Quiz: Spot The Granite Intrusion

I came across this glacially transported boulder in the Dugtu village valley near the Panchachuli Glacier in the Kumaon Himalaya.

It is a block of high grade gneiss intruded by a granite. Without scrolling beyond the first photograph, try to work out the contact between the gneiss and the granite.

Answer:

The boulder is encrusted by moss. There is some mineral staining too. And sunlight falling on the rock gives it a speckled appearance.. All this reduces the contrast in color between the gneiss and the granite.

But there is a vital clue in the orientation of structures. Both the gneiss and the granite have a planar fabric imprinted on them.

The fabric of the gneiss is due to the orientation of platy minerals like micas stacked in layers, alternating with layers richer in quartz and feldspars. Assume this is the original disposition of the rock as well. The gneiss layering you see is due to the trace of horizontal planes of separation of different mineral layers. I have outlined some of this planar fabric in brown lines.

The granite has a planar fabric too, but this is due to near vertical fractures. The rock has been broken in to thin slabs  by fractures (red lines) which may have formed during the cooling of the magma. These fractures don't pass into the surrounding host gneiss. Two arms of the granite have penetrated between the gneiss layers forming mini sills.

You can see the contact (black line) between the gneiss and the granite roughly where my wallet is. Here, the horizontal planar fabric of the gneiss abruptly juxtaposes against the vertical planar fabric of the granite.

I Want This Wine!

via @geo_teira

I think the label Malbec + Malbec implies grapes from two different wineyards. ... in any case a big Argentine steak to go with it will be great too!

Describing My Research Using Only 1000 Common Words

I have been tempted into this by a challenge issued to geoscientists  by Chris Rowan and Anne Jefferson at Highly Allochthonous. Can you use this new Text Editor and explain your research using the 1000 common word list of this editor. The editor gives you a warning if you use a word not in its list.

Here is my attempt to explain my research interests in carbonate sedimentology, the study of biogenic remains and their transformation into rock.

I study rocks made up of the hard remains of animals living in water a long time ago (10 hundred times 10 hundred years ago or more). That can tell us how deep or warm or cold the water was at the time the animals lived and also how warm or cold the air was at that time. Studying these remains from different times can tell us how things changed over a long time in the past and how things may change in the years ahead. Over many many years as the animals living in water die their hard remains turn into rock under ground. Different types of water moves through this rock leaving behind a sign and often making open spaces inside the rock. Sometimes in other near rocks soft remains change into thick matter which moves to fill these open spaces. All this happens deep under ground. It is important to know where, when and how this happened since we search for and need this matter to drive our cars and trains and to give us light and to make our lives easier in many ways.

Damn (in the list!).. that was harder than I thought .. but great fun! Here is the permalink to my short essay.

Try it out :)

Explanation of terms:

hard remains of animals - calcium carbonate skeletons of marine animals
10 hundred - thousand
hard remains turn into rock- lithification and diagenesis
open spaces - porosity
soft remains - soft tissue of marine creatures
thick matter- oil

Usually it is the technical terms that need explanation in everyday words. In this case its the other way around!

Most Difficult Geology Time Scale Mnemonic Ever

From xkcd comics:

Try beating that!

Field Photos: Driving Through A Basalt Countryside

The most prominent topographic feature of the Deccan volcanic province is the Western Ghat Escarpment that runs north south, roughly parallel to the west coast of India. The escarpment is the edge of a deeply dissected easterly tilted plateau, a result of Cenozoic crustal movement. Near Pune, several streams flowing eastwards through narrow valleys have been damned and the backwaters of these dams have some great views of a basalt landscape comprising deep valleys and spectacular exposures of basalt cliffs.

Last Sunday I drove with some friends along the backwaters of Mulshi dam. In the interactive embedded map below (Pune in south center) the western ghat escarpment is the arcuate north south ridge line on the left side of the image. You can count more than ten dams situated to the east which have flooded narrow valleys. If you pan north south you will see more reservoirs. The water is used to generate electricity and for urban and agricultural use.


