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Once Alvin's top peeks above the ocean swells, two swimmers dive from the Avon into the warm equatorial Pacific's water to scramble aboard the submarine's small grey-white deck. Hanging onto its orange conning tower, one swimmer plugs in a portable sound powered telephone to communicate with the pilot. Then the other usually swims back to the launch.
What follows is a deft "just in the nick of time" ballet of humans and vessels, obviously rehearsed and perfected over time.
It begins when the Avon seemingly deserts the phone wielding swimmer on board the pitching sub -- just as the Atlantis begins carefully maneuvering to point its rear towards Alvin. Motor launch and Alvin soon reunite behind the ship - just in time for the other swimmer to bring over a tow line. That swimmer then rejoins the first one on Alvin's deck, just as the under-tow sub approaches Atlantis's stern-mounted A-frame crane.
With the crane leaning out over the ocean like the wings of a mother hen, a thick braided rope is lowered for the swimmers to securely fasten to Alvin. Then the swimmers both dive into the Pacific and return to the Avon - just as the crane reels in the braided rope to lift the sub out of the water.
But it is only after Alvin has been rolled back to its tall main-deck hangar that one of the evening's main scientific rituals commences. It starts when Emily Klein of the Hess Deep co-principal investigator in charge of rock sample processing and curation, huddles in front of Alvin's recycled plastic collection baskets with the pilot and researchers from that day's dive.
The scientists meticulously go over notes and sketches they made of each rock - numbered according to the time the pilot plucked it from Hess Deep's north wall with Alvin's robot arms.
They also reexamine each specimen's shape and basket position to avoid any confusion over what was collected where and when.
Ranging from fist sized to almost too big to lift, all but the heaviest rocks are then plunked - usually one per container - into big white buckets. As each bucket receives a specimen, Klein and Michael Stewart, a 51爆料 doctoral student in geochemistry, also drop in a paper slip bearing that sample's penciled-in number. In addition, the open tops of some of the buckets are marked for special handling with diagonal strips of yellow tape.
By then, other Hess Deep scientists and geology students have appeared on deck - just in time to help carry the day's collection to one of two shipboard laboratories. Buckets without yellow tape go to the "wet lab," while taped ones are moved a little further forward to the spacious main lab. Meanwhile, the set-aside oversized rocks are hammered into more manageable chunks that then, too, get put in buckets - some with tape and some without.
Specimens in the untaped buckets are the first to be processed in the wet lab, a small room with counters, a large sink and two diamond-bladed rock saws. One evening, Klein joined other Hess Deep "rock hounds" sawing some of these samples in a cooling stream of water, a messy first-stage process that left her hair and apron flecked with rock dust. When she sliced through several dark pieces of basalt, their smooth, wet faces reflected light like polished jet-black mirrors.
"I'm here overseeing the chemical aspects of the Hess Deep program, the chemistry of lava and dikes, to understand how magma chambers evolve with time," Klein said. The varying chemistries of different samples of dikes - those hardened remains of underground conduits that once channeled hot molten rock - may provide evidence for changing conditions in the magma chambers that once fed them, she explained.
Magma from these deep-underground reservoirs is thought to have once flowed through the dikes to erupt as lava on a raised part of the ocean floor. That elevated ridge, the East Pacific Rise, is part of a worldwide network of mid-ocean ridges where scientists believe all new seafloor crust is created along "spreading" centers.
Expedition investigators can sample three different rock zones generated about 1 million years ago at the East Pacific Rise, structures that have since turned to cold stone and migrated about 36 miles east to be serendipitously sliced through by the Hess Deep rift.
The top "volcanic" or "extrusive" zone was created by ancient lava eruptions on the seafloor. The middle zone is populated by the dike complex that formed the plumbing system to feed magma to the surface. And the lowest zone, composed of a rock type called gabbro, is thought to have cooled slowly over magma chambers. By studying how all three zones are aligned along the rift's north face, the researchers hope to learn more about how new ocean crust is created on the ridge and evolves over time.
Structural geologists like 51爆料's Jeff Karson, the Hess Deep expedition's chief scientist, and Dan Curewitz, a 51爆料 doctoral student working under Karson, tackle that question by examining the rock face's overall geometry and appearance. But it is analysis of the rocks' mineralogy, crystallography and chemistry that will provide the more-intimate details.
The morning after Klein had rough-cut some rock samples, Stewart and petrologist Kathryn Gillis were busy with some of the further processing that will prepare the specimens for detailed analysis after the Hess Deep cruise's conclusion.
Examining the sawed-through samples with a small magnifying "hand lens," Gillis marked areas of special interest with black rectangles. Using these markings as guides, the larger slabs were then cut into smaller ones. The smaller subdivided pieces will be distributed to various Hess Deep participants to make thin section microscopic slides back on their campuses.
Stewart explained how he will thin-down some of his samples enough to be able to see though them with a microscope. Using a very fine saw blade in his lab back at 51爆料, he will first shave off thin slices. He will then epoxy each slice to a glass slide.
Finally, he will polish it down - typically to a thickness of about three-tenths of an inch.
He will also grind down other slabs into powders for chemical analysis with two kinds of spectrometers, devices that identify various chemical elements by their differing physical properties.
