Ocean island basalts geology geos 320 with mills at. Origin of basaltic magma origin geology 346 petrology 2 principal types of basalt in the ocean basins tholeiitic basalt and alkaline basalt table 101 table common petrographic differences between tholeiitic and alkaline basalts tholeiitic basalt alkaline basalt usually finegrained, intergranular no olivine olivine common clinopyroxene. The austral islands, a volcanic chain in the southcentral pacific ocean french polynesia are composed mainly of alkali basalts and basanites with subordinate amounts of olivine tholeiites and strongly undersaturated rocks phonolite foidites and phonolite tephrites. Pdf origin of primitive ocean island basalts by crustal. The genesis of ocean island basalt oib has been widely debated for more than four decades. A classification of granitoid rocks based on tectonic setting.
The mantle plumes have produced up to 26 cubic kilometers of oceanic basalt each year during the last 150 million years. Oct 23, 2011 geochemical signatures within the erupted ocean island basalts further support the idea that the regions of heterogeneity are composed of primitive, undegassed mantle material 7,9,10,11,12,14. Oceanic basalt article about oceanic basalt by the free. Basalt production at these locations begins with an eruption on the ocean floor. Ocean island basalt oib is chemically and isotopically distinct from basalt erupted at normal segments of midocean ridges normal midocean ridge basalt. The basalt of such packages exhibit ocean island basalt oib geochemical affinity ghatak et al. The tungsten isotopic data negatively correlate with 3 he 4 he. Earth and planetary science letters, 104 1991 3897 elsevier science publishers b. Trace element evidence for the origin of ocean island basalts. Well since some 34 of the earths surface is covered by oceans, its pretty easy to see that the manufacture of seafloor could easily be a full time occupation. Introduction 2 one of the fundamental advances in modern geochemistry of the solid earth is the recognition of compositional heterogeneities in the earths mantle through studies of oceanic basalts.
View 8magma generation from geology petrology at indian institute of technology, kharagpur. The incompatible trace element and isotopic ratios of oib reflect considerable heterogeneity in the mantle source regions. The effects of lithospheric thickness variation and mantle metasomatism emma r. Other articles where midoceanridge basalt is discussed. The tas diagrams of lavas from the westernmost canary islands figs. Basalt, extrusive igneous volcanic rock that is low in silica content, dark in color, and comparatively rich in iron and magnesium. A new perspective from petrology, geochemistry, and mineral physics considerations article pdf available in journal. Here we provide such a dataset, with both single sample and segment means for 241 segments from every ocean basin, which span the entire range of. Melting of oceanic crusts cannot produce highmagnesian oib lavas. Thus, oib volcanism contrasts with the other principal types of volcanism in the ocean basins that occur along plate boundaries.
Tungsten182 heterogeneity in modern ocean island basalts. Origin of basaltic magma 1 origin of basaltic magma 2 table 184. Lecture 23 ocean island basalts thursday, april 21st 2005 ocean islands and seamounts commonly associated with hot spots chapter 14. Waning activity more alkaline, episodic, diverse, and violent mauna kea 4. Basalt lava has a low viscosity, due to its low silica content. Ppt origin of basaltic magma powerpoint presentation. The magmatic origin and evolution of the oxnadalur. Ocean island basalts generally referred to as oibs are a type of basalt erupted within the oceans, mainly in intraplate settings. As one moves to southeast along the chain the age of tholeiitic volcanism becomes younger, occurring at 3.
Ocean island basalt oib is a volcanic rock, usually basaltic in composition, erupted in oceans away from tectonic plate boundaries. Compared to the familiar granite of the continents, basalt basalt is darker, denser and finer grained. Basalt definition, the dark, dense igneous rock of a lava flow or minor intrusion, composed essentially of labradorite and pyroxene and often displaying a columnar structure. They are subalkaline tholeiites that contain olivine in the norm and less than 0. Based on an evaluation of major and trace element data for ocean island basalts oib, we demonstrate that oceanic lithosphere thickness variation, which we refer to as the lid effect, exerts the. Consideration of petrology, geochemistry, and mineral physics suggests that ancient subducted oceanic crusts cannot be the source materials supplying ocean island basalts oib. Ch10magma generation origin of basaltic magma origin. Trace element evidence for the origin of oceanisland basalts. The chemistry suggests that morb was generated from a mantle that was depleted of volatile elements e. Basalt is the dark, heavy volcanic rock that makes up most of the worlds oceanic crust. Characterized by highly alkaline and silicaundersaturated magmas, including. The origin of primitive ocean island and island arc basalts. The hydrogen got there thanks to slabs of waterrich oceanic basalt forced down into the mantle along subduction zones. The vitric to crystalrich marine ash layers are a few centimeters thick, have rather uniform grain sizes around 60 40 m, and are a result of plinian eruptions.
