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

作     者：J.D.A.Piper 

作者机构：Geomagnetism LaboratoryGeology and GeophysicsSchool of Environmental SciencesUniversity of Liverpool.Liverpool L69 7ZEUK 

出 版 物：《Geoscience Frontiers》 (地学前缘（英文版）)

年 卷 期：2013年第4卷第1期

页      面：7-36页

核心收录：

学科分类：070902[理学-地球化学] 0709[理学-地质学] 07[理学] 

主　　题：Continental velocity Precambrian Palaeopangaea Palaeomagnetism Magmatism Tectonics 

摘      要：Quasi-integrity of continental crust between Mid-Archaean and Ediacaran times is demonstrated by conformity of palaeomagnetic poles to near-static positions between -2.7-2.2 Ga, -1.5-1.2 Ga and -0.75-0.6 Ga. Intervening data accord to coherent APW loops turning at ＂hairpins＂ focused near a continental-centric location. Although peripheral adjustments occurred during Early Proterozoic （-2.2 Ga） and Grenville （- 1.1 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 （VRMS） of continental crust between 2.8 and 0.6 Ga. A long interval of little polar movement between -2.7 and 2.2 Ga correlates with global magmatic shutdown between -2.45 and 2.2 Ga, whilst this interval and later slowdown at -0.75-0.6 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. VRMS vari- ations 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 VRMS recording massive heat release from beneath the continental lid at -2.2 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 i