Article
... any older strata and so to narrow down potential sources the younger portion of the age spectrum is subdivided into 750–600 Ma, 600–500 Ma, 500–350 Ma, and 350–200 Ma (Fig 4). The Upper Cretaceous spectrum has peaks ranging from 600–350 Ma that only overlap comprehensively with the Upper Mississippi ...
... any older strata and so to narrow down potential sources the younger portion of the age spectrum is subdivided into 750–600 Ma, 600–500 Ma, 500–350 Ma, and 350–200 Ma (Fig 4). The Upper Cretaceous spectrum has peaks ranging from 600–350 Ma that only overlap comprehensively with the Upper Mississippi ...
Geochemical investigation of serpentinized oceanic lithospheric
... Peacock, 1990; Mayfield and Day, 2000). It is generally agreed that the FRO is a major tectonic suture formed by the closing of an oceanic basin, and accordingly, the accretion of an island arc terrane to the North American continent. Ophiolite belts from the southwest Sierra Nevada Foothills have b ...
... Peacock, 1990; Mayfield and Day, 2000). It is generally agreed that the FRO is a major tectonic suture formed by the closing of an oceanic basin, and accordingly, the accretion of an island arc terrane to the North American continent. Ophiolite belts from the southwest Sierra Nevada Foothills have b ...
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... assembly and accretion to the Saharan Metacraton concurrent with the assembly of eastern and western Gondwana. At the end of the Precambrian it lay at one end of the East African Orogen, with its northern margin (present coordinates) forming a low-relief stable shelf facing an open ocean; to the sou ...
... assembly and accretion to the Saharan Metacraton concurrent with the assembly of eastern and western Gondwana. At the end of the Precambrian it lay at one end of the East African Orogen, with its northern margin (present coordinates) forming a low-relief stable shelf facing an open ocean; to the sou ...
The Cretaceous and Cenozoic tectonic evolution of
... blocks from this segment of the northwest Australian shelf, or whether some of these blocks originated from the New Guinea or even Greater Indian passive margin. In addition, the nature of the microcontinents on Sumatra has been dis- ...
... blocks from this segment of the northwest Australian shelf, or whether some of these blocks originated from the New Guinea or even Greater Indian passive margin. In addition, the nature of the microcontinents on Sumatra has been dis- ...
nature ano evolution of the subcontinental mantle lithosphere below
... are derived from the subcontinental mande lithosphere. The conditions of equilibration of the various types of inelusions indicate that infertile Mg-rich harzburgite is dominant at depths shallower than about 50 kilometers while at greater depths fertile garnet-Iherzolites occur· along with infertil ...
... are derived from the subcontinental mande lithosphere. The conditions of equilibration of the various types of inelusions indicate that infertile Mg-rich harzburgite is dominant at depths shallower than about 50 kilometers while at greater depths fertile garnet-Iherzolites occur· along with infertil ...
Mantle Exhumation in an Early Paleozoic Passive Margin, Northern
... well-developed plagioclase coronae on spinel and records cooling from ∼1000⬚ to 600⬚C and decompression across the spinel-plagioclase peridotite facies boundary at ∼0.7 GPa. The troctolite boudins record cooling to 850⬚C through the same facies reaction at ∼0.8 GPa. In an aureole surrounding the per ...
... well-developed plagioclase coronae on spinel and records cooling from ∼1000⬚ to 600⬚C and decompression across the spinel-plagioclase peridotite facies boundary at ∼0.7 GPa. The troctolite boudins record cooling to 850⬚C through the same facies reaction at ∼0.8 GPa. In an aureole surrounding the per ...
Dynamical geochemistry of the mantle
... models that have not simultaneously satisfied the geophysical and geochemical constraints. Whereas geophysical inferences have led to a picture of the mantle with no major vertical compositional variation, apart from the D00 zone in the lowest 200–300 km (Davies and Richards, 1992; Grand et al., 199 ...
