WHAT’S HAPPENING ON THE R/V MELVILLE?
Science Report | Katy's Journal | Rick's Journal | Crew Entries
http://www.sio.ucsd.edu/supp_groups/shipsked/News/weeklyreport/weekly.html
From Scripps Institution of Oceanography
Archived Weekly Science Reports
02/19 | 02/26 | 03/05 | 03/12 | 03/19 | 03/26 | 04/02 | 04/09 | 04/16
R/V Melville,
Weekly Scientific Report #1, 2/19/01, Cook Leg 06:
While in port in Guam, the HMR1 side-scan system was loaded aboard the R/V Melville and a 3-component magnetometer was installed aboard the ship. The R/V Melville left port on the cruise "Cook 06" at 0600Z on 10 February, sailing west into the Mariana backarc basin. At 0705Z the SeaBEAM system was turned on and we began deployment of the Hawaii MR1 side-scan sonar system. Deployment of HMR1 went smoothly and was completed by about 1010Z. To date we have completed 1690 nautical miles of survey.
The side-scan sonar survey of the Mariana backarc region began with a westerly track across the spreading center to the deep grabens at the base of the West Mariana Ridge (the remnant arc) in order to define general abyssal hill fabric and collect magnetic and gravity data. Then we turned southeast to cross the basin again on a track perpendicular to abyssal hill fabric. We crossed the spreading ridge and turned southwest along the robust portion of the spreading ridge, using our 1997 R/V Moana Wave HMR1 survey as a guide. We then headed northwest to run several lines perpendicular to the spreading fabric, which is oriented northeast-southwest in this part of the basin. At 12°45'North we began a series of east-west lines covering the western half of the backarc basin, to complete the 1997 HMR1 survey of the region. The current survey will cover the western extension of the backarc basin from the spreading center to the West Mariana Ridge (the remnant arc) and will include the western extension of the volcanic arc. We will also survey the highly deformed forearc southward to the Challenger Deep, providing the first side-scan sonar images of the deepest part of the Mariana Trench at a resolution high enough to make detailed geologic interpretations.
To date, we have discovered the westernmost extent of the spreading in this portion of the basin. It ends in a seismically active basin at 12°25'North, 141°50'East. A seismically active portion of the western-bounding fault of the backarc basin (12°25'North, 140°50'East to 12° 35'North, 141°45'East) forms the northern boundary of a 5400 meter deep graben (Becker Deep) west of the western tip of the spreading axis. The throw on this fault is over 3400 meters over much of its length. The graben is floored by low backscatter terrain, probably sedimented. There is one small volcanic edifice at the base of the graben-bounding fault within the graben and one larger composite cone in the western central part of the basin. At its western end the graben-bounding fault splays out into a series of fault traces arcing southward (concave to the southeast). Several volcanic centers have formed along the traces of the splayed faults at the western end of the graben. The shallow region south of the Becker Deep includes several volcanic edifices shallower than 2000 meters. One has a series of four apparent silicic domes aligned in an east-west chain. Another is a large volcanic center, apparently no longer active, that has a caldera at least eight kilometers in diameter. The shallow region of the survey area is highly faulted by traces oriented east-west and northeast-southwest. There is a strong magnetic anomaly associated
with the east-west lineaments. We anticipate that the forearc southward from the regions already surveyed will show an increasing degree of deformation. If the style of deformation discovered in the inner trench slope survey in 1997 is continuous westward from 143°East, as we suspect, then it involves the inner trench slope all the way to the Challenger Deep.
We are using the Smith and Sandwell gravity derived bathymetry data set as a base map for this survey. The degree of agreement between the broad highs and lows on the Smith and Sandwell data set and the much more detailed HMR1 side-scan imagery is reasonably good. However, there are major volcanic features present in the side-scan data that do not appear at all on the gravity derived bathymetry and the trends of features such as the spreading ridge and the major faults are completely indiscernible. The tectonic interpretations we have been able to make are only possible with the higher resolution data.
