Niu, Y., Generation and evolution of basaltic magmas: Some basic concepts and a new view on the origin of Mesozoic-Cenozoic basaltic volcanism in eastern China, Geological Journal of China Universities, 11, 9 – 46, 2005.

2005 年 3 月，第 1 期 9 - 46 页 高 校 地 质 学 报 March 2005, Vol. 11, No. 1, p. 9 - 46 Geological Journal of China Universities

________________________ 收稿日期：2004-09-18；改回日期：2005-01-25 作者简介：Yaoling Niu, PhD, is a Professor of Earth Sciences at Durham University, UK. His research uses petrology and geochemistry as a means to

understanding how the Earth works on all scales today and in Earth’s history! He publishes his research results mostly in prestigious journals like Journal of Geophysical Research, Journal of Petrology, Earth and Planetary Science Letters, Nature, Sciences etc. He has been honored with guest professorships by China University of Geosciences (Beijing) and Northwest University of China (Xi’an), and as an Outstanding Overseas Chinese Scientist by Natural National Science Foundation of China (NSFC). He has recently taken the leadership as the Chairman of the Commission on Solid Earth Composition and Evolution (SECE) under International Union of Geological Sciences (IUGS). Correspondence: Department of Earth Sciences, Durham University, Durham DH1 3LE, UK. E-mail: yaoling.niu@durham.ac.uk

Generation and Evolution of Basaltic Magmas: Some Basic Concepts and a New View on the

Origin of Mesozoic-Cenozoic Basaltic Volcanism in Eastern China

(玄武岩浆起源和演化的一些基本概念以及对中国

东部中-新生代基性火山岩成因的新思路)

Yaoling Niu1,2 (牛耀龄) 1Department of Earth Sciences, University of Durham, Durham DH1 3LE, UK (英国杜伦大学地球科学系)

2China University of Geosciences, Beijing (中国地质大学，北京), Beijing 100083, China

Abstract：Some basic concepts of basaltic magma generation and evolution are discussed in the context of global

tectonics. These concepts need better understanding before invoking elusive possibilities in igneous petrogenesis on all

scales and in all tectonic environments. A hypothesis for the Mesozoic lithosphere thinning and Mesozoic/Cenozoic

basaltic volcanism in eastern China is presented. This hypothesis is consistent with observations and complies with basic

physics. While the eastern China volcanism can be defined as “intra-plate” volcanism, it is in fact a special consequence of

plate tectonics. The Mesozoic lithosphere thinning in eastern China is best explained by a process that “transformed” the

deep portion of the lithosphere into convective asthenosphere by hydration. The water that did so may come from

dehydration of subducted Pacific (or predecessor) oceanic lithosphere that is presently lying horizontally in the transition

zone beneath eastern Chinese continent as detected by seismic tomographic models. The Mesozoic volcanism may be

genetically associated with the lithospheric thinning because the basaltic source is ancient isotopically enriched (εNd < 0)

lithosphere - being converted to the asthenosphere. The NNE-SSW Great Gradient Line (GGL) marked by the sharp

altitude, gravity anomaly, crustal thickness, and mantle seismic velocity changes from plateaus in the west to the hilly

plains of eastern China is an expression of variation in lithospheric thickness from probably > 150-200 km thick beneath

the plateaus in the west to probably < 80 km thick beneath eastern China. The “remote” western Pacific subduction

systems induce asthenospheric flow from beneath eastern China towards the subduction zones (“wedge suction”), which, in

turn, requires asthenospheric material replenishment from beneath the plateaus to eastern China. As a result, such eastward

asthenospheric flow experiences upwelling and decompression (from beneath thickened to thinned lithosphere), which

causes the flowing asthenosphere (e.g., εNd > 0) to partially melt and produce the Cenozoic eastern China basaltic

volcanism. Such volcanism may have actually begun at the end of the Mesozoic lithosphere thinning in the late Cretaceous.

This simple concept is currently being substantiated with detailed petrologic and geochemical data.