Northern New Mexico offers to see a beautiful story of volcanic eruptions associated with Rio Grande rifting that was active. The river of Rio Grande carved canyon in Taos plateau exposing extensive flows of 5 million year old basalts and minor andesites and dacites. Here's one particular outcrop that provides a snapshot of geological history of the region:
The story goes like this (from bottom up):
Paleosol (old soil) marks the period of surface erosion. Underlying rock is exposed to the atmosphere and is being broken down to produce soil. The paleosol contains remnants of root channels and other traces of life on land. Based on the ages of underlying rocks the soil was developing about 5 million years ago.
Baked and oxidized paleosol was developed because hot lava was flowing on top of moist soil. At high temperature, available iron and water and oxygen was reacting resulting in oxidation of that iron.
Crumbly breccia, aa-lava newly erupted lava was flowing on top of the soil, cooling down quickly which resulted in partly solidified rock flowing in highly viscous lava. Solidification of the material produced crumbly, chunky aggregate commonly called 'a'a-lava. The rock was erupted about 4.8 billion years ago.
Massive dacite is produced by massive outflow of dacitic lava that was hot enough to flow and cool down continuously.
Sheared dacite reflects interesting property of the silisic lava. Because of high SiO2 content dacite polymerizes more so than a mafic lava, resulting in its comparatively high viscosity. So when it cools down it viscosity is so high, that lava can't flow anymore, it starts to shear.
Geologist has something to learn about Taos plateau volcanic field. He was erupted about 25 years ago.
Tuesday, September 27, 2016
Thursday, September 1, 2016
Google map streets view. Also called as multi-coloured rock stop, the outcrop became famous because it shows conspicuous cross-cutting relationship between the oldest rocks in Europe. The Precambrian rocks exposed here tells us a story: from oldest to youngest units can be distinguished by cross-cutting boundaries between them. The oldest rock in Scotland is Lewisian gneiss (grey). The original rock formed about 3 billion years ago and was metamorphosed multiple times (so now it's called gneiss). Then it was cut by mafic intrusions (black), or dykes (British spelling preserved), at about 2.5 billion years ago. Then all of these units were cut by granitic intrusions (pink), much later at about 1.8 billion years ago. After than, the whole assembly of rocks experienced metamorphism that shaped it's final look (sheared and stretched). Remember, the age of the Earth is 4.54 billion years, these rocks are really old!
Here's the outcrop with boundaries shown schematically.
Here's the outcrop with boundaries shown schematically.
Saturday, August 20, 2016
Imagine a mid-ocean ridge. Between two diverging plates, a volume of molten basalt is constantly being oozed out of the mantle. The molten basalt itself is really hot, over 1000°C. In contact with cool seawater it quenches instantaneously into volcanic glass. However, in areas (open cracks, for example) where permeable freshly erupted basalt is available, seawater reacts with it at 200-500°C. After the reaction basalts acquire new look, or we say, it becomes altered, - it has new minerals in it. From igneous and water-free rock, basalt converts to water-bearing hydrothermal mineral assemblages. These areas of hydrothermal activity are partly responsible for modern seawater chemical (and isotopic) composition and its acidity. Reacting basalt supplies Mg, Si, Ca and other elements into the seawater. In turn, the reaction with basalt sucks out other elements out of seawater, such as Na and S. I will show that at some point, reacted seawater can become pretty acidic with pH of 3.8. These underwater hot springs frequently form black smokers where unusual forms of life can exist because of the supply of heat.
Here, I wanted to show the result of a modeled experiment. I virtually took basalt of common composition (MORB) and incrementally added it to fixed amount of seawater. Starting with very small amounts increasing step by step, I could model different situations where various amount of rock is reacting with seawater. In my imagination it simulates variable amount of space where seawater could touch basalt and react with it. From very wide open cracks to porous basalt. In terms of water-to-rock ratio, the numbers will go from very high (open crack - water dominated system) to a very low (rock-dominated situation, water only in pores). The purpose of my modeling was to predict what minerals form during the reaction between basalt and seawater. Knowing thermodynamic conditions of mineral formation, the program could tell me what minerals will be found stable.
