James Mehegan

Deceased - July 30, 2004

Ph.D. Thesis

Temporal, Spatial, and Chemical Evolution of the Troodos Ophiolite Lavas, Cyprus: Supra-Subduction Zone Volcanism in the Tethys Sea

(PDF -  Mb)

A new model for formation of the Troodos Ophiolite is proposed involving incipient arc volcanism in a supra subduction zone environment. Three successive cycles of sea-floor volcanism are recognized in the extrusive sequence of Troodos, all of which correspond to regionally recognizable lithostratigraphic units. The first cycle of lavas (group A) ranges in composition from basalt to rhyodacite and compares closely to arc tholeiite suites. Overlying and interfingering with group A lavas is a suite of high MgO andesite (group B) interpreted as depleted arc tholeiites. Along the southern flank of Troodos, a suite of highly depleted basalts and picrites forms group C. Trace element compositions are used to further subdivide the extrusive sequence into six subgroups: A, As, B1, B2, C and C2. Major oxide variations within the three groups can be modelled by a combination of open-system and closed-system fractionation in shallow magma chambers. Some magma mixing and assimilation of roof rocks are suggested by trace element variations. Each of the six subgroups is believed to represent a separate parental magma.

A diapir train model involving a series of mantle diapirs produced at successively shallower depths was developed to explain the observed lava geochemistry and stratigraphy. In this model, the high MgO andesites of groups B2 and C2 are produced in part by the passage of the A-As diapir through wet peridotite. The highly depleted melts of groups B1 and C are produced by 20-30% partial melting during passage of the group first-formed diapirs through the mantle at depths of about 25 km.

Supervisor: Paul Robinson


Photographs and Memories of Jim Mehegan


A short history of Jim Mehegan since his departure from Dal...

My journey from Nova Scotia to southern California was going to be via my thumb and the open road. With winter dragging on this was not a journey that I was excited about taking, but I was broke and I had achieved the status of illegal alien - thus it was time to leave! I had arranged to get a ride to New Brunswick with Steve McCutcheon (Ph.D. 90), so the morning I was to leave I went to my office to pickup my backpack, to say goodby to friends, and to meet Steve. When Brian Todd (Ph.D. 88) let me into my old office I found on my desk a small container. Within this small container was enough money for me to fly Peoples Express from Bangor, Maine to Los Angeles, California. I attempted to question Brian as to the source — all he said was it was from your friends. I have questioned Brian in later years but he is still evasive. All I can say is - Thanks!

Since then I finished my Ph.D. (1988) with much help from Becky, Paul, and others. Married Colleen Nagle in 1988. Worked as a research geologist (University of California, Riverside) studying high-temperature geothermal systems of the Salton Trough. I have also spent time in private industry studying landslide and earthquake hazards. During the last ten years I earned a pleasant living as a faculty member and chair of geology at California State University in San Bernardino. However, now I am a one person department at Riverside Community College where I teach introductory geology, I am developing a GIS certificate program, and I lead field trips. My spare time is spent whitewater kayaking, surf kayaking and long boarding. Three years ago I was thrilled to lead the Dal Honours trip through the geology of California. Brian Todd joined me for that adventure and on an earlier trip to Baja California (Mexico) for Cal State students. I hope again to show Dal students the geology of California - we might even get Becky to join us.

Life could not be better!


Riverside Community College Sets up Scholarship

Riverside Community College has set up in Jim's memory a scholarship for students that plan on transferring to a four year college to pursue geology as a major. If interested, memorial contributions can be sent to:

Riverside Community College Foundation
James M. Mehegan Memorial Scholarship
4800 Magnolia Avenue
Riverside, CA 92506

Maybe one of those transferring students will transfer to Dal. A Dal Geology student on a James M. Mehegan Memorial Scholarship sounds good to me.


RCC geology instructor James Mehegan, 52

He was known for leading field trips and suffered a heart attack while rafting with friends.

01:19 AM PDT on Wednesday, August 4, 2004

By GAIL WESSON / The Press-Enterprise

Associate Professor James M. Mehegan was known for leading geology field trips to the Sierras and Colorado River to enhance his classroom lectures at Riverside Community College.

But the whitewater-kayaking trip he paddled out from Lee's Ferry on the Colorado last month was with longtime kayaking buddies. It took about a three-year wait to get the required river permit to navigate the canyon 226 miles downstream to Lake Mead.

His trip of a lifetime became the popular teacher's last outing. He died of a heart attack Thursday at Mile 207 on the river, according to his wife, Colleen Mehegan of Riverside.

James Mehegan, associate professor at Riverside Community College was well-liked by his students and had friends in the faculty and administration, said his wife, Colleen.

His death at age 52 has left colleagues at the Riverside campus reeling. The tall, energetic adventurer had arthritis and juvenile diabetes, but no history of heart trouble, his wife said.

"He had just finished swimming a rapid that is rated a six," she said, on a scale where 10 is most difficult.

His kayak capsized in rough water and he wasn't able to get back in, so he swam the rapid, retrieved the kayak and got back in. Friends told his wife he reached the shore and said he felt like he was having a heart attack.

"Being a geologist, the Grand Canyon was pretty much his favorite place on earth," she said by phone. "He was having the time of his life on the trip," in a group of about 16, some of them paddle mates for about six years.

RCC President Salvatore Rotella accompanied Dr. Mehegan on two field trips, one along the San Andreas Fault and another to the Long Valley caldera near Mammoth Lakes.

"He made every moment a valuable moment in terms of learning about geology," Rotella said by phone. "It's a way to teach science, it's almost the most Socratic way, by touching, seeing and feeling."

After a hilltop climb, students might gather round to talk about what they were learning.

Dr. Mehegan was scheduled to teach field studies about the Italian Alps and volcanoes in the college's study-abroad fall semester in Florence, Italy. Another faculty member will step in and teach another subject, but "it's just a tremendous loss" for the program, said Jan Schall, international education coordinator.

Dr. Mehegan was well liked by students and had friendships among faculty and administration, making him a good liaison between the groups, she said by phone.

He also was just elected vice president of the campus chapter of California Teachers Association. He earned bachelor's and master's degrees in geology from UCR and his doctorate from Dalhousie University in Halifax, Nova Scotia, Canada. He taught at Dalhousie and worked as a geologist and researcher before he joined the faculty at Cal State San Bernardino in 1988. He came to RCC in 1996 and was Physical Sciences Department chairman.

In addition to his wife of 15 years, he is survived by his mother, Evelyn of Moreno Valley; and three sisters, Alana Wiles of Nebraska, Pat of Tujunga and Elizabeth of New Hampshire.

Memorial services will be at 2 p.m. Monday at Olivewood Memorial Park in Riverside.

Riverside Community College Obituary