... models that have not simultaneously satisfied the geophysical and geochemical constraints. Whereas geophysical inferences have led to a picture of the mantle with no major vertical compositional variation, apart from the D00 zone in the lowest 200–300 km (Davies and Richards, 1992; Grand et al., 199 ...
Not Getting the Drift - Personal webpages at NTNU
... Lyell completed his initial 4-volume geology textbook in 1834. After that he revised and improved it frequently. It reached maturity by the 5th edition, in 1837. Afterward, he split the subject into two major books, his Principles of Geology, which deals mostly with geological processes and how they ...
... Lyell completed his initial 4-volume geology textbook in 1834. After that he revised and improved it frequently. It reached maturity by the 5th edition, in 1837. Afterward, he split the subject into two major books, his Principles of Geology, which deals mostly with geological processes and how they ...
The anatomy and ontogeny of modern intra
... (100 –150 km) and causes the mantle to melt. This configuration must exist for long enough that melts generated in the overlying asthenospheric wedge not only reach the surface but also persist until a stable magmatic conduit system is established. When this happens, magma produced by hydrous fluxin ...
... (100 –150 km) and causes the mantle to melt. This configuration must exist for long enough that melts generated in the overlying asthenospheric wedge not only reach the surface but also persist until a stable magmatic conduit system is established. When this happens, magma produced by hydrous fluxin ...
Fast-decaying IP in frozen unconsolidated rocks and potentialities
... temperature dependence have been given by Reynolds (1997). A similar dependence of the dielectric-relaxation time constant τ on temperature T has been found for frozen coarse-grained unconsolidated rocks. In rocks with high clay content, other factors in addition to temperature, may control the rela ...
... temperature dependence have been given by Reynolds (1997). A similar dependence of the dielectric-relaxation time constant τ on temperature T has been found for frozen coarse-grained unconsolidated rocks. In rocks with high clay content, other factors in addition to temperature, may control the rela ...
- Wiley Online Library
... [13] The Byerlee [1978] failure criterion is commonly used to represent the yield strength behavior of rocks. Byerlee’s law is written in terms of principal stresses. Hence, it may account for porefluid pressure or any other deviations from lithostatic pressure. Extrapolating Byerlee’s law at pressur ...
... [13] The Byerlee [1978] failure criterion is commonly used to represent the yield strength behavior of rocks. Byerlee’s law is written in terms of principal stresses. Hence, it may account for porefluid pressure or any other deviations from lithostatic pressure. Extrapolating Byerlee’s law at pressur ...
Origin of carbonatites in the South Qinling orogen:
... (SQ), which merges with the Lesser Qinling orogen (LQ) to separate the South and North China Blocks. The SQ carbonatites occur mainly as stock associated with syenites. The data presented here show that zircon from the syenites yields an age of 766 ± 25 Ma, which differs significantly from the age of ...
... (SQ), which merges with the Lesser Qinling orogen (LQ) to separate the South and North China Blocks. The SQ carbonatites occur mainly as stock associated with syenites. The data presented here show that zircon from the syenites yields an age of 766 ± 25 Ma, which differs significantly from the age of ...
Mantle mixing - Earth and Environmental Sciences
... enriched components that have compositions quite unlike primitive mantle. Similarly, the constancy of Nb/U and Ce/Pb (Hofmann, 1986; Newsom et al., 1986) suggests that there is no current reservoir with primitive mantle ratios. Interestingly, there is a strong correlation between a depleted componen ...
... enriched components that have compositions quite unlike primitive mantle. Similarly, the constancy of Nb/U and Ce/Pb (Hofmann, 1986; Newsom et al., 1986) suggests that there is no current reservoir with primitive mantle ratios. Interestingly, there is a strong correlation between a depleted componen ...
Fluid Processes in Subduction Zones Hydrous Minerals and
... H2O Content of Arc Magmas • Significantly more H2O than MORBs, OIBs • Explosive eruptions (more H2O degassing, higher SiO2 content) • Hornblende (amphibole) is common phenocryst • H2O dramatically lowers melting T of rocks, mantle by 100s of degrees. key to arc magma genesis ...
