Plate Tectonics & Geology of the Galapagos Archipelago
Plate Tectonics & Geology of theGalápagos ArchipelagoUniversity Honors Program, UH 204D-002:Great Expeditions Spring 2013
HMS Beagle• HMS Beagle was a Cherokee-class 10-gun brig-sloop of the RoyalNavy• She was launched on 11 May 1820 from the Woolwich Dockyard onthe River Thames, at a cost of £7,803 and named after the beagledog breed• In July of that year she took part in a fleet review celebrating thecoronation of King George IV in which she was the first ship to sailunder the new London Bridge• She was adapted as a survey barque (three or more masts) andtook part in three major surveying expeditions• On the second survey voyage the young naturalist Charles Darwinwas on board, and his work would eventually make Beagle one ofthe most famous ships in history• 1870 – scrapped
Beagle: Vital Statistics• 90.3-feet-long• Beam 25-feet-wide• Draught (draft) 12.5 feet– Vertical distance from water line and bottom of the hull – keel– Determines the minimum depth of water the vessel can safelynavigate, and the weight of cargo she can carry• Tons burthen 235 bm; 242 for second voyage• Initially outfitted as a 10-gun Brig• 1825 re-rigged as a three-masted Barque (Bark) withonly 6-guns• When she was in the Galapagos, she had 65 men on board– very cramped living conditions!
Tons Burthen• Builders Old Measurement (BOM or bm) is the method of calculating thecargo capacity of a ship used in England from approximately 1650 to 1849• It estimated the “tonnage” of a ship based on length and maximum beam• It is a volumetric measurement of cubic capacity and NOT of weight; it isexpressed in "tons burthen”
Beagle’s History• First voyage (1826-1830)– Hydrographic survey of Patagonia and Tierra del Fuego• Second voyage (1831-1836) – Darwin’s voyage– Extensive surveys in South America, returning via NewZealand and Australia to England on 2 October 1836• Third voyage (1837-1843)– Survey large parts of the coast of Australia• Final years– In 1845 the Beagle was refitted as a static coastguardwatch vessel to control smuggling on the Essex coast in thenavigable waterways beyond the north bank of theThames Estuary
Second Voyage (1831-1836)1. Fix the longitude of Rio de Janeiro, fromwhich all other distances would be measured2. Make a hydrographic survey of the coast ofSouth America and other places visited3. Make astronomical and tidal observations4. Report on the geology, climate, naturalhistory, people and cultures of the placesvisited Darwin’s arena
Voyage of the HMS Beagle27 December 1831 to 2 October 1836
A watercolour by HMS Beagles draughtsman, ConradMartens. Painted during the survey of Tierra delFuego, it depicts native Fuegians hailing the Beagle.
Darwin’s Beagle Experience(1831-1836)• The Beagle set sail from England on December27, 1831 when Darwin was 22 years old; hewould not see England again for almost five years• Living quarters = one corner of the ship’s chartroom in the stern (“poop cabin”)– 3 x 3.5m and 1.813m high (5.95 ft.)– 250 books, wash stand, chest of drawers, instrumentcabinet, two hammocks, and a large central charttable– Shared the room with midshipman Philip Gidley Kingand Ship’s Mate John Lort Stokes (who slept in a smallannex to the cabin)
Darwin’s Quarters: Chart RoomHMS Beagle, 1832. Interior layout memory sketch by Philip GidleyKing, midshipman during the second voyage, prepared in 1897.
The C&GS Ship Pioneer passing under the Golden Gate Bridge. The first towed marinemagnetometer, which was invented at the Scripps Institution of Oceanography, was firstdeployed on this ship beginning in August 1955. (NOAA Photo Library)
Integrated Ocean Drilling Program (IODP)Scientific deep sea drilling vesselChikyu has set a new world recordby drilling down and obtaining rocksamples from deeper than 2,111meters below the seafloor off theShimokita Peninsula of Japan
Alfred Wegener Institutefor Polar & Marine Researchhttp://www.awi.de/en/home/
Galápagos Archipelago• Spanish names:– Archipiélago de Colón– Islas de Colón– Islas Galápagos• Archipelago island group, island chain, cluster of islands, or a sea containing a large number ofscattered islands• Derived from the Greek ἄρχι- – arkhi- ("chief") and πέλαγος – pélagos ("sea")• Types of archipelagos:– Continental fragments (tectonically rifted continental margins) – active margin– Continental islands (“drowned” margins – Scotland) – passive margin– Oceanic islands• Volcanic arcs – subduction zones• Island chains – Hawaiian Islands (hot spots)• The Galápagos consists of 13 main islands, 3 smaller islands, and 107 rocks and islets• Located at the confluence of three ocean currents, the Galápagos are a “melting pot” of marine species
Location• 973 km (525 nmi; 605 mi) west of continental Ecuador• 1°40N–1°36S, 89°16–92°01W– Volcán Wolf and Volcán Ecuador on Isla Isabela lie directly on the equator• The first crude navigation chart of the islands was made by the buccaneerAmbrose Cowley in 1684 (??); he named the individual islands after someof his fellow pirates, or after the British noblemen who helped theprivateers cause– English pirates pilfered Spanish galleons carrying gold and silver from SouthAmerica to Spain• More recently, the Ecuadorian government gave most of the islandsSpanish names, but many biological researchers still use the older Englishnames because those were used by Darwin
