Journal of petrology volume 41 number 3 pages 411430 2000 enriched endmember of primitive morb melts. These, including the last three, constitute over 99. Compared with the same type rocks in the world, the mafic rocks generally display lower nbu and cepb ratios and some have nb depletion and pb enrichment. This is characteristic of most morb from all ocean basins. What are the differences between n morb, e morb and oib with regards to. Geochemistry of the oldest morb and oib in the isua. The field of geochemistry involves study of the chemical composition of the earth and other planets, the composition of rocks and soils, the cycles that involve the earths chemical components, and the interaction of those cycles with land and water. A new perspective from petrology, geochemistry, and mineral physics considerations yaoling niu1 and michael j. Petrology and sr, nd, and pb isotope geochemistry of mid. Pdf trace element and isotope geochemistry of depleted. Geochronological and geochemical constraints on the.
Petrology and geochemistry of morb and oib in the midarchean. The oibtype alkaline rocks are characterized by significant enrichments in lile, hfse and lmree, and a. Petrology and geochemistry of glasses from macquarie island sw paci. A global compositional dichotomy for n morb magma n1n2 is recognized on the basis of na 2 o, tio 2, cao, and al 2 o 3 contents, and their respective ratios. Lecture 38 igneous geochemistry read white chapter 7 if you havent already today 1. Comparison of normalized incompatible element abundance patterns for n and ptype morb. Petrology and geochemistry of pliocenepleistocene volcanic rocks from the izu arc, leg 1261 james b. Also within the sinjrani formation are a sequence of senonian basaltdacite lavas that were generated from an n morb type mantle source, and although they are initially.
Petrology and geochemistry of morb from 25e to 46e along the southwest indian ridge. We have characterized the two magma subtypes by means of their trace element patterns, and attempted to explain the differences in major and trace element contents in terms of a partial melting. The mar between 10 and 24n contains a segment at 1415n with e. The smar basalt samples feature n morb like geochemical compositions, which indicate that they were derived from a dm source. The oceanic crust made of basalts is formed on midocean ridges. Morb of sun and mcdonough, however, is even more depleted than the new estimate for d. Geochemistry and tectonic implications of proterozoic. The vrissi unit includes an incomplete volcanic sequence consisting of morb type volcanics linked with and crosscut by middlelate jurassic arctype volcanic rocks and dykes. Isotope geochemistry isotopes do not fractionate during partial melting or fractional crystallization processes. Minerals free fulltext geochemistry and mineralogy of. For full access to this pdf, sign in to an existing account, or purchase an annual subscription. The spider diagrams of the oibs a, convergent margins e, and morbs i show that different degrees of fractional crystallization have occurred at each setting. For example when normalized to n morb they are large ion lithophile element lile enriched, high field strength element hfse depleted, and have negative nb and ti anomalies. The mafic volcanic association is made up of oib, e morb and n morb in the anyemaqen paleozoic ophiolites.
So they will reflect the characteristics of the mantle source oibs, which sample a great expanse of oceanic mantle in places where crustal contamination is minimal, provide incomparable evidence for the nature of the mantle. Basalts belong to the tholeiite series whereas granites, diorites and rhyolites belong to the calcalkaline series. Our detailed geological, geochemical and geochronological investigations indicate the coexistence of late paleozoic 270265 ma normal middle ocean ridge basalt nmorbtype and suprasubductionzone ssztype ophiolites in the babu area sw china. Geochemistry american association of petroleum geologists. A key point for understanding the geochemistry of the rees and interpret it properly. Ocean drilling program scientific results volume 123. Morb which are enriched up to 40 times in highly incompatible elements over the depleted n. Geochemistry of volcanic and subvolcanic rocks and. Geochemistry, scientific discipline that deals with the relative abundance, distribution, and migration of the earths chemical elements and their isotopes. Loubet2 abstract legs 106109 achieved the first basaltic barerock drill hole, on a small volcano serocki volcano located on the flanks of the rift valley in the mar about 70 km south of the kane fracture zone. Figure 3, normal morb n type or n morb exhibit characteristic smooth concavedown patterns resecting the fact that they were derived from incompatible elementdepleted mantle. Some samples have negative nbta anomalies whereas others have positive nata anomalies to average nmorbs. Pdf petrology and geochemistry of morb and oib in the mid. Per\t, department of geology, university of florida, po box 112120, gainesville, fl 326112120, usa.
