Melting depths and mantle heterogeneity beneath Hawaii and the East Pacific Rise: Constraints from Na/Ti and rare earth element ratios

Putirka, Keith

doi:10.1029/1998jb900048

Cited by 91 publications

(49 citation statements)

References 107 publications

(82 reference statements)

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“…Because the K Na of cpx/melt increases with increased P, while clinopyroxene and garnet K Ti min/melt remain constant or decrease, Na/Ti ranges in the same way as Lu/Hf ratio [Putirka, 1999]. Figure 7 shows the variations of Zr/Y, (Dy/ Yb) N , Lu/Hf, and Na Ã /Ti Ã ratios across Asal Rift.…”

Section: Results Of the Major Elements Forward Modelingmentioning

confidence: 99%

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Petrological constraints on melt generation beneath the Asal Rift (Djibouti) using quaternary basalts

Pinzuti

Humler

Manighetti

2013

Geochem Geophys Geosyst

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[1] The temporal evolution of the mantle melting processes in the Asal Rift is evaluated from the chemical composition of 56 new lava flows sampled along 10 km of the rift axis and 9 km off-axis (i.e., erupted within the last 620 kyr). Petrological and primary geochemical results show that most of the samples of the inner floor of the Asal Rift are affected by plagioclase accumulation. Trace element ratios and major element compositions corrected for mineral accumulation and crystallization show a symmetric pattern relative to the rift axis and preserved a clear signal of mantle melting depth variations. While FeO, Fe 8.0 , Zr/Y, and (Dy/Yb) N decrease from the rift shoulders to the rift axis, SiO 2 , Na/Ti, Lu/Hf increase and Na 2 O and Na 8.0 are constant across the rift. These variations are qualitatively consistent with shallow melting beneath the rift axis and deeper melting for off-axis lava flows. Na 8.0 and Fe 8.0 contents show that beneath the rift axis, melting paths are shallow, from 81 6 4 to 43 6 5 km. These melting paths are consistent with adiabatic melting in normal-temperature fertile asthenosphere, beneath an extensively thinned mantle lithosphere. On the contrary, melting on the rift shoulders (from 107 6 7 to 67 6 8 km) occurred beneath thicker lithosphere, requiring a mantle solidus temperature 100 6 40 C hotter. In this geodynamic environment, the calculated rate of lithospheric thinning appears to be 4.0 6 2.0 cm yr À1 , a value close to the mean spreading rate (2.9 6 0.2 cm yr À1 ) over the last 620 kyr.

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Section: Results Of the Major Elements Forward Modelingmentioning

confidence: 99%

“…[Fram et al, 1998;Putirka, 1999;Wang et al, 2002]. Heavy REE and HFSE favor garnet structure, because their partition coefficients change during melting of spinel versus garnet peridotites.…”

Section: Results Of the Major Elements Forward Modelingmentioning

confidence: 99%

Petrological constraints on melt generation beneath the Asal Rift (Djibouti) using quaternary basalts

Pinzuti

Humler

Manighetti

2013

Geochem Geophys Geosyst

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“…A source of excess thermal energy seems inescapable. These excess temperatures are favored by us because they explain the coincidence at some hot spots of high excess topography (Sleep, 1990;Schilling, 1991;Watson and McKenzie, 1991), and primitive liquids that contain (a) high TiO 2 /Na 2 O and high Sm/Yb ratios (Putirka, 1999), and (b) high FeO, and low SiO 2 contents (Langmuir et al, 1992;Albarede, 1992). What is particularly compelling is that Ti/Na ratios are controlled by clinopyroxene-, and Sm/ Yb ratios by garnet-liquid equilibria.…”

Section: Discussionmentioning

confidence: 99%

“…This value of 1280°C has been much utilized since 1988, and Presnall et al (2002) have recently estimated that T p MOR is between 1260-1310°C. However, many independent analyses of T p MOR undertaken since 1988, based on crustal thickness and new experiments and thermodynamic models of mantle melting, yield much higher values for T p MOR : 1340-1475°C (Kinzler and Grove, 1992b;Herzberg and O'Hara, 1998;Putirka, 1999;Asimow et al, 2001;Green et al, 2001;Wang et al, 2002;Herzberg, 2004;Putirka, 2005). The value for the average potential temperature beneath MORs is thus almost certainly much greater than 1280°C, and more likely in the range of 1450 ± 50°C (Wang et al, 2002;Putirka, 2005).…”

Section: Prior T Estimates Of the Sub-mid-ocean Ridge (Mor) Mantlementioning

confidence: 99%

“…Albarede (1992), Herzberg and O'Hara (1998), Herzberg (2004) and Putirka (1999Putirka ( , 2005 have also estimated melting depths and temperatures. Their work shows that major oxide compositions are sufficiently different between MORBs and ocean-island basalts (OIBs) so as to require that at least some OIBs are derived at greater pressures and temperatures.…”

