Geochemical Evidence for Slab Melting in the Trans-Mexican Volcanic Belt   总被引：3，自引：0，他引：3  

Gomez-Tuena  Arturo; Langmuir  Charles H.; Goldstein  Steven L.; Straub  Susanne M.; Ortega-Gutierrez  Fernando 《Journal of Petrology》2007,48(3):537-562

Geochemical studies of Plio-Quaternary volcanic rocks from theValle de Bravo–Zitácuaro volcanic field (VBZ) incentral Mexico indicate that slab melting plays a key role inthe petrogenesis of the Trans-Mexican Volcanic Belt. Rocks fromthe VBZ are typical arc-related high-Mg andesites, but two differentrock suites with distinct trace element patterns and isotopiccompositions erupted concurrently in the area, with a traceelement character that is also distinct from that of other Mexicanvolcanoes. The geochemical differences between the VBZ suitescannot be explained by simple crystal fractionation and/or crustalassimilation of a common primitive magma, but can be reconciledby the participation of different proportions of melts derivedfrom the subducted basalt and sediments interacting with themantle wedge. Sr/Y and Sr/Pb ratios of the VBZ rocks correlateinversely with Pb and Sr isotopic compositions, indicating thatthe Sr and Pb budgets are strongly controlled by melt additionsfrom the subducted slab. In contrast, an inverse correlationbetween Pb(Th)/Nd and ¹⁴³Nd/¹⁴⁴Nd ratios, which extend to lowerisotopic values than those for Pacific mid-ocean ridge basalts,indicates the participation of an enriched mantle wedge thatis similar to the source of Mexican intraplate basalts. In addition,a systematic decrease in middle and heavy rare earth concentrationsand Nb/Ta ratios with increasing SiO₂ contents in the VBZ rocksis best explained if these elements are mobilized to some extentin the subduction flux, and suggests that slab partial fusionoccurred under garnet amphibolite-facies conditions. KEY WORDS: arcs; mantle; Mexico; sediment melting; slab melting  相似文献   

Hydrogen and carbon isotopic ratios of the cellulose nitrate and saponifiable lipid fractions prepared from annual growth rings of a California redwood     

Donald W. Northfelt  Michael J. DeNiro  Samuel Epstein 《Geochimica et cosmochimica acta》1981,45(10):1895-1898

The $\text{D}\text{H}$ and ${}^{13}\text{C}{}^{12}$C ratios of the cellulose nitrate and saponifiable lipid fractions prepared from eleven annual growth rings of a California redwood were determined. The $\text{D}\text{H}$ ratios of the two fractions are related to one another for the annual rings in the sapwood portion of the tree, but not for those in the heartwood or in the wood undergoing the transition from sapwood to heartwood. No relationship was observed between the ${}^{13}\text{C}{}^{12}$ ratios of the two fractions. These results suggest that analysis of the hydrogen isotopic composition of the saponifiable lipid fractions in plants will provide information useful for climatic reconstruction provided the initial isotopic record has not been changed by subsequent physiological or diagenetic processes.  相似文献   

Crustal growth and mantle evolution: inferences from models of element transport and Nd and Sr isotopes: (reply to a comment by R. L. Armstrong)     

Donald J. Depaolo 《Geochimica et cosmochimica acta》1981,45(7):1253-1254

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Discussion of “Thermodynamic parameters of CaMgSi2O6-Mg2Si2O6 pyroxenes based on regular solution and cooperative disordering models” by Holland,Navrotsky, and Newton     

Donald H. Lindsley  Paula M. Davidson  T. J. B. Holland  A. Navrotsky  R. C. Newton 《Contributions to Mineralogy and Petrology》1981,75(3):301-306

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A general mixing equation with applications to Icelandic basalts   总被引：4，自引：0，他引：4  

Charles H. Langmuir  Robert D. Vocke  Gilbert N. Hanson  Stanley R. Hart 《Earth and Planetary Science Letters》1978,37(3):380-392

