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41.
《International Geology Review》2012,54(2):158-184
Early Miocene igneous rocks associated with the Dalli porphyry ore body are exposed within the Urumieh-Dokhtar Magmatic Arc (UDMA). The Dalli porphyry Cu–Au deposit is hosted by subduction-related subvolcanic plutons with chemical composition from diorite to granodiorite, which intruded andesitic and dacitic volcanic rocks and a variety of sedimentary sequences. 40Ar/39Ar age data indicate a minimum emplacement age of ~21 million years for a potasically altered porphyritic diorite that hosts the porphyry system. The deposit has a proven reserve of 8 million tonnes of rock containing 0.75 g/t Au and 0.5% Cu. Chondrite-normalized rare earth element (REE) patterns for the subvolcanic rocks are characterized by light REE enrichments [(La/Sm) n ?=?2.57–6.40] and flat to gently upward-sloping profiles from middle to heavy REEs [(Dy/Yb) n ?=?0.99–2.78; (Gd/Yb) n ?=?1.37–3.54], with no significant Eu anomalies. These characteristics are generated by the fractionation of amphibole and the suppression of plagioclase crystallization from hydrous calc-alkaline magmas. In normalized multi-element diagrams, all analysed rocks are characterized by enrichments in large ion lithophile elements and depletions in high field strength elements, and display typical features of subduction-related calc-alkaline magmas. We used igneous mineral compositions to constrain the conditions of crystallization and emplacement. Biotite compositions plot above the nickel–nickel oxide (NNO) buffer and close to oxygen fugacity values defined by the hematite–magnetite (HM) buffer, indicating oxidizing conditions during crystallization. Assuming a minimum crystallization temperature of 775°C, the oxygen (fO2) and water (fH2O) fugacities are estimated to be 10?10.3 bars (~ΔNNO+4) and ≤748 bars, respectively, during the crystallization of biotite phenocrysts. The temperature and pressure conditions, estimated from temperature–corrected Al-in-hornblende barometry and amphibole-plagioclase thermometry, suggest that the hornblende phenocrysts in Dalli rocks crystallized at around 780 ± 20°C and 3.8 ± 0.4 kbar. An alternative method using the calcic amphibole thermobarometer indicates that the Dalli magmas were, on average, characterized by an H2O content of 4.3 wt.%, a relatively high oxygen fugacity of 10?11.0 bars (ΔNNO+1.3), and a hornblende phenocryst crystallization temperature of 880 ± 68°C and pressure of 2.6 ± 1.7 kbar. 相似文献
42.
43.
云南大坪金矿床赋矿闪长岩锆石SHRIMP U-Pb定年及其地质意义 总被引:2,自引:0,他引:2
云南大坪金矿床是哀牢山金矿带中最重要的金矿之一,主要赋存在受到强烈剪切和水-岩反应的闪长岩中,是典型的喜马拉雅期造山型金矿。本文对大坪金矿床赋矿闪长岩中锆石进行了SHRIMP U-Pb定年,得出闪长岩围岩的年龄为773±12Ma,为晚元古代,显示该岩体为华南地区晋宁-澄江期大规模基性到酸性岩浆活动的产物,是Rodinia 超大陆形成、裂解后冈瓦纳大陆形成过程的响应,而不是前人普遍认为的加里东期岩体。该岩体侵入年龄与大坪金矿脉石英流体包裹体40Ar-39Ar 年龄测定给出的高温坪年龄(765.5±7.0Ma)基本一致,显示大坪金矿床具有多期成矿的特征,其主体形成于喜马拉雅期碰撞造山运动,但早在晋宁造山运动中就有金的初步富集。在闪长岩中还发现了年龄为33.7±1.1Ma的锆石,其时代与大坪金矿床含金石英脉中热液绢云母的40Ar-39Ar定年结果(33.76Ma)基本一致,显示它们很可能为该区强烈的韧性剪切和局部岩浆部分熔融作用的产物。 相似文献
44.