Dr. Patricia Fryer (Chief Scientist), University of Hawaii
R/V Melville,
Weekly Scientific Report #1, 2/26/01, Cook Leg 06:
We completed the HAWAII MR1 survey of the southern Mariana Trench region on. The data collected include complete bathymetric and imagery coverage of the backarc basin, arc, forearc and trench regions of the convergent margin system south of 13°N. This includes high-resolution side-scan imagery of the Challenger Deep. We also collected gravity and magnetics data throughout the survey area. The HMR1 mapping system was recovered on Feb. 23 and the sampling portion of the cruise began with a series of dredges on bathymetric highs. Recovery included manganese encrusted reefal limestone from morphologically striking features, a series of thick platforms with discrete oval growths currently at depths of from 1500 to 3000 m and from 1 to 2 km diameters. A steep fault slope bounding the eastern side of the West Mariana ridge yielded a variety of volcanic and upper crustal material of diverse compositions. A spreading center feature in the western part of the backarc basin ridge crest yielded fresh lavas from two small volcanic sites. Wax cores from elsewhere along its length recovered fresh volcanic glass. Between the sampling sites the Seabeam was used to fill in gaps in the HMR1 bathymetry coverage over shallow areas.
The survey data was merged with an HMR1 data set collected in the eastern half of the backarc basin, arc and forearc areas to just oceanward of the Mariana Trench axis. The resultant data set shows the tectonic elements of region. These include a highly deformed forearc, the fragmentation of older volcanic arc centers just inboard of the forearc, the structure of a robust spreading ridge province in the eastern backarc basin, and a more normal spreading center in the westernmost portion of the backarc basin, an unusually deep graben in the narrow western tip of the basin and several horsts that likely separated from the West Mariana Ridge. This separation probably occurred recently because numerous earthquakes occur along its length. These faults have first motion solutions indicative of normal-faults.
Dr. Patricia Fryer (Chief Scientist), University of Hawaii
R/V Melville,
Weekly Scientific Report #1, 03/05/01, Cook Leg 07:
We left Apra harbor on schedule March 4 and began immediate deployment of HAWAII MR-1 towfish to image the Mariana arc and backarc basin system. Along with the Lau-Tonga system in the SW Pacific, the Mariana arc-backarc basin system defines the classic arc-backarc basin system and the extensional endmember of Earth's convergent plate boundaries. The Marianas are part of the 3500km-long Izu-Bonin-Mariana convergent plate margin that stretches from Japan to Guam and which has been targeted for focussed studies under the Subduction Factory experiment of NSF's MARGINS program. Our 6-week long scientific program consists of regional remote sensing of the seafloor using the HAWAII MR-1 sonar swath-mapping system followed by dredging, to test the hypothesis of sequential melting at convergent margins which have active magmatic arcs and back-arc basin seafloor spreading. Scientific party consists of 4 HMR-1 scientists from the University of Hawaii (led by Dr. Margo Edwards), 7 students and senior scientists from the University of Texas at Dallas (led by Chief Scientist R. J. Stern). Two members of the UTD team are Geosciences undergraduate students (Adam Robinson and Jill Shipman). Three members of the UTD team provide a Science Education component that is bringing a near-real-time Oceanography/Marine Geology experience to Dallas-area schools (Prof. Homer Montgomery (UTD Science & Math Education Dept.) and teachers Rick Ford (Keller ISD) and Katy Myrick (Garland ISD). UTD Geosciences graduate student Trey Hargrove rounds out the UTD team. U. Edinburgh graduate student Theo Edwards has been a most welcome addition to the scientific team.
The first week has gone very well indeed. The seas have mostly been smooth and we have been able to tow H-MR1 at 9 knots, about 10 miles per hour. We have been running long E-W lines (125 to 200 km) extending from the line of submarine arc volcanoes westwards across the back-arc basin spreading axis, beginning west of Guam and proceeding northwards. We work around the clock, with 3 4-hour shifts made up of 2-3 watch-standers. We have mapped from the latitude of Guam (13d30'N continuously as far as 15d N), covering about 20,000 sq km this week. Mapping includes 130 km of the slow-spreading Mariana Trough and 10 submarine arc volcanoes. This is the first time that the details of the seafloor of this region have been revealed. This work also completes mapping of the Mariana Trough spreading axis, which is shown to have the classic rift-like morphology of a slow-spreading ridge. Several new submarine volcanoes have been identified and mapped. We plan to sample the ridt axis and submarine volcanoes by dredging during the second half of the cruise.
We have also discovered channels cut into bedrock of the frontal arc ridge at depths shallower than 1500m. We speculate that these channels may have been carved during subaerial exposure of the frontal arc ridge caused by broad uplift. This uplift may have accompanied rifting, 3 to 7 million years ago.
The ship's crew has been having good luck fishing, and sashimi has been a welcome addition to lunch and dinner. Today's highlight was a birthday party for Katy Myrick, with a delicious raspberry-vanilla cake baked by the ship's cook, complete with candles, which Katy successfully extinguished. After a round of 'Happy Birthday to You', a healthy slice of cake and ice cream was enjoyed by all.
