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Oliver Strimpel @geologybites.bsky.social · 2d

🧪⚒️I just posted an episode on the orogenies that shaped central Europe: the Cadomian and the Variscan. The former took place on the northern margin of Gondwana, rifting north later to dock to Europe. The latter marked the final assembly of Pangea. It's complex, but I hope you enjoy it! #geology

Map of Europe showing the main geological units as defined by their structural origin and presumed terrane provenance. As the map shows, practically all of central and southern Europe (shaded grey) was derived from Gondwana. These terranes contain Cadmonian and Lower Paleozoic basement rocks. The map also shows the main suture zones. A Alps, AM Armorican massif, B Balkans, BM Bohemian massif, BV Brunovistulia, CIZ Central Iberia Zone, D Dinarides, DO Dobrogea, EC Eastern Carpathians, H Hellenides, IM Iberian massif, IST Istanbul terrane, KB Kirsehir block, MC massif Central, MGCR Mid-German Crystalline Rise, MM Menderes massif, MP Malopolska block, MU Moldanubian unit, OMZ Ossa-Morena Zone, P Pyrenees, R Rhodope, S Schwarzwald, SC Scythian platform, SM Serbo-Macedonian massif, SPZ South Portuguese Zone, SX Saxothuringian unit, TBU Teplá–Barrandian unit, V Vosges.

Sen, F. (2021), International Geology Review 64, 2416

There is a debate as to how far the Cadomian terranes, specifically the major Teplá–Barrandian unit of the central Bohemian Massif, traveled away from Gondwana before they accreted to Baltica, eventually to become part of Europe. These figures illustrate contrasting models that have been proposed. (a) In this model there is a large separation between the Teplá–Barrandian unit and Gondwana, and the unit forms a completely detached microplate called Perunica (P). (b)-(d) In these models, there is little separation, and the Teplá–Barrandian unit remains part of the hyper-extended Gondwana shelf.

Žák, J et al. (2018), International Geology Review 60, 319

A paleogeographic model showing the break-up of the former northern Gondwanan Cadomian active margin in the late Cambrian and early Ordovician, opening of the Rheic Ocean, transition to an early Paleozoic passive margin, and, finally, the Laurussia-Gondwana collision to form the Variscan orogenic belt. The terranes discussed in the podcast form parts of Avalonia, the Saxothuringian and Ossa-Morena Zones, the Variscan Autochthon, and the Mid-Variscan Allochthon. The Saxothuringian Zone now makes up the northwestern part of the Bohemian Massif. The Ossa-Morena Zone now forms part of the Iberian Massif in Spain and Portugal. The Variscan Autochthon comprises geological units now mainly exposed in southern Europe. The Mid-Variscan Allochthon includes the Teplá-Barrandian and Moldanubian units of the present-day Bohemian Massif.

Catalán, J.R et al. (2021), Earth-Science Reviews 220, 103700

Geological map of the present-day Bohemian Massif. The geological structure is complex, largely as a result of the Cadmonian and Variscan orogenies. The map covers a region stretching from southern Poland in the north to northern Austria in the south. It reveals a section across the Variscan orogen from the outer foreland basins (Rhenohercynian) through low-grade Cadomian basement terranes (Saxothuringian and Teplá-Barrandian) to the exhumed high-grade orogenic core (Moldanubian).

Adapted from the Geological map of the Czech Republic 1:5,000,000 published by the Czech Geological Survey, Prague, 2007

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Oliver Strimpel @geologybites.bsky.social · 21d

🧪⚒️Just released an episode on the dynamics of subduction zones with Claudio Faccenna. Not only do trenches roll back and move laterally, they also advance and flip polarity. But when they penetrate the viscous lower mantle they get locked in place. Enjoy listening!

The figure shows sections of P-wave tomography anomalies along the yellow lines on the map (Fukao & Obayashi, 2013), seismicity (orange dots on profiles; Engdahl et al., 1998), plate velocities (orange vectors; Argus et al., 2011), and volcanoes (cyan inverted triangles; Siebert & Simkin, 2023). The Western Pacific and Japan subduction zones (the two most northerly zones) do not appear to penetrate the lower mantle, unlike those of Indonesia and Kermadec (north of New Zealand). Whether a slab penetrates the lower mantle depends on factors such as the duration of subduction and the angle at which the slab reaches the 660-km discontinuity, with steeper angles favoring descent.