对鲁西沂南铜井岩体的中生代闪长玢岩进行了主量元素、微量及稀土元素、Sr-Nd-Pb同位素以及锆石U-Pb年龄、Hf同位素研究,结果表明,铜井闪长玢岩SiO2含量为54.68%~63.01%,富Na,Na2O/K2O为0.93~4.46,Mg#较高,为55~66,为中钾-高钾钙碱性系列,TiO2含量较低,0.2%~0.71%。样品具有显著的LREE富集[(La/Yb)n=10~15]以及高场强元素Nb、Ta和Ti的负异常,Eu基本无异常,Sr、Ba含量高(分别为241×10-6~711×10-6和554×10-6~822×10-6)的特征。ISr和εNd(t)值分别为0.706473~0.708867和-15.13~-9.18,与鲁西方城玄武岩和前人所研究的沂南辉长岩结果有所差异,显示其源区具有多端员混合特征,除了富集岩石圈地幔外,亏损地幔和地壳物质的贡献也很重要,Pb同位素也显示其源区有扬子克拉通物质的贡献,佐证了华北克拉通中生代富集岩石圈地幔的形成与扬子克拉通的俯冲有关。闪长岩中锆石具有典型的岩浆锆石特征,U-Pb年龄为128~129Ma,锆石εHf(t)值主要在-13~-8(平均值为-10.3)范围内,暗示了岩浆来源于富集岩石圈地幔,但受到亏损地幔物质的混染。沂南铜井闪长玢岩岩浆源区的多元性以及亏损地幔物质参与程度的逐渐增强,说明该地区中生代岩石圈减薄已达到最大,岩浆源区的差异可能也是该地区与胶东地区成矿性差异的主要原因之一。 相似文献
45.
First record of 1.2 Ga quartz dioritic magmatism in the Archaean Yilgarn Craton,Western Australia,and its significance 总被引:1,自引:0,他引:1
Y. Qiu N. J. McNaughton D. I. Groves J. M. Dunphy 《Australian Journal of Earth Sciences》2013,60(3):421-428
Farming of southern bluefin tuna in South Australia currently contributes to more than 30% of the value of the aquaculture production in Australia. This study investigated the natural sedimentary setting of the area designated for this important industry in coastal waters off Port Lincoln, and explored the links between the natural distribution of sediments and potential environmental effects and risks to the industry. Sediments were mostly composed of poorly sorted silts and fine sands, predominantly skeletal remains of carbonate-secreting organisms. The contribution of plankton to the organic matter remaining in the sediments was calculated to be in excess of 80% using concentration-dependent stable-isotope mixing models. An erosional area was identified south of Rabbit Island where sediments contained up to 50% siliciclastic material, grainsize distributions were better sorted and coarser, and organic carbon and total nitrogen contents were very low. In contrast, deeper waters north of Cape Donington were identified as a depocentre for fine sediments, which contained organic matter levels twice those elsewhere in the region despite the extremely high carbonate contents (>80%). The heavier stable isotopic signature of nitrogen suggested that this organic matter comprised a greater fraction of weathered components, probably advected to the area by suspended and bedload transport. This local variability of sediment characteristics in the farming zone suggests that the benthic assimilative capacity of farmed sites will depend on their location. Wastes from pens located south of Rabbit Island in particular are likely to be quickly winnowed out by wave and tidal action. These pens are also less likely to be affected by resuspension of fine sediments that might be associated with unusually severe storms. 相似文献
46.
