Early Cretaceous trachybasalt-trachyte-trachyrhyolitic volcanism in the Nyalga basin (Central Mongolia): sources and evolution of continental rift magmas     

I.S. Peretyazhko  E.A. Savina  S.I. Dril’ 《Russian Geology and Geophysics》2018,59(12):1679-1701

As shown by geological, mineralogical, and isotope geochemical data, trachybasaltic-trachytic-trachyrhyolitic (TTT) rocks from the Nyalga basin in Central Mongolia result from several eruptions of fractionated magmas within a short time span at about 120 Ma. Their parental basaltic melts formed by partial melting of mantle peridotite which was metasomatized and hydrated during previous subduction events. Basaltic trachyandesites have high TiO₂ and K₂O, relatively high P₂O₅, and low MgO contents, medium ⁸⁷Sr/⁸⁶Sr(₀) ratios (0.70526-0.70567), and almost zero or slightly negative ε_Nd(T) values. The isotope geochemical signatures of TTT rocks are typical of Late Mesozoic basaltic rocks from rift zones of Mongolia and Transbaikalia. The sources of basaltic magma at volcanic centers of Northern and Central Asia apparently moved from a shallower and more hydrous region to deeper and less hydrated lithospheric mantle (from spinel to garnet-bearing peridotite) between the Late Paleozoic and the latest Mesozoic. The geochemistry and mineralogy of TTT rocks fit the best models implying fractional crystallization of basaltic trachyandesitic, trachytic, and trachyrhyodacitic magmas. Mass balance calculations indicate that trachytic and trachydacitic magmas formed after crystallization of labradorite-andesine, Ti-augite, Sr-apatite, Ti-magnetite, and ilmenite from basaltic trachyandesitic melts. The melts evolved from trachytic to trachyrhyodacitic and trachyrhyolitic compositions as a result of prevalent crystallization of K-Na feldspar, with zircon, chevkinite-Ce, and LREE-enriched apatite involved in fractionation. Trachytic, trachyrhyodacitic, and trachyrhyolitic residual melts were produced by the evolution of compositionally different parental melts (basaltic trachyandesitic, trachytic, and trachyrhyodacitic, respectively), which moved to shallower continental crust and accumulated in isolated chambers. Judging by their isotopic signatures, the melts assimilated some crustal material, according to the assimilation and fractional crystallization (AFC) model.  相似文献   

内蒙古巴林右旗晚二叠世埃达克质火山岩特征及其地质意义     

杨文鹏  张生旭  姜海洋  刘洪大  隋成禹  孙江军  张俭峰  吕石佳  李新鹏 《地质通报》2018,37(9):1710-1721

内蒙古东南部巴林右旗地区发育晚二叠世埃达克质火山岩,岩石组合为安山岩、粗安岩、英安岩及辉石安山岩,其LA-ICP-MS锆石U-Pb测年结果为256.7±2.7Ma,指示其形成于晚二叠世。地球化学特征显示,该套火山岩属准铝质-弱铝质中钾钙碱性岩石系列,具富Si(SiO_256%)、高Al(Al_2O_315%)、富Na、贫K、高Sr、低Yb和Y等特征,Na_2O/K_2O值为2.33~3.90,Mg~#值为35.3~60.8;稀土元素总量为96.69×10~(-6)~192.4×10~(-6)、轻重稀土元素分馏较明显((La/Yb)_N值为6.27~13.82),具正的Eu(δEu=1~1.67)异常,在原始地幔标准化蛛网图中,富集大离子亲石元素Rb、Ba、U,亏损高场强元素Nb、Ta,为O型(大洋型)埃达克质火山岩地球化学特征。综合区域资料,巴林右旗埃达克质火山岩是残留在地幔中的古亚洲洋残余洋壳部分熔融并受到地幔橄榄岩混染形成的,暗示晚二叠世存在古亚洲洋向华北板块俯冲消亡事件。  相似文献   

Petrogenesis of plio-quaternary intra-plate continental alkaline lavas from the İskenderun Gulf (Southern Turkey): Evidence for metasomatized lithospheric mantle     