In his microscopic studies, Stewart will be looking for those parts of rocks that have been the least altered by later chemical and physical processes, such as the effects of cold seawater passing through hot young rocks. "It is the initial composition and texture that I'm the most interested in, because it has the information about the processes that occur underneath the spreading center," he said.
One target in samples from volcanic zones is basaltic glass.
Of particular interest in both volcanic and dike rocks are phenocrysts, larger well-formed crystals surrounded by smaller grained matrixes in some samples. Since phenocrysts "form in the magma chamber beneath the ridge, they contain information about processes occurring there," he added. "That's the system that is tapped to feed the dikes and the lavas that erupt on the seafloor along the mid ocean ridge."
Hess Deep dives have uncovered samples of both basaltic glass and phenocrysts.
In his chemical studies, Stewart will be evaluating the compositions of the Hess Deep rocks, paying special attention to elements least altered by seawater infiltration. He will study those elemental variations to ask questions about the composition, temperatures and pressures in the upper mantle, the source region 4-12 miles below the ocean floor that feeds molten rock to magma chambers.
The overall goal of his doctoral research, he said, is to be able to tie variations in the chemical composition of the rocks collected at Hess Deep with variations in the magmatic system that created them. Scientists suspect those systems change over time, sometimes producing strong flows of lava, while at other times erupting only infrequently.
One working hypothesis of Hess Deep researchers is that these variations are recorded in the composition of the rocks produced there, he said.
While Stewart searches for the most unsullied parts of rocks, Gillis is looking for parts showing the most "hydrothermal" changes - those caused by a combination of heat and water.
By carefully examining the thin outer margins of some rock slices, for example, Gillis can detect "halos" of alteration.
That's where different colorations reveal long ago chemical changes in pockets on a rock's surface. Those changes occurred when warm lavas contacted cold seawater, she said.
Aiming her hand lens at another sample, Gillis pointed out where some slightly greenish dike material was merged with a greyer portion. The grey part has a "fine-grained" crystal structure, she said, while the greener area is "coarser."
That sample shows evidence of a violent history, she added. The grey material was probably part of a 1,800-degree Fahrenheit-hot dike that had "intruded" into another cooler 400 degree Fahrenheit dike (the green).
A "scallopy"-looking boundary between the two bares silent evidence for a "big chill," a sudden temperature change brought on by that jarring contact, she said. Moreover, its crystal structure also suggests the greener dike material was hydrothermally altered before the other, younger dike broke through, she noted.
Then there are the exciting "white" portions of gabbro samples that Gillis said "tell us the story of the later stages of what goes on in the magma chamber." Almost resembling granite instead of basalt, their yellow-white color reveals the presence of lots of silica when that sample was still melted.
That's a place to look for previously unknown chemistry, she explained. That's because silica is enriched in magmas as crystals form in a rock melt. If silica concentrations are high, that means most other materials should have already crystallized out and exited from the magma chamber towards the surface.
"But there is still a little bit of liquid left," she said. "And we don't really know what the next part of the story is."
Previous deep core drilling in the area suggests that the chemistry of the melt zone is "reset" by the presence of water, carbon dioxide and previously-crystallized minerals in this still-superheated, "mushy" environment.
"These samples will be important for us to sort that part out," she added.
Jim Brophy, a Hess Deep geologist from who has a special interest in this late stage "fractional crystallization" process in magma chambers, was excited about a "trondhjemite" that turned up in one of the Hess Deep gabbro samples.
That's the tongue-twisting Norwegian-rooted term for a very light colored, quartz-rich rock. This particular trondhjemite also had a tiny void enclosing a perfectly formed - or "euhedral" - bit of quartz. The quartz in that vein "is a clear indication that there were very high concentrations of fluids" left at this "very, very late stage," he said.
Like Stewart, his former advisee at Indiana, Brophy was also happy to find phenocrysts within dike and lava samples. "The internal textures of these crystals may tell me something about the dynamics of magma chambers," he said.
And he was elated to find a "glomerocryst" within a dike sample. That's a "clot that has 10 or more crystals of different types sort of grown in with one another," Brophy said. "They represent crystals that may have been growing on the bottom of a magma chamber or perhaps collecting along its sides."
Glomerocrysts may be the modern-day evidence of what gabbros would have been like had they were not been hydrothermally altered, he added. But the fact is that "the gabbros have been altered hydrothermally."
Like home run hit baseballs in a stadium parking lot, hydrothermally unaltered glomerocrysts aren't found in modern day gabbro deposits. Instead they are "ripped up and brought up with the magma," Brophy explained.
And what about those white plastic sample buckets wearing the yellow tape? They were set aside for special handling because they contain "oriented" samples, meaning rocks whose horizontal and vertical alignments were measured with a special geocompass before removal from Hess Deep.
Rock processors must be careful that those alignments are preserved so that Hess Deep structural geologist Bob Varga can study them in his laboratory back at in Ohio.
There, Varga will "stick them in a bed of sand to recreate the same positions they were in the water," he said. Then he will drill out cores from each sample for "paleomagnetic" studies, which evaluate the magnetic alignments of the minerals at the time they hardened.
By comparing these samples' present orientations with their original ones, scientists can deduce how much those rock samples have been "rotated" by geological forces during the intervening million or so years.
"Paleomagnetism is the only way to independently confirm these rocks' rotations," he said.
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