文献类型：期刊文献

中文题名：云南个旧地区龙岔河岩体中钾长石巨晶的成因及对晶粥储库形成的启示

英文题名：Origin of K-feldspar megacrysts in Longchahe pluton in Gejiu area,Yunnan Province,and its implications for the formation of crystal mush reservoir

作者：占义勇 冷成彪 王艳军 张颖 莫雷

第一作者：占义勇

通信作者：Leng, CB[1];Leng, CB[2]

机构：[1]东华理工大学,铀资源探采与核遥感全国重点实验室,南昌330013;[2]东华理工大学地球与行星科学学院,南昌330013;[3]贵州理工学院资源与环境工程学院,贵阳550025

第一机构：东华理工大学,铀资源探采与核遥感全国重点实验室,南昌330013

通信机构：corresponding author), East China Univ Technol, Natl Key Lab Uranium Resource Explorat Min & Nucl, Nanchang 330013, Peoples R China;corresponding author), East China Univ Technol, Sch Earth & Planetary Sci, Nanchang 330013, Peoples R China.

年份：2026

卷号：42

期号：6

起止页码：2257-2272

中文期刊名：岩石学报

外文期刊名：Acta Petrologica Sinica

收录：;WOS:【SCI-EXPANDED(收录号:WOS:001786715300017)】；北大核心:【北大核心2023】；

基金：国家自然科学基金项目(42022021)资助。

语种：中文

中文关键词：龙岔河岩体;钾长石巨晶;晶体粒度分布;元素含量;晶粥储库

外文关键词：Longchahe Pluton;K-feldspar megacrysts;Crystal size distribution;Element Content;Crystal mush reservoir

摘要：钾长石巨晶在云南个旧西区的晚白垩世龙岔河岩体中大量发育,然而,其成因及岩浆动力学意义尚不明确。本文对该岩体中的钾长石巨晶开展了晶体粒度分布(CSD)、岩相学和原位主微量元素分析。结果表明,岩体为似斑状结构的黑云母花岗岩,岩体中钾长石巨晶具有较大的特征长度(7.90~11.93mm),计算显示其存留时间为0.25~60kyr,指示其为长周期结晶的产物。CSD模式的截距与钾长石含量呈正相关关系,当截距不变而矿物含量变化显著时可能出现了堆晶过程,进一步揭示其形成受堆晶作用的影响较大。镜下观察发现钾长石巨晶可分为两类:TypeⅠ为发育卡氏双晶的正长石,TypeⅡ为具格子双晶的微斜长石。两类钾长石在成分上均属碱性长石(Or_(88-95)),但TypeⅠ与TypeⅡ相比更富集Ba,而亏损Sr和Rb,暗示二者为不平衡结晶的产物。Ti温度计计算结果表明,TypeⅠ巨晶的核部温度为653~699℃,低于边部温度(751~756℃);而TypeⅡ的核部与边部的温度均为750±2℃。两类钾长石随着结晶温度的升高,其Rb/Sr、Ba/Sr、Eu呈现下降的趋势,指示岩浆储库的升温可能是钾长石巨晶的生长机制。结合前人资料,本文提出龙岔河岩体钾长石的核部形成于地壳浅部的长英质晶粥储库,随后经历了中基性岩浆注入导致的晶粥活化过程,使其形成了富Ba、Sr的边部。钾长石的环带结构和成分变化,进一步印证多(期)次岩浆注入与岩浆混合对晶体生长的延时作用,以致形成巨晶。
Despite the widespread occurrence of K-feldspar megacrysts in the Late Cretaceous Longchahe pluton in western Gejiu,Yunnan,their origin and magmatic dynamic implications remain unclear.In this study,crystal size distribution(CSD),petrographic characteristics,and in situ major and trace element compositions of K-feldspar megacrysts from the pluton were investigated.The results show that the pluton is composed of porphyritic biotite granite.The K-feldspar megacrysts display relatively large characteristic lengths(7.90~11.93mm).Calculated residence times range from 0.25kyr to 60kyr,indicating that these megacrysts formed through prolonged crystallization.The intercepts of the CSD plots are positively correlated with K-feldspar modal abundance.Where the intercept remains constant but mineral abundance varies markedly,crystal accumulation is inferred,indicating that accumulation processes played an important role in megacryst formation.Petrographic observations identify two types of K-feldspar megacrysts:TypeⅠorthoclase with well-developed Carlsbad twinning,and TypeⅡmicrocline characterized by tartan twinning.Both types are compositionally classified as alkali feldspar(Or_(88-95)).However,TypeⅠmegacrysts are relatively enriched in Ba and depleted in Sr and Rb compared with TypeⅡ,implying crystallization under disequilibrium conditions.Ti-in-feldspar thermometry yields core temperatures of 653~699℃and rim temperatures of 751~756℃for TypeⅠmegacrysts,whereas both cores and rims of TypeⅡmegacrysts have yield uniform temperatures of 750±2℃.With the increase of crystallization temperature,the Rb/Sr,Ba/Sr,and Eu of the two types of K-feldspar show a decreasing trend,indicating that heating of the magma reservoir may be the growth mechanism of the K-feldspar megacrysts.Integrating these results with previous studies,we propose that the cores of the K-feldspar megacrysts crystallized within a shallow crustal felsic crystal-mush reservoir.Subsequent injections of intermediate-mafic magma rejuvenated the mush and promoted the development of Ba-and Sr-rich rims.The pronounced zoning patterns and compositional variations of the K-feldspar megacrysts further support a model in which repeated magma recharge and magma mixing retarded crystal growth,ultimately leading to the formation of megacrysts.