Becker, T and Faccenna, C. (2025), Tectonic Geodynamics, Princeton University Press

Subduction zones along the west coast of the Americas. In the podcast, Faccenna described how the slab subducting below the Andes has entered the lower mantle where its lateral movement is restricted by the higher viscosity there. The subduction zones beneath northern South America and Central America show evidence of penetration into the lower mantle, reaching depths of 1,300 km or more. By contrast, the younger Caribbean subduction zone does not.

Becker, T and Faccenna, C. (2025), Tectonic Geodynamics, Princeton University Press

Left: map showing seafloor ages in the western Pacific. The back-arc basins shown appear mainly as the red and orange regions, i.e., having the youngest ages of 0 and 30 million years. Center: more detailed seafloor age map of the Izu-Bonin-Marianas region. Right: P-wave tomography sections along the green lines labeled A, B, and C, revealing the varying shape of the subduction zone going from north to south.

The western Pacific subduction zone is characterized by back-arc extension in the overriding plate that began within the last 30 million years (left panel). Tomography and seismicity data show that along the Izu–Bonin region (section B1–B2), a double subduction system is present, resulting from subduction of both the Pacific Plate (to the east) and the Philippine Plate (to the west).

Becker, T and Faccenna, C. (2025), Tectonic Geodynamics, Princeton University Press

The Izu–Mariana subduction system is unique in that the trench is advancing toward the overriding plate (right panel). Bottom left: tomographic section along the red line on the map at right shows the two subducting slabs. Top left: numerical model of single subduction and double subduction. The double subduction simulation replicates quite a few features appearing on the tomographic section, such as the apparent flattening out of the subducting slabs between the depths of 400 and 600 km. In a single-slab system, the trench migrates backward, whereas in a double-slab system, the rear slab drives trench advance. The simulation also reproduces the tomographic section (bottom left, section along the red line on the map at right), which clearly shows the presence of two subducting slabs.

Faccenna, C. et al. (2018), Tectonophysics, 746, 229

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Oliver Strimpel @geologybites.bsky.social · Aug 17

🧪⚒️I just released Cees Van Staal on the Origin of the Appalachians. The story is closely tied to the Caledonian orogeny across the Atlantic. But today's topography stems from the rifting and magmatism of the much later opening of the Atlantic and the recent ice ages ending 10,000 years ago.

Van Staal studying the rocks of the highly deformed basaltic and bonninitic rocks of the c. 490 Ma Advocate ophiolite on the north coast of the Baie Verte peninsula. These are part of the the Baie Verte ophiolite complexes.

Reconstruction of continental plate locations in the Silurian and Devonian. Between 420 and 405 Ma, Laurentia moved south at a speed that may have been as fast as 11 cm/year while the Iapetus ocean was subducting beneath the margins of Laurentia. This led to the collisions of the Caledonian and Appalachian orogenies discussed in the podcast. AM=Amazonia; WA=West Africa; L=Laurentia; BA=Baltica; SIB=Siberia.

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Oliver Strimpel @geologybites.bsky.social · Jul 22

🧪⚒️Just released Andreas Fichtner on the frontiers of seismic imaging. Our images are becoming much sharper— see the episode web page. Really novel is the use of fiber-optic cables to sense seismic waves with unprecedented resolution.

Horizontal slice at a depth of 100 km showing relative variations in the speed of vertically polarized S-waves (Vsv). The mid-oceanic ridges in the Atlantic and South Pacific show up prominently, as do hot-spot regions with active volcanism, such as Hawaii (H), Iceland (I), the Canaries (C), and La Réunion (R). The model also shows the contrast between the old, cold cratons and hot spots in Africa.

Thrastarson, S. et al. (2024) RVEAL: A Global Full-Waveform Inversion Model, Bulletin of the Seismological Society of America

At a depth of around 200 km, subducting slabs come into sharper focus. The figure shows several of these, including the Nazca (N), Cocos (Co), and Caribbean (C) slabs, as well as the almost continuous subduction of the Pacific plate (PP) beneath its neighboring plates toward Asia and Oceania.

The slice at a depth of 400 km reveals the subducting slabs that have advanced deeper into the mantle along the direction of subduction.

Close to the core-mantle boundary at 2,800 km depth, the slice shows the large low-shear velocity provinces. These play an important role in our understanding of mantle dynamics and heat transport and are discussed in the podcast episode with Allen McNamara.