The mixing equation applied by Vollmer [1] to Pb and Sr isotope ratios is shown to be a general equation applicable to consideration of element and isotope ratios. The mixing equation is hyperbolic and has the form:Ax + Bxy + Cy + D = 0where the coefficients are dependent on the type of plot considered: i.e. ratio-ratio, ratio-element, or element-element. Careful use of this equation permits testing whether mixing is a viable process, places constraints on end member compositions, allows distinction between mixing of sources and mixing of magmas, and should allow distinction between recent mixing and long-term evolution of sources.The available chemical data for postglacial basalts from Iceland and along the Reykjanes Ridge are not consistent with either mixing of magmas or simple mixing of an enriched ocean island source with a depleted ocean ridge source. If the available analyses for basalts are representative of the source regions, the data are consistent with at least two models neither of which can be properly tested with the available data.(1) There are two separate mixing trends: one beneath Iceland with the alkali basalt source and a depleted Iceland source as end members; the second along the Reykjanes Ridge with a heterogeneous ocean ridge basalt source and a source similar to that for intermediate basalts on Iceland as end members. The depleted Iceland source and the depleted ocean ridge source are not the same.(2) The chemistry of the basalts is not determined by mixing. Instead the basalts are derived from a multiplicity of sources with a similar history which have been isolated for hundreds of millions of years.  相似文献   

Elasticity of orthoenstatite     

Donald J. Weidner  Herbert Wang  Jun Ito 《Physics of the Earth and Planetary Interiors》1978,17(2):P7-P13

Elastic constants of orthoenstatite have been determined from Brillouin-scattering measurements. They are c₁₁ = 2.247, c₂₂ = 1.779, c₃₃ = 2.136, c₄₄ = 0.776, c₅₅ = 0.759, c₆₆ = 0.816, c₂₃ = 0.527, c₃₁ = 0.541 and c₁₂ = 0.724 Mbar. Each elastic constant is uniquely defined by the data. Acoustic velocities measured for two directions ultrasonically on the same samples are within 1% of those determined from Brillouin-scattering spectra.  相似文献   

Modelling of major elements in mantle-melt systems using trace element approaches   总被引：1，自引：0，他引：1  

Gilbert N. Hanson  Charles H. Langmuir 《Geochimica et cosmochimica acta》1978,42(6):725-741

Major elements can be modelled in ways similar to the quantitative petrogenetic modelling used for trace elements. In contrast to modelling with trace elements, however, modelling with major elements is constrained by the stoichiometry of the solid phases. Within these constraints, the same equations for partial melting and crystallization which have been used to such advantage for trace elements may be used for major elements.Calculated MgO and FeO abundances in a mantle-melt system are used as an example of the modelling technique. Such modelling yields limited fields of permissible melts and residues for a given parent composition, but does not give the paths of melting. It does allow the temperature and extent of melting which gave rise to a melt to be determined from the MgO and FeO abundances of the melt or residual solid. Applying the results of the modelling to igneous rocks and ultramafic nodules leads to the following conclusions, which are subject to the uncertainties in the available distribution coefficients. Least differentiated basalt glasses from the ocean floor are derived from parent melts with less than 15.5 weight % MgO and 8.2 wt. % FeO. Komatiites may be derived by less than 60% melting of a pyrolite source leaving a residue of olivine and pyroxene. Many nodules from the subcontinental mantle appear to be residues of large fractions of melting (>30%) at high temperature and pressure, whereas ultramafic nodules from oceanic basalts appear to be residues of smaller fractions of melting (<30%) at lower temperatures and pressures.  相似文献   

Barrier-island genesis: evidence from the central atlantic shelf,eastern U.S.A.     

