Geology of the world and the Environment

2021-05-04 01:50:14 Professeur John Graham Ramsay
John Graham Ramsay, is the father of modern structural geology.

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Ramsay's 1967 book still tops the list of structural geology books published in the last five decades in terms of citations and influence. This 568-page book was reprinted in 2004 (Blackburn Press).

Two features distinguish the Ramsay book from many other structural geology textbooks. First, it applied mathematics to the tension of rocks; and second, it was very original, and not simply a synthesis of earlier works.

In the field of structural geology, the textbook written by John G Ramsay in 1967, reprinted in 2004 and translated into Spanish and Chinese, has had the greatest impact on research. With more than 4,000 citations (Google Scholar), it far surpasses the books of other authors on the subject, a figure that is only addressed in his latest book, Modern Structural Geology (Ramsay and Huber 1983). Open / Comment

2021-05-03 12:43:15 The sense of #stress determines the type of #fault that forms, and we usually categorize different ways: #tension , #compression, and #shear.

Handily, these three senses of stress also correlate with the three types of #plate #boundaries.

Tensional stress happens at #divergent plate boundaries where two plates are moving away from each other.

Compressive stress happens at #convergent plate boundaries where two plates move toward each other.

Shear stress is experienced at #transform boundaries where two plates are sliding past each other.

#GeologyHere #Note
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2021-05-02 02:53:47 This post is the second part of the topic of HOW DO GEOLOGISTS KNOW HOW OLD A ROCK IS? ( )

Faunal Succession: Similar to the law of superposition is the law of faunal succession, which states that groups of fossil animals and plants occur throughout the geologic record in a distinct and identifiable order. Following this law, sedimentary rocks can be “dated” by their characteristic #fossil content. Particularly useful are index fossils, #geographically widespread fossils that evolved rapidly through time.
Crosscutting Relationships: Relative ages of rocks and events may also be determined using the law of crosscutting relationships, which states that geologic features such as #igneous #intrusions or #faults are younger than the units they cut across.
Inclusions: #Inclusions, which are #fragments of older rock within a younger igneous rock or coarse-grained sedimentary rock, also facilitate relative dating. Inclusions are useful at contacts with igneous rock bodies where #magma moving upward through the crust has dislodged and engulfed pieces of the older surrounding rock.
Gaps in the geologic record, called #unconformities, are common where deposition stopped and #erosion removed the previously deposited material. #Fortunately, distinctive features such as index fossils can aid in matching, or #correlating, rocks and formations from several incomplete areas to create a more complete geologic record for relative dating. Relative dating techniques provide geologists abundant #evidence of the incredible vastness of geologic time and ancient age of many rocks and formations. However, in order to place absolute dates on the relative time #scale, other dating methods must be considered.
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2021-05-02 02:33:37 𝑷𝒆𝒕𝒓𝒐𝒍𝒆𝒖𝒎 𝑮𝒆𝒐𝒍𝒐𝒈𝒚: 𝑭𝒓𝒐𝒎 𝑴𝒂𝒕𝒖𝒓𝒆 𝑩𝒂𝒔𝒊𝒏𝒔 𝒕𝒐 𝑵𝒆𝒘 𝑭𝒓𝒐𝒏𝒕𝒊𝒆𝒓𝒔 - 𝑷𝒓𝒐𝒄𝒆𝒆𝒅𝒊𝒏𝒈𝒔 𝒐𝒇 𝒕𝒉𝒆 7𝒕𝒉 𝑷𝒆𝒕𝒓𝒐𝒍𝒆𝒖𝒎 𝑮𝒆𝒐𝒍𝒐𝒈𝒚 𝑪𝒐𝒏𝒇𝒆𝒓𝒆𝒏𝒄𝒆 𝑺𝒍𝒑 𝑬𝒅𝒊𝒕𝒊𝒐𝒏

