Geochemical Characteristics and Metallogenesis of Volcanic Rocks as Exemplified by Volcanic Rocks in Ertix,Xinjiang

Volcanic rocks in Ertix,Xinjiang,occurring in the collision zone between the Siberia Plate and the Junggar Plate,are distributed along the Eritix River Valley in northern Xinjiang.The volcanic rocks were dated at Late Paleozoic and can be divided into the spilite-keratophyre series and the basalt-andesite series.The spilite-keratophyre series volcanic rocks occur in the Altay orogenic belt at the southwest margin of the Siberia Plate.In addition to sodic volcanic rocks.There are also associated potassic-sodic volcanic rocks and potassic volcanic rocks.The potassic-sodic volcanic rocks occur at the bottom of the eruption cycle and control the distribution of Pb and Zn deposits.The potassic volcanic rocks occur at the top of the eruption cycle and are associated with Au and Cu mineralizations.The sodic volcanic rocks occur in the middle stage of eruption cycle and control the occurrence of Cu(Zn) deposits.The basalt-andesite series volcanic rocks distributed in the North Junggar orogenic belt at the north margin of the Junggar-Kazakstan Plate belong to the potassic sodic volcain rocks.The volcanic rocks distributed along the Ulungur fault are relatively rich in sodium and poor in potassium and are predominated by Cu mineralization and associated with Au mineralization.Those volcanic rocks distributed along the Ertix fault are relatively rich in K and poor in Na,with Au mineralization being dominant.     

Geochemical Characteristics of the Plagiogranites in the Vicinity of Bingdaban,Central Tianshan

The tectonic and geochemical characteristics suggest that the plagiogranites exposed in the vicinity of Bingdaban on the northen margin of the central Tianshan uplift zone show a distinct mantle-source character, and their enrichment in LREE and selected enrichment in LILE(large ion lithophile elements)reflect a setting related to an arc tectonic regime.These rocks represent the products formed at shallow levels from mantle-derived magmas modified with subduction components(or super crustal rocks).     

Geochemical Characteristics of Cenozoic Basaltic High-K Volcanic Rocks from Maguan Area, Eastern Tibet

The major element, trace element and Nd-Sr isotopic composition of Cenozoic basaltic volcanic rocks from the Maguan area, eastern Tibet, indicates that the volcanic rocks are enriched in alkalis, especially K (K2O up to 3.81%) and depleted in Ti (TiO2 = 1.27%-2.00%). These rocks may be classified as two groups, based on their Mg# numbers: one may represent primary magma (Mg# numbers from 68 to 69), and the other, the evolved magma(Mg# numbers from 49 to 57). Their REE contents are very high (∑REE = 155.06-239.04μg/g). Their REE distribution patterns are of the right-inclined type, characterized by LREE enrichment [(La/Yb)N =12.0-19.2], no Ce anomaly (Ce/Ce*=1.0), and weak negative Eu anomaly (Eu/Eu*=0.9). The rocks are highly enriched in Rb, Sr and Ba (59.5-93.8μg/g, 732-999 μg/g, and 450-632 g/g, respectively), high in U and Th (1.59-2.31μg/g and 4.73-8.16 μg/g, respectively), and high in Nb, Ta, Zr and Hf (70-118 μg/g,3.72-5.93 μg/g, 215-381 μg/g, and 5.47-9.03 μg/g, respectively). In the primitive mantle-normalized incompatible element spidergram, Nb, Ta, Zr, Hf and P show positive anomalies, whereas Ba, Ti and Y show negative anomalies. The 87Sr/86Sr ratios range from 0. 704029 to 0.704761; 143Nd/144Nd from 0. 512769 to 0. 512949; and εNd from 2.6 to 6.1. These geochemical features might suggest that the potential source of the basaltic high-K volcanic rocks in the Maguan area is similar to the OIB-source mantle of Hawaii and Kergeulen volcanic rocks.     