The graph shows concentrations of products of reaction between seawater and basalt at 300°C. The right side of the graph can be interpreted as pure seawater (very little rock added), thus the water-to-rock ratio is really high. Without any involvement of basalt, seawater is oversaturated with anhydrite and brucite. Depending on the proportion of rock in the mixture, different minerals will precipitate. Moving to the left along the horizontal axis, more rock is reacting with seawater. At very high water-rock ratios, basalt turns into a mixture mostly consisting of anhydrite, serpentine, hematite, talc and chlorite. At low water-rock ratios (basalt-dominated system), the products of reacting are albite, amphibole (mostly tremolite), zeolites, pyrite, quartz and epidote. These minerals compose a large portion of seafloor, mostly it's deeper layers because at some point they underwent high temperature hydrothermal alteration at mid-ocean ridges.
In turn, the left over seawater has modified concentrations of ion dissolved in it.
Saturday, August 29, 2015
Fig. 1. A fragment of canonical map of the USSR; The Precambrian is shown in bright-red colors
For the last couple years I have been studying the Precambrian exposed within the East European craton (platform), so-called Baltic Shield (or sometimes called Fennoscandian) (Fig. 1). My current research project is related to the early Paleoproterozoic igneous activity and associated hydrothermal processes on the Baltic Shield. This summer I needed to visit several localities in the region (Fig. 2):
- The Kiy Island in the White Sea, located near the city of Onega with ~2.45 billion-year-old (hereinafter, Ga) gabbro-norite
- The 2.45 Ga Vetreny Belt rift on its southern edge, where its overlain by Phanerozoic sediments
- The Vetreny Belt at its northern inclination
- The Shueretskoe occurrence of garnet- and gedrite-bearing rocks
Fig. 2. Generalized route taken during the field work
The Kiy Island, the White Sea
Fig. 3. The Kiysky monastery, build in 17th century
The Kiy Island is known for the orthodox cathedral that was built by patriarch Nikon, a reformer of the Russian Orthodox Church in the 17th century (Fig. 3). The island itself is composed of 2.45 Ga metamorphosed ultramafic-mafic intrusion (Fig. 4). The metamorphism occurred much later, at 1.8 Ga.
Fig. 4. Intensely metamorphosed part of the gabbro-norite complex
Thursday, July 30, 2015
Tuesday, April 14, 2015
Melt inclusions (the round circles in the video below) are little pockets of melt that are trapped in growing crystals during cooling of magma. If magma was erupted and cooled quickly, melt inclusions preserve the composition of the melt in which their host crystal formed. However, slow cooling will cause these melt inclusions to form daughter crystals (shown as the dark grains in the round circles) which change their original composition. In order to restore the pre-eruptive melt composition, I reheated these quartz-hosted crystallized melt inclusions (diameter=50 micrometers) at the USGS in Menlo Park, using a reheating stage and the assistance of Dr. Jake Lowenstern, scientist-in-Charge of the Yellowstone Volcano Observatory. These quartz crystals were taken from the upper portions of the Huckleberry Ridge Tuff fall deposit (2.1 Ma, 2,500km3), the oldest and largest of the three volcanic cycles that form the Yellowstone Volcanic Field. The bottom part of the deposit contains beautifully glassy, and bubble-free melt inclusions, however the upper portion had the unfortunate experience of being reheated after emplacement when the larger, and much hotter, ignimbrite was deposited.
In order to continue our evaluation of the composition of the magma that was being erupted at the onset of the Huckleberry Ridge Tuff eruption, I reheated around 10 quartz grains (each takes 1-2 hours, with the process violently halted if the quartz grain explodes due to it's initial experience at the alpha/beta transition) and videoed the process. Enjoy...
Ph.D candidate at the Department of Geological Sciences, University of Oregon.
PS I want to thank Madison for sharing her awesome research on my blog. I hope that there will be more of collaborative effort in exposing our research experience to the web-based audience.