@article{fdi:010062313,
  title = {{W}hy {A}rchaean {TTG} cannot be generated by {MORB} melting in subduction zones},
  author = {{M}artin, {H}. and {M}oyen, {J}. {F}. and {G}uitreau, {M}. and {B}lichert-{T}oft, {J}. and {L}e {P}ennec, {J}ean-{L}uc},
  editor = {},
  language = {{ENG}},
  abstract = {{U}ntil recently it was assumed that the {A}rchaean continental crust (made of {TTG}s: tonalites, trondhjemites, and granodiorites) was generated through partial melting of {MORB}-like basalts in hot subduction environments, where the subducted oceanic crust melted at high pressure, leaving a garnet-bearing amphibolitic or eclogitic residue. {H}owever, recent geochemical models as well as basalt melting experiments have precluded {MORB} as a plausible source for {TTG}s. {R}ather, geochemical and experimental evidences indicate that formation of {TTG} required a {LIE}-enriched source, similar to oceanic plateau basalts. {M}oreover, subduction is a continuous process, while continental growth is episodic. {S}everal "super-growth events" have been identified at similar to 4.2, similar to 3.8, similar to 3.2, similar to 2.7, similar to 1.8, similar to 1.1, and similar to 0.5 {G}a, which is inconsistent with the regular pattern that would be expected from a subduction-driven process. {I}n order to account for this periodicity, it has been proposed that, as subduction proceeds, descending residual slabs accumulate at the 660-km seismic discontinuity. {W}hen stored oceanic crust exceeds a certain mass threshold, it rapidly sinks into the mantle as a cold avalanche, which induces the ascent of mantle plumes that in turn produce large amounts of magmas resulting in oceanic plateaus. {H}owever, melting at the base of thick oceanic plateaus does not appear to be a realistic process that can account for {TTG} genesis. {M}odern oceanic plateaus contain only small volumes (<= 5%) of felsic magmas generally formed by high degrees of fractional crystallization of basaltic magmas. {T}he composition of these felsic magmas drastically differs from that of {TTG}s. {I}n {I}celand, the interaction between a mantle plume and the mid-{A}tlantic ridge gives rise to an anomalously ({A}rchaean-like) high geothermal gradient resulting in thick basaltic crust able to melt at shallow depth. {E}ven in this favorable context though, the characteristic {A}rchaean {TUG} trace element signature is not being produced. {C}onsequently, internal recycling of oceanic plateaus does not appear to be a suitable process for the genesis of {A}rchaean continental crust. {A} possible alternative to this scenario is the subduction of oceanic plateaus. {T}his hypothesis is supported by a present-day analog. {I}n {E}cuador, the {C}arnegie ridge, which is an oceanic plateau resulting from the {G}alapagos hot spot activity, is being subducted beneath the {S}outh {A}merican plate. {N}ot only are the resulting magmas adakitic ({TTG}-like) in composition, but the volcanic productivity is several times greater than in other parts of the {A}ndean volcanic arc. {A}bove the location where the plateau is subducted, the arc is wide and the quaternary volcanoes numerous (about 80 active edifices). {T}he volcanic productivity of each individual volcano also is more intense than away from the subduction focal point with an average output rate of about 0.4-0.5 km(3).ka(-1) compared with only about 0.05-0.2 km(3).ka(-1) for production rates at volcanoes erupting in the rest of the arc. {C}onsequently, we infer that occasional subduction of oceanic plateaus throughout {E}arth's history can account for the episodic nature of crustal growth. {A}dditionally, the generation by this mechanism of huge volumes of {TTG}-like magmas would readily dominate the crustal growth record.},
  keywords = {{A}rchaean {TTG} ; {S}ubduction ; {O}ceanic plateau ; {C}arnegie ridge ; {B}asalt ; partial melting ; {C}rustal growth ; {ANDES} ; {EQUATEUR}},
  booktitle = {},
  journal = {{L}ithos},
  volume = {198},
  numero = {},
  pages = {1--13},
  ISSN = {0024-4937},
  year = {2014},
  DOI = {10.1016/j.lithos.2014.02.017},
  URL = {https://www.documentation.ird.fr/hor/fdi:010062313},
}