The origin of lavas from the Ninetyeast Ridge, eastern Indian Ocean: An evaluation of fractional crystallization models
26
Citation
32
Reference
10
Related Paper
Citation Trend
Abstract:
Ferrobasalts from DSDP sites 214 and 216 on the Ninetyeast Ridge are characterized by high absolute iron (FeO>12.9 wt %), FeO/MgO>1.9, and TiO 2 >2.0 wt %. Their trace element abundances indicate a tholeiitic affinity; however, they are distinct from midocean ridge incompatible element‐depleted tholeiites owing to higher contents of Ba, Zr, and Sr and flat to slightly light‐REE‐enriched, chondritenormalized REE patterns. Calculations using major and trace element abundances and phase compositions are generally consistent with a model relating most major elements and phase compositions in site 214 and 216 ferrobasalts by fractionation of clinopyroxene and plagioclase. However, some incompatible element abundances for site 216 basalts are not consistent with the fractional crystallization models. Basalts from site 214 can be related to andesitic rocks from the same site by fractionating clinopyroxene, plagioclase and titanomagnetite. Site 254 basalts, at the southern end of the Ninetyeast Ridge, and island tholeiites in the southern Indian Ocean (Amsterdam‐St. Paul or Kerguelen‐Heard volcanic provinces) possibly represent the most recent activity associated with a hot spot forming the Ninetyeast Ridge. These incompatible‐element‐enriched tholeiites have major element compositions consistent with those expected for a parental liquid for the site 214 and 216 ferrobasalts. However, differences in the trace element contents of the basalts from the Ninetyeast Ridge sites are not consistent with simple fractional crystallization derivation but require either a complex melting model or a heterogeneous mantle source.Keywords:
Fractional crystallization (geology)
Trace element
Incompatible element
Fractional crystallization (geology)
Trace element
Incompatible element
Lile
Igneous differentiation
Cite
Citations (160)
The chemical components involved in the mantle source of the North Luzon lavas have been an issue of debate. In existing mixing models, the depleted end-member was assigned to MORB source, while EMI, subducting sediments, and metasomatic fluids and melts were considered as enriched components. These models were all developed from chemical and isotope compositions of lavas from entire North Luzon arc without a detailed investigation on chemical variations of lavas in individual islands. In this study, the chemical compositions and Sr, Nd, and Hf isotope ratios of Lutao volcanic rocks are used to address the process and source controls on lavas chemistry. Twenty-eight volcanic rock samples were collected from Lutao. Based on their SiO2 and total alkali contents, these samples were classified into basalt (B), basaltic andesite (BA), andesite (A) and dacite. Basalts and andesites were subdivided into isotopically enriched groups (BE and AE, respectively) and depleted groups (BD and AD, respectively). The andesite (group A) samples have similar Sr, Nd, and Hf isotope ratios with inverse correlations between MgO and incompatible element contents, reflecting fractional crystallization after partial melting from a common source. Based on trace element variations, the group A samples are modeled to be residual melts after intensive fractional crystallization. The two group AE samples have enriched 87Sr/86Sr, 143Nd/144Nd, and 176Hf/177Hf ratios, but their abundance ratios of incompatible elements resemble those of the group A samples. A plausible explanation is that the mantle sources of the groups A and AE lavas were metasomatized by same materials; however, the metasomatic process occurred earlier in the source of AE lavas, leading to enriched 87Sr/86Sr, 143Nd/144Nd, and 176Hf/177Hf ratios. The group AD samples plot closer to MORB in the 87Sr/86Sr-143Nd/144Nd- 176Hf/177Hf space. Their Nb/La and Ti/HREE ratios are lower than MORB values implying subjection to metasomatism, an inference consistent with their Sr, Nd, and Hf isotope data. 87Sr/86Sr, 143Nd/144Nd, and 176Hf/177Hf ratios of the group BE samples are similar to those of the group AE samples. However, model calculations show that their incompatible element abundances can not be explained by derivation from a common source by different degrees of partial melting. An incompatible element enriched source is required for the group AE lavas. The groups BD and AD samples have similar 143Nd/144Nd and 176Hf/177Hf ratios, but group BD has higher Sm/Nd and Lu/Hf ratios. These results imply that the source of the group BD samples was metasomatized later than that of the group AD samples. Overall, the composition and isotope data require that the mantle sources of Lutao lavas were subjected to various metasomatic agents at different time. Based on the mixing models of Kuo (2007), the 87Sr/86Sr, 143Nd/144Nd, and 176Hf/177Hf ratios of the Lutao samples are best explained by mixing sub-equal amounts of siliceous melts derived from subducted sediments and oceanic crust.
