摘要
新嘎果地区位于西藏南冈底斯中段北部,洛巴堆-米拉山断裂南侧,区内发育的林子宗群典中组火山岩主要为流纹质岩屑晶屑凝灰岩,出露面积小。该区典中组火山岩具有富硅(SiO_2=75.09%~78.10%)、贫碱(K_2O+Na_2O=4.84~6.52%)、贫镁(MgO=0.24~0.37%)、过铝质(A/CNK=1.02~1.75)特征,富集轻稀土元素,轻重稀土元素分馏明显,(La/Yb)N=9.49~11.30,Eu异常从弱负异常到弱正异常(δEu=0.76~1.15),相对富集大离子亲石元素(Rb、Th、U、K),亏损Nb、Ta、P、Ti等高场强元素,并且明显亏损Ba和Sr,属于钙碱性过铝质系列,具有陆源弧火山岩的特点。锆石U-Pb年龄为70.89±0.31 Ma,是目前典中组火山岩最老的年龄;锆石176Hf/177Hf值比较均一,分布于0.282 820~0.282 939之间,εHf(t)值为+3.2^+7.4,tDM模式年龄变化于662~930 Ma之间。地球化学研究表明,新嘎果地区典中组火山岩形成于俯冲构造环境,岩浆源区主要来源于地幔组分,并在岩浆演化过程中混染古老地壳。
The volcanic rocks in Linzizong Group are developed in the Gangdise belt of Tibet, and can reflect the important information of Neo-Tethys from its subduction to the India-Asia collision. The Xingaguo area is located in the northern middle part of south Gangdise, Tibet, lying to the south of Luobadui-Milashan Fault. The volcanic rocks in Dianzhong Formation consist of rhyolitic detritus crystal tuff, and are distributed in a limited area in the north of the ore district. The volcanic rocks in Dianzhong Formation from Xingaguo are composed of rhyolitic detritus crystal tuff and are distributed in the northern area, with the exposed area being small. Chemical analyses show that the volcanic rocks in Dianzhong Formation have high SiO2（ SiO2 = 75.09% N 78.10 % ）, low alkali （K2O ＋ Na2O = 4.84 % -- 6.52 % ）, and low Mg （MgO = 0.24 % - 0.37 % ）, with peraluminous nature （A/CNK = 1.02--1.75 ）＂ they are characterized by LREE enrichment and obvious REE differentiation [ （ La/Yb）N = 9.49- 11.30 ], with weak positive and negative Eu anomalies （ δEu = 0.76 - 1.15 ） ; they are enriched in LILEs （Rb, Th, U and K）, depleted in HFSEs （Nb, Ta, P and Ti）, and obviously depleted in Ba and Sr, thus belonging to calc-alkalic and peraluminous series and having the characteristics of continental margin arc volcanic rocks. The LA-MC-ICP-MS zircon U-Pb chronology indicates that the volcanic rocks in Dianzhong Formation were emplaced at 70.89 ± 0.31 Ma, which is the oldest age for the volcanic rocks in Dianzhong Formation, and has 176Hf/177Hf values in the range of 0.282 820 -0. 282 939, eHf（ t ） values in the range of ＋ 3.2N ＋ 7.4 and single-stage model ages （tDM） between 662 and 930 Ma. The volcanic rocks in Dianzhong Formation from Xingaguo area were formed in a tectonic environment of ocean subduction, mainly derived their materials from the mantle components, and contaminated crustal material in the process of magma rising.
出处
《岩石矿物学杂志》
CAS
CSCD
北大核心
2018年第1期47-60,共14页
Acta Petrologica et Mineralogica
基金
公益性行业专项(201511022-05
201511017)
国家自然科学基金项目(41302060)
中国地质科学院基本科研业务费(YYWF201608)~~