Section: Prior Estimates Of T Ex and Sub-mor T Variationsmentioning

confidence: 99%

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Ambient and excess mantle temperatures, olivine thermometry, and active vs. passive upwelling

et al. 2007

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Mantle temperatures provide a key test of the mantle plume hypothesis, and olivine-liquid equilibria provide perhaps the most certain means of estimating mantle temperatures. Here, we review mantle temperature estimates and olivine thermometers, and calculate a new convective geotherm for the upper mantle. The convective geotherm is determined from estimates of sub-midocean ridge (MOR) mantle potential temperatures (T p is the T the mantle would have if it rose adiabatically without melting, and provides a reference for measuring excess temperatures at volcanic hot spots; T ex = T p hot spot − T p MOR ). The Siqueiros Transform has high MgO glass compositions that have been affected only by olivine fractionation, and yields T p Siqueiros = 1441 ± 63°C. Most midocean ridge basalts (MORB) have slightly higher FeO liq than at Siqueiros; if Fo max (= 91.5) and Fe 2+ -Mg exchange at Siqueiros apply globally, then upper mantle T p is closer to1466 ± 59°C. Since our global MORB database was not filtered for hot spots besides Iceland, Siqueiros may in fact be representative of ambient mantle, so we average these estimates to obtain T p MOR = 1454 ± 81°C; this value is used to calculate T ex . Global MORB variations in FeO liq indicate that 95% of the sub-MORB mantle has a global T range of ±140°C; 68% of this range (1σ) exhibits temperature variations of ± 34°C. Our estimate for T p MOR defines the convective mantle geotherm; this estimate is consistent with T estimates from sea floor bathymetry, and overlaps within 1σ estimates derived from phase transitions at the 410 km and 670 km seismic discontinuities. Mantle potential temperatures at Hawaii and Samoa are identical at 1722°C and at Iceland is 1616°C; hence T ex is ≈ 268°C at Hawaii and Samoa and 162°C at Iceland. Furthermore, T p estimates at Hawaii and Samoa exceed maximum T p estimates at MORs by N 100°C. Our T ex estimates agree with estimates based on excess topography and dynamic models of mantle flow and melt generation. Rayleigh number calculations further show that if our values for T ex extend to depths as small as 135 km, thermally driven, active upwellings will ensue. Hawaii, Samoa and Iceland thus almost assuredly result from thermally driven active upwellings, or mantle plumes. Estimates of T ex account for generalized differences in H 2 O contents between ocean islands and MORs, and are robust against variations in CO 2 , and major element components, and thus cannot be explained away by the presence of volatiles or more fusible source materials. However, our temperature variations at MORs do not account for H 2 O variations within the MORB source region.

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The Role of Crustal Strength in Controlling Magmatism and Melt Chemistry During Rifting and Breakup

Armitage

Petersen

Pérez‐Gussinyé

2018

Geochem Geophys Geosyst

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The strength of the crust has a strong impact on the evolution of continental extension and breakup. Strong crust may promote focused narrow rifting, while wide rifting might be due to a weaker crustal architecture. The strength of the crust also influences deeper processes within the asthenosphere. To quantitatively test the implications of crustal strength on the evolution of continental rift zones, we developed a 2‐D numerical model of lithosphere extension that can predict the rare Earth element (REE) chemistry of erupted lava. We find that a difference in crustal strength leads to a different rate of depletion in light elements relative to heavy elements. By comparing the model predictions to rock samples from the Basin and Range, USA, we can demonstrate that slow extension of a weak continental crust can explain the observed depletion in melt chemistry. The same comparison for the Main Ethiopian Rift suggests that magmatism within this narrow rift zone can be explained by the localization of strain caused by a strong lower crust. We demonstrate that the slow extension of a strong lower crust above a mantle of potential temperature of 1,350 °C can fit the observed REE trends and the upper mantle seismic velocity for the Main Ethiopian Rift. The thermo‐mechanical model implies that melt composition could provide quantitative information on the style of breakup and the initial strength of the continental crust.

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Melting depths and mantle heterogeneity beneath Hawaii and the East Pacific Rise: Constraints from Na/Ti and rare earth element ratios

Cited by 91 publications

References 107 publications

Petrological constraints on melt generation beneath the Asal Rift (Djibouti) using quaternary basalts

Petrological constraints on melt generation beneath the Asal Rift (Djibouti) using quaternary basalts

Ambient and excess mantle temperatures, olivine thermometry, and active vs. passive upwelling

The Role of Crustal Strength in Controlling Magmatism and Melt Chemistry During Rifting and Breakup

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