Monterey Bay Aquarium Research Institute


Los volcanes y los montes submarinos
Diario de campaña
DÍa 10: Rocas raras en la cordillera Alarcón
Abril 30, 2012

En algunas de las entradas que se han hecho en la bitácora se ha mencionada la relación jóven/viejo así que el día de hoy voy a explicar cómo obtenemos esta relación utilizando lo que llamamos fechado relativo.

Para familiarizarnos con los términos usados en fechado relativo utilizaré un ejemplo; si le preguntamos a una persona que nos diga lo que hizo el día anterior pero que las actividades realizadas nos la diga en una manera desordenada, tal vez su respuesta sería; cena, desayuno, correr, televisión, restaurante, levantarse temprano, regresar a casa, bañarme, trabajar, irme a dormir, regresar al trabajo. Estas palabras realmente no tendrán sentido y no podremos saber realmente lo que hizo el día de ayer. Pero si le pedimos que nos vuelva a decir lo que hizo pero ahora de una forma ordenada empezando por la mañana y terminando por la noche, tal vez su respuesta será; me levanté muy temprano por la mañana y fui a correr, cuando regresé a casa desayune y luego me bañe. Posteriormente me fui a trabajar y comí en un restaurante, luego regresé al trabajo, cuando termine de trabajar regrese a casa, cené, luego vi un poco de televisión y finalmente me fui a dormir.

Ahora todas estas palabras tienen sentido y finalmente sabemos que hizo desde el momento en que se despertó hasta el momento que se durmió. Esto que acabamos de hacer es un fechado relativo, es decir, sabemos que hizo y se han ordenado cronológicamente todos los eventos que sucedieron ese día. Si nosotros le preguntáramos a esta persona cuando vio televisión, su respuesta podría ser; a) después de cenar, b) antes de irme a dormir o c) después de cenar y antes de irme a dormir. Si la respuesta fue después de cenar él está diciendo que el evento más joven (ver televisión) sucedió antes del evento más viejo (cenar), si la respuesta fue antes de irme a dormir está diciendo que el evento más viejo (ver televisión) sucedió antes del evento más joven (dormirse) y si su respuesta es que después de comer y antes de irse a dormir, lo que esta haciendo es colocar el evento de ver televisión entre un evento más viejo (después de cenar) y antes de un evento (irse a dormir). Esto es establecer relaciones joven/viejo, conocer que sucedió antes y que después.

Las personas que estudian la historia de la tierra hacen exactamente lo mismo para conocer el orden en que se dieron los eventos en la historia de la tierra. ¡Hagamos un pequeño ejercicio de fechado relativo geológico! Supongamos que alguien nos pide hacer el fechado relativo del bloque geológico que aparece en la figura 1.

figure 1
Figura 1: Apariencia hipotética de un bloque geológico.

Empezaremos diciendo que en un primer momento se depositaron los estratos A a E, siendo el estrato A el más viejo (primero en depositarse)y el estrato E el más joven (el último en depositarse—Figura 2).

figure 2
Figura 2: Manera en que los estratos debieron depositarse originalmente.

Después se dio una falla que desfasó los estratos de manera vertical como se muestra en la figura 3.

figure 3
Figura 3: Después de que los estratos se depositaron se sucedió una falla que desfasó los estratos de manera vertical como se muestra en la figura.

Y con esto ya realizamos el fechado relativo de los eventos que dieron origen al bloque mostrado en la figura 1. y que podemos resumir de la siguiente manera:

  1. Depositación del estrato A (que aparece solamente después de que se presentó la falla ya que antes se encontraba bajo el estrato B)
  2. Depositación del estrato B
  3. Depositación del estrato C
  4. Depositación del estrato D
  5. Depositación del estrato E
  6. Fallamiento

Y de esto se trata el fechado relativo. De esta manera podemos dar respuestas a preguntas como; a) ¿Cuando se dio la falla? La respuesta es después de la depositación del estrato E (porque la falla está rompiendo todos los estrato incluyendo el estrato E, b) ¿qué tan vieja es la falla? Definitivamente más joven que la edad del estrato E ya que se presentó una vez que este estrato ya estaba depositado. ¿Te das cuenta de la importancia del fechado relativo cuando se trata de poner orden a los eventos o procesos geológicos para comprender la historia de la tierra?

