Subduction Zone: Kamchecka, Russia

Here I will discuss the specifics of the Volcanic Subduction System in Kamchecka Russia.

Tectonic Setting

The tectonic setting is the plate margin of the Pacific plate and the Eurasian plate. The Pacific Plate was subducting below the Eurasian plate. This creates the volcanoes on the Eurasian Plate. The melting that is occurring here is due to the  introduction of water into the system.

 I will also list some of the major volcanic products and features evident in this area. The major volcano range present is named the Sredinny Range. There are  basalt planes called the Kamtchecka Basalt plane. It makes up the Kamtchecka peninsula. The kuril trench is the point where the Pacific Plate is subjecting under the Eurasian Plate. The Kuril Islands are products of volcanism occurring on the oceanic crust of the Eurasian Plate. This volcanism forms small volcanic islands.

This is a google map image of all of the important Volcanic products and the volcanoes themselves.

Notable Volcano

One Notable volcano is Sheveluch, It is located on the main peninsula. This volcano has been very active since 1999. This volcano started erupting in late 1999 and is still continuing to erupt to today. In the 1990s there were several small eruptions. It is a very active volcano and has many eruptions since its formation 65,000 years ago. One of the major volcanic landforms, in addition to the strata volcanoes, is the lava dome found at the center of the top of the volcano. That is where it erupts from.

This is an image of the Kamtchecka Peninsula
This is an image of one of the active lava domes

Geochemistry

Here I will discuss the geochemistry of the magma derived from the volcanoes at the volcanoes in Kamchecka, Russia.

Harker Diagrams

The Harker Diagrams below illustrates the changes that occur in the magma chambers of a subduction zone volcano. Below illustrate the dramatic trends that occur when the magma begins to crystalize or some of it is erupted. The low levels of Magnesium indicates that it might have crystalized out of the magma before it was erupted. Iron and Calcium also decreased quickly due to their ability to also crystalize out of solution with relative ease. This is also illustrated by the Magnesium number.

The trend exhibited by the trend exhibited of in the Alkalies. The increase in the alkalies illustrates the amount of incompatible in the melt. This is due to their large size and inability to go into the melt. The alkalies present appear to go through a slight decrease. This might indicate that the magma started to crystalize the incompatibles. This occurs when the magma has sat in the crust long enough for the incompatibles to start to crystalize out of the melt.

REE/Chondrite

This REE/ Chondrite diagram illustrates how the Light Rare Earth Elements (LREEs) are in a higher concentration than the Heavy Rare Earth Elements (HREEs). The reason for this increase in the LREEs in the melt comes from the magma’s journey to the surface. As the magma moves towards the surface, the it partially melts and assimilates the rock its moving though. This increases the incompatible elements in the magma because they are some the first to come out of the melt.

TSA Plot

The range of rocks that could form range from basalts to rhyolite. This illustrates the greater range of magma present at this volcanic system. This TAS diagram illustrates the preference to more rhyolitic magma. This is common for the system.

AFM Plot

This AFM diagram indicates the evolution of the magma. The magma present at Kamchecha has a range of Tholeiitic to Calc-Alkaline magma. This is common for a subduction zone. The magma at a subduction zone is typically more calc-alkaline because it is able to fractionate in the crust for longer. However, the majority of the magma is tholeiitic because that is the easiest magma to produce.

Rocks and Thin Sections

Intrusive

Hand Sample

Handsample P63

Plane Polarized Thin Section
This image is of hand sample P63 in hand sample under plane polarized light. This image there are large crystals that are interlocking. This is evidence of the rock cooling gradually underground. Biotite, muscovite and quartz are evident in this hand sample.
Crossed Polarized Thin Section
This is that same view as the Plane Polarized Thin section of P63. However, this time it is in Crossed polarized view. Here you can see that this rock is mostly made up of quartz. These crystals grew together to make it interlocking.
Identification Diagram
This graph indicates that the rock is a Quartz Rich Granitoid. This is due to the large amount of Quartz present in the rock (85% ). The feldspars make up around 15% of the rock, individually they make up 5% Alkali feldspar and 10% for the Plagioclase Feldspar.

Extrusive

Hand Sample
Hand Sample 1811
Plane Polarized Thin Section
This image is of a Plane Polarized view of hand sample 1811 in thin section. There were small thin minerals present along with obvious quartz crystals. However, the majority of the rock is made up of volcanic glass. It shows no motion because it called so fast.
Crossed Polarized Thin Section
This image of the Crossed Polarized view of a thin section of P1811. There is very little variation as the majority of this thin section is an image of the glassy matrix of the volcanic rock. Most of the minerals present appear to be quartz. With a biotite or an amphibole present. The fact that the minerals are very small in size indicates that the lava cooled very quickly. The sporadic phenocrysts illustrate that some of minerals had a short window to grow.
Identification Diagram

This image illustrates the classification of this rock. It is a Rhyolite. It is composed of 58% Quartz, 38% Alkali and 4% Plagioclase.