Dr. R.J. Stern (Chief Scientist), The University of Texas at Dallas
R/V Melville,
Weekly Scientific Report #1, 03/12/01, Cook Leg 07:
Mapping of the southern Mariana Arc system with HMR-1 swathmapping and imaging towfish has been successfully completed. We also mapped and imaged the Diamante cross-chain and cross-chains west of Guguan Island at 17d20'N, our most northerly point on this leg. Return to the south along the Mariana Trough backarc basin spreading axis has allowed us to image the spreading axis from 17d20'N to 13d30'N, the axial rift of which varies in depth from 3000 to 5000m and is characterized by an intermittent neovolcanic zone. This completes the imaging portion of the Bloomer/Stern portion of Leg 7. HMR-1 has performed flawlessly and all credit belongs to the HMR-1 imaging team, led by Dr. Margo Edwards of the University of Hawaii. The seas have been calm and the week has passed without major problems, due to the tireless and good-natured efforts of Captain Curl, Res Tech Bob Wilson, and crew of the Melville. We now begin 5 days of imaging the Mariana forearc east of Guam, Dr. Patty Fryer PI. Dr. Fryer is also participating in ODP Leg 195, now drilling a serpentine mud volcano east of Guam. We originally planned to transfer Dr. Fryer from the JOIDES Resolution to the Melville on March 17 but unforseen drilling difficulties require her to stay aboard the drillship. Mr. Nathan Becker, a graduate student studying under the supervision of Dr. Fryer, has taken over her duties as chief scientist from now until we dock in Guam on March 23 to offload the HMR-1, exchange scientists and Res Techs, and begin dredging the volcanoes imaged with HMR-1.
Dr. R.J. Stern (Chief Scientist), The University of Texas at Dallas
R/V Melville,
Weekly Scientific Report #1, 03/19/01:
Coming soon…
R/V Melville,
Weekly Scientific Report #1, 03/26/01:
Melville arrived in Guam on March 23 and offloaded Hawaii's HMR-1 system. The surveys yielded near complete side scan coverage of the arc and back-arc south of 16oN. The HMR group departed, with hearty thanks from the chief scientists, and we sailed on the morning of the 24th. We sampled WSW of Tracy Seamount and then up the axis of the back-arc rift from 13o30'N to 14o30'N. We then worked eastward along a cross-chain of arc volcanoes and into the main arc front. We have been working around Esmeralda Bank the last two days, and are now moving north towards an arc cross-chain west of Guguan Island.
We have completed 32 dredge lowering and eight glass core samples. The weather has been remarkably good, though the days have not passed without incident. A very unusual wire snag on D23 cost us a dredge and pinger, and the port thruster fell ill and has gone on holiday for the remainder of the cruise. We are consequently picking our dredge courses carefully and cruising at a leisurely 8 knots.
Most of the cross-chain arc volcanoes and subsidiary volcanic structures we have dredged are inactive, but have yielded interesting samples. There are a number of relatively mafic olivine-plagioclase phyric basaltís, as well as andesites, dacites, and a variety of volcaniclastic rocks. Olivine and clinopyroxene-rich ankaramitic rocks have been recovered from the southern flanks of Esmeralda Bank and Ruby Seamount. The pipe dredge was successful--in fact a bit too successful, as we had a hard time dealing with 200 kg of cold, wet mud. A couple minor modifications to one of the dredges (small pipe catchers on the side and a weighted plastic bucket in the chain bag) have yielded more modest, but very useful, sediment and volcaniclastic samples in many hauls. We are now at 15degrees55'N. …
R/V Melville,
Weekly Scientific Report, 04/02/01:
We are steaming west
at 14d20'N to complete our sampling of the southern Mariana Trough spreading
center. We have just completed mapping
and sampling a large volcano at 14o20' N, 145o20'E. We recovered large volumes of pumice and evidence of extensive
silicic eruptions, presumably related to collapse and formation of a
substantial (5 km x 3 km) caldera. As at some of the other large calderas,
there quite mafic lavas recovered from the flanks of the edifice. We will come back east tomorrow afternoon,
towards Guam, and sample the two southernmost large seamounts in the Mariana
arc before entering Apra Harbor on Thursday morning. Our last dredge should be
completed an hour from the buoy.