Mid ocean ridge basalt is fondly called morb, while ocean island basalt is called oib. All of the islands in the hawaiian island chain were built up from basalt eruptions on the sea floor. A grossly homogeneous mantle with a bulk composition depleted in largeion lithophile elements lile. Tectonic influence on chemical composition of ocean island basalts in the west and south pacific. Received 29 june 2008 accepted 29 april 2009 available online 6 june 2009 keywords. Tectonic influence on chemical composition of ocean island. Jul 21, 2011 here we average the data further within a number of 10 km lithosphere thickness intervals regardless of geographical location or ocean basin, the number of islands, the number of samples and range of basalt compositional variation within a given island see table 1 and fig. The oib paradox plates, plumes and planetary processes. Ppt origin of basaltic magma powerpoint presentation free. The magmatic origin and evolution of the oxnadalur volcanic. Partial melting experiments on peridotite and origin of mid. Ocean island basalt an overview sciencedirect topics.
The origin of ocean basins the origin of ocean basins ocean basin is defined as that part of the sea floor. A new perspective from petrology, geochemistry, and mineral physics considerations yaoling niu1 and michael j. Some of it erupts on land, too, but to a first approximation, basalt is an oceanic rock. The origin of primitive ocean island and island arc. Limestone horizons are commonly tens of meters in thickness, and the thickest limestone horizon m is associated with the permanente terrane. The initial phase of surtseys eruption was highly explosive, as the magma was quite fluid, causing the rock to be blown apart by the boiling steam to form a tuff and cinder cone. Oib derived from sources with a high upb ratio have trace element characteristics consistent with a source dominated by recycled ancient oceanic crust. Mantle melting and origin of basaltic magma 2 principal types of. The cameroon line, west africa, and its bearing on the.
The origin of ocean island basalt endmember compositions. Oceanisland basalt oib suites display significant and consistent differences in highly incompatible trace element ratios between islands which have endmember radiogenic isotope signatures. Nmorb, and this distinction is frequently cited as evidence that the two basalt types originate in different parts of the mantle. Origin of diverentiated volcanic and plutonic rocks from. Both the plagioclase and pyroxene phenocrysts of the basalt are larger in size in the younger flows. Geochemical signatures within the erupted ocean island basalts further support the idea that the regions of heterogeneity are composed of primitive, undegassed mantle material 7,9,10,11,12,14. A suite of alkaliolivine to tholefitic basalts, newly dredged from the tasmantid seamounts, are possible primary and nearprimary compositions e. Tests of models of melt generation and mantle source variations beneath mid ocean ridges require a definitive set of mid ocean ridge basalt morb compositions corrected for shallowlevel processes. A long period of dormancy, followed by a late, posterosional stage.
Mantle melting and origin of basaltic magma 2 principal types of basalt in the ocean basins tholeiitic. The generally accepted wholemantle convection theory is supported by geochemical data on oibs, which. A new perspective from petrology, geochemistry, and mineral physics considerations article pdf available in journal of geophysical research. Although ocean island basaltic magma is mainly erupted as basalt lava, the basaltic magma is sometimes modified by igneous differentiation to produce a range of other volcanic rock types, for example, rhyolite in iceland, and phonolite and trachyte at the. New tungsten isotope data for modern ocean island basalts oib from hawaii, samoa, and iceland reveal variable 182 w 184 w, ranging from that of the ambient upper mantle to ratios as much as 18 parts per million lower. Midocean ridge basalts morb also originate within the convecting upper mantle and so must share a common source with the cameroon line alkali basalts and, by implication, ocean island and continental rift basalts. These data indicate that each oib system accesses domains within. A deep mantle origin for the primitive signature of ocean. In addition to the distinctive sr, nd and pb isotopic signatures of the himu, emi and emii oib endmembers, differences in incompatible trace element. Origin and evolution of lord howe island, southwest. Ocean island basalts oib are particularly variable in composition such that several isotopically distinct mantle source end. Shieldbuilding stage begins with tremendous outpourings of tholeiitic basalts kilauea and mauna loa.