Aykut Güçtekin 《Chemie der Erde / Geochemistry》2018,78(4):521-534

The Quaternary alkaline volcanic field of Southern Turkey is characterized by intra-continental plate-type magmatic products, exposed to the north of the ?skenderun Gulf along a NE-SW trending East Anatolian Fault, to the west of its intersection with the N–S trending Dead Sea Fault zone. The ?skenderun Gulf alkaline rocks are mostly silica-undersaturated with normative nepheline and olivine and are mostly classified as basanites and alkaline basalts with their low-silica contents ranging between 43 and 48?wt.% SiO₂. They display Ocean Island Basalt (OIB)–type trace element patterns characterized by enrichments in large-ion-lithophile elements (LILE) and light rare earth element (LREE), and have (La/Yb)_N?=?8.8–17.7 and (Hf/Sm)_N?=?0.9–1.6 similar to those of basaltic rocks found in intraplate suites. The basanitic rocks have limited variations Sr-Nd isotopic ratios (⁸⁷Sr/⁸⁶Sr?=?0.70307–0.70324, ¹⁴³Nd/¹⁴⁴Nd?=?0.512918–0.521947), whereas the alkali basalts display more evolved Sr-Nd isotopic ratios (⁸⁷Sr/⁸⁶Sr?=?0.70346-0.70365, ¹⁴³Nd/¹⁴⁴Nd?=?0.512887–0.521896). The ?skenderun Gulf alkaline rocks also display limited Pb isotopic variations with ²⁰⁶Pb/²⁰⁴Pb?=?18.75–19.09 ²⁰⁷Pb/²⁰⁴Pb?=?15.61–15.66 and²⁰⁸Pb/²⁰⁴Pb?=?38.65–39.02, indicating that they originated from an enriched lithospheric mantle source. Calculated fractionation vectors indicate that clinopyroxene and olivine are the main fractionating mineral phases. Similarly, based on Sr-Nd isotopic ratios, the assimilation and fractional crystallization (AFC) modeling shows that the alkali basalts were affected by AFC processes (r?=?0.2) and were slightly contaminated by the upper crustal material.The high TiO₂ contents, enrichments in Ba and Nb, and depletions in Rb can likely be explained by the existence of amphibole in the mantle source, which might, in turn, indicate that the source mantle has been affected by metasomatic processes. The modeling based on relative abundances of trace elements suggests involvement of amphibole-bearing peridotite as the source material. ?skenderun Gulf alkaline rocks can thus be interpreted as the products of variable extent of mixing between melts from both amphibole-bearing peridotite and dry peridotite.  相似文献   

Sugarloaf Mountain,central Arizona,USA: A small-scale example of Miocene basalt-rhyolite magma mixing to yield andesitic magmas     

Ellen J. Craig  R.V. Fodor 《Chemie der Erde / Geochemistry》2018,78(1):116-139

Sugarloaf Mountain is a 200-m high volcanic landform in central Arizona, USA, within the transition from the southern Basin and Range to the Colorado Plateau. It is composed of Miocene alkalic basalt (47.2–49.1?wt.% SiO₂; 6.7–7.7?wt.% MgO) and overlying andesite and dacite lavas (61.4–63.9?wt.% SiO₂; 3.5–4.7?wt.% MgO). Sugarloaf Mountain therefore offers an opportunity to evaluate the origin of andesite magmas with respect to coexisting basalt. Important for evaluating Sugarloaf basalt and andesite (plus dacite) is that the andesites contain basaltic minerals olivine (cores Fo_76-86) and clinopyroxene (～Fs_9-18Wo_35-44) coexisting with Na-plagioclase (An_48-28Or_1.4–7), quartz, amphibole, and minor orthopyroxene, biotite, and sanidine. Noteworthy is that andesite mineral textures include reaction and spongy zones and embayments in and on Na-plagioclase and quartz phenocrysts, where some reacted Na-plagioclases have higher-An mantles, plus some similarly reacted and embayed olivine, clinopyroxene, and amphibole phenocrysts.Fractional crystallization of Sugarloaf basaltic magmas cannot alone yield the andesites because their ～61 to 64?wt.% SiO₂ is attended by incompatible REE and HFSE abundances lower than in the basalts (e.g., Ce 77–105 in andesites vs 114–166?ppm in basalts; Zr 149–173 vs 183–237; Nb 21–25 vs 34–42). On the other hand, andesite mineral assemblages, textures, and compositions are consistent with basaltic magmas having mixed with rhyolitic magmas, provided the rhyolite(s) had relatively low REE and HFSE abundances. Linear binary mixing calculations yield good first approximation results for producing andesitic compositions from Sugarloaf basalt compositions and a central Arizona low-REE, low-HFSE rhyolite. For example, mixing proportions 52:48 of Sugarloaf basalt and low incompatible-element rhyolite yields a hybrid composition that matches Sugarloaf andesite well ? although we do not claim to have exact endmembers, but rather, viable proxies. Additionally, the observed mineral textures are all consistent with hot basalt magma mixing into rhyolite magma. Compositional differences among the phenocrysts of Na-plagioclase, clinopyroxene, and amphibole in the andesites suggest several mixing events, and amphibole thermobarometry calculates depths corresponding to 8–16?km and 850° to 980?°C. The amphibole P-T observed for a rather tight compositional range of andesite compositions is consistent with the gathering of several different basalt-rhyolite hybrids into a homogenizing ‘collection' zone prior to eruptions. We interpret Sugarloaf Mountain to represent basalt-rhyolite mixings on a relatively small scale as part of the large scale Miocene (～20 to 15 Ma) magmatism of central Arizona. A particular qualification for this example of hybridization, however, is that the rhyolite endmember have relatively low REE and HFSE abundances.  相似文献   