Our return to the southern reaches of the arc has greatly improved the
fishing, and grilled mahi mahi and sashimi are on the evening menu. The weather has remained lovely and our work
has gone very smoothly. The Melville
has proved, as usual, to be a very able vessel for marine geological
sampling. Her crew has been superb,
providing very professional seamanship, good company, and a remarkable
willingness to improvise, innovate, and explore. It has been a real pleasure to work with them.
A summary of our principal scientific results to date follows. We've
come away with enough survey data and rock samples to keep ourselves and many
of our colleagues busy for some time.
We have studied the southern Mariana Arc system intensively, with a
focus on volcanoes along the magmatic arc and associated cross-chains. Sonar backscatter imagery of about 15,000
square miles or 50,000 square kilometers was obtained with the towed HMR-1
sonar towfish. This allowed us to image
28 submarine volcanoes of the Mariana arc which had not been previously
studied. We also imaged the spreading
axis of the Mariana Trough from 13d45' to 17d30', about half the length of this
slow-spreading ridge. In addition, we
sampled the back-arc basin extension axis from 13d20'N to almost 15d N, which
completes a first-order along-axis sampling of this archetypal example of a
back-arc basin spreading axis.
Our survey of 450 km along the arc magmatic axis, from 13d30'N to
17d20'N, indicates that these volcanoes vary widely in volume, from a third to
1000 cubic kilometers. They are
constructed on abase that ranges in depth from 1000 to 3000 meters, are from
200 to 2700m in height, and are spaced at distances of 7 to 45 km. The average volcano along the Mariana
magmatic front is spaced 20km from its neighbor, is built on a platform that
lies at 1800m below sealevel, rises 1000m above this platform, and occupies a
volume of about 200 cubic kilometers.
Lavas collected from 24 edifices along the magmatic front include
abundant basalt (many with olivine) and dacite; we also collected several
cumulate gabbroic xenoliths. Phenocryst
phases are dominated by plagioclase, olivine, pyroxene and hornblende.
Five of the volcanoes in the study area - the islands of Guguan,
Sarigan, and Anatahan, and the submarine edifices of S. Ruby and Esmeralda -are
active. The other volcanoes are extinct
or dormant, and our study suggests that, to a first approximation, the smaller
the edifice, the less likely it is to be active. Some extinct edifices have
flat summits at depths that range from 40 to 300 m that are capped with coral,
or, farther north in the study area, shelly material or carbonate sand. These are guyots, although smaller and much
younger than the drowned carbonate platforms that formed in the Western Pacific
during the Cretaceous period. Those we
have found in the Marianas probably drowned during Pleistocene time and provide
opportunities for others to study how guyots form.
Volcanoes extending westward from the magmatic front were an important target of our survey. A major cross-chain of small volcanoes along 14d40'N was studied and
sampled for the first time. These
volcanoes yielded a range of lavas, from basalt to dacite. Volcanoes from
another cross-chain, extending along 17d20'N latitude west of Guguan, yielded
only basalt. Shorter cross-chains were
also studied in the Diamantes and near Sarigan. Comparisons of lava compositions will provide the basis for us to
test the hypothesis that convecting mantle is sequentially melted first beneath
the back-arc basin spreading axis and then under cross-chains and finally under
the volcanoes along the magmatic axis.
This provided the philosophical basis for our work, sponsored as part of
the Izu-Mariana-Bonin "Subduction Factory" experiment of NSF's
MARGINS initiative. Recovery of basalts
which have not experienced a lot of fractionation was an important objective of
our sampling, and HMR-1 imagery was very useful for identifying basaltic
parasitic cones and associated flows as dredge targets. Using this imagery allowed us to recovered a
large number of aphyric and sparsely phyric olivine basalts.
We recovered abundant pumice from 6 volcanoes in the northernmost 100km
of the arc. Each volcano yielded a
homogeneous and compositionally distinctive suite. This fact, coupled with the large size and angular shape of
pumice blocks, indicates that these pumice hauls are in situ. These dredges were made at depths of 800 to
1700m, indicating that vesiculation to form pumice can happen when felsic lavas
erupt at relatively high pressures.
These hauls also reinforce the idea that felsic magmas are a much more
important part of the Mariana arc system than previously appreciated. Another interesting feature related to
igneous activity in the region is unusually thick crusts of Mn- and other
oxides. This probably manifests
hydrothermal activity in the vicinity of these deposits.
Our surveys traversed active areas of sediment deposition between the
active arc and the back arc basin.