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Oliver Strimpel @geologybites.bsky.social · Jul 4

🧪⚒️ Just reposting an invitation to listen to the latest Geology Bites episode on the origin of continents. Adding the 🧪⚒️ icons this time. Renée Tamblyn raises fascinating questions about the Archean water cycle and the role of molecular H in powering the first life forms - the archaea.

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Oliver Strimpel @geologybites.bsky.social · Jul 3

When the Earth formed, it was covered by a hot magma ocean. So when and how did thick, silica-rich continental lithosphere form? In the podcast, Renée Tamblyn addresses these questions, as well as how Archaean processes created molecular hydrogen that may have powered the first forms of life.

Sample of the Acasta gneiss, the oldest known rock (4.03 billion years old). It is a deformed tonalite-granodiorite and formed as a member of the type of intrusive rock discussed in the podcast. These formed the bulk of the early continents — the tonalites, trondhjemites, and granodiorites (TTGs).

Chip Clark/Smithsonian Institution National Museum of Natural History

Graph showing the amount of continental crust over time as predicted by different crustal growth models with time advancing to the left. The models use a variety of different methodologies and approaches and differ widely in their predictions. As Tamblyn says in the podcast, the timing of continental crust formation is one of the big unsolved problems in Earth science.

Korenga, J. (2018), https://doi.org/10.1098/rsta.2017.0408

Kaapvaal Craton, South Africa. The hills are formed of TTGs , which dominate the geological record of the craton.

When rocks undergo partial melting, they separate into lighter-colored leucosomes and darker melanosomes. The leucosomes then segregate themselves from the unmelted rock and, when they cool, form rocks containing predominantly plagioclase feldspar and quartz, i.e., TTG in composition. In the migmatite shown here, these melts have been frozen during their escape of the parent rock. The parent rock was a metamorphosed basalt containing garnet and amphibole.

Kendrick, J. et al. (2024), Journal of Petrology, 65, egae066

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Oliver Strimpel @geologybites.bsky.social · Jun 18

That’s great to hear, Brian.

Oliver Strimpel @geologybites.bsky.social · Jun 3

Because continents are thick and cold, so generally strong.

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Oliver Strimpel @geologybites.bsky.social · Jun 2

🧪⚒️Just posted Folarin Kolawole @lamont.columbia.edu on continental rifting. I've always thought that the rifting of continents is a really counterintuitive notion. After teasing out the various early stages with Kolawole and invoking plumes and far-field forces the process makes more sense to me.

Widespread faulting at the rift axis in the Afar region of northern Ethiopia.

Locations of active continental rifts with their extension velocities. In the podcast, Kolawole focuses on the East African rifting that extends from the northeast corner of the continent down to Malawi and Botswana. Though only in its early phase today, Kolawole explains why he thinks the rift will continue to stretch and eventually lead to a full continental breakup.

Heckenbach, E.L. et al.(2021), Geochemistry, Geophysics, Geosystems 22, e2020GC0095777

Schematic representation of the mantle plume location beneath East Africa on the basis of seismic tomography. Plume structure at depth is consistent with the distribution of volcanism shown at left.

Brune, S. et al. (2023), Nature Reviews Earth & Environment https://doi.org/10.1038/s43017-023-00391-3

Diagram of the driving forces, resisting factors, and weakening processes that accompany rifting. In the podcast, Kolawole points out the importance of pre-existing zones of weakness in a continent in determining where rifting initiates. The block diagram illustrates a preexisting shear zone (1) that can determine a rift location and also break a rift into segments (2). Faults and shear zones (3) can weaken the crust as can necking and thermal weakening (4). Shallow intrusion of melt (5) as well as alteration of the rock (6) can also cause weakening. Outside forces caused by erosion (7) and sedimentation (8) also promote long-lived faulting.

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Oliver Strimpel @geologybites.bsky.social · May 11

🧪⚒️Just released Mike Hudec on salt tectonics. Amazingly, salt structures can be many tens of kilometers across. And because salt is extremely weak compared to other rocks and minerals, it is the first to deform in the presence of stresses. It's often involved in forming hydrocarbon reserves.

Salt mountain in the Zagros mountains of Iran.

Salt mountain in the Zagros mountains of Iran. Courtesy of Kayvan Karimi.

Salt glacier flowing down a valley in the Zagros mountains, Iran.

Block diagram showing the wide range of shapes that salt diapirs can assume.

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Oliver Strimpel @geologybites.bsky.social · May 3

🧪⚒️Just back from the European Geophyiscal Union conference. The medalist lectures were great and I signed up two medal winners for Geology Bites. One exciting strand was on the planned probes to the icy moons of Jupiter & Saturn. We’ll be melting our way down through km of ice to reach water!