Geochemical Characteristics of Volcanic Rocks of the Laochang Ag Polymetallic Deposit,Lancang,Yunnan Province,China

In terms of major element, trace element and REE geochemical characteristics ofvolcanic rocks in the area studied and by making use of the TiO2-K2O-P2O5,The-Hf-Ta and Zr-Nb-Y trianglar diagrams and the environmental discrimination diagrams of incompatible ele-ment distribution pattems,the authors have drawn some conclusions that are different from those by previous workers.It is concluded that volcanic rocks in the Laochang Ag polymetallic deposit at Lancang,Yunnan belong to continental within-plate alkali basalts, and that their geotectonic setting seems to be at the northeastern margin of East Gondwana Land.     

Tectonic Environments of Cenozoic Volcanic Rocks in China and Characteristics of the Source Regions in the Mantle

Extensive volcanism is one of the important features of Cenozoic geology in China.Based on temporal-spatial distribution,the volcanism was associated with three major different geological settings:1)the continental rift basalts in Northeast and North China;2)the tension-fault basalts on the continental margins of Southeast China; and 3) the collision-zone high-K volcanics in the Qinghai-Xizang Plateau and its vicinities.The characteristics of “depletion in the south and enrichment in the north“of the China continental mantle are strongly supported by isotopic evidence.The Cenozoic continental cal characters,into the following geochemical provinces:1)the depleted mantle in South China;2)the primary mantle in Northeast and NorthChina; 3)the hybrid and transi-tional mantle in the region of Shandong ,Anhui,Jiangsu and northern Zhejiang;4)the depleted mantle around the Bohai Bay and the Lower Liaohe River;5)the K-metasomatic enriched mantle in the northern part of Northeast China;and 6)the re-cycled enriched mantle in the ancient subduction zone in the Qinghai-Xizang Plateau and its surround-ings.These geochemical characteristics on a regional scale must be a reflection of the nature of lithosphere evolution.     

Geology,Geochemistry and Genesis of the Mazhuangshan Gold Deposit in Hami,East Tianshan,Xinjiang,China

The Mazhuangshan area is located in the east of the Aqikekuduke Island Arc, where there are distributed intermediate-acid magmatic rocks emplaced during the Middle-Late Carboniferous. There are more than 20 orebodies in the area with an average gold grade 6.4 × 10⁻⁶ at present. The dominant metallic minerals are natural gold, auriferous silver, natural silver, pyrite and galena. Pyrite is the key gold carrier, high in Fe and low in S. Wall-rock alterations mainly include pyritization, silicification, and sericitization. Carbonation alteration was extensive at the late stage, often resulting in a high-grade orebody. Three mineralization stages may be distinguished. The peak homogenization temperatures of primary fluid inclusions range from 240 to 260°C. Mineralization pressures and depths are 47.2–68.8 MPa and 1.6–2.3 km respectively, showing the ore-forming features of hypergene gold deposit. The average salinity is 15 wt% NaCl equivalent. Fluid inclusion geochemistry data show that Ca²⁺ is far higher than Mg²⁺, and m_K ⁺/m_Na ⁺, m_Na^{2 +}/m_Ca ²⁺ (0.001∼0.338), m_ΣCl/m_ΣS and m_ΣC/m_ΣS ratios change with the reduction parameter [R = (CO + CH₄)/CO₂] and temperature. And the gold contents of ores and gangues are positively correlated withR.     

Geochemical Characteristics of Danfeng Meta-Volcanic Rocks in Shangzhou Area,Shaanxi Province

The Danfeng meta-volcanics in the Shangzhou area, Shaanxi Province are characterized by oceanic island arc volcanic geochemistry. They are a suite of low-K tholeiitic series and calc-alkaline series meta-volcanic rocks derived from different sources respectively.These meta-volcanics have high Th/Ta ratios and low contents of Ni,Ta,Ti,Y and Yb, suggesting that they were influenced by the subduction zone components.Many lines of evidence show that the Danfeng meta-volcanics were produced in an oceanic island are setting of the supra-subduction zone at the southern margin of the North China Block during the Early Paleozoic.     

