composed of two normal faults , with

7684-411: The fault typically attempts to orient itself perpendicular to the plane of least principal stress. This results in an out-of-plane shear relative to the initial reference plane. Therefore, these cannot necessarily be qualified as Mode II or III fractures. An additional, important characteristic of shear-mode fractures is the process by which they spawn wing cracks , which are tensile cracks that form at

7797-527: The first initial breaks resulting from shear forces exceeding the cohesive strength in that plane. After those two initial deformations, several other types of secondary brittle deformation can be observed, such as frictional sliding or cataclastic flow on reactivated joints or faults. Most often, fracture profiles will look like either a blade, ellipsoid, or circle. Fractures in rocks can be formed either due to compression or tension. Fractures due to compression include thrust faults . Fractures may also be

7910-422: The fracture face is actually touching the other face. The cumulative impact of asperities is a reduction of the real area of contact' , which is important when establishing frictional forces. Sometimes, it is possible for fluids within the fracture to cause fracture propagation with a much lower pressure than initially required. The reaction between certain fluids and the minerals the rock is composed of can lower

8023-403: The fundamental question regarding the history of the Moon was of its origin . Early hypotheses included fission from Earth, capture , and co-accretion . Today, the giant-impact hypothesis is widely accepted by the scientific community. The geological history of the Moon has been defined into six major epochs, called the lunar geologic timescale . Starting about 4.5 billion years ago,

8136-564: The globe that are caused by the contraction due to cooling of the Moon. At the top of the Moon’s stratigraphy is the Copernican unit consisting of craters with a ray system. Below this is the Eratosthenian unit, defined by craters with established impact crater morphology, but lacking the ray system of the Copernican. These two units are present in smaller spots on the lunar surface. Further down

8249-434: The highland areas, are the "dark mantle" deposits. These deposits cannot be seen with the naked eye, but they can be seen in images taken from telescopes or orbiting spacecraft. Before the Apollo missions, scientists predicted that they were deposits produced by pyroclastic eruptions. Some deposits appear to be associated with dark elongated ash cones , reinforcing the idea of pyroclasts. The existence of pyroclastic eruptions

8362-490: The highlands is rich in aluminium and silica , just as the rocks in those regions. The regolith in the maria is rich in iron and magnesium and is silica-poor, as are the basaltic rocks from which it is formed. The lunar regolith is very important because it also stores information about the history of the Sun . The atoms that compose the solar wind – mostly hydrogen , helium , neon , carbon and nitrogen – hit

8475-412: The hypothetical giant-impact event is that the materials that re-accreted to form the Moon must have been hot. Current models predict that a large portion of the Moon would have been molten shortly after the Moon formed, with estimates for the depth of this magma ocean ranging from about 500 km to complete melting. Crystallization of this magma ocean would have given rise to a differentiated body with

8588-403: The impact body breaks up prior to impact. Generally speaking, a lunar crater is roughly circular in form. Laboratory experiments at NASA's Ames Research Center have demonstrated that even very low-angle impacts tend to produce circular craters, and that elliptical craters start forming at impact angles below five degrees. However, a low angle impact can produce a central peak that is offset from

8701-417: The largest impact basins were formed during the early periods, and these were successively overlaid by smaller craters. The size frequency distribution (SFD) of crater diameters on a given surface (that is, the number of craters as a function of diameter) approximately follows a power law with increasing number of craters with decreasing crater size. The vertical position of this curve can be used to estimate

8814-408: The least principal normal stress, σ n . When this occurs, a tensile fracture opens perpendicular to the plane of least stress. Tensile fracturing may also be induced by applied compressive loads, σ n , along an axis such as in a Brazilian disk test. This applied compression force results in longitudinal splitting. In this situation, tiny tensile fractures form parallel to the loading axis while

8927-425: The liquid phase) would have been progressively concentrated into the magma as crystallization progressed, forming a KREEP -rich magma that initially should have been sandwiched between the crust and mantle. Evidence for this scenario comes from the highly anorthositic composition of the lunar highland crust, as well as the existence of KREEP-rich materials. Additionally, zircon analysis of Apollo 14 samples suggests

