摘要
本文是对大冶铁矿床接触带“大理岩”及其中分布的“条带状辉石-石榴石大理岩”进行专门研究的阶段性结果。在野外观察到“大理岩”呈岩墙、岩枝和细脉侵入石英闪长岩。根据石准立等的趋势面分析资料,在深部,本矿区“大理岩”与石英闪长岩的接触带总是以突入石英闪长岩内为特征。在“大理岩”与灰岩接触带附近观察到大理岩粒度由于温度冷却快而变细和在“大理岩”中有灰岩残留体。“大理岩”本身的方解石粒度中部粗两侧细。本矿区的“大理岩”矿物结晶颗粒比长江中下游许多接触热变质形成的大理岩粗。“大理岩”内部浅色大理岩为白色,常具有定向的细条纹构造(可能为流动构造或构造事件引起的线性构造),局部产状变化急剧。在尖山矿段产在“大理岩”中的“条带状辉石-石榴石大理岩”,主要含辉石和石榴石条带,其条带走向与“大理岩”岩体延伸方向斜交,且与区内一组断裂构造有关。显微镜观察结果表明,在制备的约65块包裹体切片中均观察到熔融包裹体或流体-熔融包裹体及流体包裹体。包裹体加热实验结果显示,“大理岩”中方解石及“条带状辉石-石榴石大理岩”中的石榴子石和方解石中熔融包裹体接近均一的温度为880～1055℃,流体-熔融包裹体均一温度为645～740℃。“大理岩”及“条带状辉石-石榴石大理岩”的C?
This paper is a stage result of specia l research for“marble”in contact of Daye iron deposit and“banded pyroxene-garnet marble”distributed in the“marble”.According to traditional theory th at the quartz diorite intruded into limestone first,then marble wa s formed by contact metamorphism and skarns were formed by metasomatism i n this area.However,finding of melt i nclusions in skarn minerals from skarns and in carbonate minerals from“marble”compelled us to consider the truth of traditional theory in respect of int erpretation for formations of skarn and marble in Daye Jianshan district.The“marbles”protrude into quartz diorite in the s hape of dyke,apophysis and veinlets.A quartz diorite xenolith with 1.5m ×3m in the“marble”from the ore block has been found.According to data of trend surface an alyses made by Shi Zhun-li,et al .the contact zone between“marble”and quartz diorite is always characterized by“marble”protruding into quartz diorite.It i s seen that in the vicinity of the contact between the“marble”and limestone(wall rock),grain size of the calcite from the“marble”became fine due to high cooling rate of temperatu re and the limestone xenoliths existed in the“marble”.Light-colored“marble”is white and usually has oriented-fine ribbon structure(it is possible for the flow structure or linear feature caused by tectonic event )and its occurrence locally sharply c hanged.“Banded pyroxene-garnet marble”occurred in the“marble”within Jianshan ore block is distrib uted in a narrow range and is mainly ch aracterized by pyroxene-garnet bands,the strike of which bevels the extension direction of the“marble”.The distribution of the“banded pyroxene-garnet marble”is related to a group of fault structu res in this area.The observations un der microscope indicate that melt inclusions,flui d-melt inclusions and fluid inclusions are almost found in 65inclusion t hin sections.The results of heating exp eriments show that melt inclusions i n the calcite from the“marble”and in the calcite and the garnet from the“banded pyroxene-garnet marble”have approximate homogenization te mperatures of880～1055℃.Fluid-melt inclusions h ave homogenization temperatures of645～740℃.C and O isotopes of“marble”and the“banded pyroxene-garnet marble”are roughly consistent with the lime stone from lower-middle reaches of Yangtze River.Projectio n points of C and O isotopic data are all fallen into the range of sedimentary carbonate rocks in the C-O dependent diagram.Electron probe analysis re sults indicate that one melt inclusion in the calcite from the“banded pyroxene-garnet marble”has the composition of Si,Ca,Mg,Al,K-bearing mixture,namely glass.The compositions of th e round solid inclusion in calcite fr om“marble”are calcite and dolomite from“dolomite marble”are similar to the dolomite,but different from host mineral.“Marble”and“banded pyroxene-garnet marble”reported here are not marble formed b y the contact metamorphism,they pro bably are a new carbonatite type—crust-derived carbonatite of magma tic type based on preliminary studie s mentioned above.
出处
《地球化学》
CAS
CSCD
北大核心
2004年第6期649-662,共14页
Geochimica
基金
国家自然科学基金(40373019)