View Larger Map

All pictures courtesy Bharat Parikh and Rajesh Sarde.

The countryside was lush. Wild grasses in full bloom.

A wide grassland meets distant peaks and ridges.

Steep basalt cliffs. Notice the layering of the lava flows.

The edge of the plateau is penetrated by fracture sets oriented in the NNW-SSE direction parallel to the coast and a NE-SW set. Some of these represent extensional stresses developed during rifting of India from Seychelles around 66 my to 65 my years ago and may have been conduits for the magmas. There are plenty of dykes intruding the lava pile oriented in a north south and north-east south-west direction. There are fracture sets too which may represent a later Cenozoic stress regime related to the uplift of the province. These provide a structural control on drainage.

The image below shows a north-east south-west oriented fracture set (red arrow) which has controlled the dissection of a deep valley. I call it Anil's valley in honor of my friend who told me about it. White arrows point to the NNW-SSE oriented lineaments. They may represent dykes or fractures.

 A view of Anil's valley. It is a box canyon with near vertical walls of basalt.

The main basalt flow type in this region are compound flows. These are made up of discrete blobs of lava that overlapped and coalesced with other blobs of lava to form a compound unit. During one eruptive episode several compound units may be stacked to form a thick lava pile.  These compound flows have weathered over time into a steep hummocky topography with domal summits accentuated by erosion along fractures. (Picture below taken on a previous field trip in February 2010).

A lonely road in the woods.

Bed load! A dry bouldery stream bed. Its just three weeks after the rains stopped and the streams in the upland areas are dry already. Small farming communities make by mostly through water in the monsoons and then rely on small springs to water their fields. Life gets quite hard here after the rains.

Food of a civilization. Yellow ripe paddy grown in the lowlands near the water source. Lava flows in the backdrop. You can smell the fresh rice as you pass by.

Until next time..

Thoughts On The "Irrefutable" Evidence Of The Yeti

Is there a connection between last year's discovery of Denisovans and the recent surge in interest in the Yeti. Last year a team of scientist found fragments of a human finger bone in a cave in the Altai region of Siberia. Materials dated in the cave indicate that these humans lived about 41,000 years ago.  The surprise was when DNA recovered from the bone was sequenced and compared with living humans and Neanderthals. The differences in the DNA sequence suggested that these fossils represented a distinct human population, as different from living humans as we are from the Neanderthals. They were called the Denisovans after the area where these remains were found.

What is the story of the origins of these Denisovans? After the origin of our genus Homo in Africa around 2 million years ago, humans from time to time migrated out of Africa.  Descendants of one such migration around half a million years or so evolved into the Neanderthals in Europe and the Denisovans in East Asia. These were long lived populations. Within Africa too there were probably different varieties of humans. We Homo sapiens evolved from one such population and when members of Homo sapiens migrated out of Africa around 75 thousand to 50 thousand years ago they would have encountered and interacted with the Neanderthals and Denisovans. Did we interbreed? The answer is most likely ..yes. Genetic analysis now strongly suggests that both Neanderthals and Denisovans have left a small but distinct genetic legacy in us.

The status of Neanderthals and Denisovans as separate species of humans now stands challenged. They had certainly evolved into a distinct variety of humans, much more different than the differences seen between the broad groups of living humans. But not enough so as to prevent them from successfully interbreeding with a population (us) they confronted after a few hundred thousand years of separation.

The Yeti off course would be the ideal candidate to imagine a still living Denisovan population in the isolation of Siberia. The ecology described historically for the Yeti includes remote mountainous regions, caves, cold weather, temperate forests.. landscapes that also describe one of habitats of the Denisovans, although the Denisovans probably had a range that include the tropics too.