Ahora que sabes como se hace un fechado relativo para determinar las relaciones joven/viejo te debes estar preguntando si es posible asignar una edad específica a cada uno de estos eventos. ¡Esto sería interesante!

Bueno, permítanme decirles que los geólogos tienen una manera de asignar edades a los eventos utilizando una técnica que se llama fechado absoluto o radiométrico. Esta técnica se basa en el estudio de isótopos radioactivos, cuando se forma un mineral, algunos de ellos contienen isótopos radioactivos que pueden ser utilizados para asignarles una edad rocas. Imagínate que compras un reloj y que a las 12 de media noche le pones una batería que tiene un tiempo de vida de 12 horas, cuando le pones la batería al reloj éste empieza a funcionar, si queremos saber que hora es simplemente vemos la hora que marca el reloj. Supongamos que marca las 6:00 pm. Otra manera en la que podríamos saber la hora es quitándole la bacteria y midiendo la carga que le queda, si tenemos solo un 50% de la carga significa que son las 6:00 Pm ya que si el tiempo de vida de la batería era de 12 horas y tiene sólo el 50% de la carga, significa que han pasado 6 horas. Los isótopos radioactivos que encontramos en los minerales trabajan de la misma manera, empiezan a funcionar como relojes cuando se enfría el magma formando rocas. Si en nuestro ejemplo de fechado relativo tuviésemos rocas en cada uno de los estratos que contuviesen minerales radioactivos podríamos asignarle una edad a cada roca y por lo tanto saber tanto el orden en que se dieron los eventos (fechado relativo) como el tiempo en que se dieron (fechado absoluto). Precisamente esto es lo que están hacienda los científicos a bordo del barco Western Flyer para tratar de descifrar la historia volcánica de la cordillera Alarcón.

—Rigoberto Guardado

Previous log

Volcanoes & Seamounts
 Equipment

R/V Western Flyer

The R/V Western Flyer is a small water-plane area twin hull (SWATH) oceanographic research vessel measuring 35.6 meters long and 16.2 meters wide. It was designed and constructed for MBARI to serve as the support vessel for ROV operations. Her missions include the Monterey Bay as well as extended cruises to Hawaii, Gulf of California and the Pacific Northwest.

ROV Doc Ricketts

ROV Doc Ricketts is MBARI's next generation ROV. The system breaks new ground in providing an integrated unmanned submersible research platform, with many powerful features providing efficient, reliable and precise sampling and data collection in a wide range of missions.

Push cores

A push-core looks like a clear plastic tube with a rubber handle on one end. Just as its name implies, the push core is pushed down into loose sediment using the ROV's manipulator arm. As the sediment fills up the core, water exits out the top through one-way valves. When the core is pulled up again, these valves close, which (most of the time) keeps the sediment from sliding out of the core tube. When we bring these cores back to the surface, we typically look for living animals and organic material in the sediments.

Niskin bottles

Niskin bottles are used to collect water samples as well as the tiny bacteria and plankton in that volume. The caps at both ends are open until the bottles are tripped, when the caps snap closed.


Biobox

The box fits in a partition in the sample drawer. It is shown open, with an animal being placed into it by the ROV's manipulator. When the lid is closed, the box will hold water to protect the animals inside.


Rock crusher

This device is used to collect volcanic glass fragments from the surface of a flow. It is made of about 450kg of lead and steel and is launched over the stern of the ship on a wire. Fragments of rock that break off of the lava flow on impact are trapped in wax-tipped cones mounted around the crusher. The wax is melted in the lab to liberate the rock particles for analysis.

