A record of 0.5 Ga of evolution of the continental crust along the northern edge of the Kaapvaal Craton, South Africa: Consequences for the understanding of Archean geodynamic processes

作者：Vezinet Adrien^*; Moyen Jean Francois; Stevens Gary; Nicoli Gautier; Laurent Oscar; Couzinie Simon; Frei Dirk

来源：Precambrian Research, 2018, 305: 310-326.

DOI：10.1016/j.precamres.2017.11.019

• Continental crust
• Northern Kaapvaal craton
• Zircon and monazite U-Pb dating
• Phase equilibrium modelling

Geodynamics of crustal growth and evolution consist in one of the thorniest questions of the early Earth. In order to solve it, Archean cratons are intensively studied through geophysical, geochemical and geochronological investigations. However, timing and mechanisms leading to accretion and stabilization of crustal blocks are still under question. In this study, new information on the evolution of Archean cratons is provided through complementary approaches applied to the northern margin of the Archean Kaapvaal craton (KC). The study area comprises the Pietersburg Block (PB) and the terrane immediately adjacent to the North: the Southern Marginal Zone of the Limpopo Complex (SMZ). We present a comprehensive petro-metamorphic study coupled with LA-ICP-MS U-Pb isotope examination of both Na- and K-rich granitoids from the two areas. This dataset points toward a new interpretation of the northern KC (PB + SMZ). Two significant magmatic events are newly recognized: (i) a ca. 3.2 Ga event, and (ii) a protracted magmatic event between ca. 2.95-2.75 Ga. These events affected in both investigated areas and are unrelated to the ca. 2.7 Ga-old event usually attributed to the SMZ. More importantly, phase equilibrium modelling of several lithologies from the SMZ basement points to middle-amphibolite fades conditions of equilibration instead of granulite-facies conditions historically assumed.
This study has both important regional and global implications. Firstly, the presence of a continuous basement from the Thabazimbi-Murchison Lineament to the Palala Shear Zone, different than Central Zone of the Limpopo Complex basement, implies a complete reviewing of the whole Limpopo Complex concept. Secondly, the geometry observed in the northern Kaapvaal craton is assumed to testify for a complete accretionary orogenic sequence with formation of both mafic and TTG lithologies through arc-back arc geodynamic. This was followed by a long-lived lateral compression triggering partial melting of the lower continental crust and emplacement of Bt-granitoids bodies that stabilizes the continental crust. Lastly, partial melting of the underlying enriched mantle stabilized the entire lithosphere allowing long-term preservation of the crustal block.

• 出版日期2018-2