Stories of a mysterious human-like creature wandering the wilds are part of the mythology of many cultures.  Such a creature thought to be living anywhere from Tibet to Siberia has been called the Yeti.  Now, Russian scientists a year after the sensational discovery of the Denisovans have found "irrefutable" evidence of the Yeti in the form of  impressions on the ground and some hair and a supposed bed from a setting uncannily similar to the Denisovan fossils.... In the cold of Siberia in a cave surrounded by temperate forests.

I can't help thinking that the Denisovans more than prompted this latest "evidence" of the Yeti.

The Yeti has always been thought of and pictured as a brutish sort of a creature.  It is usually described as a bipedal ape,  hinting at its proto-human like character. One famous picture of the Sasquatch (the Yeti's equivalent in north America) shows a hairy gorilla like creature  turning its head to face the camera.  The Yeti in East Asia has also been described as big and hairy. It has traditionally been a creature which has been emphasized to be more "primitive" than humans but occasionally with some redeeming qualities. In Tintin In Tibet ( Picture Source),  the Yeti saves and looks after Chang, a Chinese boy who is a survivor of a high altitude Himalayan plane crash.

These depictions of the Yeti may be a reflection of how we thought and maybe still do about archaic populations of humans. They were thought to be separate species. Different from us reproductively. We didn't breed with them. There was no intimacy between us. They were sub-human.  The Neanderthals for long were considered primitive dumb brutish cave dwellers whom we superior modern humans drove to extinction. We were wrong about that. As we learn more about Neanderthal society that perception has changed over the last couple of decades. And now we know that all of us are part Neanderthal and part Denisovans.

Will our description and iconography of the Yeti change to accommodate this new understanding of human evolution? Now that we understand that there is a continuity and not a chasm between us and other varieties of humans who lived on earth, will we depict the Yeti as a less grotesque, less intimidating, more empathetic social creature, and not the one solitary ape roaming the expanses of Tibet and Siberia. Will the Yeti become more human and less beast? Will science guide this particular theater of science fiction?

Will the Yeti become no more abominable, but just an ancient snowman?

India Asia Collision And The Evolution Of Hindu Thought

Wendy Doniger in her book The Hindus: An Alternative History draws the following parallel between the collision of a piece of Africa (the Indian plate) with the Asian plate and the evolution of Hindu thought:

In part because of the intertextuality and interpracticality of Hinduism, one text or ritual building on another through the centuries, right back to the Vedas, scholars looking at the history of transmission have assumed that the Veda was the base onto which other things were added in the course of Indian history, just as Central Asia was the base that absorbed the impact of that interloping piece of Africa so long ago. And in the textual tradition, at least, this is true enough of the form in which ideas were preserved, the chain of memorized texts. But from the standpoint of the ideas themselves, it was quite the opposite. The Vedas was the newcomer that, like the African island fusing onto a preexisting continental base, combined with a preexisting cultural world consisting perhaps of the Indus Valley, perhaps of any of several other, more widely dispersed non -Vedic cultures. 

One can get carried away to the point of silliness comparing geological evolution of India with the coming together of cultural and religious thinking during the evolution of Hinduism. So don't take this too seriously but I couldn't resist extending the comparison a little.

One aspect that comes to my mind is the retention of the original state. All along the geological landscape of the Indian subcontinent it is easy to make out which  is the original fragment of Africa (Gondwana)  and which the original Asian plate. Over much of the Indian subcontinent the original Gondwana characters of India remained unchanged after the two continents collided as is the case with the Asian continent. They are in proximity only along a narrow zone called the Indus-Tsangpo Suture in the Ladakh -Tibetan Himalayan region. Over there the crustal blocks of the two plates, their provenance recognizable, lie next to each other along  faulted contacts, slivers of ancient Gondwana pasted onto fragments of Central Asia. The boundaries between the two are sharp. It is like as Doniger puts it components of a salad. It may appear mixed but you can recognize the greens from the nuts easily. 

