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新疆西天山阿吾拉勒铁成矿带内众多铁矿床的围岩火山岩时代、岩石成因和构造背景迄今尚未得到很好地约束。文章对该铁成矿带内的松湖铁矿床围岩粗面英安岩和流纹岩进行了锆石LA_ICP_MS U_Pb测年和地球化学研究。粗面英安岩和流纹岩的锆石206Pb/238U加权平均年龄分别为(326.8±2.7)Ma和(327.3±1.7)Ma。粗面英安岩和流纹岩准铝质,均富集轻稀土元素、Rb、K、Zr、Hf,显示中等Eu负异常,亏损Ba、Sr、P、Ta、Nb和Ti。锆石饱和温度计算结果显示,粗面英安岩的母岩浆温度较高(774~812℃,平均792℃),流纹岩母岩浆的温度较低(713~790℃,平均750℃)。粗面英安岩具有非常低Sr高Yb的特征,Nb/Ta比值为10.8~11.4,具有较高的w(Th)(≥8.1×10-6)和高的Th/Ce比值(≥0.31);流纹岩具有低Sr低Yb特征,Nb/Ta比值为8.5~9.7,w(Th)(≥5.3×10-6)较高,Th/Ce比值为0.14~0.75,据此推测粗面英安岩母岩浆可能是上地壳部分熔融的产物,流纹岩母岩浆可能源于比粗面英安岩母岩浆更深的地壳的部分熔融。松湖铁矿区粗面英安岩和流纹岩具有弧火山岩的地球化学特征,结合构造环境判别图解和区域地质情况,推断其形成于大陆弧环境。 相似文献
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塔吾尔别克金矿床是西天山吐拉苏断陷盆地中一个重要的金矿床。矿体主要赋存于早石炭世二长斑岩及大哈拉军组第五岩性段安山岩、蚀变凝灰岩中,受断裂构造控制,矿床围岩蚀变作用普遍而强烈。矿石金属矿物主要为黄铁矿、自然金、赤铁矿和黄铜矿等,非金属矿物主要为石英、斜长石、方解石等。成矿过程大致划分为3个成矿阶段:1石英-黄铁矿阶段;2石英-硫化物脉阶段;3石英-碳酸盐阶段。石英及方解石中流体包裹体类型简单,主要为气液两相水包裹体和纯液相水包裹体。包裹体测试均一温度为100~196℃,流体盐度为0.0%~7.3%(质量分数,NaCl_(eq)),流体密度为0.9~1.0 g/cm~3,计算出成矿压力为5.2~81.9 MPa,对应成矿深度为0.5~7.4 km。塔吾尔别克金矿床成矿流体包裹体显示低温度、低盐度和较低密度的流体特征,表明成矿压力小和深度较浅。结合矿床地质特征、流体包裹体特征及前人研究成果,初步认为该矿床为浅成低温热液型金矿床。 相似文献
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Precise hydrogeochemical modeling of early diagenesis is a key in the reconstruction of sedimentary basin models. This determines the mineralogical evolution of the sediment and consequently the porosity of the rock. During early diagenesis also part of the initial organic matter is converted into biogenic gas: CH4 CO2, and H2S. These processes are part of complex reaction chains during sedimentation, and biogeochemical reactions leave different signals that can be observed today. In this work, we reproduce the early diagenetic processes as integrated signals over geological times in sediments of the Demerara Rise by applying chemical thermodynamics using the PHREEQC (version 2) computer code. The investigated sediments are characterized by the presence of black shales in 410–490 mbsf and by a diagenetic barite layer above in 300–350 mbsf at depth of sulfate-methane transition (SMT). We determine the parameters that influence the location of diagenetic barite peaks in sediments overlying black shales by means of a novel modeling approach. Crucial parameters are the amount of bacterial organic matter mineralization, sedimentation rates and bottom water sulfate concentrations. All parameters are intertwining and influence the sulfate-methane cycle. They affect the location of the SMT visualized by diagenetic barite peaks. However, our model approach opens a wide field in exploring early diagenetic reactions, processes and products (such as biogenic methane) over geological times mirrored by diagenetic minerals and pore water concentration profiles that can be detected in present-day sediments. 相似文献
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桃子窝锡矿位于莲花山断裂带西段,是典型的火山-次火山岩型锡矿。本文以桃子窝锡矿赋矿火山-次火山岩及花岗岩为研究对象,首次开展LA-ICP-MS锆石U-Pb定年和Hf同位素特征研究。获得两个次火山岩样品的锆石206Pb/238 U加权平均年龄为172.1±1.1 Ma和171.8±0.9 Ma,一个花岗岩样品的锆石206 Pb/238 U加权平均年龄为168.9±1.5 Ma,表明桃子窝锡矿火山-侵入岩为中侏罗世同一岩浆事件不同阶段的产物。锆石εHf(t)值大多数为负值,只有3个点的值大于0,变化于-13.96~9.53之间,平均值为-7.92。在εHf(t)-t图解上,εHf(t)值大多落在球粒陨石演化线之下,有3个点落在球粒陨石与亏损地幔演化线之间。二阶段模式年龄除3个点介于609.6~795.5 Ma外,其余点年龄为1 450.8~2 102.5 Ma,Hf同位素特征指示成岩物质主要来源于早中元古代古老地壳的部分熔融,还有新元古代新生地壳物质的加入。结合区内已有的研究成果,认为桃子窝锡矿及有关的火山-次火山岩与中生代太平洋板块向欧亚大陆俯冲有关。 相似文献