9040-422: The load also forces any other microfractures closed. To picture this, imagine an envelope, with loading from the top. A load is applied on the top edge, the sides of the envelope open outward, even though nothing was pulling on them. Rapid deposition and compaction can sometimes induce these fractures. Tensile fractures are almost always referred to as joints , which are fractures where no appreciable slip or shear

9153-540: The lunar crust differentiated 4.51±0.01 billion years ago. The Apollo program brought back 380.05 kilograms (837.87 lb) of lunar surface material , most of which is stored at the Lunar Receiving Laboratory in Houston, Texas , and the uncrewed Soviet Luna programme returned 326 grams (11.5 oz) of lunar material. These rocks have proved to be invaluable in deciphering the geologic evolution of

9266-487: The lunar surface and insert themselves into the mineral grains. Upon analyzing the composition of the regolith, particularly its isotopic composition, it is possible to determine if the activity of the Sun has changed with time. The gases of the solar wind could be useful for future lunar bases, because oxygen, hydrogen ( water ), carbon and nitrogen are not only essential to sustain life, but are also potentially very useful in

9379-419: The lunar surface include, among others, oxygen (O), silicon (Si), iron (Fe), magnesium (Mg), calcium (Ca), aluminium (Al), manganese (Mn) and titanium (Ti). Among the more abundant are oxygen, iron and silicon. The oxygen content is estimated at 45% (by weight). Carbon (C) and nitrogen (N) appear to be present only in trace quantities from deposition by solar wind . For a long period of time,

9492-438: The magma ocean crystallized quickly (within about 100 million years or less), though the final remaining KREEP -rich magmas, which are highly enriched in incompatible and heat-producing elements, could have remained partially molten for several hundred million (or perhaps 1 billion) years. It appears that the final KREEP-rich magmas of the magma ocean eventually became concentrated within the region of Oceanus Procellarum and

9605-416: The main crater. This can occur when an area of darker basaltic material, such as that found on the maria , is later covered by lighter ejecta derived from more distant impacts in the highlands. This covering conceals the darker material below, which is later excavated by subsequent craters. The largest impacts produced melt sheets of molten rock that covered portions of the surface that could be as thick as

9718-407: The majority of basalt in the landing site lies below the depth of excavation of Cone crater or (2) the presence of a basalt flow beneath the landing area excavated by a nearby crater with a diameter of 100 m (330 ft). It is believed that the former seems more likely, as the basalts are similar to the basalts recovered at Cone crater. It is inconclusive whether or not the recovered basalts have

9831-468: The mare formed between about 3 and 3.5 Ga before present. The youngest lavas erupted within Oceanus Procellarum , whereas some of the oldest appear to be located on the farside. The maria are clearly younger than the surrounding highlands given their lower density of impact craters. A large portion of maria erupted within, or flowed into, the low-lying impact basins on the lunar nearside. However, it

9944-540: The maria are basaltic . The maria often coincide with the "lowlands," but the lowlands (such as within the South Pole-Aitken basin ) are not always covered by maria. The highlands are older than the visible maria, and hence are more heavily cratered. The major products of volcanic processes on the Moon are evident to Earth-bound observers in the form of the lunar maria . These are large flows of basaltic lava that correspond to low- albedo surfaces covering nearly

10057-421: The midpoint of the crater. Additionally, the ejecta from oblique impacts show distinctive patterns at different impact angles: asymmetry starting around 60˚ and a wedge-shaped "zone of avoidance" free of ejecta in the direction the projectile came from starting around 45˚. Dark-halo craters are formed when an impact excavates lower albedo material from beneath the surface, then deposits this darker ejecta around

10170-463: The mission landed on Mare Tranquillitatis , a few millimetric fragments of rocks coming from the highlands were picked up. These are composed mainly of plagioclase feldspar ; some fragments were composed exclusively of anorthite . The identification of these mineral fragments led to the bold hypothesis that a large portion of the Moon was once molten, and that the crust formed by fractional crystallization of this magma ocean . A natural outcome of