𝘽𝙮 𝘽 𝘼 𝙑𝙞𝙣𝙞𝙣𝙜 (𝘼𝙪𝙩𝙝𝙤𝙧), 𝙎 𝘾 𝙋𝙞𝙘𝙠𝙚𝙧𝙞𝙣𝙜 (𝘼𝙪𝙩𝙝𝙤𝙧)

#𝙵𝚛𝚎𝚎 #𝙳𝚘𝚠𝚗𝚕𝚘𝚊𝚍 https://t.me/geominerals/433

𝘗𝘶𝘣𝘭𝘪𝘴𝘩𝘦𝘳 : 𝘎𝘦𝘰𝘭𝘰𝘨𝘪𝘤𝘢𝘭 𝘚𝘰𝘤𝘪𝘦𝘵𝘺 𝘰𝘧 𝘓𝘰𝘯𝘥𝘰𝘯; 𝘚𝘭𝘱 𝘦𝘥𝘪𝘵𝘪𝘰𝘯 (𝘕𝘰𝘷𝘦𝘮𝘣𝘦𝘳 15, 2010) Open / Comment

2021-05-01 06:44:57 What is Bowen's Reaction Series?

#Bowen's reaction series is the work of the #petrologist Norman L. Bowen, who summarized, based on experiments and observations of natural rocks, the sequence of #crystallization of common silicate minerals from typical basaltic #magma undergoing fractional crystallization (i.e. crystallization wherein early-formed crystals are removed from the magma by crystal settling, leaving behind a liquid of slightly different composition). Bowen's reaction series is able to explain why certain types of #minerals tend to be found together while others are almost never associated with one another.

 
Bowen determined that specific minerals form at specific temperatures as a #magma cools. At the higher temperatures associated with mafic and #intermediate magmas, the general progression can be separated into two branches. The continuous branch describes the evolution of the #plagioclase #feldspars as they evolve from being #calcium-rich to more #sodium-rich. The discontinuous branch describes the formation of the #mafic minerals #olivine, #pyroxene, #amphibole, and #biotite mica.

The weird thing that Bowen found concerned the discontinuous branch. At a certain temperature a magma might produce olivine, but if that same magma was allowed to cool further, the olivine would "react" with the residual magma, and change to the next mineral on the series (in this case pyroxene). Continue cooling and the pyroxene would convert to amphibole, and then to #biotite. Mighty strange #stuff, but if you consider that most #silicate minerals are made from slightly different proportions of the same 8 elements, all we're really doing here is adjusting the internal crystalline lattice to achieve stability at different temperatures. Really no big deal.
At lower temperatures, the branches merge and we obtain the minerals common to the #felsic rocks - #orthoclase feldspar, #muscovite #mica, and #quartz (the banana slug of the mineral world).

#GeologyHere
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2021-05-01 02:16:55 HOW DO GEOLOGISTS KNOW HOW OLD A ROCK IS? (PART 1)

#Geologists generally know the #age of a rock by #determining the age of the group of #rocks, or formation, that it is found in. The age of formations is marked on a geologic calendar known as the geologic time scale. Development of the geologic time scale and #dating of formations and rocks relies upon two fundamentally different ways of telling time: relative and absolute.

Relative dating places events or rocks in their #chronologic sequence or order of occurrence. Absolute dating places events or rocks at a specific time. If a geologist claims to be younger than his or her co-worker, that is a relative age. If a geologist claims to be 45 years old, that is an absolute age.
Relative Dating

#Superposition: The most basic concept used in relative dating is the law of superposition. Simply stated, each bed in a #sequence of #sedimentary rocks (or #layered #volcanic rocks) is younger than the bed below it and older than the bed above it. This law follows two basic assumptions: (1) the beds were originally deposited near horizontal, and (2) the beds were not overturned after their deposition.
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2021-04-30 01:59:35 𝑰𝒏𝒕𝒆𝒓𝒂𝒄𝒕𝒊𝒗𝒆 𝒕𝒐𝒑𝒐𝒈𝒓𝒂𝒑𝒉𝒚 𝒔𝒂𝒏𝒅𝒃𝒐𝒙... 𝑺𝒐 𝒔𝒂𝒕𝒊𝒔𝒇𝒚𝒊𝒏𝒈 Open / Comment