And since we know that average age of the ocean floor about 200 million. Ohara department of earth sciences, cardiff university, cardiff, uk. Basalts may be broadly classified on a chemical and petrographic basis into two main groups. The basaltic rocks have geochemical features typical of oceanic island suites.
Origin of primitive ocean island basalts by crustal gabbro assimilation and multiple recharge of plumederived melts article pdf available in geochemistry geophysics geosystems 187. The chemistry of the icelandic basalts is more characteristic of ocean island basalt emorb. The rhyolite ashes contain no primary crystals, but numerous basalt xenoliths and pumice fragments. Weaver school of geologv and geophysics, university of oklahoma, norman, ok 73019, usa received may 29, 1990. Lecture 23 oibs university of massachusetts amherst.
Ocean island basalt oib is chemically and isotopically distinct from basalt erupted at normal segments of mid ocean ridges normal mid ocean ridge basalt. Ancient oceanic crusts 1 ga are isotopically too depleted to meet the required values of most oib. Limestone is rare in the franciscan complex and much less abundant than chert sliter 1984. Fundamental aspects concerning the origin of ocean island basalts and primitive island arc magmas are addressed using examples from the vanuatu arc, hawaii, and the tasmantid seamounts. Origin and evolution of lord howe island, southwest pacific ocean. At the northwestern end of the island chain is the island of kauai. Origin of primitive ocean island basalts by crustal gabbro assimilation and multiple recharge of plumederived melts article pdf available in geochemistry geophysics geosystems 187 july. The island of surtsey in the atlantic ocean is a basalt volcano which breached the ocean surface in 1963. If the hotspot is sustained, repeated eruptions can build the volcanic cone larger and larger until it becomes high enough to become an island. Some second thoughts about the origin of basaltic magma some second thoughts about the origin of basaltic magma ocean island basalt hawaiian alkaline. Ocean island basalt oib suites display a wide diversity of major element, trace element, and isotopic compositions.
Tests of models of melt generation and mantle source variations beneath midocean ridges require a definitive set of midocean ridge basalt morb compositions corrected for shallowlevel processes. The basal pebble conglomerate of site 748 has an oceanicisland basalt oib composition and denotes erosion and reworking of seamount to oceanicislandtype volcanic sources. Midocean ridge basalt is fondly called morb, while ocean island basalt is called oib. Ocean island basalt oib suites display significant and consistent differences in highly incompatible trace element ratios between islands which have endmember radiogenic isotope signatures. Try before you buy demos and trials and score totally free games.
Trace element evidence for the origin of ocean island. Trace element evidence for the origin of oceanisland. More than 90% of all volcanic rock on earth is basalt. Global systematics of ocean ridge basalts and their origin. The 89 million year old volcanic complex of oxnadalur is host to largevolume basalt flows, small and large volume rhyolite ash and lava flows, and a gabbroic intrusion. Journal of petrology volume 39 number 5 pages 10091024 1998 origin of diverentiated volcanic and plutonic rocks from ascension island, south atlantic ocean a. Thus, oib volcanism contrasts with the other principal types of. Department of earth sciences, durham university, durham dh1 3le, uk article info abstract article history. The meaning of global ocean ridge basalt major element. Partial melting experiments on peridotite and origin of. Ocean island basalts geology geos 320 with mills at depauw. Ocean island basalts oibs volcanic region thought to be fed by an underlying magma plume deep within the mantle that is relatively stationary while the lithosphere moves over it the processes of hotspots are more enigmatic to desire and are less voluminous than activity at plate marigins.