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Oliver Strimpel @geologybites.bsky.social · Apr 13

🧪⚒️I just posted an episode on megafloods with Vic Baker, a pioneer in the field. Megafloods are cataclysmic events that devastate the landscape. The Mediterranean Basin was filled by two successive megafloods. And a Black Sea megaflood might be the basis for the Biblical account of Noah's flood.

Until about 425,000 years ago, Great Britain was joined to Europe by a narrow isthmus along the Weald-Artois anticline, a fold consisting of the Cretaceous chalk that is today cut at the cliffs of Dover in England and the Cap Blanc Nez near Calais in France. As Baker discusses in the podcast, a large glacial lake formed south of an ice cap spanning northern Britain and Scandinavia. This lake eventually breached the isthmus, resulting in a megaflood that eroded what is now the seafloor below the English Channel into a steep-sided inner channel and plunge pools.

Map view (right) and topography (below right) of the Kasei Vallis megaflood channel. Kasei Vallis is the largest of the Martian outflow channels, about 3,000 km long and up to as much as 400 km wide in the areas shown at right.

Rock basins eroded into Columbia River Basalt at Lenore canyon, Lower Grand Coulee in the Channeled Scabland of Eastern Washington. Note the roads for scale.

Giant current ripples at West Bar, near Trinidad, Washington.

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Oliver Strimpel @geologybites.bsky.social · Mar 27

🧪⚒️New episode - Lindy Elkins-Tanton on the origin of Earth's water. Only about 0.02% of the Earth is water, but even that's been a puzzle as Earth formed within the snow line where no liquid water would have been present. Isotopic analysis provides the clues to resolve this apparent paradox.

Microwave image of a protoplanetary disk surrounding the young star HL Tauri. The disk includes gaps possibly cleared by amalgamation onto newly-forming planets. This image was taken by the Atacama Large Millimeter/submillimeter Array interferometer, consisting of 66 radio telescopes in the Atacama Desert of northern Chile.

ALMA (ESO/NAOJ/NRAO)

Artist’s impression of a region of a giant molecular cloud that is collapsing to form a protoplanetary disk of gas and dust. A star forms at the center of the disk, and planets form out of the disk.

NASA/JPL CalTech

Plot of various solar system materials. The plot shows that the isotope ratios of hydrogen (D/H) and nitrogen (15N/14N) on Earth are very different from those of comets but quite similar to those of a certain class of meteorites called enstatite chondrites. If comets had delivered Earth’s water, they would have changed its nitrogen isotopic ratios as well as its hydrogen isotopic ratios. Isotopic fingerprinting strongly suggests that Earth’s water has come from the enstatite chondrites.

Marty, B. (2012), Earth and Planetary Science Letters 313, 56

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Oliver Strimpel @geologybites.bsky.social · Mar 16

🧪⚒️In this episode, Joeri Witteveen says there is something paradoxical about selecting a single point on Earth to define a global boundary. We also place spikes where the depositional record is continuous. But that is also a bit paradoxical, as such places do not look like boundaries at all.

The December 2024 version of the international chronostratigraphic chart. The right-hand part of each column lists the stages/ages. Each stages is a specific, formally defined interval of rock strata that represents a corresponding interval of time called an age. Golden spikes are marked at the base of the stages they define.

Golden spike at the base of the Selandian Stage, Zumaia, Spain.

Locations of golden spikes as of early 2020. The circles are color-coded according to the colors of their corresponding stages on the chronostratigraphic chart.

Monument at the golden spike at Meishan, China, marking the boundary between the Permian and the Triassic. There is also a geological museum at Meishan. It includes a hall on the golden spike and an enlarged model of a conodont species, which makes its first appearance above this golden spike and is key to the definition of the base of the Triassic.

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Oliver Strimpel @geologybites.bsky.social · Mar 8

🧪⚒️I just posted an episode about using the late Paleozoic ice age as an analog to climate conditions today. It was similar in that there was low but rising CO2 and continental ice sheets. Her models suggest possible major ocean anoxia and dramatically increased runoff as CO2 climbs.

Results of the Earth-System Model for atmospheric CO2 levels of 280 parts per million (ppm) and 560 ppm for the late Paleozoic. Top row: sea ice forms at 280 ppm but not at 560 ppm. Bottom row: at 280 ppm, the late-winter mixed layer of the ocean is moderately deep but becomes much shallower at 560 ppm.

