Temperatures in ambient mantle and plumes: Constraints from basalts, picrites, and komatiites

Abstract

International audienceSeveral methods have been developed to assess the thermal state of the mantle below oceanic ridges, islands, and plateaus, on the basis of the petrology and geochemistry of erupted lavas. One leads to the conclusion that mantle potential temperature (i.e., TP) of ambient mantle below oceanic ridges is 1430°C, the same as Hawaii. Another has ridges with a large range in ambient mantle potential temperature (i.e., TP = 1300–1570°C), comparable in some cases to hot spots (Klein and Langmuir, 1987; Langmuir et al., 1992). A third has uniformly low temperatures for ambient mantle below ridges, ∼1300°C, with localized 250°C anomalies associated with mantle plumes. All methods involve assumptions and uncertainties that we critically evaluate. A new evaluation is made of parental magma compositions that would crystallize olivines with the maximum forsterite contents observed in lava flows. These are generally in good agreement with primary magma compositions calculated using the mass balance method of Herzberg and O'Hara (2002), and differences reflect the well-known effects of fractional crystallization. Results of primary magma compositions we obtain for mid-ocean ridge basalts and various oceanic islands and plateaus generally favor the third type of model but with ambient mantle potential temperatures in the range 1280–1400°C and thermal anomalies that can be 200–300°C above this background. Our results are consistent with the plume model

An 850–820Ma LIP dismembered during breakup of the Rodinia supercontinent and destroyed by Early Paleozoic continental subduction in the northern Tibetan Plateau, NW China

“…Among the Yingfeng dolerites/basalts, samples 13MH-13/18/67 are least-evolved, and have the highest MgO contents (9.5-11.5 wt.%) and compatible elements. With these samples, we calculated the compositions of primary magma based on the procedure of Herzberg et al (2007) and Wang et al (1434-1524°C) are obtained, which are higher than that of contemporary ambient MORB-source asthenosphere mantle (1350-1450°C; references in Li et al, 2008b), implying an origin of anomalously hot mantle source. In addition, the North Qaidam mafic rocks are characterized by high Ti/V, mostly >20 for the low-Ti tholeiitic group and >50 for the high-Ti alkaline group, compatible with continental flood tholeiites and ocean-island basalts, respectively ( Fig.…”

2.24 Ga mafic dykes from Taihua Complex, southern Trans-North China Orogen, and their tectonic implications

“…The high Fe contents can be obtained from: (1) up-welling mantle plume (Gibson et al, 2000); (2) garnet-bearing lherzolite (Takahahshi et al, 1998); (3) mantle-wedge metasomatized by slab-derived fluids/melts (Leybourne et al, 1999); (4) garnet-free refractory mantle (Hanski and Smolkin, 1995). Although mafic dyke swarms dated at ∼2.2 Ga were found globally in recent years and perhaps were related with mantle plumes (French and Heaman, 2010), the genesis of the Zhaiwa mafic dykes was unlikely to be associated with mantle plumes, because: (1) the Zhaiwa mafic dykes are only sparsely distributed, inconsistent with the widespread mafic rocks associated with mantle plumes; (2) plume-related basalts are generally enriched in Nb, Ta and have high Ce/Pb ratios (Callegaro et al, 2013), which is inconsistent with the Zhaiwa mafic dykes; (3) the calculated mantle potential temperatures (Tp) via the formula Tp = 1463 + 12.74MgO-2924/MgO (MgO in wt%) range 722-1135 • C (Herzberg et al, 2007;Herzberg and Asimow, 2008;Herzberg and Gazel, 2009), which is clearly lower that that related to mantle plume (i.e., 1560-1620 • C for the Galapagos mantle plume; Herzberg and Asimow, 2008). (Shaw, 1970) of a lherzolitic mantle source.…”

Terrestrial aftermath of the Moon-forming impact

“…Furthermore, most of the mantle was probably already frozen on the adiabat of the slurry epoch. Only modest cooling (at most a few hundred kelvins) of the mantle on average is allowed between approximately 10 Myr after the Moon-forming impact and the approximately 3.8 Ga age in the Archaean for which petrologists are able to infer mantle temperatures by studying komatiite lavas [48,49]. The hottest Archaean komatiites were probably the product of mantle plumes, indicating that Archaean mantle temperatures were heterogeneous.…”

“…The available heat budget indicates that Hadean plate velocities were on average low and subducting slabs were typically old [48,49]. However, brief periods of rapid subduction were likely once slabs with thick oceanic crust penetrated to depths of several tens of kilometres, where eclogite is stable at cool slab temperatures (figure 5).…”

“…[48,49]). Evidence of heterogeneous mantle temperatures is then provided by Archaean igneous rocks, but there are no relevant Hadean data [48][49][50].…”