Detailed chemical icpms and sims techniques and isotopic investigations on very. Wholerock trace element geochemistry shows that the morb type rocks range in composition from light rare earth element lreedepleted varieties n morb. Hydrothermal vents fueled by magmatic and volcanic heat are a common feature at oceanic spreading centers. The crystallized magma forms new crust of basalt known as morb for midocean ridge basalt, and gabbro below it in the lower oceanic crust. The mafic volcanic association is made up of oib, emorb and nmorb in the anyemaqen paleozoic ophiolites. Gill,2 conrad seales,2 patricia thompson,2 alfred g. View enhanced pdf access article on wiley online library html view download pdf. The low smnd and 143nd144nd ratio of all morb and n. Abstract the chagairaskoh arc is located in western pakistan and extends into iran and afghanistan. Age and morb geochemistry of the sabah ophiolite basement. Age and morb geochemistry of the sabah ophiolite basement ijohn e. Howardite, eucrite and diogenite hed clan of achondritic meteorites constitute the. Metaperidotite samples from the babu ophiolites show high os concentrations and low reos, 187os188os and 187re188os ratios, and represent. Implications for the composition and temperature of the upper mantle at 3.
Trace element and isotope geochemistry of depleted peridotites from an nmorb type ophiolite internal liguride, n. The basalts belong to the tholeiitic series and exhibit normal midocean ridge basalt nmorb geochemical features with variable enrichments of rb, th, u, and pb and depletions of ba and sr relative to primitive mantle. Using the normalization and ordering scheme of pearce 1983 with lil on the left and hfs on the right and compatibility increasing outward from bath. Petrology and geochemistry of morb and oib in the midarchean north pole region, pilbara craton, western australia. Basalt geochemistry as a diagnostic indicator of tectonic. The enrichment correlates with radiogenic isotope enrichments indicating that it is primarily a property of the sources. Lecture 22 more morb wednesday, april nth, 2005 trace element and isotope chemistry of morb ree and spider diagrams tend to be relatively flat at the less incompatible end and depleted at the highly incompatible end. On the nbyb versus thyb diagram figure 11a, smar samples plot near the n morb field that supports a dm source. The nomenclature is confusing and recent studies have shown that among midocean. In addition, it is noted that the levels of the immobile elements ti, zr, sm, p, y and yb are all signi.
Geochemistry of the oldest morb and oib in the isua supracrustal belt, southern west greenland. Origin of morb enrichment and relative trace element. Geological processes at the midocean ridges are responsible for the bulk of the earths heat loss and volcanic activity. Hochstaedter,2 and charles dunlap2 abstract the igneous geochemistry of lavas and breccias from the basement of sites 790 and 791, and pumice clasts from the. Structural analysis, metamorphism, and geochemistry of the. Metaperidotite samples from the babu ophiolites show high os concentrations and low reos, 187os188os. Basalt geochemistry can be used as a diagnostic indicator for determining the tectonic setting of origin, because specific plate tectonic settings often impart distinctive geochemical characteristics. Comparison of normalized incompatible element abundance patterns for nand ptype morb. The mavrolakkos unit consists of sheeted dykes, lavas, and individual dykes with n morb affinity, which are crosscut by dykes showing volcanic arc affinity. Figure 3, normal morb n type or n morb exhibit characteristic smooth concavedown patterns resecting the fact that they were derived from. A fortran77 program has been written to realize these suggestions. We estimate the mantle magmasource characteristics and identify the relative n contributions of the mantle endmember components in the glasses erupted along the 1500km transect using.
Lecture 23 ocean island basalts thursday, april 21st 2005 ocean islands and seamounts commonly associated with hot spots chapter 14. Midocean ridge basalts morb, oceanic crust and ophiolites. Petrology and geochemistry of morb from 25e to 46e along. Compared with n morb, this new endmember is characterized by relatively low contents of mgo, feo, sio 2 and cao. Morb normalized spider diagrams for selected island arc basalts. Geochemistry and smnd and rbsr isotopic composition of. Group i glasses define a seriate variation within the compositional spectrum of morb, and extend the compositional range from n morb compositions to enriched compositions that represent a new primitive enriched morb endmember. Germ reservoir database geochemistry of the nmorb reservoir.
Some samples have negative nbta anomalies whereas others have positive nata anomalies to average n morbs. Geodynamic sets i mean tectonic settings artem bich jan 12 18 at 15. Compared with n morb, this new endmember is characterized by relatively low contents of mgo, feo, sio 2 and. Morb of these ridge segments are tholeiitic, relatively depleted large ion lithophile element abundances chondrite normalized lasm n type morb displays a range of compositions and the definition of n type morb is arbitrary. Complex arc dynamics spanning the cretaceous to the quaternary.