10283-484: The mission took place. A variety of shield volcanoes can be found in selected locations on the lunar surface, such as on Mons Rümker . These are thought to be formed by relatively viscous, possibly silica-rich lava, erupting from localized vents. The resulting lunar domes are wide, rounded, circular features with a gentle slope rising in elevation a few hundred meters to the midpoint. They are typically 8–12 km in diameter, but can be up to 20 km across. Some of

10396-542: The most famous examples of a prolific naturally fractured reservoir was the Austin Chalk formation in South Texas. The chalk had very little porosity, and even less permeability. However, tectonic stresses over time created one of the most extensive fractured reservoirs in the world. By predicting the location and connectivity of fracture networks, geologists were able to plan horizontal wellbores to intersect as many fracture networks as possible. Many people credit this field for

10509-587: The most notable sinuous rilles is the Vallis Schröteri feature, located in the Aristarchus plateau along the eastern edge of Oceanus Procellarum . An example of a sinuous rille exists at the Apollo 15 landing site, Rima Hadley , located on the rim of the Imbrium Basin . Based on observations from the mission, it is generally thought that this rille was formed by volcanic processes, a topic long debated before

10622-453: The name of "high titanium" basalts. The Apollo 12 mission returned to Earth with basalts of lower titanium concentrations, and these were dubbed "low titanium" basalts. Subsequent missions, including the Soviet robotic probes, returned with basalts with even lower concentrations, now called "very low titanium" basalts. The Clementine space probe returned data showing that the mare basalts have

10735-404: The near-surface regolith layer. The regolith contains rocks, fragments of minerals from the original bedrock, and glassy particles formed during the impacts. In most of the lunar regolith, half of the particles are made of mineral fragments fused by the glassy particles; these objects are called agglutinates. The chemical composition of the regolith varies according to its location; the regolith in

10848-422: The newly formed Moon was in a molten state and was orbiting much closer to Earth resulting in tidal forces . These tidal forces deformed the molten body into an ellipsoid , with the major axis pointed towards Earth. The first important event in the geologic evolution of the Moon was the crystallization of the near global magma ocean. It is not known with certainty what its depth was, but several studies imply

10961-486: The only abrupt geologic force acting on the Moon today, though the variation of Earth tides on the scale of the Lunar anomalistic month causes small variations in stresses. Some of the most important craters used in lunar stratigraphy formed in this recent epoch. For example, the crater Copernicus , which has a depth of 3.76 km and a radius of 93 km, is estimated to have formed about 900 million years ago (though this

11074-407: The plastic regime cracks acts like a plastic bag being torn. In this case stress at crack tips goes to two mechanisms, one which will drive propagation of the crack and the other which will blunt the crack tip . In the brittle-ductile transition zone , material will exhibit both brittle and plastic traits with the gradual onset of plasticity in the polycrystalline rock. The main form of deformation

11187-443: The production of fuel . The composition of the lunar regolith can also be used to infer its source origin. Lunar lava tubes form a potentially important location for constructing a future lunar base, which may be used for local exploration and development, or as a human outpost to serve exploration beyond the Moon. A lunar lava cave potential has long been suggested and discussed in literature and thesis. Any intact lava tube on

11300-417: The propagation tip of the shear fractures. As the faces slide in opposite directions, tension is created at the tip, and a mode I fracture is created in the direction of the σ h-max , which is the direction of maximum principal stress. Shear-failure criteria is an expression that attempts to describe the stress at which a shear rupture creates a crack and separation. This criterion is based largely off of

11413-598: The stratigraphy are the Mare units (previously known as the Procellarian unit), and the Imbrian unit which is related to ejecta and tectonics from the Imbrium basin. The bottom of the lunar stratigraphy is the pre-Nectarian unit, which consists of old crater plains. The lunar landscape is characterized by impact craters , their ejecta, a few volcanoes , hills, lava flows and depressions filled by lava. The most distinctive aspect of

11526-444: The strength of the rock is reached and a new fault is formed. While the applied stresses may be high enough to form a new fault, existing fracture planes will slip before fracture occurs. One important idea when evaluating the friction behavior within a fracture is the impact of asperities , which are the irregularities that stick out from the rough surfaces of fractures. Since both faces have bumps and pieces that stick out, not all of