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Located in the western part of the Min–Li metallogenic belt within the western Qinling Mountains, the Zhaishang gold deposit is a giant Carlin-like disseminated gold deposit discovered recently. The ore deposit is present both in rocks of low grade metamorphic Middle Devonian and Lower Permian clastic formation, which is composed of quartz sandstone, siltstone, calcareous slate and argillaceous limestone. Gold mineralization is strictly controlled by a fault zone. Minerals in ores are quite complex and consist of sulfides, sulfosalt, oxides, sulfate, carbonate, tungstate, telluride, native metals, and polymetallic alloys. The diversity of mineral in the ores and the existence of microscopic visible native gold constitute the outstanding features of the gold deposit.We believe that the mineral source of the ore deposit has a close connection with the host rocks, because all samples show the light of the REE distribution patterns. The S, C, Pb, H and O isotopic compositions show that the ore-forming elements were mainly derived from the country rocks, the underlying rocks, and partially deep sources. Data obtained suggest that the ore-forming fluids were derived predominantly from an active meteoric groundwater system. Mineralization and related alteration have features of a low water/rock ratio. Ore-forming temperatures are estimated to have been in the range from 120 to 240 °C. The dissolution of ferruginous limestone in the host rocks and the sulfidation of the dissolved iron by H2S introduced by ore fluids constituted not only the most important depositional mechanisms for the existence of microscopic visible gold grains but also favorable conditions for gold enrichment in the Zhaishang gold deposit. 相似文献
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阿勒泰组变质碎屑岩局部夹变质火山岩广泛分布于南阿尔泰的冲乎尔、克兰和麦兹盆地,其沉积时代和构造环境对于研究阿尔泰造山带的演化过程有重要意义。阿勒泰组碎屑锆石的年代学研究表明,碎唐锆石年龄主要集中在417-383 Ma和507-445 Ma,并出现少量元古宙和太古宙碎屑锆石。少数锆石年龄为380-354 Ma,与阿勒泰组凝灰岩和流纹岩年龄一致(376~354 Ma)。综合研究认为阿勒泰组时代为中-晚泥盆世(382-354 Ma)。阿勒泰组长石石英砂岩分选性和磨圆度较差,为近源沉积,物源岩石主要来自泥盆纪火山岩,其次是晚寒武一早奥陶世火山岩和奥陶纪花岗岩。长石石英砂岩样品具有高的La/Sc(3.9-6.3),La/Y(1.0~1.6),较低的Sc/Cr(0.2~0.4)比值,类似于大陆岛弧相关环境碎屑沉积物,结合Th-Co-Zr/10和Th-Sc-Zr/10以及La-Th-Sc判别图,认为阿勒泰组形成于与岛弧相关的构造环境(弧后盆地),为研究阿尔泰造山带泥盆纪构造演化提供了重要证据。 相似文献
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八宿吉利地区寒武纪变质花岗岩位于曲扎湖-提卡一带,主要由变质二长花岗岩和变质花岗闪长岩组成。这一新发现对于认识和恢复原特提斯构造历史演化具有重要意义。锆石CL图像显示变质花岗岩锆石为岩浆成因。锆石LA-ICP-MS测年得出片理化变质二长花岗岩年龄为503.7±4.7Ma、变质花岗闪长岩年龄为494.7±3.4Ma,表明该岩体形成时代属于寒武纪。通过岩石地球化学分析,变质二长花岗岩SiO2含量介于69.87%~79.89%之间;变质花岗闪长岩SiO2含量介于66.63%~70.15%之间。前者Al2O3含量变化于12.36%~14.82%,Na2O含量为2.54%~7.16%,K2O含量为0.15%~5.95%,K2O/Na2O=0.02~2.34;后者Al2O3含量变化于14.66%~15.41%,Na2O含量为3.60%~5.63%,K2O含量为0.77%~2.78%,K2O/Na2O=0.14~0.77,属于钙碱性-碱性过铝质花岗岩。在侵入岩构造环境Rb-(Y+Nb)判别图解、Rb-(Yb+Ta)判别图解中,样品均落入“火山弧花岗岩”区域中,表明其形成于大陆边缘火山弧环境。结合锆石测年结果及区域地质背景分析,认为吉利地区变质花岗岩形成于冈瓦纳大陆裂离卡穷微陆块阶段,同时表明原特提斯洋形成最早时限可追溯至寒武纪。 相似文献
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新疆北部青河县阿斯喀尔特铍矿区花岗质岩石年代学及地球化学特征 总被引：1，自引：1，他引：0
新疆北部青河县阿斯喀尔特铍矿床的形成与岩浆活动密切相关,是中国花岗岩型铍矿床的典型代表。对矿区斑状二云母二长花岗岩进行LA-ICP-MS锆石U-Pb年龄测试,获得其加权平均年龄为(216.7±2.8)Ma(MSWD=0.48),表明该岩体形成时代为晚三叠世,据此限定阿斯喀尔特铍矿床成矿时代略晚于216 Ma,为晚三叠世—早侏罗世。岩石具有高硅(w(Si O2)=70.86%~76.34%)、富碱(ALK=5.54~9.30)、富铝(w(Al_2O_3)=13.00%~14.74%,A/CNK=0.99~1.23)、低钛(w(Ti O2)=0.02%~0.18%)和镁(w(Mg O)=0.02%~1.21%)特征,为过铝质中钾-高钾岩石系列。稀土元素配分型式显示LREE的相对弱富集,HREE较平坦以及Eu弱-中等的负异常(δEu=0.37~0.90),呈略右倾型。微量元素Ba、Sr、Hf、Ti等具负异常,Rb、Th、K、Nb、Ta、La、Ce、Nd、Sm等具正异常,Rb/Sr比值较高(9.34~26.81),显示出S型花岗岩特征。结合区域资料,认为阿斯喀尔特铍矿矿区印支期花岗岩形成于后造山构造阶段,可能是上地壳含砂泥质岩石部分熔融的产物。 相似文献