Geochemistry and mineralogy of basalts from the south mid. However, all analyzed samples have negative nb anomalies in morb normalized trace element patterns suggesting a suprasubduction zone influence. Petrogenetic modeling suggests n morb values suggesting the enrichment of the light rare earth elements, which means that mantle magma source was an e morb. Recent geological investigations of the isua supracrustal belt 3. Stable isotopes 362 the elements of interest in radiogenic isotope geochemistry are heavy sr, nd, hf, os, pb, most form dominantly ionic bonds, generally exist in only one oxidation state, and there is only small relative mass differences between the isotopes of interest. Geochemical characteristics of midocean ridge basalts. Helena residue plume material into the asthenosphere douglass et al. It is necessary and important to determine the tectonic setting of mafic volcanism, because compositions of magma are strongly related to tectonic setting. Nd t for the eclogites suggest that their protoliths were lowk oceanic tholeiites, similar to typical n morb, derived from a depleted mantle source. Comparing morb, oib and cm geochemistry comparing morb. Geochemistry of morb and oib in the yuejinshan complex, ne. Compared with the same type rocks in the world, the mafic rocks generally display lower nbu and cepb ratios. Midocean ridge basalt is a tholeiitic basalt and is low in incompatible elements.
The mean composition of ocean ridge basalts harvard dash. Pdf collections of midocean ridge basalts morb do not represent. Pdf geochemical characteristics of midocean ridge basalts. Petrology and sr, nd, and pb isotope geochemistry of midocean ridge basalt glasses from the 11 degrees 45 n to 15 degrees 00 n segment of the east pacific rise. The shergol mafic intrusives show fe enrichment with basalt to basalticandesite composition. Based on their mineralogy and textures, these mafic rocks. There are no universally agreed geochemical criteria in the literature for defining. Petrology and geochemistry of mafic intrusive rocks from. Physical research laboratory, ahmedabad 380 009, india. Chondrite normalized rare earth element pattern of basalt is flat and plot slightly below the average n morb values suggesting the enrichment of the light rare earth elements, which means that mantle magma source was an e morb. The lasm and smyb ratios are also compatible with an n morb classification and a dm source figure 11b. We report analyses of o, sr, nd and pb isotope ratios in 52 fresh glasses of midocean ridge basalt morb.
Isotopic investigations have conclusively shown that values of the radiogenic isotopes of sr, nd, hf and pb in n morb are consistent with their depleted charac. This is the main site of volcanic activity on earth, and the most abundant igneous rock. Thermodynamic consideration of te solid solutions pdf 3. The mean composition of ocean ridge basalts gale 20. The compositions of materials erupted at these locations, dominantly midocean ridge basalts morb s, have profound implications for the inner workings of the earths mantle, the construction of oceanic crust, and global plate tectonics. We report analyses of 0, sr, nd and pb isotope ratios in 52 fresh glasses of midocean ridge basalt morb. The basalts belong to the tholeiitic series and exhibit normal midocean ridge basalt n morb geochemical features with variable enrichments of rb, th, u, and pb and depletions of ba and sr relative to primitive mantle. Geochemistry and spatial distribution of oib and morb in a. Samples tend to be assigned to one type or the other on an ad. Implications for the composition and temperature of the upper mantle at.
Spot light on using the rare earth elements ree to constrain mantle sources and conditions of petrogenesis gg325 l38, f20 modeling igneous petrogenesis however, other concurrent processes can obscure the. Morb from the south atlantic ridge was explained to be related to the partial melting and dispersion of the tristan and st. The spider diagrams of the oibs a, convergent margins e, and morbs i show that different degrees of fractional crystallization have occurred at each. Trace elements geochemistry and petrogenesis of basalt from the. Our recent geological investigation of the north pole np region 3. Castillo, pr, klein e, bender j, langmuir c, shirey s, batiza r, white w. Ionic model for bonding and the role of ionic radii in understanding the partitioning of trace elements between phases pdf 5.
Implications for the composition and temperature of early archean upper mantle. Pdf petrology and geochemistry of morb and oib in the. Mcdonough department of geology, university of maryland, college park, md, 20742, usa. Trace element and isotope geochemistry of depleted. Find materials for this course in the pages linked along the left. Mantle peridotites of the internal liguride il units northern apennines constitute a rare example of the depleted lithosphere of the jurassic ligurian tethys. Mantle reservoir geochemistry from statistical analysis of. Nomenclature for trace element classification pdf 6. Authors personal copy chemical variations and regional diversity observed in morb ricardo arevalo jr. Ohara department of earth sciences, cardiff university, cardiff, uk. Download course materials traceelement geochemistry. They are tholeiitic lavas with typical island arc characteristics and an n morb source.
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