11639-456: The stress required for fracture below the stress required throughout the rest of the rock. For instance, water and quartz can react to form a substitution of OH molecules for the O molecules in the quartz mineral lattice near the fracture tip. Since the OH bond is much lower than that with O, it effectively reduces the necessary tensile stress required to extend the fracture. In geotechnical engineering

11752-407: The tensile forces associated with the stretching of the upper half of the layers during folding can induce tensile fractures parallel to the fold axis. Another, similar tensile fracture mechanism is hydraulic fracturing . In a natural environment, this occurs when rapid sediment compaction, thermal fluid expansion, or fluid injection causes the pore fluid pressure, σ p , to exceed the pressure of

11865-462: The three members of the Apollo 11 crew) was first discovered in the lunar samples. The maria are composed predominantly of basalt , whereas the highland regions are iron-poor and composed primarily of anorthosite , a rock composed primarily of calcium -rich plagioclase feldspar. Another significant component of the crust are the igneous Mg-suite rocks, such as the troctolites , norites , and KREEP-basalts. These rocks are thought to be related to

11978-551: The wellbore can flow very rapidly into the fractures, causing a loss of hydrostatic pressure and creating the potential for a blowout from a formation further up the hole. Since the mid-1980s, 2D and 3D computer modeling of fault and fracture networks has become common practice in Earth Sciences. This technology became known as "DFN" (discrete fracture network") modeling, later modified into "DFFN" (discrete fault and fracture network") modeling. The technology consists of defining

12091-409: The work of Charles Coulomb, who suggested that as long as all stresses are compressive, as is the case in shear fracture, the shear stress is related to the normal stress by: σ s = C+μ(σ n -σ f ), where C is the cohesion of the rock, or the shear stress necessary to cause failure given the normal stress across that plane equals 0. μ is the coefficient of internal friction, which serves as

12204-403: The younger. The amount of erosion experienced by a crater was another clue to its age, though this is more subjective. Adopting this approach in the late 1950s, Gene Shoemaker took the systematic study of the Moon away from the astronomers and placed it firmly in the hands of the lunar geologists. Impact cratering is the most notable geological process on the Moon. The craters are formed when

12317-497: The youngest large impact basins on the Moon) should be found at all of the Apollo landing sites. It is thus possible that ages for some impact basins (in particular Mare Nectaris ) could have been mistakenly assigned the same age as Imbrium. The lunar maria represent ancient flood basaltic eruptions. In comparison to terrestrial lavas, these contain higher iron abundances, have low viscosities, and some contain highly elevated abundances of

12430-444: The youngest maria lavas have been determined from crater counting to be about 1 Ga. Due to better resolution of more recent imagery, about 70 small areas called irregular mare patches (each area only a few hundred meters or a few kilometers across) have been found in the maria that crater counting suggests were sites of volcanic activity in the geologically much more recent past (less than 50 million years). Volumetrically, most of

12543-625: Was largely confined to the region of the Procellarum KREEP Terrane, and that these magmas are genetically related to KREEP in some manner, though their origin is still highly debated in the scientific community. The oldest of the Mg-suite rocks have crystallization ages of about 3.85 Ga . However, the last large impact that could have been excavated deep into the crust (the Imbrium basin ) also occurred at 3.85 Ga before present. Thus, it seems probable that Mg-suite plutonic activity continued for

12656-510: Was later confirmed by the discovery of glass spherules similar to those found in pyroclastic eruptions here on Earth. Many of the lunar basalts contain small holes called vesicles , which were formed by gas bubbles exsolving from the magma at the vacuum conditions encountered at the surface. It is not known with certainty which gases escaped these rocks, but carbon monoxide is one candidate. The samples of pyroclastic glasses are of green, yellow, and red tints. The difference in color indicates

12769-401: Was originally scheduled to land in the Fra Mauro highlands, but was unable due to an in-flight technical failure. Fra Mauro is thought to have been formed from ejecta , or debris, from the impact which formed Mare Imbrium . During Apollo 14, the crew members sampled ejecta from Cone crater, a feature close in proximity to the immediate landing site of the mission, which provided insight into

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