Magmatic Source Composition and Magmatism of the Volcanic Rocks in the Area of Kuruktag, Southern Xinjiang

1. Geological setting The terrane of Kuruktag lies in the north-eastern margin of the Tarim Basin and is a faulted marginal uplift of the basin. In the terrane, there occur extensively Dagelagebulake Group and Xinditage Group of Archaean-Paleoprotozoic metamorphic sequences overlain by Sinian-Cambrian sequences (Geological and mineral bureau of Xingjiang ulger atonomous region, 1993). The sedimentology of the Sinian-Cambrian strata have been studied (South Xinjiang petrollum exploratio…     

Geochemistry of the Baishitouquan Amazonite—and Topaz—bearing Granite in the Mid—Tianshan Belt,Xinjiang,China

The Baishitouquan amazonite and topaz-bearing granite is one of the typical high-rubidium and high-fluorine granites in the eastern part of the Mid-Tianshan belt. This intrusion is in sharp contact with Mid-Proterozoic schists, gneisses and marbles, and is composed of four zones transitional from the bottom upwards: leucogranite, amazonite granite, topaz-bearing amazonite granite and topaz quartz albitite. The Baishitouquan granite contains highly ordered K-feldspar, Li-rich mica, Mn-rich garnet, α-quartz and low temperature zircon and is chemically high in Si, K, Na, Al, Li, Rb, Cs and F, and low in Ti, Fe, Ca, Mg, P, Co, Ni, Cr, V, Sr and Ba, with Na₂O<K₂O. Amazonite from the amazonite granite zone contains 1867 ppm Rb. The F contents of bulk rocks are 3040 and 4597 for the amazonite granite and topaz-bearing amazonite granite zones, respectively. These two zones have δ¹⁸O values of 8.97–9.85‰ (SMOW) and show flat REE distribution patterns with strong Eu depletion. K-Ar and Rb-Sr ages of this intrusion are 226. 6 Ma and 209. 6 Ma respectively, with an initial⁸⁷Sr/⁸⁶Sr ratio of 0.987±0.213. The Baishitouquan granite is the product of crystallization of a low temperature, and water, rubidium and fluorine-rich magma, which may have been derived from partial melting of muscovite-rich crustal rocks. Consolidation of this granite involved two contrasting and successive stages: melt crystallization and hydrothermal metasomatism and precipitation. Various geological features of this granite were formed during the transition from the magmatic to the hydrothermal stage.     

Carboniferous Bimodal Volcanic Rocks and Their Plate Tectonic Setting,Hainan Island

The Carboniferous volcanic rocks in western Hainan Island consist of a series of oceanic tholeite and rhyoporphyrite,showing bimodal nature.Similar geochemical characters,in terms of abun-daces and relative rations of incompatible elements and REE and the REE patterns,between the basalt and continental rift-associated tholeiite indicate the occurrence of Late Paleozoic rifting in the area.The basaltic magma,with a low degree of evolution,was originated from deep mantle,show-ing contamination by low crustal material.The rhyolite is thought to be formed from partial melting of the continental crust by higher thermal flow in a rift environment rather than from fractional crystallization of a basaltic magma.     

新疆北天山沙湾地区晚石炭世火山岩地球化学特征及地质意义

天山北部沙湾地区火山岩由火山碎屑岩和火山熔岩组成,主要包括安山质(岩屑)晶屑凝灰岩、英安质熔结凝灰岩、玄武安山岩和流纹岩,为钙碱性系列。玄武安山岩和流纹岩主量元素平均含量分别为:SiO2=51.03%、77.33%,TiO2=0.76%、0.16%,CaO=10.30%、0.43%,MgO=5.19%、0.89%,Na2O=2.10%、1.27%,K2O=1.28%、2.54%;稀土元素特征分别为:∑REE=369.1×10-6、729.0×10-6,(La/Yb)N=5.0、3.5,(La/Sm)N=2.7、2.4,δEu=0.82、0.54;Sr、Nd、Pb同位素特征分别为:(87Sr/86Sr)t=0.70680和0.70476,(143Nd/144Nd)t=0.52224和0.51225,εNd(t)=0.2和0.1,(206Pb/204Pb)t=17.775和17.720,(207Pb/204Pb)t=15.790和15.826,(208Pb/204Pb)t=38.240和38.876。火山熔岩亏损Nb、Ta、Ti和P,富集K、Rb、U、Th、Zr和Hf,玄武安山岩的Zr为117×10-6～121×...     