Benthic toolsled

The benthic toolsled is attached to the bottom of the ROV for our geology dives. Its components are the manipulator arm and the sample drawer. The sample drawer is shown open on deck, full of rocks. Normally it is closed when the vehicle is operating and is opened only when a sample needs to be stowed. Partitions in the drawer help us keep the rocks in order. The rocks often look alike, but the conditions and chemistries of the eruptions are different so it is important that we know where each came from.

Glass suction sampler

This equipment is used to vacuum glass particles and larval animals from cracks and crevices. The carousel of small plastic jars fitted with wire mesh will be mounted in the benthic toolsled. The hose will be held by the ROV's manipulator and a suction will be drawn by the pump.

Sediment scoops

Canvas bags on a T-handle for collecting gravel or other materials that fall out of a push-core.


Temperature probe

Held by the ROV's manipulator, the wire on the right is placed into the fluid emitted from a hydrothermal vent to record the temperature.


Vibracores

Vibracoring is a common technique used to obtain samples from water-saturated sediment. These corers work by attaching a motor that induces high frequency vibrations in the core liner that in turn liquefies the sediment directly around the core cutter, enabling it to pass through the sediment with little resistance.


 Crew

R/V Western Flyer

Ian Young
Master


 

George Gunther
First Mate


 

Matt Noyes
Chief Engineer


 

Andrew McKee
Second Mate


 

Lance Wardle
First Engineer


 

Shaun Summer
Relief First Engineer


 

Olin Jordan
Oiler


 

Craig Heihn
Relief Deckhand


 

Jason Jordan
Relief Deckhand


 

Dan Chamberlain
Electronics Officer


 

Patrick Mitts
Steward


 

ROV Doc Ricketts

Knute Brekke
Chief ROV Pilot


 

Mark Talkovic
Senior ROV Pilot


 

Randy Prickett
Senior ROV Pilot


 

Bryan Schaefer
ROV Pilot/Technician


 

Eric Martin
ROV Pilot/Technician


 

 Research Team

Dave Clague
Chief Scientist
MBARI

Dave's research interests are nearly all related to the formation and degradation of oceanic volcanoes, particularly Hawaiian volcanoes, mid-ocean ridges, and isolated seamounts. Topics of interest include: compositions of mantle sources for basaltic magmas and conditions of melting; volatile and rare-gas components in basaltic magmas and their degassing history; chronostratigraphic studies of eruption sequence and evolution of lava chemistry during volcano growth; subsidence of ocean volcanoes and its related crustal flexure, plate deformation, and magmatic activity; geologic setting of hydrothermal activity; origin of isolated seamounts; and monitoring of magmatic, tectonic, and hydrothermal activity at submarine and subaerial volcanoes.

Jenny Paduan
Research Specialist
MBARI

Jenny works with Dave Clague in the submarine volcanism project, processing the high-resolution MBARI mapping AUV data and interpreting the maps using ROV observations and samples from our research sites. On this cruise, she will stand watches in the ROV control room, help with rock and sediment sample workup and curation once the vehicle is on deck, and coordinate these cruise logs. She is now quite solidly a marine geologist, but her degrees are in biochemistry (Smith College) and biological oceanography (Oregon State University). She is thankful for the opportunities that have led her to study volcanoes, and loves being involved with the research and going to sea. She looks forward to discovering more about how Earth works.

Lonny Lundsten
Senior Research Technician
MBARI

On this cruise, Lonny will be in charge of biological sample collection and processing and video data management. This work entails identifying unique biological and geological features that will be seen during the dive, while using MBARI-designed software to log the observations. He is especially excited about this expedition, because no one has surveyed this particular seamount before, and he expects to find many new species on this cruise.

