The Cyclic Process of Tectonic Plates at
Oceanic-Continental Boundaries
An Introductory Step-By-Step Description for Geoscience Students
Written by David Bossie
Figure 1. Detailed Oceanic-Continental Plate Boundary Diagram
The Cyclic Process of Tectonic Plates at Oceanic-Continental Boundaries
Audience and Scope
The intention of this document is to provide a basic understanding of the cyclic nature and processes of
oceanic-continental plate boundaries. It is written to serve as an educational guide for students enrolled
in an introductory collegiate geoscience course. Again, it is important to note that these processes have
been simplified and summarized to an extremely basic level of understanding. In further studies,
students may take a more in-depth look into these processes and gain a deeper comprehension of
tectonic plate boundaries.
Introduction
The process that occurs at the boundary of oceanic and continental tectonic plates is an interdependent
and cyclic development that involves forces inside the earth and surface-level interactions. The solid
radioactive core of the earth provides the necessary force for the entire process to take place. This
document uses a five-step approach to highlight the main interactions and resulting formations that are
important for geoscience students to be familiar with. The first step focuses on the flow within the
mantle that results from the radioactivity in the core. Next, the forces from the mantle’s flow cause the
plates to move. When this happens, the attention shifts to two specific plate boundaries: the divergent
boundary at the oceanic plate and the convergent boundary that occurs between the oceanic and
continental plates. Finally, the interaction between the oceanic and continental plates results in the
formation of a volcanic mountain chain and trench. This process, described in more detail to follow, is
cyclic in nature due to the melting effect of the mantle and the cooling effect of the ocean. These
temperature differences cause the material of the plates to change form over time.
Words in bolded and italicized dark red font are defined in the glossary at the end of this document.
Written by David Bossie
10 October 2014
The Cyclic Process of Tectonic Plates at Oceanic-Continental Boundaries
Step 1
Convection Currents Form
Underneath the earth’s crust, hot molten
magma circulates in a manner that is commonly
referred to as convection currents. At the
interface between the magma and crust, in the
lithosphere, these convection currents provide
the driving force that drags the plates.
Step 2
Sea-Floor Spreading (Divergent
Boundary)
Figure 2. Step 1: Convection Currents Form. Blue
arrows represent the opposing currents at this region.
As the convection currents within the mantle
circulate, a hot plume of magma forms and
makes its way towards the earth’s crust. In this
region, on either side of the plume, the
mantle’s currents move in opposing directions
away from each other, causing the oceanic
plate to be pulled in opposite directions. When
this happens, a divergent boundary is formed
where the plate splits and the plume surfaces.
Step 3
Oceanic Plate Subducts Under
Continental Plate (Convergent
Boundary)
Figure 3. Step 2: Sea-Floor Spreading. Blue arrow represents
plume direction. Black arrows represent divergent boundary
forces (convection currents) acting on the plate. Red line
along spreading ridge represents divergent boundary.
As the divergent boundary is forming, there is a
simultaneous convergent boundary occurring
at the ocean-land boundary. As the convection
currents continue to move the oceanic plate
into a collision with the continental plate, it is
important to consider the plates’ densities.
During the formation of the earth’s crust, the
oceanic plates become significantly denser than
the continental plates. The main concept
behind this development is that during the
solidification of these plates, the ocean places a
tremendous amount of pressure on the
material beneath it. This makes the oceanic
plates extremely compacted and much denser
Written by David Bossie
Figure 4. Step 3: Oceanic Plate Subducts Under Continental
Plate. Black arrow represents oceanic plate direction as it
subucts into asthenosphere. Red line represents convergent
boundary.
10 October 2014
The Cyclic Process of Tectonic Plates at Oceanic-Continental Boundaries
than the continental plates, which have
essentially no weight to carry in comparison.
plume that forms underneath the oceanic plate,
described in Step 2.
This causes the oceanic plate to subduct
underneath the continental plate due to the
significant difference in relative densities. The
material with a heavier unit weight is pulled
closer to the center of the earth, underneath
the lighter material.
Step 5
Plume Rises Under Continental Plate
and Creates a Volcanic Mountain
Chain
Step 4
Subducted Plate Melts in
Asthenosphere and Contributes to
New Magma Plume
As the oceanic plate subducts into the
asthenosphere and underneath the continental
plate, it melts due to the intense increase in
temperature. This new melted material causes a
new plume to rise underneath the continental
plate. This plume is not to be confused with the
As a result of convergent boundary forces and
upward pressure from the new magma plume,
the continental plate reacts and forms a
mountain chain. In cases where magma rises
enough to exit the top of these mountains and
onto the earth’s surface, these mountain chains
are considered to be volcanic mountain chains.