天山地区新元古代-早寒武世火山岩地球化学和岩石成因

天山地区新元古代-早寒武世玄武质熔岩包括拉斑玄武质和碱性玄武质两个主要岩浆系列，前者是早期（早南华世贝义西组、早震旦世扎摩克提组）喷发的火山岩系的主要组成，后者是晚期（早震旦世苏盖特布拉克组、晚震旦世水泉组、早寒武世西山布拉克组）喷发的火山岩系的主要组成。稀土、微量元素和Sr、Nd同位素特征揭示，这些火山岩均形成于大陆裂谷环境，其源区可能是源于一种似洋岛玄武岩源的软流圈地幔源，并且在岩浆上侵喷发过程中发生了岩石圈的混染。     

新疆东天山哈密五堡地区中奥陶世大柳沟组火山岩岩石学和地球化学特征

新疆东天山哈密五堡地区中奥陶世大柳沟组是研究区出露的最老的火山岩地层,大地构造属于准噶尔板块-大南湖复合岛弧火山岩带。大柳沟组火山岩以钙碱性系列为主,大离子亲石元素(LIL)的Ba、Th等富集,呈现正异常;高场强元素(HFS)Nb、Ta、Zr、Hf和Ti呈负异常。中基性火山岩的稀土配分曲线为轻稀土富集、重稀土亏损型式。其常量和微量元素特征总体上具岛弧火山岩的特点。     

西南天山特克斯科桑溶洞火山岩的锆石U-Pb年代学研究

新疆特克斯县乌孙山科桑溶洞火山-沉积岩剖面由变质岩、火山-沉积岩(中酸性火山熔岩、火山碎屑岩、生物碎屑灰岩)和侵入其中的花岗质岩石组成,花岗岩中保留着英安岩-安山岩顶垂体。夹在火山岩地层之间的厚层生物碎屑灰岩(其中发育溶洞)发生褶皱变形。在剖面多处见到逆冲构造,断裂带局部塑性变形。采自剖面下部英安岩样品的锆石232Th/238U比值为0.4～0.6,U-Pb谐和年龄368.3±1.7Ma(MSWD=1.5,n=15)。剖面上部流纹岩中锆石的232Th/238U比值为0.8～2.2,U-Pb谐和年龄为356.4±1.7Ma(MSWD=1.3,n=19)。大约12Ma的时差说明存在两次火山喷发事件,在这两次火山喷发的间歇形成了巨厚生物碎屑灰岩(1000m)。这种间歇性的火山喷发在西天山地区普遍发育,形成了规模巨大的滨海相火山-沉积盆地。剖面下部的英安岩与剖面上部的流纹岩的锆石具有不同的微量元素组成,预示着其岩浆源区性质的差异。     

新疆伊犁北部石炭纪火山岩地球化学特征及其地质意义

石炭纪火山岩广泛分布于西天山伊犁陆块周缘,其岩性复杂,并大多与陆源碎屑岩伴生或互层。其中伊宁阿希、尼勒克和那拉提3个剖面的火山岩岩石地球化学特征显示,这些火山岩属于钙碱性系列,由玄武岩、粗玄岩、玄武质安山岩、玄武质粗面安山岩、安山岩、流纹岩、英安岩和粗面岩组成。稀土元素含量较高,轻稀土元素较重稀土元素富集。这些火山岩亏损高场强元素Nb,Ta,Zr等,而富集大离子亲石元素Th,Rb等,因而这些岩石的形成与板块俯冲有关。微量元素地球化学图解进一步表明,这些岩石形成于大陆岛弧环境。与之共生的早、中石炭世浅海—滨海相沉积地层以及伊犁陆块北缘巴音沟—莫托沙拉沟晚泥盆世—早石炭世蛇绿岩带的存在,表明伊犁陆块北缘在石炭纪时其环境为活动大陆边缘,石炭纪火山岩的形成可能与晚泥盆世—中石炭世早期北天山洋盆向南的俯冲作用有关。     

新疆博格达造山带西段石炭纪双峰式火山岩地球化学特征及成因

新疆博格达造山带博格达峰南侧柳树沟组出露大量双峰式火山岩组合.本文对博格达造山带西段石炭纪双峰式火山岩地球化学特征研究结果表明:①玄武岩具有贫K富Na、富Ti富Al和富Mg的特征,w(K2O)/w(TiO2)、w(K2O)/w(P2O5)值较低且范围较小,总体上玄武岩有轻度的地壳物质混染作用;HREE相对富集,轻重稀土...     

