Continental velocity through Precambrian times: The link to magmatism, crustal accretion and episodes of global cooling

Abstract

a b s t r a c tQuasi-integrity of continental crust between Mid-Archaean and Ediacaran times is demonstrated by conformity of palaeomagnetic poles to near-static positions between w2.7e2.2 Ga, w1.5e1.2 Ga and w0.75e0.6 Ga. Intervening data accord to coherent APW loops turning at "hairpins" focused near a continental-centric location. Although peripheral adjustments occurred during Early Proterozoic (w2.2 Ga) and Grenville (w1.1 Ga) times, the crust retained a low order symmetrical crescent-shaped form constrained to a single global hemisphere until break-up in Ediacaran times. Conformity of palaeomagnetic data to specific Eulerian parameters enables definition of a master Precambrian APW path used to estimate the root mean square velocity (v RMS ) of continental crust between 2.8 and 0.6 Ga. A long interval of little polar movement between w2.7 and 2.2 Ga correlates with global magmatic shutdown between w2.45 and 2.2 Ga, whilst this interval and later slowdown at w0.75e0.6 Ga to velocities of <2 cm/year correlate with episodes of widespread glaciation implying that these prolonged climatic anomalies had an internal origin; the reduced input of volcanically-derived atmospheric greenhouse gases is inferred to have permitted freeze-over conditions with active ice sheets extending into equatorial latitudes as established by low magnetic inclinations in glaciogenic deposits. v RMS variations through Precambrian times correspond to the distribution of U-Pb ages in orogenic granitoids and detrital zircons and demonstrate that mobility of continental crust has been closely related to crustal tectonism and incrementation. Both periods of near-stillstand were followed by rapid v RMS recording massive heat release from beneath the continental lid at w2.2 and 0.6 Ga. The first coincided with the Lomagundi-Jatuli isotopic event and led to prolonged orogenesis accompanied by continental flooding and reconfiguration of the crust on the Earth's surface; the second led to continental break-up and instigated the comprehensive Plate Tectonics that has characterised Phanerozoic times. The Mesoproterozoic interval characterised by anorogenic magmatism correlates with low v RMS between w1.5 and 1.1 Ga. Insulation of the sub-continental mantle evidently permitted high temperature melting and weakening of the crustal lid to enable buoyant emplacement of large plutons at high crustal levels during this magmatic event unique to Mesoproterozoic and early Neoproterozoic times.Ó 2012, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. All rights reserved.

Tectonic speed limits from plate kinematic reconstructions

“…Continental RMS velocity analyses derived from paleomagnetic Apparent Polar Wander (APW) paths indicate significant variations in velocities, with values greater than ∼20 cm/yr in the Archean, and with ∼10 cm/yr maximum limits since the Mesoproterozoic (∼1600 Ma) (Piper, 2013), similar to what we find for the Mesozoic and Cenozoic. Much larger RMS (plate or continental) velocities in the past may represent more vigorous mantle convection, and hence faster plate motions, from (∼150-200 • C) hotter mantle temperatures (Abbott et al, 1994).…”

The structural, metamorphic and magmatic evolution of Mesoproterozoic orogens

“…The Mesoproterozoic (1600 to 1000 Ma) is an Era of Earth history that has been defined in the literature as being quiescent in terms of both tectonics and the evolution of the biosphere and atmosphere (Holland, 2006;Piper, 2013b;Young, 2013). The 'boring billion' is an informal term that is given to a time period overlapping the Mesoproterozoic period, extending from 1.85 to 0.85 Ga (Holland, 2006).…”

Geodynamic Significance of the Updated Statherian-Calymmian (at C. 1.65 and 1.46 Ga) Palaeomagnetic Results from Mafic Dykes of the Indian Shield

“…More data from future studies may validate the linkage. A proposal suggesting remagnetization of Calymmian (1.466 Ga) dykes at Grenville age, in view of their proximity to the EGMB tectonic front, appears to be in conformity with Palaeopangaea B reconstruction 13 , however, such an argument remains equivocal at this stage. Further analysis of recently reported geochemical data suggests that the 1.466 Ga felsic/mafic dyke magmatism has affinity to a subduction-related shoshonite-calcalkaline and high-K calc-alkaline magmatism, and it is spatially confined to the Bastar craton near the EGMB.…”

“…The angular distances between the three pairs of poles plotted from Baltica and India are remarkably in agreement ( Figure 6) suggesting their movement as a single entity. Extensional processes with accompanied basin formation in the Late Palaeoproterozoic both in Australia and India, the presence of significant juvenile felsic volcanic source of 1650 Ma as evident from €Nd values of the Proterozoic detritus in Australian sedimentary successions 59 , the c. We also evaluated the present results with respect to the Palaeopangaea reconstruction models proposed by Piper 13 . Both poles are rotated according to the Palaeopangaea rotation parameters 13 and none of these poles correlates with the proposed reconstructions (figure not shown).…”

“…Piper 13 , on the other hand, argues for quasi-integral property of palaeomagnetic pole positions across most Precambrian shields for over 2 Ga, challenging the popular models of 'Rodinia' and 'Columbia' supercontinents as well as the general thesis of 'supercontinent cycles'.…”