Fractional crystallization (geology)
Incompatible element
Metasomatism
Dacite
Trace element
Andesites
Cite
Citations (0)
Peridotite
Trace element
Incompatible element
Fractional crystallization (geology)
Alkali basalt
Cite
Citations (84)
Understanding the evolution of the mantle requires a knowledge of the relative variations of the major elements, trace elements and isotopes in the mantle. Most of the evidence for mantle heterogeneity is based on variations in the trace element and isotopic ratios of basaltic rocks. These ratios are presumed to reflect variations in the mantle sources. To compare major element heterogeneities with trace element and isotopic heterogeneities, it is necessary that the major element abundances in basalts also reflect variations in the mantle sources. Probably the only major element for which this is so is iron. If a basalt has only undergone fractional crystallization of olivine, then the abundance of FeO in the basalt reflects the FeO/MgO ratio of the mantle source, the degree of melting, and the pressure at which melting occurs. Relative pressures and degrees of melting can often be constrained, so that variations in the abundances of FeO can be used to obtain information about variations in the FeO/MgO ratio of the mantle sources of basalts. Comparison of FeO contents with trace element and isotopic contents of basalts shows some striking correlations and leads to the following conclusions. 1. Parental magmas for Kilauean basalts from Hawaii may be related by different degrees of melting of a homogeneous, garnet-bearing source. 2. Mid-ocean ridge basalts from the North Atlantic show a negative correlation of La/Sm with FeO, suggesting that the sources that are most enriched in incompatible trace elements are most depleted in FeO relative to MgO, and are probably also depleted in the other components of basalt. This correlation does not apply to the entire suboceanic mantle. 3. A comparison of tholeiites from near the Azores and from Hawaii shows that sources with similar Nd and Sr isotope ratios may have undergone distinctly different histories in the development of their major and trace element abundances. 4. Ocean island tholeiites tend to be more enriched in FeO than ocean floor tholeiites. Either the ocean island sources have greater FeO/MgO ratios, or melting begins at significantly greater pressures beneath ocean islands than beneath ocean ridges. 5. Major element variations in the mantle are controlled mainly by tectonics and the addition or removal of silicate melts. Trace element variations, however, may be controlled by the addition or removal of fluids as well. Thus major elements, trace elements and isotopes may each give a different perspective important to the understanding of the evolution of the mantle.
Trace element
Incompatible element
Fractional crystallization (geology)
Cite
Citations (171)
Reliable analyses of K, Rb and Cs in dredge basalts require samples which show no petrographic evidence of alteration minerals and which have H 2 O + contents less than 0.7 %. Very fresh glass samples usually have H 2 O + levels of 0.1 to 0.2 %, and this probably represents the primary level of H 2 O in most submarine basalt magmas. A dredge haul containing both basalt and andesite was studied for major element and trace element variations. The major elements were consistent with a differentiation model involving crystallization of plagioclase, olivine, clinopyroxene and titanomagnetite. This differentiation had little effect on Sr concentration and on K/Rb and K/Cs ratios; these parameters are thus especially useful in studying mantle chemistry and partial melting processes. Twenty-eight unaltered dredge basalts were analysed, with K/Rb ratios varying from 360 to 1350. K contents of most samples, after correction for high level (shallow) differentiation processes, fall in the range 500 to 1200 parts/10 6 . A comparison of unaltered basalts from ‘fast-spreading ridges’ and ‘slowspreading ridges’ shows that K, Rb, Cs and Sr contents and K/Rb, K/Cs and Rb/Sr ratios are identical for both environments, while Ba contents and 87 Sr/ 86 Sr ratios may be significantly different. Thus mantle chemistry appears to be largely decoupled from the dynamic processes of plate movement. It is shown that submarine ridge basalts have lower 87 Sr/ 86 Sr ratios than the basalts of the oceanic islands, suggesting an early depletion of parts of the mantle in the dispersed elements. Average values for 15 samples from 11 different ridge localities: K = 1160 parts/10 6 ; Rb = 1.11 parts/ 10 6 ; Cs = 0.016 parts/10 6 ; Sr = 135 parts/10 6 ; Ba = 10 parts/10 6 ; K/Rb = 1060; K/Cs = 70000; Rb/Sr = 0.0082; 87 Sr/ 86 Sr = 0.70265.
Trace element
Incompatible element
Fractional crystallization (geology)
Cite
Citations (227)
Melt inclusions
Pyroxene
Trace element
Mid-Atlantic Ridge
Phenocryst
Incompatible element
Cite
Citations (382)
Reported in this paper are the chemical compositions and trace element (REE,Ba,Rb,Sr,Nb,Zr,Ni,Cr,V,Ga,Y,Sc,Zn,Cu,etc)abundances of Tertiary continental alkali basalts from the Liube-yizheng area,Jiangsu Province,China.The olivine basalt,alkali olivine basalt and basanite are all derived from evolved melts which were once af-fected by different degrees of fractional crystallization of olivine and clinopyroxene(1:2)under high pres-sures.The initial melts were derived from the garnet lherzolite-type mantle source through low-degree par-tial melting.The mantle source has been affected by recent mantle-enrichment events(e.g.mantle metasomatism),resulting in incompatible trace element enrichment and long-term depletion of radiogenic isotopic compositions of Sr and Nd.
Trace element
Fractional crystallization (geology)
Metasomatism
Radiogenic nuclide
Incompatible element
Alkali basalt
Cite
Citations (0)
Fractional crystallization (geology)
Trace element
Incompatible element
Cite
Citations (45)
Trace element
Fractional crystallization (geology)
Metasomatism
Radiogenic nuclide
Incompatible element
Alkali basalt
Cite
Citations (6)
Dok island comprises Pliocene volcanic products such as a series of volcanoclastic rocks and lavas ranging in composition from alkali basalts, and trachyandesites to trachytes. Compositional variation of the basaltic rocks can be attributed to fractional crystallization of olivine, clinopyroxene, plagioclase, and magnetite. Chemical variations among the trachyandesites are caused by fractionation of clinopyroxene, plagioclase, and magnetite with minor amphibole, while trachytes are controlled mainly by feldspar fractionation. Incompatible element abundance ratios and chondrite normalized LREE/HREE ratios (e.g., (La/Yb)c: 24.8 to 32.8 for basalts, 15.6 to 31.2 for trachyandesites) suggest that the origins of the basalts and trachyandesites involve both different degrees of partial melting and subsequent fractional crystallization processes. Trace element ratios of the basalts from Dok island are characterized by high Ba/Nb, La/Nb, Ba/Th and Th/U and isotopic ratios (Tasumoto and Nakamura, 1991) that are similar to the EM 1 type of oceanic island basalts such as Gough and Tristan da Cunha basalts.
Fractional crystallization (geology)
Petrogenesis
Amphibole
Cite
Citations (1)