... H2O Content of Arc Magmas • Significantly more H2O than MORBs, OIBs • Explosive eruptions (more H2O degassing, higher SiO2 content) • Hornblende (amphibole) is common phenocryst • H2O dramatically lowers melting T of rocks, mantle by 100s of degrees. key to arc magma genesis ...
Geologic Structures
... The hypothesis given here is based on calculations about the behavior of dust and gas in space and on observations of stars and dust clouds in our galaxy. Refer to the “Focus On” box on page 12 for a discussion of how scientists formulate a hypothesis. The hypothesis states that about 5 billion year ...
... The hypothesis given here is based on calculations about the behavior of dust and gas in space and on observations of stars and dust clouds in our galaxy. Refer to the “Focus On” box on page 12 for a discussion of how scientists formulate a hypothesis. The hypothesis states that about 5 billion year ...
Barrovian metamorphism in the central Kootenay Arc, British
... internal zone of the southeastern Canadian Cordillera. The following zones of increasing metamorphic grade are recognised in metapelites: chlorite/biotite, garnet, staurolite, kyanite, sillimanite, and sillimanite + K-feldspar. The garnet and higher-grade zones outline two joined domains: a N- to NN ...
... internal zone of the southeastern Canadian Cordillera. The following zones of increasing metamorphic grade are recognised in metapelites: chlorite/biotite, garnet, staurolite, kyanite, sillimanite, and sillimanite + K-feldspar. The garnet and higher-grade zones outline two joined domains: a N- to NN ...
Exhumation of (ultra-)high-pressure terranes: concepts
... been shown in some orogens to have occurred only once, during a single short-lived event; in other cases exhumation appears to have occurred multiple discrete times or during a single, long-lived, protracted event. It is becoming increasingly clear that no single exhumation mechanism dominates in an ...
... been shown in some orogens to have occurred only once, during a single short-lived event; in other cases exhumation appears to have occurred multiple discrete times or during a single, long-lived, protracted event. It is becoming increasingly clear that no single exhumation mechanism dominates in an ...
Numerical models, geochemistry and the zero-paradox noble
... and indeed is entirely consistent with the layered-mantle concept (Kurz et al . 1982; Allègre et al . 1986). The very low concentration of 3 He in the atmosphere and oceans results in small magmatic additions to sea water being readily resolvable (Clarke et al . 1969). Given the mean residence time ...
... and indeed is entirely consistent with the layered-mantle concept (Kurz et al . 1982; Allègre et al . 1986). The very low concentration of 3 He in the atmosphere and oceans results in small magmatic additions to sea water being readily resolvable (Clarke et al . 1969). Given the mean residence time ...
Origin of ocean island basalts: A new perspective from petrology
... Lu/176Hf) of the DM along these curves are then constrained at any given time in the last 2.5 Gyr. [8] The significant coupling between radiogenic isotopes and incompatible element abundances and ratios in many OIB suites, seamount lavas, and MORB [e.g., Saunders et al., 1988; Sun and McDonough, 198 ...
... Lu/176Hf) of the DM along these curves are then constrained at any given time in the last 2.5 Gyr. [8] The significant coupling between radiogenic isotopes and incompatible element abundances and ratios in many OIB suites, seamount lavas, and MORB [e.g., Saunders et al., 1988; Sun and McDonough, 198 ...
Supercontinents, mantle dynamics and plate
... destruction of ocean floor, with the oldest oceanic crust on the planet aged more than 200 Ma. Among various distinctions between the two cycles, one important aspect is the time interval, with a shorter time span for the Wilson Cycle as against a much longer time span in which supercontinent cycle o ...
... destruction of ocean floor, with the oldest oceanic crust on the planet aged more than 200 Ma. Among various distinctions between the two cycles, one important aspect is the time interval, with a shorter time span for the Wilson Cycle as against a much longer time span in which supercontinent cycle o ...