新疆天山表壳元素地球化学特征

根据天山地区(42～44^oN，81～89^oE)1：20万，七探采集的900余个岩石样品的分析结果，基于全样本统计和迭代剔除方法，得到新疆天山地区表壳(出露地壳)的39种元素丰度值；对其中的SiO2、TiO2、Al2O3、TFe2O3、MgO、MnO、CaO、Na2O、K2O、P2O5 10种常量元素，按氧化物之和为100％进行归算。与全球大陆上地壳元素丰度值相比，天山地区表壳元素丰度富集SiO2、MnO和Ag、As、Hj、Sb元素，明显亏损CaO和。Be、Co、Cr、Ni、Mo、Sn，V、W等元素。从元素比值来看，该区表壳的Ba/La、K／La、K／Th、Nb/La、Th/La、Y／La值与全球大陆上地壳相应元素值相当；而K／Na、La／As、La／Sb值明显低于全球大陆上地壳。该区表壳化学成分相当于花岗闪长岩，同时表现出相对富钠和As、Sb元素的特征；这一地球化学特征与区内出露的表壳岩石主要是加里东期和海西期岛弧造山作用的产物有关，相对富钠的成分特征与岛弧岩浆活动中的Adakite质岩浆作用有关。     

东天山博格达晚石炭世双峰式火山岩地球化学特征及意义

东天山博格达造山带晚石炭世柳树沟组为一套由玄武岩和流纹岩组成的双峰式火山岩,形成于晚石炭世,其Si O₂含量介于46.18%～46.56%和76.06%～76.25%之间,具有明显的Daly成分间断。其中,玄武岩具富Na贫K特征,Ti O₂、Al₂O₃、Ca O和MgO含量均较高,∑REE为75.54×10^-6～80.22×10^-6,LREE/HREE值为3.00～3.12,以富集Ba、Rb等大离子亲石元素(LILE)和不相容元素(P、K),相对亏损Ti、Ta、Nb等高场强元素(HFSE)和不相容元素(U、Th)为特征;流纹岩Na₂O/K₂O值为0.32～0.36,属低Ti、低Mg类流纹岩,∑REE为520.72×10^-6～595.26×10^-6,LREE/HREE值为5.60～6.53,具有Rb、Th、K、La、Ce、Zr、Hf、Sm等元素的富集以及Ba、U、Ta、N...     

东天山卡拉塔格钠质火山岩岩石学、地球化学及成因

东天山卡拉塔格早泥盆世卡拉塔格组火山岩主要岩性为海相富钠质的安山岩、流纹岩和英安岩，夹少量的钠质玄武安山岩和钠质玄武岩以及正常系列的玄武安山岩。钠质火山岩的特征是：Na2O=1．69～6．38％，Na2O／K，O〉1，多在2～100间：无论是斑晶还是基质，斜长石均为富钠长石；酸性岩石斑晶主要是钠长石和石英，中基性岩石斑晶主要是钠长石（少量更长石）：酸性岩以斑状结构、霏细结构、球粒结构为主，而中基性岩以交织结构、玻晶交织结构为主。各类岩石全岩化学分析计算结果均含标准矿物Q、Hy、Hm，一部分含Di或C，在TAS图上全都投于亚碱性区；∑REE=25、96-96．11ppm，LaN／YbN=1．68-5．32，Eu／E^＊=0．46-1．25，LaN／SmN=1．01-2．95；强不相容元素适度富集，Nb和Ta强烈亏损，部分样品Cs、Rb、K、Zr和Hf适度亏损。这些特征表明，该区钠质火山岩的原始岩浆可能来自富钠俯冲洋壳熔体与地幔楔岩石反应的产物部分熔融。这样的岩浆形成机制与前人有关卡拉塔格是早泥盆世岛弧的认识相一致。