Galápagos Geology• The Galápagos Islands are:– An active group of basaltic volcanoes– Located near two seafloor spreading ridges– Part of a west-ward propagating seafloorspreading ridge– Sitting on top of a mantle hotspot– Site of the first discovery of seafloor hydrothermalvents on a spreading ridge (“Black Smokers”)
Name Last EruptionDarwin Island ExtinctFernandina 2009Ecuador (volcano) 1150Wolf Island ExtinctCerro Azul 2008Wolf (volcano) 1982Darwin (volcano) 1813Alcedo 1993Sierra Negra 2005Santiago Island 1906Pinta Island 1928Marchena Island 1991Santa Cruz Island UnknownFloreana Island ExtinctGenovesa Island UnknownSan Cristóbal Island Unknown
Geology Overview• The islands are located at the Galápagos triple junction• The archipelago is located on the north margin of the NazcaPlate, which is moving ESE and diving under the SouthAmerican Plate at a rate of 2.5 inches (6.4 cm) per year• It is also atop the Galápagos volcanic hotspot (mantleplume)• The islands have a volcanic legacy going back 10s of millionsof years
Seafloor Morphology• Complex interplay of N-S trending structures associated with theEPR and E-W trending structures associated with the GalápagosRidge• EPR changes from fast spreading to intermediate spreading anddevelops an axial rift valley• Galápagos Ridge develops an axial graben that deepenswestward, reaching >4000m in the Hess Deep• West of the Hess Deep there is no clear expression of theGalápagos Ridge– Gap of 25-km between the spreading centers– Magmatic gap?
The first guyot - discovered by Harry Hess of Princeton University(guy-ot [gee-o ])
Guyot• (guy-ot [gee-o ])• Flat-topped submarine seamount, the summit of which lies l000-2000 m belowthe ocean surface• Seamount is a mountain rising from the ocean seafloor that does not reach to thewaters surface (sea level) and thus is not an island• The term “guyot” is named after Arnold Guyot (1807-1884), 19th century Swiss-American geologistRodriguez Seamount/Guyot
Galápagos Hotspot• Responsible for the creation of the Galápagos Islandsand three major aseismic ridges– Carnegie Ridge– Cocos Ridge– Malpelso Ridge• Hotspot is complicated by its proximity to theGalápagos triple junction (i.e., relative motion of threeplates, not just simple divergent seafloor spreading)• Unlike many hotspots, the magmatic system isheterogeneous – evidence of four major reservoirsfeeding the hotspot
Black Smokers• Hydrothermal vent fields at or near ridge crests• Vent fluids = up to 400oC• Fluid chemistry from different spreading centers isremarkably similar despite big differences inspreading rates• vent fluids have equilibrated with greenschistassemblage of minerals• Metalliferous deposits are common– Hot, acidic, sulfide-rich solutions– Base metals are precipitated when vent fluids come incontact with cold seawater
Galápagos Black Smokers• The first warm springs to be found on the mid-ocean ridge werediscovered in 1977 on the Galápagos spreading center• Astonishing communities of animals around them, but they were weakly-flowing vents emitting room-temperature fluids into the frigid surroundingbottom waters• In 1979, scalding hot “black smokers” jetting from the seafloor werediscovered elsewhere on the global mid-ocean ridge system• Since 1977, additional exploration of the eastern Galápagos spreadingcenter located a few more diffuse vents populated by animals, but did notsucceed in finding any black smokers; some workers suggest that theinfluence of the Galápagos hotspot on the Galápagos spreading centermay inhibit formation of cracks required to provide deep, hot fluidpathways for black smokers, making smokers rare and hard to find
Fast Spreading9-18 cm/yrIntermediateSpreading5-9 cm/yrSlow Spreading1-5 cm/yr“Rise”Spreading rates versus topography
Galápagos Triple Junction• RRR triple junction that separates the Nazca, Cocos andPacific seafloor plates• The fast-spreading East Pacific Rise trends N-S in thisregion and continues without offset past the triplejunction– Smooth topography across the rise• Galápagos Ridge E-W trending and slow-spreading– Separates the Cocos and Nazca plates, to the north andsouth, respectively– Rough, more faulted topography across the ridge
Triple Junctions• The Earth’s lithosphere comprises a mosaic ofinterlocking plates• There are several places on the planet where threeplates come together - these are called triple junctions• Triple junctions mark the intersection of combinationsof:– Rifts or ridges (spreading centers)– Transform fault boundaries– Convergent boundaries (subduction zones)
Galápagos Gore• Intersection of EPR & GR V-shaped, triangular, faulted region called theGalápagos Gore– “V” opens to the east– Older crust in the east than the west based onmagnetic anomalies– The Galápagos Ridge has propagated from east-to-west as it developed