12.753 | Spring 2001 | Graduate

Geodynamics Seminar


Course Meeting Times

Lectures: 1 session / week, 3 hours / session

Plume Ridge Interactions

The Earth’s crust is primarily composed of melting products from mantle plumes and mid-ocean ridges - both presently and over the course of Earth history. While both systems represent upwelling features in a convective mantle, they can be viewed as end-member systems in that plumes represent buoyant flow whereas mid-ocean ridges represent passive corner flow. This paradigm is not strict - flow beneath ridges may be buoyant in some places, for example, but it does provide a reasonable framework for enquiry.

Plumes and ridges can be studied independently, but in many places across the globe the systems interact, often in intriguing fashion. The nature of these interactions provides an opportunity to improve our understanding of both systems, and provides new perspectives on the mantle, crustal, and water column processes associated converting heat from the Earth’s interior into new crust, hydrothermal flow, and biological communities on the seafloor.

The approach taken for the 2001 Plume-Ridge Interactions Seminar series was to start with basic ideas about mantle convection and tectonics, and an overview of the global hotspot and ridge systems. We then addressed three case studies of plume-ridge interactions in detail. Our first case was the interaction of the Iceland plume - one of the largest plumes in the world - with the Northern Mid-Atlantic Ridge. We then turned to the interaction of the Galapagos plume with the Galapagos Spreading Center, and finished with the interaction of the Cobb Plume with the Juan de Fuca Ridge. Each of these systems provides a different perspective on the nature of plume-ridge interactions, and by comparison and contrast we are able to distill the fundamental aspects out of the complex array of geophysical and geochemical data associated with plume-ridge systems.


Joint Program students enrolled in the Geodynamics seminar are required to complete a project for the class. This includes research, an oral presentation during the last two or three seminar meetings, and a written paper due at the end of the semester. For first and second year students, the project must be on a topic related to the theme of the seminar and must be different from their main research interest. For more advanced students, the topic may be closely related to their dissertation research.

Course Outline

Background on Tectonics and Mantle Convection

How do plumes and ridges fit into ideas regarding mantle convection?

What is a plume, how are they distributed around the globe?

How do the properties of plumes and ridges vary?

What would be a canonical model for the chronology of a p/r interaction?

What are the burning, unanswered questions regarding plumes, ridges, and p/r interactions?

What kinds of data and modeling are needed to answer the important questions?

Case Study 1: Iceland/Northern MAR - Stuck in the Middle?

What is the pattern of mantle flow beneath Iceland?

How big is the Iceland plume? Where is it?

How far downrift can the chemical and mechanical influence of the Iceland plume be traced?

How and where is the plume fragmented and distributed to discrete volcanic systems?

What is the role of the Iceland plume in the early stages of rifting on the northern MAR?

What do the V-shaped ridges tell us about the p/r interaction and its influence on parameters such as lithospheric strength and upper mantle flow?

Case Study 2: Galapagos/GSC - Gone but Not Forgotten

How has the interaction between the Galapagos plume and the Galapagos Spreading Center evolved over time?

How does lava chemistry vary along the GSC and what does this imply regarding the p/r interaction?

What is the present pattern of mantle flow beneath this system?

What does the mantle matrix do between the two upwelling features?

Is there still a melt connection?

How big is the Galapagos plume? Where is it?

Case Study 3: Cobb/JdFR - The First Days are the Hardest Days

Is the Cobb hotspot a plume?

How has it behaved in the hot-spot reference frame?

Does it have a geochemical signature?

Where is it presently located?

How deep is it rooted?

What is the pattern of mantle flow beneath this system?

When did the JdFR start bending towards the Cobb hotspot?

How is melt distributed beneath the central JdFR?

How does lava chemistry vary along the JdFR/Cobb region?

What patterns of matrix and melt flow are consistent with the observational and theoretical constraints?

How might long-term observatories, such as NeMO and Neptune contribute to our understanding of the p/r interaction?


How do ridges, plumes, and p/r interactions influence the global biogeography of chemosynthetic systems?

How do the myriad millions of near-ridge seamounts relate to p/r interactions?

How fixed is the hot spot reference frame?

Can large plumes create new plate boundaries?

How deep is the source region for hotspots?

Course Info

As Taught In
Spring 2001
Learning Resource Types
Image Gallery