At a convergent boundary, mountains are a
common feature. In this case, where a
convergent boundary occurs with an oceanic
and continental plate, a trench along the ocean
floor is a common feature as well.
Figure 6. Step 5: Plume Rises Under Continental Plate and
Creates a Volcanic Mountain Chain. Blue arrow represents
direction of new magma plume, which contributes to the
convergent boundary forces.
Figure 5. Step4: Subducted Plate Melts in Asthenosphere
and Contributes to New Magma Plume. Brown dotted line
represents the solid plate melting in asthenosphere.
Figure 7. Step 5: Plume Rises Under Continental Plate and
Creates a Volcanic Mountain Chain. Shown here is the
resulting mountain chain and trench.
Written by David Bossie
10 October 2014
The Cyclic Process of Tectonic Plates at Oceanic-Continental Boundaries
Conclusion
This process is crucial to the understanding of how the earth’s internal forces shape the world as it is
seen today. To summarize, the solid radioactive core of the earth is the true beginning of this process,
although it is not specifically covered in this document. The process begins when the core creates
circulating convection currents within the surrounding mantle. These currents drive the boundary forces
that occur as the shifting plates split and collide. At the divergent boundary of an oceanic plate, the sea
floor spreads as the rising plume surfaces. At the convergent boundary between an oceanic and
continental plate, a volcanic mountain chain and trench often form as the oceanic plate subducts into
the asthenosphere and strengthens a new plume. As solid plates subduct, the material melts into the
mantle. Similarly, as magma plumes surface, the material solidifies, giving the overall process a cyclic
nature. The concepts introduced in this document are fundamental to the field of geoscience and are
further explored as students continue their studies.
Glossary
Asthenosphere: highly liquid region of the mantle directly beneath the lithosphere.
Continental plate: less dense portion of the earth’s crust located beneath dry land.
Convection currents: circular flow in the liquid mantle driven by the earth’s solid radioactive core.
Convergent boundary: region where plates experience a collision due to opposing forces.
Divergent boundary: region where plate experiences separation due to opposing forces.
Lithosphere: highly plastic region of the mantle closest to the earth’s crust where the convection
currents exert forces at the mantle-crust interface.
Oceanic plate: denser portion of the earth’s crust located beneath an ocean.
Plume: particularly hot and pressurized region of the mantle where magma rises to the earth’s crust.
Subduction: process undergone by the heavier oceanic plate when it collides with the lighter continental
plate and is forced into the asthenosphere where it melts.
Written by David Bossie
10 October 2014
The Cyclic Process of Tectonic Plates at Oceanic-Continental Boundaries
Works Cited
“Plate Tectonics: Earthview.” Plate Tectonics: Earthview. Platetectonics.com, 2010. Web. 06 Oct. 2014.
<http://www.platetectonics.com/book/index.asp>.
Figure 1 (cropped)
Detailed Oceanic-Continental Plate Boundary Diagram. Digital Image. The McGraw-Hill Companies, Inc., n.d. Web.
04 Oct. 2014.
Figure 2 (cropped and arrows added)
Detailed Oceanic-Continental Plate Boundary Diagram. Digital Image. The McGraw-Hill Companies, Inc., n.d. Web.
04 Oct. 2014.
Figure 3 (cropped and arrow added)
Detailed Oceanic-Continental Plate Boundary Diagram. Digital Image. The McGraw-Hill Companies, Inc., n.d. Web.
04 Oct. 2014.
Figure 4 (cropped and line added)
Detailed Oceanic-Continental Plate Boundary Diagram. Digital Image. The McGraw-Hill Companies, Inc., n.d. Web.
04 Oct. 2014.
Figure 5 (cropped)
Detailed Oceanic-Continental Plate Boundary Diagram. Digital Image. The McGraw-Hill Companies, Inc., n.d. Web.
04 Oct. 2014.
Figure 6 (cropped and arrow added)
Detailed Oceanic-Continental Plate Boundary Diagram. Digital Image. The McGraw-Hill Companies, Inc., n.d. Web.
04 Oct. 2014.
Figure 7 (cropped)
Detailed Oceanic-Continental Plate Boundary Diagram. Digital Image. The McGraw-Hill Companies, Inc., n.d. Web.
04 Oct. 2014.
Written by David Bossie
10 October 2014