Julie Martin
Senior Research Technician
MBARI

Julie works with the submarine volcanism group, where she currently produces high resolution maps of the seafloor that are used to identify geologic features along submarine ridges and seamounts. Her research interests also include modeling of volcanic ash from sub-aerial, large-scale explosive eruptions.

Ryan Portner
Postdoctoral Fellow
MBARI

Ryan's work with the submarine volcanism project primarily focuses on the formation and distribution of volcaniclastic deposits on active and extinct seamounts and mid-ocean ridges. By categorizing the diversity in these deposits with respect to volcanic landforms he hopes to better understand the underlying controls on explosive vs. non-explosive deep marine eruptions. His background research on deep-marine gravity flow deposits preserved in sedimentary-volcanic successions exposed on land lends a comparable platform to study similar deposits of the modern oceans.

Julie Bowles
Collaborator

Julie is a Research Associate and Staff Scientist with the Institute for Rock Magnetism at the University of Minnesota. As a paleomagnetist, Julie studies variations in Earth's magnetic field and how those variations get recorded in rocks and sediments. One of Julie's particular interests involves using paleofield variations recorded in mid-ocean ridge lava flows to place age constraints on the flows. On this expedition, Julie is interested both in using this technique to try to date some of the young lava flows and in gaining a better understanding of how the Earth's field has varied in this particular location.

Paterno Castillo
Collaborator

Pat is a Professor of Geology at the Scripps Institution of Oceanography, University of California, San Diego. His research interests include petrology and geochemistry of magmas produced within and along divergent and convergent boundaries of tectonic plates, magmatic and tectonic evolution of continental margins and mantle geodynamics. On this expedition, Pat is interested in the petrologic and tectonic evolution of the newly formed oceanic basement in the Gulf of California.

Brian Dreyer
Isotope Geologist
UC Santa Cruz
Institute of Marine Sciences

Brian studies the recent magmagenesis and petrology of the Juan de Fuca Ridge. His interest in mid-ocean ridges began during his postdoctoral fellowship with MBARI's submarine volcanism project; there, he utilized uranium-series disequilibria within individual lavas of Axial Seamount to clarify eruption and petrogenetic timescales. At mid-ocean ridge systems globally, Brian is interested in a) how variability in lava morphology, geochemistry, and petrology reflect deeper mantle-melting and magmatic processes and their complex interplay with tectonism and b) improving the chronological framework of the ridge magmatic plumbing systems. Brian received his Ph.D. in Earth and Planetary Science from Washington University in St. Louis in 2007.

Rigoberto Guardado
Collaborator
Universidad Autónoma de Baja California

Rigoberto Guardado is a teacher and research scientist with the Facultad de Ciencias Marinas (Marine Sciences Faculty) at the University of Baja California in Mexico. As a oceanographer, Rigoberto studies sedimentation processes in the ocean. On this expedition, Rigoberto is interested in learning more about the sediments in this area of the Gulf of California.

Ronald Michael Spelz Madero
Collaborator
CICESE

Ronald Spelz earned his Ph.D. in earth sciences from Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE) in 2008. His research interests are mainly focused in the structural geology and tectonic geomorphology of fault bounded basins and mountain range-fronts in northern Baja California. He is also part of the multidisciplinary research team studying the origin and effects of the El Mayor-Cucapah 7.2 magnitude earthquake which struck northern Baja in April 4, 2010. Ronald presently works in the Marine Sciences Faculty at the Universidad Autónoma de Baja California.

Hiram Rivera
Collaborator
Universidad Autónoma de Baja California

Hiram Rivera is part of the Coastal Management group and teacher in the Faculty of Marine Science at Universidad Autónoma de Baja California. Since 2008 he has worked as a technician with geographic information systems (GIS) applied to fisheries resource management. From 2010 to now he has worked with his students in public participation geographic information systems (PPGIS) 3D models applied to the use of GIS to broaden public involvement in policymaking. His interest for this cruise is to learn about the techniques associated with digital cartography of the Gulf of California.



Last updated: May. 01, 2012