2021-04-29 03:36:42 𝗚𝗲𝗼𝗺𝗼𝗱𝗲𝗹𝘀 𝗶𝗻 𝗘𝗻𝗴𝗶𝗻𝗲𝗲𝗿𝗶𝗻𝗴 𝗚𝗲𝗼𝗹𝗼𝗴𝘆
𝗔𝗻 𝗜𝗻𝘁𝗿𝗼𝗱𝘂𝗰𝘁𝗶𝗼𝗻 (pdf)
𝘈𝘶𝘵𝘩𝘰𝘳𝘴: 𝘛𝘰𝘯𝘺 𝘞𝘢𝘭𝘵𝘩𝘢𝘮, 𝘎𝘦𝘰𝘧𝘧 𝘗𝘦𝘵𝘵𝘪𝘧𝘦𝘳, 𝘗𝘦𝘵𝘦𝘳 𝘍𝘰𝘰𝘬𝘦𝘴.

#𝙵𝚛𝚎𝚎 #𝙳𝚘𝚠𝚗𝚕𝚘𝚊𝚍 https://t.me/geominerals/428

𝑉𝑖𝑠𝑢𝑎𝑙 𝑔𝑢𝑖𝑑𝑒 𝑡𝑜 𝑣𝑎𝑟𝑖𝑒𝑑 𝑔𝑒𝑜𝑙𝑜𝑔𝑖𝑐𝑎𝑙/𝑔𝑒𝑜𝑚𝑜𝑟𝑝ℎ𝑜𝑙𝑜𝑔𝑖𝑐𝑎𝑙 𝑠𝑖𝑡𝑢𝑎𝑡𝑖𝑜𝑛𝑠.
𝑃𝑟𝑜𝑓𝑢𝑠𝑒𝑙𝑦 𝑖𝑙𝑙𝑢𝑠𝑡𝑟𝑎𝑡𝑒𝑑 𝑤𝑖𝑡ℎ 𝑜𝑣𝑒𝑟 400 𝑝ℎ𝑜𝑡𝑜𝑔𝑟𝑎𝑝ℎ𝑠 𝑎𝑛𝑑 𝑑𝑖𝑎𝑔𝑟𝑎𝑚𝑠.
𝑇ℎ𝑒 𝑖𝑑𝑒𝑎𝑙 𝑓𝑖𝑟𝑠𝑡 𝑠𝑡𝑒𝑝 𝑡𝑜 𝑔𝑎𝑖𝑛 𝑎𝑛 𝑜𝑣𝑒𝑟𝑣𝑖𝑒𝑤 𝑜𝑓 𝑎 𝑠𝑖𝑡𝑒 𝑓𝑜𝑟 𝑖𝑛𝑣𝑒𝑠𝑡𝑖𝑔𝑎𝑡𝑖𝑜𝑛. Open / Comment

2021-04-28 15:45:00 Red Rock Canyon National Conservation Area

The #geologic story of Red Rock #Canyon is told by its unique #rock formations. Layers of red and white #sediments, creating the accordion-like #folds in the #cliff faces, are capped with a harder, more resistant black #basaltic rock or pink #volcanic tuff. These sedimentary and #igneous #layers were deposited in an ancient inland lake and valley millions of years ago and have subsequently been lifted by the Garlock, El Paso, and Sierra Frontal #Faults. Streams and rivers have carved the canyon that we see today with its colorful cliff faces. The red coloring between the layers is an #iron #oxide (rust) staining.

#GeologyHere #Geology #Geomorphology #environment
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2021-04-28 06:06:55 PLAT TECTONICS AND CRUSTAL EVOLUTION

Author : Kent C. Condie

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