The coming together of the Vedic and non-Vedic worlds has resulted in a more diffuse landscape of ideas and people. Unlike geology there is no spatial boundary within the Indian subcontinent where the Vedic world collides with the non-Vedic. You might be tempted to put this at the junction where Indo-Aryan languages give way in the south to Dravidian languages..but that boundary between the two peoples has shifted geographically and evolved over time to be more a language boundary than a boundary of ideas. Gods and cultural and social practices have flown to and fro between Indo-Aryan and Dravidian speaking people across geography and social strata. So have genes, and the result is more a milkshake than a mixed salad. 

Beyond the Dravidian speaking pariah, farmers, merchants, kings and priest, a social hierarchy likely imported from the Indo-Aryan world, there were many groups speaking Austro-Asiatic and other now extinct languages who progressively became marginalized with the encroachment of Indo-Aryan and Dravidian farming communities and city states. These were the adivasis or tribal populations who at first sight might seem to be a world apart from Vedic and mainstream Hindu thought. They would seem to resemble the discrete pieces of Gondwana and Central Asia, living in close proximity but separated from mainstream Hindus by sharp social, cultural and genetic fault lines. There is some truth to the salad bowl analogy here. But over millenia these fault lines must have been breached and boundaries blurred. Once thought to be unchanged descendants of the first migrants from Africa many tribal populations have to a degree assimilated with the Indo-Aryan and Dravidian speaking populace. Recent studies have shown substantial amounts of Eurasian and south east Asian genetic components within different Indian tribal populations.

There must have been linguistic and cultural exchanges as well.. for example many marginalized groups adopted Indo-Aryan and Dravidian languages. Going the other way it is likely that both the elite Sanskrit literature and popular vernacular mythology borrowed from animist tribal traditions and folklore.

Within the Ladakh and Tibetan region and the Karakorum and Hindu Kush ranges though there are indicators of geological processes that resulted in the two plates not just residing side by side but forming a more complete mix. As the Indian plate subducted underneath the Asian plate, deep inside the crust, very high pressures and temperatures caused the rocks at the contact between the two plates to melt.  In that magma, elements scavenged from two different plates recombined into new minerals. The two plates created one entity.  These mixed rocks called anatexic granites form chains of plutons north of  the Indus -Tsangpo suture, the zone of collision of the two continents. 

So although the fault bounded terrain of the Indus-Tsango suture works as an analogy particularly for some marginalized groups, it is in these granites that geology comes to being the closest analogy to the evolution of mainstream Hindu thought in which ideas from the Vedic and non-Vedic worlds have come together, some traceable to their sources, others having synthesized into inseparable traditions, multiplicities within an individual.

Get The Beer Out: The Geologists Are Coming

Wired Science has a fun article by Betsy Mason on why geologists like beer. The fluid has been flowing freely at the recent AGU meeting in San Francisco and bartenders are swearing that geology conferences see more of that stuff being consumed than at any other science meeting.

Why do geologists love beer so much?

When it’s hot, and you’ve been hiking all day carrying 50 pounds of rocks, do you want a Merlot? - Jim Metcalf of Syracuse University

It goes down a lot easier than water because a lot of the places we go, we can’t drink the water - Jonathan Gourley of Trinity College.

Science doesn’t work when people keep secrets and don’t share their data, And what could be better to help with the free flow of information? - Daniel Jaffe of the University of Washington.

More theories here:



In India you get a decent collection of lagers but not much selection in ales. Hopefully that might be changing soon. I attended a wine festival in Pune last year and there were stalls by a couple of breweries showing off their new ales which will be in shops soon.

Good stuff.

I drink mostly  Okocim Palone  a Polish  malt lager which is now being brewed in India. In my opinion it is the best of the Indian lagers. Richer, toastier and more flavorful than the rest.

....geologists in India gulp down a lot too.

Geological Refurbishings For Your House

A friend sent me this image:

I haven't made much use of geological motifs in my house. This is the farthest I have gone:

A Precambrian  chert cemented conglomerate from the west coast Konkan region and a giant Nautilus from the Cretaceous of South India stop the balcony door from being slammed shut by the monsoon winds.