西准噶尔包古图地区广泛发育富镁闪长质岩墙.对这些岩墙进行角闪石Ar-Ar和锆石U-Pb定年分别获得(313.1±3.5)Ma和(316.3±3.8) Ma的年龄,显示其主要形成于晚石炭世.闪长质岩墙以富Si(SiO2=56.8 %~62.9%)、Mg(MgO=2.39%~4.04%、Mg#=54-62)、Cr(Cr=30×10-6~80×10-6)、Ni(Ni=20×10-6~62×10-6)为特征,具有弱的Eu负异常和高Sr/Y比值(36~44),强烈亏损HREE (Yb=1.32×10-6~1.54×10-6、Y=13.1×10-6~15.5×10-6),富集LILE (K、Sr、Ba),亏损HFSE(Nb、Ta、Ti).这些特点显示,这些闪长质岩墙可能是由俯冲的板片熔体与地幔橄榄岩反应而成,与洋脊俯冲有关.而闪长质岩墙的形成过程也有利于铜金矿床的形成,显示该区有良好的成矿远景. 相似文献
47.
差应力与岩石熔融性状关系的实验研究 总被引:1,自引:0,他引:1
为考察不同应力状态下岩石应变与岩石熔融作用的关系,利用英国Instron公司生产的电液伺服实验系统,配以围压和加温系统设计了动、静态不同条件下细粒闪长岩的对比熔融实验,力图找到差应力与岩石熔融程度及其熔体成分的关系。通过岩石动、静态熔融实验结果的对比得出:差应力的存在能够导致细粒闪长岩的熔融,随着差应力(应变速率)的增加,熔体的量增加,熔体成分向富Si、Al方向转变。 相似文献
48.
新疆哈密三岔口石英闪长岩体中发现锌铜矿 总被引:1,自引:0,他引:1
锌铜矿是自然界较为少见的含金矿物,以往均发现于基性——超基性岩中,在中酸性岩中发现锌铜矿,在新疆尚属首次. 相似文献
49.
九三沟金矿区石英闪长玢岩在火山盆地内呈脉状或岩株状产出,与金矿化空间上密切伴生。本文通过岩石地球化学和LA-ICP-MS锆石U-Pb年代学研究,讨论了石英闪长玢岩的成因、源区和构造背景,厘定了成岩时代。研究表明,九三沟石英闪长玢岩属于钙碱性、过铝质系列岩石,富集大离子亲石元素(Ba、Sr)、活泼的不相容元素Th、U和轻稀土元素,亏损高场强元素Ta、Nb、Ti和重稀土元素。岩石的Nb/Ta、La/Nb、Th/La比值都显示其具壳源特征,在Al_2O_3-MgO-FeO_t和R1-R2判别图解上均表现为活动大陆边缘岩浆岩特征。石英闪长玢岩LA-ICP-MS锆石U-Pb年龄为104.2±1.4 Ma,MSWD=0.17,为早白垩世晚期(燕山晚期),形成于太平洋板块斜向俯冲引起的东亚大陆走滑伸展的构造环境。而吉黑东部中生代浅成低温热液成矿作用与该期钙碱性–碱性火山岩–浅成浅成侵位活动密切相关,因此早白垩世晚期的火山机构和浅成钙碱性–碱性侵入体是吉黑东部中生代浅成低温热液的找矿目标。 相似文献
50.
北淮阳东段张冲闪长玢岩地球化学特征、LA-ICP-MS锆石U-Pb年龄及其地质意义 总被引:1,自引:0,他引:1
张冲闪长玢岩呈不规则状侵入佛子岭岩群诸佛庵岩组和毛坦厂组中。岩体具较高的SiO_2和Al_2O_3含量,为偏碱性、准铝质、高钾钙碱性系列岩石。富集大离子亲石元素(LILE)和轻稀土元素(LREE),亏损高场强元素(HFSE)、重稀土(HREE)和Y,无明显Eu异常,Sr正异常。通过LA-ICP-MS锆石U-Pb法确定张冲闪长玢岩年龄为129±3 Ma,表明该岩体侵位于早白垩世。通过对岩石主、微量元素特征研究,认为岩浆可能来源于底侵玄武岩,并受到地壳物质的混染。岩体形成于中生代构造体制转换期,可能属于北淮阳东段中生代第一旋回侵入岩。 相似文献