Here, the sediment-covered seafloor is the upper surface of a
volcaniclastic 'apron' that slopes westward at 2-4 degrees and buries the
igneous infrastructure of the arc and the join between arc and backarc basin
crust. The HMR-1 imagery revealed two
features on the seafloor that provide important clues about how sediments move
west from sources around the active volcanoes.
A 160 km2 tract on the western flanks of Esmeralda Bank is composed of
dunes with a wavelength of about 1km and an amplitude of 20m. This dune field
formed by westward flow of sediments, due either to bottom currents, explosive
volcanic surge, or collapse of parts of the volcanic edifices. We dredged one of these and recovered
volcanic sand, silt, and mud. A channel
system, well-defined on the seafloor to depths of 3800 m, extends 60 km from
the northern slopes of Guguan. The
channel flows down a slope of a few degrees and is up to 2km wide and 70m
deep. This channel is presumably occupied
episodically by turbidity currents, the abyssal equivalent of "flash
floods".
Sampling in the back-arc basin spreading axis recovered fresh glassy
basalts from ridge segments shallower than 4000m but was largely unsuccessful
for deeper ridge segments, where the igneous basement appears to be buried
beneath sediments. Serpentinites and
metagabbroes were recovered from rift wall exposures near 14d36'N.
This study largely completes our mapping and sampling of the submarine
Mariana arc and back-arc basin system, begun in 1985.
R/V Melville,
Weekly Scientific Report, 04/09/01:
Coming soon…
R/V Melville,
Weekly Scientific Report, 04/16/01:
Coming soon…
This cruise is being funded from a grant
from the National Science Foundation.
We asked several of our shipmates to write a "guest journal entry" for us.
Hello from somewhere in the western Pacific off the coast of Guam. Today is our last day out at sea. Where do I begin?
Let's start with a little background. My name is Claire McKee. I am a graduate student at Oregon State University pursuing a master's degree in volcanology and geochemistry. My master's research involves studying a volcano in the Andes of northern Chile, South America. I have been to my field area twice to study and map volcanic landforms and collect volcanic rocks for analytical research. I will defend my master's degree this summer and hope to continue on in education. I plan to pursue a teaching position either at the high school level or possibly continue on for a PhD in geology.
I am originally from Columbus, Ohio and completed my undergraduate degree in geology at Miami University in Oxford, Ohio. The mountains and coast drew me to Oregon, much to my parent's dismay.
So that brings me to why am I here aboard the Melville? Well one day, while sifting through my e-mail messages, a message popped up on the screen that looked especially interesting. The message read something like, "in search for graduate students to assist in research along the Marianas Arc, western Pacific." You can imagine my excitement. I immediately wrote back expressing my interest in the cruise.
So, that's how I ended up here on this crazy big boat. This is my very first sea-going experience. It's been great! Not only has it been an awesome compliment to my own research studying land-based volcanoes, it's also been a ton of fun. I've met the greatest people onboard. The shipboard scientists and crew are an eccentric bunch. We get along famously. At first, I didn't know what to expect especially concerning the crew. I always imagined shipman to be rough around the edges, with patches on their eyes, crooked teeth, and a parrot on each shoulder. Not quite accurate. They actually have great hygiene. We're from all around the world, scientists from Japan and Great Britain, Canada and the U.S. The collaborating universities include University of Texas at Dallas, Oregon State University, and University of Hawaii. The crew come from the states, Russia, the Phillipines. After three weeks together, we've learned lots about one another.
I remember seeing the ship for the first time at the naval base in Guam... thinking to myself... wow it's really not that big. Three weeks, huh? Hope I don't get seasick, or experience cabin fever, or want to jump ship. No problems to speak of. The seas have been calm. The skies have been sunny. I lucked out with the noon to midnight shift. My daily routine...wake up, workout on the ship stairmaster, lay out on deck for a half hour or so, eat lunch, report on duty, work until midnight, go to bed, and awake to a new day. My favorite part of the day, well all of it really. No complaints from me.
I
really love the people on my watch.
We've become great friends and will hopefully continue to keep in touch
after the cruise. Our days consisted of
dragging a dredge along the seafloor with the hopes of sampling volcanic rocks
from the Marianas Arc. We spent lots of
time identifying rocks and minerals that the dredge brought up and distributing
rock samples to the shipboard scientists.
There would occasionally be adequate downtime for a movie, or a game of
trivial pursuit.