Simulations show the response of seawater density & temperature by depth for a doubling of CO2. Sea surface salinity (i.e., density) increases at low CO2 due to sea ice formation, which excludes salt, thus creating briny water, whereas at high CO2 less sea ice formation leads to decreased density overall.

Plots of oceanic depth vs. latitude of the time since a water mass has been in contact with the surface.

Younger ages in shades of purple indicate well-ventilated waters, whereas older ages in orange and yellow indicate poorly ventilated waters that typically correlate with low dissolved O2 in the deep ocean.

Together with the sea ice and mixing depth results, this suggests the onset of widespread seafloor anoxia during the CO2-forced warming despite being under deep glacial conditions.

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Oliver Strimpel @geologybites.bsky.social · Mar 8

I just learned that Richard Fortey passed away yesterday. I loved his books, especially Life and Trilobite. It was so lucky that I managed to get him onto Geology Bites for the second time, this time talking about Deep Time. He was his usual eloquent self, full of insights.

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Oliver Strimpel @geologybites.bsky.social · Mar 8

I loved his books - especially Life and Trilobite. I was lucky to have recorded a second podcast with him on Geology Bites only two months ago. It was about Deep Time.

Reposted by Oliver Strimpel

Steve Brusatte @stevebrusatte.bsky.social · Mar 7

I devoured Richard Fortey's books as a teenager. His magnum opus, Life, was one of my gateways into science.

Then when I was writing my first pop science book, Richard generously blurbed it. Getting his testamonial was one of the proudest moments of my life.

RIP to a great scientist & writer.

Paul Barrett @profpaulbarrett.bsky.social · Mar 7

Really sad to report that our friend and colleague Richard Fortey passed away this morning after a short battle with cancer. We’ll all miss his wit and wisdom. Here he is checking out a dino footprint we found while filming together on the Isle of Wight

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Oliver Strimpel @geologybites.bsky.social · Feb 21

🧪⚒️ Just posted Ruth Siddall @pavementgeology.bsky.social on #urbangeology. You can see so much geology on display in the building stone of almost any city, and often more clearly and certainly more conveniently than going to the field. She guides us through her favorite London urban geology walk.

Santa Maria del Fiore Cathedral and Baptistry. Brunelleschi kept good accounts of the sourcing of the Pietra Serena sandstone used to build the dome. Decorative white marble was sourced from Carrara and Pisa, pink limestone came from Verona and other locations in Tuscany, and green serpentinite came from Prato.

Nautiloid in the pale-brown stone walls of Plantation Place. This is an Upper Jurassic limestone sourced from the Southern Frankonian Alb of Bavaria. It comes from the Treuchtlingen Formation, representing a marine platform limestone with sporadic sponge reefs and bioherms (reef knoll comprising a pile of calcareous material that had previously accumulated on an ancient sea floor).

St. Paul’s cathedral in London, completed in 1710, was built with Portland Stone. There is a rich archive documenting architect Christopher Wren’s ordering of Portland Stone from the quarries.

Monument commemorating the Great Fire of London of 1666 which started close to this site and raged across the City for the next three days. The main building material is Portland Stone, the stone chosen by Christopher Wren and his fellow architects to rebuild London in a monumental style.

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Oliver Strimpel @geologybites.bsky.social · Jan 9

In this episode, Richard Fortey and I have kept the discussion fairly broad so that it can be appreciated by listeners with no background in Earth science. Since it's a bit different from other episodes, I'd especially welcome any feedback.

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Oliver Strimpel @geologybites.bsky.social · Jan 9

🧪⚒️ On to the 2nd century of podcasts with Richard Fortey on deep time. Fossils in the geological record were our first markers along the runway of deep time, providing the structure and language within which our modern conception of deep time emerged. #science #geosciences #geology+rocks+Fossils

The major angular unconformity at Siccar Point on the east coast of Scotland. Here the more gently sloping Devonian sandstones (c.375 Ma) overlay the near vertical Silurian greywackes (c.440 Ma). Viewed by James Hutton while on a boat trip in 1788, this was one of the sites that solidified Hutton and Lyell's new concepts of Earth's geology: that it was formed by slow continuous processes similar to those still occurring today operating over vast periods of time.

Title page of Usher’s Annals of the World. Bishop Usher (1591-1656) calculated the date of Creation to have been nightfall on 22 October, 4004 BC. He determined this from a literal reading of the Old Testament.