Depositional setting,provenance, and tectonic-volcanic setting of Eocene–Recent deep-sea sediments of the oceanic Izu–Bonin forearc,northwest Pacific (IODP Expedition 352)     

Alastair H. F. Robertson  Steffen Kutterolf  Aaron Avery  Alan T. Baxter  Katerina Petronotis  Gary D. Acton 《International Geology Review》2018,60(15):1816-1854

New biostratigraphical, geochemical, and magnetic evidence is synthesized with IODP Expedition 352 shipboard results to understand the sedimentary and tectono-magmatic development of the Izu–Bonin outer forearc region. The oceanic basement of the Izu–Bonin forearc was created by supra-subduction zone seafloor spreading during early Eocene (c. 50–51 Ma). Seafloor spreading created an irregular seafloor topography on which talus locally accumulated. Oxide-rich sediments accumulated above the igneous basement by mixing of hydrothermal and pelagic sediment. Basaltic volcanism was followed by a hiatus of up to 15 million years as a result of topographic isolation or sediment bypassing. Variably tuffaceous deep-sea sediments were deposited during Oligocene to early Miocene and from mid-Miocene to Pleistocene. The sediments ponded into extensional fault-controlled basins, whereas condensed sediments accumulated on a local basement high. Oligocene nannofossil ooze accumulated together with felsic tuff that was mainly derived from the nearby Izu–Bonin arc. Accumulation of radiolarian-bearing mud, silty clay, and hydrogenous metal oxides beneath the carbonate compensation depth (CCD) characterized the early Miocene, followed by middle Miocene–Pleistocene increased carbonate preservation, deepened CCD and tephra input from both the oceanic Izu–Bonin arc and the continental margin Honshu arc. The Izu–Bonin forearc basement formed in a near-equatorial setting, with late Mesozoic arc remnants to the west. Subduction-initiation magmatism is likely to have taken place near a pre-existing continent–oceanic crust boundary. The Izu–Bonin arc migrated northward and clockwise to collide with Honshu by early Miocene, strongly influencing regional sedimentation.  相似文献   

印度尼西亚苏门答腊岛Woyla金矿流体包裹体研究及矿床成因分析     

胡鹏 《地质与勘探》2018,54(6):1215-1226

印度尼西亚Woyla金矿床位于西苏门答腊地体北段,为一中型规模的金矿床。本文通过对含矿石英脉开展详细的流体包裹体显微测温、成分分析,结合石英的H-O同位素和黄铁矿的S同位素特征分析,结果如下：其中,流体包裹体研究结果表明,含金石英脉中的石英主要发育气液两相包裹体,包裹体均一温度变化范围为152～324℃,集中在200～280℃。盐度为(0.88～6.16)wt%NaCleqv,集中在(1.00～3.00)wt%NaCleqv,成矿流体密度为0.70～0.94g/cm3,平均为0.82g/cm3。成矿压力为9.63～25.84MPa,平均值为18.37 MPa。成矿深度为0.96～2.58km,平均为1.86km,以上显示Woyla矿床成矿流体具有中低温低盐度和浅成的特征。包裹体气、液相成分测定显示气相成分以H2、N2、CO 、CO2、CH4和H2O为主;液相成分中阳离子以Na+、K+和Ca2+为主,阴离子以富SO42-和Cl-为特征,成矿流体属Cl--SO42--Ca2+-K+型。氢氧同位素测定显示成矿流体δ18DV-SMOW=-78.3‰～-92.4‰,δ18OH2O=-3.0‰～-5.5‰,主要来自大气降水,可能有少量岩浆水参与。黄铁矿硫同位素组成为-0.21‰～1.22‰,平均值为0.34‰,说明成矿物质的S具有深源岩浆硫的特征。结合矿床地质特征和成矿流体研究,首次提出Woyla金矿床属典型的低硫型浅成低温热液型金矿床。  相似文献   

