新疆天山石炭—二叠纪大规模岩浆成矿事件与形成机制探讨

天山地质构造演化复杂,多阶段演化中岩浆活动与成矿作用规模并不均衡。而石炭-二叠纪却是天山成矿带大规模岩浆活动和金属成矿作用的"爆发"期。本研究紧紧围绕岩浆铜镍矿床、斑岩型铜(钼)矿床及火山岩型磁铁矿矿床,从含矿岩体的岩浆起源、岩浆演化及成矿特点,系统研究地球深部相应岩浆活动的地质过程。通过典型矿床的深入剖析,建立相应矿床类型的成矿模式,破解制约找矿突破的控制因素,系统阐述了板块构造与地幔柱体制叠加并存的地质特征与成矿表现。联系塔里木地幔柱的活动特点和成矿表现,将其与天山造山带三类主要矿床类型建立关联,对比岩石学、年代学及地球化学研究,发现天山成矿带成矿类型与塔里木地幔柱及板块构造存有密切关系,可能是两种构造体制叠加并存的结果。塔里木克拉通深部熔融的地幔物质,围绕刚性塔里木克拉通边缘不断上涌,并与表壳物质发生交换,随着板块俯冲的持续和减弱,深部上涌的地幔物质不断加强,先后形成因深部地幔物质多寡而金属聚集的不同矿床类型。该地幔柱形成时深部过程与成矿作用认识模型的建立,极大地推进了板块构造、地幔柱与岩浆成矿作用的研究,同时可为天山及邻区找矿突破提供借鉴和指导。     

东昆仑祁漫塔格地区构造岩浆作用与成矿关系初步探讨

以钾、钠含量变化为主要指标获取祁漫塔格地区各个地史时期花岗岩类的成因类型.结果表明,区内构造岩浆作用在时间上具有明显的阶段性,加里东中晚期是本区第一次侵入岩浆作用的高峰期,印支中晚期为本区花岗岩浆作用的鼎盛时期,加里东中晚期和印支中晚期也是区内两次区域成矿作用的大爆发期.岩体分布具有明显的方向性.主要由北东向和北西向两...     

Crustal accretion beneath the Koyna coastal region (India) and Late Cretaceous geodynamics

In 1967 a major earthquake in the Koyna region attracted attention to the hitherto considered stable Indian shield. The region is covered by a thick pile of Deccan lava flows and characterized by several hidden tectonic features and complex geophysical signatures. Although deep seismic sounding studies have provided vital information regarding the crustal structure of the Koyna region, much remains unknown. The two available DSS profiles in the region have been combined along the trend of Bouguer gravity anomalies. Unified 2-D density modelling of the Koyna crust/mantle suggests a ca. 3 km thick and 40 km wide high velocity/high density anomalous layer at the base of the crust along the coastline. The thickness of this anomalous layer decreases gradually towards the east and ahead of the Koyna gravity low the layer ceases to be visible. Based on the seismic and gravity data interpretation in the geodynamical/rheological boundary conditions the anomalous layer is attributed to igneous crustal accretion at the base of the crust. It is suggested that the underplated layer is the imprint of the magmatism caused by the deep mantle plume when the northward migrating Indian plate passed over the Reunion hotspot.     