Clock of the Long Now
Prototype of the Clock of the Long Now. It was activated on December 31, 1999, and is on display at the Science Museum, London. The clock is intended to keep time for 10,000 years. The final version of the clock is intended to be an enormously enlarged version of this prototype — a vast mechanism big enough for visitors to walk through and installed near a National Park in Nevada in a chamber hollowed out of a limestone cliff.

The clock uses a torsional pendulum that rotates slowly, making the clock tick once every 30 seconds. This prototype is driven by falling weights (right), but the full-size clock would be powered by the energy from footfalls of visitors or by changes in temperature. Any drift in the clock’s rate will be corrected by a mechanism sensing the sun passing overhead at noon.

Portrait of James Hutton, often referred to as the “Father of Modern Geology.” Here is the final paragraph of this 1788 paper Theory of the Earth.

WE have now got to the end of our reasoning; we have no data further to conclude immediately from that which actually is: But we have got enough; we have the satisfaction to find, that in nature there is wisdom, system, and consistency. For having, in the natural history of this earth, seen a succession of worlds, we may from this conclude that there is a system in nature; in like manner as, from seeing revolutions of the planets, it is concluded, that there is a system by which they are intended to continue those revolutions. But if the succession of worlds is established in the system of nature, it is in vain to look for any thing higher in the origin of the earth. The result, therefore, of our present enquiry is, that we find no vestige of a beginning,--no prospect of an end.

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Oliver Strimpel @geologybites.bsky.social · Dec 21

Hi Mae, thanks for adding me to the science feed. I used the test tube emoji for the last 2 posts, which is what you suggested. There appear to be many other hashtags relating to geology. Do you know if there is a listing somewhere? Thanks for doing all this work - I bet the pay is lavish!

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Oliver Strimpel @geologybites.bsky.social · Dec 21

🧪Geology Bites now has 100 episodes! I hope it will be enough to carry you through any quiet moments during the holidays. Do give me feedback and suggestions and spread the word. #geology #earthscience

Photograph of the Pamir and Karakoram looking east, taken from the International Space station.

Photo: Tim Peake and NASA; geological interpretation: Searle, M. P., et al. (2018), Geol. Soc. London Special Publication 483

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Oliver Strimpel @geologybites.bsky.social · Dec 21

🧪 I just posted Mike Searle on the massive mountain ranges of central Asia — the Karakoram, Hindu Kush, Pamir, and 3 others. Each has its own tectonic history and unique features. E.g., an ultra-deep seismic zone in the Hindu Kush and a 700-km-long granite batholith in the Karakoram. #geology

Satellite image labeled with five of the mountain ranges Searle discusses in the podcast - the Karakoram, the Hindu Kush, the Pamir, the Kunlun Shan and the Tien Shan. The Gangdese, also discussed, is to the east of the region covered by the image along the southern margin of Tibet.

NASA

The Trango Towers are granite cliffs that rise about 3,000 meters above the Baltoro glacier in the far northeast of Pakistan. In the podcast, Searle explains that the Baltoro granite, which is what is exposed in the Trango Towers, is a giant, continuous batholith that was emplaced 13-20 million years ago during the intense regional metamorphism accompanying the India-Asia collision.

Annotated photographs of mountains that lie within the region imaged by Landsat above. (b) Layla peak, the sharply pointed summit at left, consists of orthogneissses (formed by metamorphosing igneous rocks) with a granite intrusion (K7 granite) dated at 21.7 Ma. (c) Taken from the rock-strewn surface of the Baltoro glacier, the photograph shows the northern margin of the Baltoro batholith. The heat from the intruding Baltoro granite metamorphosed the adjacent Carboniferous black shales to sillimanite, cordierite, and andalusite hornfels. (d) Another image showing the northern margin of the Baltoro batholith, here consisting of the Baltoro granite of the Lobsang Spire (foreground at right with a climber near the bottom for scale). The rest of the image shows the pre-collision orthogneisses of the Cretaceous Muztagh Tower (top left). (e) South face of the Uli Biaho Tower (6,427 m) showing homogeneous granite. (f) Another homogeneous granite tower, here with 1,800-m-high cliffs (Shipton Spire, 5,885 m).

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Oliver Strimpel @geologybites.bsky.social · Dec 12

Hi Mae, many thanks! My account is GeologyBites; that was the one I have been using since I joined Bluesky. Do you see another account as well?

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