Donald J.P. Swift 《Sedimentary Geology》1975,14(1):1-43

Since most barrier systems appear to have retreated into their present positions from further out on the continental shelf, the continental shelf is a logical place in which to investigate barrier genesis. The Middle Atlantic Bight of North America, one of the best known shelf sectors, does not appear to contain any drowned barriers. Instead, a series of terraces bear on their surfaces a discontinuous carpet of lagoonal sediments beneath a discontinuous sand sheet formed by erosional barrier retreat. Scarps separating terraces are the lower shorefaces of stillstand barriers whose superstructures were destroyed when shoreface retreat resumed. Thus the “origin” of most barriers is that they have retreated in from the position of their immediate predecessors. Barrier genesis, in the classic sense of large-scale, coastwise spit progradation or mainland-beach detachment, could only have occurred at Late Wisconsin lowstand, when the sense of sea-level displacement was reversed. The relative roles of coastwise spit progradation and mainland-beach detachment depend on coastal relief and slope, with steep, rugged coasts favoring spit progradation at the expense of mainland-beach detachment. Since most major barrier systems form on flat coastal plains, it would appear that mainland-beach detachment is the more important mode of barrier formation.During stillstands or periods of reduction in the rate of sea-level rise, coasts can more nearly approach their climax configuration, in which the shoreline is relatively straight, and the shoreface is well developed and of maximum possible slope. Coastal adjustments during such periods may require localized mainland-beach detachment and coastwise spit progradation, in order to attain such a configuration.  相似文献   

Age and intensity of thermal events by fission track analysis: The Ries impact crater     

Donald S. Miller  Günther A. Wagner 《Earth and Planetary Science Letters》1979,43(3):351-358

A thermal event reduces the number of previously registered fission tracks in a mineral dependent upon the track retention properties of the individual mineral. Apatite, sphene and zircon have retention properties over a wide range of temperatures (from 100° to 550°C); apatite data reveal information at lowest temperatures while sphene and zircon data are useful for higher temperatures.Thermal events within this temperature range of 100°C to about 550°C are suitable for study with this technique. The age of the event is determined from samples in which the fission tracks are completely erased, while minerals containing partially removed (erased) tracks provide information on the temperatures occurring during the thermal event.As a test case, the analysis of the temperatures developed by the meteorite impact which produced the Ries crater at 14.7 m.y. ago is presented.  相似文献   

The Nazca Group of south-central Peru: Age,source, and regional volcanic and tectonic significance     

Donald Charles Noble  Edward Farrar  Edwin John Cobbing 《Earth and Planetary Science Letters》1979,45(1):80-86

The Nazca Group, exposed east of Nazca, Peru, consists of a lower part composed of conglomerate and finer-grained clastic strata and an upper part made up of at least seven ash-flow sheets (cooling units or ignimbrites), collectively known as the Nazca Tuff. These tuffs were erupted between about 22 and 18 m.y. ago from a vent area in the vicinity of Pampa Galeras now marked by a collapse caldera. The early Miocene age of the Nazca Tuff provides additional evidence for a major pulse of largely pyroclastic felsic volcanism throughout the central Andes during the early Miocene. Recognition of the Pampa Galeras caldera supports the idea that many of these rocks were erupted from vent areas of the collapse-caldera type located near the eastern margin of the Coastal batholith.The Nazca Group overlies a major erosional surface cut on the Coastal batholith and its envelope that can be traced southward to the Chilean border. This surface is a continuation of the post-Incaic erosional surface to the north, which is overlain by conglomerate and radiometrically dated volcanic rock of late Eocene age. The post-Incaic surface therefore represents a major episode of regional uplift and pedimentation that followed early Tertiary orogeny. The absence of volcanic rocks of late Eocene/early Oligocene age overlying the Coastal batholith near Nazca and in southern Peru may reflect a general absence of post-Incaic volcanism in this portion of the Andes possibly related to differences in the angle of subduction and/or restriction of volcanic and volcaniclastic rocks of this age to depositional basins east of the batholith.  相似文献