Well, my time at sea is drawing to a close and so must this e-mail message. I have mixed feelings about heading in to port. I will miss the Melville and my time here, but will enjoy sleeping in a bed that doesn't rock and roll in the swaying seas. Hope this gives you a good feel for our adventures. - Claire
Hi, my name is Amy and I have been on Katy's watch since I came onboard
the Melville three weeks ago. I'm from Boston, and am looking forward to going
home to catch the last couple of weeks of the ski season up in New England; I
hear they have been having a great ski season with more than 300 inches of snow
falling in some places!
While I was at Colgate University I began to be interested in Geology,
and eventually majored in it. When I started college I had no intention of
majoring in Geology; I'm not really sure I knew it was a major offered! At
first I thought I wanted to become a doctor, then I wanted to major in
Political Science or History, then a friend of mine suggested I take a geology
course since I liked the outdoors and hiking. I took one course and was hooked.
I loved the fact that during most "lab" classes we would go traveling
around the Central New York countryside and hike. The professors in our
department were really cool. They made you call them by their first names and
often had us over to their houses for bbq's. During the spring of my junior
year I decided to go "abroad" and participate in a semester-long
program named SEA Semester. It is not like the Semester at Sea program you
might have seen on MTV's Real World a couple of years ago where they traveled
around the world on a cruise ship. This program consists of spending 6 weeks
taking classes in Woods Hole Massachusetts (on Cape Cod) and then sailing on a
big sailboat in the Caribbean. Each person in the program designed a research
project and we spent our time collecting the data for their projects. The
equipment we used were much like the things we use aboard the Melville. For my
project I studied two carbonate reef systems, one that was considered healthy
and one that was failing. We did some dredging and took some cores of the area;
we also measured the temperature, salinity, and certain chemical components in
the water. We were trying to figure out what may be causing the survival and
failure of each system. When I came back from that semester, I was very
interested in learning more about marine geology.
The summer after I did Sea Semester I went on a
field camp with the other geology majors and our professors. The professors
team taught us for a couple of months. We studied certain areas of Central New
York and Northern Vermont, then we went out west to Utah, Arizona, New Mexico,
and Colorado. We hiked and learned about the geology of Canyonlands, Arches,
Zion, Bryce Canyon, and the Grand Canyon National Parks. It was an amazing summer;
we saw such beautiful sights in nature and learned about the processes that
created them. The following year, during my senior year, I took a class in
structural geology (where you study faults and processes related to the
movement of our tectonic plates) and decided I wanted to become a marine
structural geologist. The year after I graduated from Colgate I traveled to
Australia and New Zealand while I applied to graduate schools. I decided to
enroll in the joint program in oceanography that is run by M.I.T. and Woods Hole
Oceanographic Institute. For two years I lived in Boston and took classes at
M.I.T. and commuted to the Cape to do research. At the end of those two years I
moved down to the Cape to finish my research. My research combined my interest
in the ocean and my interest in structural geology; I studied the faulting
structure along the Mid-Atlantic Ridge.
As you may have learned, the tectonic plates that comprise the crust of the earth move around and are pushed and pulled by certain mechanisms. When plates come together you can have them push together and well up in a big pile (like the Himalayas are created by the plate that India is on colliding with the plate that China is on) or you can have one go under the other (like the plate that contains the Pacific Ocean is going under the South American plate) which is called subduction. When plates come apart, you create ridges - places where the empty space created by the separation of the two plates is filled with hot magma which cools and becomes part of the plate. Studies have shown that the force created by subduction (pull) is greater than the force created by the upwelling of the magma (push). Therefore, subduction of the plates is what mostly controls the pulling apart of the plates. In a perfect world, the space created by the pulling apart of the plates would be filled with new magma; this is what is taught in most geology classes. However, when there isn't enough magma to fill these voids some mechanism other than magma upwelling at the ridge must occur. This is what I studied in graduate school. It turns out that what people think is happening in situations like this is a special kind of low angle faulting. A similar mechanism created the Basin and Range province in the United States. As a result of this faulting, large domes are created along the ridge and in old ridge crust (that has now moved away from the ridge axis due to the continued pulling apart of the plates). Scientists don't really know what type of rock comprises these domes and they are trying to figure that out as I write this message on another research cruise way off the coast of Florida.
Well, I guess I should finish up this brief summary of my career in geology. I hope I haven't bored you all too much! I also hope Katy and Rick's experiences aboard the Melville have inspired some of you to think about studying science once you get out of High school; it is definitely a fun thing to do, and you get to travel a lot!! Take care! - Amy