河岭式酸性稀土火山岩系的演化特征与稀土富集

EVOLUTION AND RE CONCENTRATION OF HELING-TYPE RE ACIDIC VOLCANIC ROCK SERIES

河岭式酸性稀土火山岩系位于南岭东段稀土成矿带内,形成于燕山晚期,由富含稀土的酸性火山熔岩和次花岗斑岩组成,是一独立的稀土岩浆岩演化系列。从火山熔岩到次花岗斑岩,岩浆向偏基性富破方向演化,稀土元素在演化的中、晚期被富集,特别是晚期侵入的偏基性富碱的次花岗斑岩中,稀土元素丰度最高,并有向更富轻稀土方向演化的趋势。岩浆房的对流扩散和结晶分异作用可解释这些演化趋势。

Heling-type of RE volcanic rock series, locating in the RE metallogenic belt of east Nanling section, formed in late Yanshan movement, and consisted of acidic lava and subvolcanic granite poyphry both with high RE contents. Alkali, especially the potassium, enrichments are characterized, among them Heling volcanic rock series is typical.From early period to late period, magmatie evolution tends to become more and more marie and alkali, SiO_2 decreasing and K_2O+Na_2O, CaO, MgO, TiO_2, FeO increasing. With respect to this, RE, LRE/HRE and δEu values increase. RE were enriched in the middle and late evolution stages. Espeeialiy the late intrusive granite porphyry with more mafie and alkali contents has the highest concentration of RE.Convection-driven diffusion and crystallization in magma chamber might be responsible for this evolution trend. Magma riehed in Si, volatile components (and related Rb, Li and some HRE) and poored in RE in the upper part of the chamber was first erupted and formed volcanic rocks; these relatively riched in marie and alkali and RE contents in the lower part of the chamber were late intruded and formed granite porphyry.The RE acidic volcanic rock series were formed after RE granitic series which occurred in the same region, but no evolution relation is recognized. The RE volcanic rock series are assumed to be independent. On the light of Heling volcanic rock series, their evolution trends are from bastnaesite, monazite rhylite to bastnaesite, britholite granite porphyry which seems to have more LRE concentration.