华北克拉通南缘豫西下汤地区2.3 Ga岩浆作用和1.94 Ga变质作用

本文报道了华北克拉通南缘豫西鲁山下汤地区古元古代片麻状花岗岩和黑云角闪斜长片麻岩的全岩地球化学和锆石SHRIMP U-Pb年龄和Hf同位素组成。岩石呈包体形式存在于中元古代花岗岩中。片麻状花岗岩具深熔特征,岩浆锆石年龄为2.30Ga;岩石高SiO2和K2O,低ΣFeO、MgO和CaO,具稀土总量较高(ΣREE=165.8×10-6)、轻重稀土分离较强[(La/Yb)n=37.8]及弱负铕异常(Eu/Eu*=0.76)的稀土模式;εNd(t)(t=2.30Ga)=-0.75;tDM(Nd)=2.66Ga。黑云角闪斜长片麻岩变质原岩为辉长闪长岩,捕获锆石年龄为2.25Ga;岩石低SiO2和MgO,高Al2O3和P2O5,具稀土总量高(ΣREE=373.4×10-6)、轻重稀土分离不强[(La/Yb)n=9.4]及较强负铕异常(Eu/Eu*=0.44)的稀土模式;εNd(t)(t=2.25Ga)=-1.21;tDM(Nd)=2.75Ga。片麻状花岗岩和黑云角闪斜长片麻岩都记录了1.94Ga变质锆石年龄。片麻状花岗岩的岩浆锆石组成域的εHf(t)(t=2.30Ga)=-6.71～0.38,tDM1(Hf)=2627～2910Ma,tDM2(CC)(Hf)=2823～3255Ma。黑云角闪斜长片麻岩的捕获锆石组成域的εHf(t)(t=2.25Ga)=-19.58～-1.73,tDM1(Hf)=2664～3360Ma,tDM2(CC)(Hf)=2968～4011Ma。结合前人资料,得出如下结论:华北克拉通南缘豫陕晋结合部地区存在一规模较大的约2.3Ga地质体分布区;华北克拉通南缘很可能存在规模巨大的>2.7Ga基底;中部造山带与孔兹岩带具有类似的古元古代晚期构造热事件演化历史。     

山旺盆地的成因及其地质意义

前人一般认为山旺盆地是一个深度不大的封闭性淡水剥蚀盆地。笔者认为它是一个火山口成因的封闭—半封闭盆地。盆地的发展经历了3个发展阶段:早期为火山喷发作用形成火山口,并造成火山碎屑物堆积:中期堆积了较厚层的沉积物,主要为粘土质岩石,如硅藻质页岩、泥岩,此外,还有少量的砂岩、砾岩;晚期为玄武岩充填,致使整个盆地完全封闭。在盆地发展过程中,早期为封闭环境,中、晚期为半封闭环境。火山碎屑物的再堆积和分解对于生物死亡和埋藏可能具有重要的意义;该区第三纪中心式火山作用非常强烈,通过详细的区域地质调查,有可能找到更多的化石产地和硅藻土矿。     

Constraints from Thorium/Lanthanum on Sediment Recycling at Subduction Zones and the Evolution of the Continents

Arc magmas and the continental crust share many chemical features,but a major question remains as to whether these features arecreated by subduction or are recycled from subducting sediment.This question is explored here using Th/La, which is low inoceanic basalts (<0·2), elevated in the continents(>0·25) and varies in arc basalts and marine sediments(0·09–0·34). Volcanic arcs form linear mixingarrays between mantle and sediment in plots of Th/La vs Sm/La.The mantle end-member for different arcs varies between highlydepleted and enriched compositions. The sedimentary end-memberis typically the same as local trench sediment. Thus, arc magmasinherit their Th/La from subducting sediment and high Th/Lais not newly created during subduction (or by intraplate, adakiteor Archaean magmatism). Instead, there is a large fractionationin Th/La within the continental crust, caused by the preferentialpartitioning of La over Th in mafic and accessory minerals.These observations suggest a mechanism of ‘fractionation& foundering’, whereby continents differentiate intoa granitic upper crust and restite-cumulate lower crust, whichperiodically founders into the mantle. The bulk continentalcrust can reach its current elevated Th/La if arc crust differentiatesand loses 25–60% of its mafic residues to foundering. KEY WORDS: arc magmatism; continental crust; delamination; thorium; sediment subduction     