水库运行对漫湾库区洲滩水热交换影响          下载免费PDF全文

姬雨雨  陈求稳  施文卿  易齐涛  林育青 《水科学进展》2018,29(1):73-79

以澜沧江漫湾水库库区洲滩为研究对象,依据水库运行导致的水位波动特征,同步监测洲滩内部水位、水温变化过程,核算洲滩侧向潜流交换量,建立水温与水位之间的响应关系,分析潜流交换水流路径上溶解氧、溶解性碳素变化。结果表明:水库运行引起洲滩水位周期性波动,侧向潜流交换加强,洲滩水位最大变幅达2.2 m,水库一次蓄泄过程进出洲滩的水量达3 956 m^3,洲滩边缘区潜流交换量为中心区的4~5倍;在涨水过程中,洲滩水温下降,中底层温度梯度较大,而在落水过程中,洲滩水温上升,中表层温度梯度较大;溶解氧、溶解性有机碳和无机碳在河流至洲滩潜流交换路径上同步递减,分别从3.27 mg/L、7.3 mg/L和66.0 mg/L下降至0.17 mg/L、2.4mg/L和40.6 mg/L。水库运行导致的水位波动加强了库区洲滩潜流交换,对河流物质循环产生潜在影响。  相似文献   

甘孜—理塘蛇绿混杂岩带中段理塘地区混杂岩物质组成及其洋盆演化史          下载免费PDF全文

严松涛  吴青松  李虎  秦蒙  毛世东  李余生  张勇 《中国地质》2021,48(6):1875-1895

理塘混杂岩位于甘孜-理塘蛇绿混杂岩带中段新龙县-理塘县一带,其内部保存有完整的混杂岩系,包括蛇绿岩残片、洋岛残块、洋内弧残块、复理石建造、裂谷残片、高压变质岩等,是恢复和反演甘孜-理塘洋盆演化的理想地区。在总结前人研究的基础上,结合笔者近年来的研究成果,详细阐述了理塘混杂岩的物质组成、构造环境及形成时代,进一步约束了甘孜-理塘洋盆的时空、性质以及演化历程。LA-ICP-MS锆石U-Pb测年结果表明,甘孜-理塘混杂岩带内蛇绿岩年龄为（346±17）Ma、（286.2±5.1）Ma、（219.5±2.2）Ma、（216.1±2.3）Ma,洋岛年龄为（271±10）Ma、（245.1±1.5）Ma、（211.8±1.8）Ma,在侏罗纪瑞环山组粉砂岩夹层中测得碎屑锆石最新年龄为（196±3）Ma,结合大量的古生物化石鉴定结果,分析认为理塘混杂岩最早的年龄记录可追溯至中泥盆世,最晚可延至早白垩世,是甘孜-理塘洋盆中泥盆世-早白垩世连续演化的记录。综合以上研究成果,笔者还大致建立了甘孜-理塘洋盆晚古生代-中生代的演化过程模式。  相似文献   

黔西南泥堡金矿床容矿火山岩系中“粉砂岩”夹层的岩石类型归属研究          下载免费PDF全文

祁连素 《贵州地质》2021,38(1):22-28, 64

原先认为泥堡金矿床容矿火山岩系中间的"粉砂岩夹层",研究发现其具有与火山碎屑岩的成分与结构构造特征,包括熔蚀石英晶屑和长石板状晶假象,局部还出现大量生物化石碎片,应归属为蚀变凝灰岩。火山岩系的原"粉砂岩夹层"并不存在,只是短暂的火山喷发间隙,整个容矿火山岩系形成从偏基性火山碎屑岩到中基性火山角砾岩的晚二叠世火山喷发旋回。火山岩旋回的早期到晚期,金矿成矿作用强度逐渐增强,印证金成矿作用与火山岩的密切成因联系。  相似文献   

鱼粪化石特征对早侏罗世托阿尔期湖泊生态系统的启示:以川东大安寨段为例^*          下载免费PDF全文

周小梅  金鑫  吴强旺  葛禹  时志强 《古地理学报》2021,23(3):600-609

早侏罗世托阿尔期早期大洋缺氧事件(Toarcian Oceanic Anoxic Event,~183.8 Ma)是一次全球性的多幕式生物—环境事件,其在四川盆地下侏罗统自流井组大安寨段亦有显示。对采集自川东北地区大安寨段的鱼粪化石进行形态学描述和内含物分析,发现鱼粪化石中含有大量的磷质成分,多为未经消化的鱼骨化石,另有大量介壳类化石与有机质混杂在一起。据露头岩性和显微薄片特征认为: (1)粪化石呈螺旋状,生产该粪化石的鱼类为大型肉食性鱼类,其喜食小型鱼类和软体动物等,推测可能是肺鱼类(角齿鱼);(2)鱼粪化石形成于开放型淡水湖泊中的半深湖—深湖区,其中湖泊表层含氧量丰富,主要由生产者、消费者构成了研究区早侏罗世托阿尔期大型湖泊生态系统,食物链较为复杂,而湖底为水动力条件较弱的还原环境。该研究成果可为早侏罗世托阿尔期大洋缺氧事件在湖泊中的沉积响应及生态影响研究提供依据。  相似文献