ON THE SCALE OF MANTLE CONVECTION The relative motion of
... which is perhaps driven by heat from the earth’s core. Plate motions may interact with large+cale flow in the mantle, and are probably not completely decoupled from flow in the lower mantle, Lateral variations in flow properties in the upper mantle may be more important than vertical variations, and ...
... which is perhaps driven by heat from the earth’s core. Plate motions may interact with large+cale flow in the mantle, and are probably not completely decoupled from flow in the lower mantle, Lateral variations in flow properties in the upper mantle may be more important than vertical variations, and ...
Yin and yang of continental crust creation and destruction by plate
... by Armstrong 1991), but when the question ‘has continental crust volume increased or decreased with time?’ is addressed thoughtfully, it must be admitted that there is much that is not known. It is clear from truncations of ancient orogenic belts (Dickinson 2009) and the presence of >4.0 Ga zircons ...
... by Armstrong 1991), but when the question ‘has continental crust volume increased or decreased with time?’ is addressed thoughtfully, it must be admitted that there is much that is not known. It is clear from truncations of ancient orogenic belts (Dickinson 2009) and the presence of >4.0 Ga zircons ...
Bennington, J Bret, Merguerian, Charles, and Sanders, J.E., 1999
... whole, but the whole comprises (or is comprised of) the parts. ...
... whole, but the whole comprises (or is comprised of) the parts. ...
Simulating the thermochemical magmatic and tectonic evolution of
... could instead be explained by an equilibrium “random resurfacing” model [Bjonnes et al., 2012; Hauck et al., 1998; Phillips et al., 1992]. Also, Brown and Grimm [1999] argue that the lithospheric thickness required by surface features implies monotonic thickening over the recorded history, although ...
... could instead be explained by an equilibrium “random resurfacing” model [Bjonnes et al., 2012; Hauck et al., 1998; Phillips et al., 1992]. Also, Brown and Grimm [1999] argue that the lithospheric thickness required by surface features implies monotonic thickening over the recorded history, although ...
History of Earth
The history of Earth concerns the development of the planet Earth from its formation to the present day. Nearly all branches of natural science have contributed to the understanding of the main events of the Earth's past. The age of Earth is approximately one-third of the age of the universe. An immense amount of biological and geological change has occurred in that time span.Earth formed around 4.54 billion years ago by accretion from the solar nebula. Volcanic outgassing probably created the primordial atmosphere, but it contained almost no oxygen and would have been toxic to humans and most modern life. Much of the Earth was molten because of frequent collisions with other bodies which led to extreme volcanism. One very large collision is thought to have been responsible for tilting the Earth at an angle and forming the Moon. Over time, the planet cooled and formed a solid crust, allowing liquid water to exist on the surface.The first life forms appeared between 3.8 and 3.5 billion years ago. The earliest evidences for life on Earth are graphite found to be biogenic in 3.7-billion-year-old metasedimentary rocks discovered in Western Greenland and microbial mat fossils found in 3.48-billion-year-old sandstone discovered in Western Australia. Photosynthetic life appeared around 2 billion years ago, enriching the atmosphere with oxygen. Life remained mostly small and microscopic until about 580 million years ago, when complex multicellular life arose. During the Cambrian period it experienced a rapid diversification into most major phyla. More than 99 percent of all species, amounting to over five billion species, that ever lived on Earth are estimated to be extinct. Estimates on the number of Earth's current species range from 10 million to 14 million, of which about 1.2 million have been documented and over 86 percent have not yet been described.Geological change has been constantly occurring on Earth since the time of its formation and biological change since the first appearance of life. Species continuously evolve, taking on new forms, splitting into daughter species, or going extinct in response to an ever-changing planet. The process of plate tectonics has played a major role in the shaping of Earth's oceans and continents, as well as the life they harbor. The biosphere, in turn, has had a significant effect on the atmosphere and other abiotic conditions on the planet, such as the formation of the ozone layer, the proliferation of oxygen, and the creation of soil.