辽宁五龙地区中生代火成岩成因及其找矿意义

辽宁五龙金矿是辽东地区大型岩浆热液型矿床之一,成矿作用主要与中生代火成岩有关,为了进一步理清五龙地区中生代火成岩成因,本文对五龙金矿区大量花岗斑岩脉、闪长岩脉、三股流岩体和其中的各类脉岩进行了单颗粒锆石LA-ICPMS U-Pb测年和岩石主、微量元素地球化学研究。结果表明,五龙地区岩浆岩形成时代主要有晚侏罗世和早白垩世,矿区内近南北向展布的花岗斑岩脉形成于晚侏罗世（154.3±0.9~155.6±1.1 Ma）,指示矿区在晚侏罗世受到区域最大主应力方向为近南北向;三股流岩体成岩最新年龄（116.8±0.8~117.3±0.7 Ma）基本位于前人报道的年龄范围（111~129 Ma）;地球化学数据表明各类岩浆岩属于高钾钙碱性—钾玄岩系列,具有相同源区特征,形成于活动大陆边缘俯冲伸展环境下的弧岩浆,并且具有壳幔混合及进一步演化特征;结合不同深度标高成矿元素丰度特征,指示闪长岩与成矿作用密切相关,并且越往深部成矿潜力越大,对该地区找矿预测具有重要指导意义。     

武夷地区燕山期成矿特征及找矿方向

武夷及邻区燕山期成矿作用在环太平洋成矿带中具有四大特色：（１）成岩成矿在时空上从陆内向陆缘发展；（２）岩浆成矿作用具多层次造浆与多层次就位成矿；（３）华夏系列多字型复合构造控岩控矿；（４）成岩成矿具北北东向向洋分带与纬向分带叠加的“双向”分带。武夷地区是寻找火山－斑岩铜、金、锡、银铅锌等矿产的重要成矿带，又是找寻动热变质或花岗岩－剪切带型金矿床的有利地带。     

青藏高原西部蛇绿岩中玻安岩(boninite)及其地质意义

简要报道了在青藏高原西部班公湖蛇绿岩带和狮泉河蛇绿岩带之间的火山岩中识别出的玻安岩。玻安岩是俯冲岩浆作用的产物,在青藏高原东部及周边地区已有玻安岩或玻安岩系岩石存在的报道。结合西部出现的玻安岩说明青藏高原地区俯冲作用普遍存在。玻安岩的形成时代为J₂-K₁,埃达克岩的形成时代为K₁,由J₂-K₁,的玻安岩至K₁的埃达克岩反映冈底斯北部岛弧带由不成熟的洋内弧向成熟岛弧转变的过程,它们是中生代冈底斯北部大陆水平生长(侧向增生)的记录。     

Geochemical and isotope data from the Acatlán Volcanic Field, western Trans-Mexican Volcanic Belt: Origin and evolution

The Quaternary Acatlán Volcanic Field (AVF) is located at the western edge of the Trans-Mexican Volcanic Belt (TMVB). This region is related to the subduction of the Pacific Cocos and Rivera plates beneath the North American plate since the late Miocene. AVF rocks are products of Pleistocene volcanic activity and include lava flows, domes, erupted basaltic andesite, trachyandesite, trachydacite, and rhyolite of calc–alkaline affinity. Most rocks show depletion in high field-strength elements and enrichment in large ion lithophile elements and light rare earth elements as is typical for magmas in subduction-related volcanic arcs. ⁸⁷Sr/⁸⁶Sr values range from 0.70361 to 0.70412, while Nd values vary from +2.3 to +5.2. Sr–Nd isotopic data plot along the mantle array. On the other hand, lead isotope compositions (²⁰⁶Pb/²⁰⁴Pb=18.62–18.75, ²⁰⁷Pb/²⁰⁴Pb=15.57–15.64, and ²⁰⁸Pb/²⁰⁴Pb=38.37–38.67) give evidence for combined influences of the upper mantle, fluxes derived from subducted sediments, and the upper continental crust involved in magma genesis at AVF. Additionally δ¹⁸O whole rock analyses range from +6.35‰ in black pumice to +10.9‰ in white pumice of the Acatlán Ignimbrite. A fairly good correlation is displayed between Sr as well as O isotopes and SiO₂ emphasizing the effects of crustal contamination. Compositional and isotopic data suggest that the different AVF series derived from distinct parental magmas, which were generated by partial melting of a heterogeneous mantle source.