北天山西段晚石炭世—早二叠世花岗岩成因及其构造意义

北天山增生杂岩带是北天山洋最终闭合的产物，对其中的地质体进行详细研究是揭示北天山洋演化过程的关键。北天山增生杂岩带内存在一些花岗质侵入体，然而目前为止，对这些岩体的形成时代及成因研究十分有限。本文对北天山西段的萨尔萨拉岩体和艾鲁逊岩体进行了锆石U- Pb年代学、地球化学和锆石Lu- Hf同位素分析，并探讨其成因及大地构造意义。萨尔萨拉岩体和艾鲁逊岩体主要岩石类型均为二长花岗岩，锆石U- Pb年龄分别为303 Ma和298 Ma，为晚石炭世—早二叠世侵入体。两个岩体的锆石均具有非常高的εHf(t)值，分别为9. 7~12. 1（平均为11. 2）和12. 1~15. 0（平均为13. 2），相应的两阶段模式年龄为696~547 Ma和541~357 Ma，表明其源区为新生的地壳物质。两个岩体的样品均具有高硅、富碱、富钾特征，为弱过铝质高钾钙碱性花岗岩，其较高的CaO/Na2O比值（>0. 3）和Al2O3/(MgO+FeOT)mol值暗示其可能源于变质杂砂岩的部分熔融，北天山增生楔中的复理石砂岩为可能的源区岩石。结合区域资料，本文认为萨尔萨拉岩体和艾鲁逊岩体形成于同碰撞向后碰撞转换阶段，限定了北天山洋在晚石炭世末闭合。     

Petrogenesis of early Silurian intrusions in the Sanchakou area of Eastern Tianshan,Northwest China,and tectonic implications: geochronological,geochemical, and Hf isotopic evidence

ABSTRACT

Palaeozoic intrusions in Eastern Tianshan are important for understanding the evolution of the Central Asian Orogenic Belt (CAOB). The Sanchakou intrusions situated in Eastern Tianshan (southern CAOB), are mainly quartz diorite and granodiorite. A comprehensive study of zircon U–Pb ages, zircon trace elements, whole-rock geochemistry, and Lu–Hf isotopes were carried out for the Sanchakou intrusive rocks. LA-ICP-MS zircon U–Pb dating yielded crystallization ages of 439.7 ± 2.5 Ma (MSWD = 0.63, n = 21) for the quartz diorite, and 430.9 ± 2.5 Ma (MSWD = 0.21, n = 21) and 425.5 ± 2.7 Ma (MSWD = 0.04; n = 20) for the granodiorites. These data, in combination with other Silurian ages reported for the intrusive suites from Eastern Tianshan, indicate an early Palaeozoic magmatic event in the orogen. In situ zircon Hf isotope data for the Sanchakou quartz diorite shows ε_Hf(t) values of +11.2 to +19.6, and the two granodioritic samples exhibit similar ε_Hf(t) values from +13.0 to +19.5. The Sanchakou plutons show metaluminous to weakly peraluminous, arc-type geochemical and low-K tholeiite affinities, and display trace element patterns characterized by enrichment in K, Ba, Sr, and Sm, and depletion in Nb, Ta, Pb, and Ti. The geochemical and isotopic signatures indicate that the Sanchakou dioritic and granodioritic magmas were sourced from a subducted oceanic slab, and subsequently underwent some interaction with peridotite in the mantle wedge. Combined with the regional geological history, we suggest the Sanchakou intrusions formed due to the northward subduction of the Palaeo-Tianshan Ocean beneath the Dananhu–Tousuquan arc during early Silurian time.     

Detrital zircon ages and Hf isotopic compositions of metasedimentary rocks in the Wuqia area of Southwest Tianshan,NW China: implications for the early Paleozoic tectonic evolution of the Tianshan orogenic belt

ABSTRACT

The Chinese Southwest Tianshan Orogenic Belt is located along the boundary between the Central Asian Orogenic Belt (CAOB) and the Tarim Block (TB), NW China. It records the convergence of the Tarim Block and the Middle Tianshan, and is, therefore, a crucial region for understanding the Eurasia continental growth and evolution. The Wulagen (geographical name) metasedimentary rocks of the Wuqia area (mainly metamorphic sandstones and mica schists) form one of the metamorphic terranes in the Southwestern Tianshan Orogenic Belt. The geochronology of these rocks is poorly known, which hampers our understanding of the tectonic evolution of the belt. We analyzed 517 zircon grains for detrital zircon U–Pb dating and 93 zircon grains for in situ Lu–Hf isotopic compositions from the Wulagen metasedimentary rocks. The analyzed zircon grains yield Neoarchean to late Paleozoic U–Pb ages with major age peaks at ~2543 Ma, 1814 Ma, 830 Ma, 460 Ma, and the youngest cluster of zircon (magmatogene) ages is 395 Ma. The zircon U–Pb data show that the late Paleozoic (Early Devonian) is the maximum depositional age of the Wulagen metasedimentary rocks, rather than the previously considered Precambrian period. The zircons with Paleozoic ages yield εHf(t) values of ?22.0 to +11.3 and two-stage model ages (TDM₂) of 3.95 to 1.30 Ga, suggesting that the parental magmas were formed from partial melting of pre-existing crustal rocks. Our zircon U–Pb geochronology and Hf isotopic data indicate the major source regions for the Wulagen metasedimentary rocks was the Kyrgyzstan North Tianshan. The zircon age population of 600–400 Ma (peak at ~460 Ma) has negative εHf(t) values (?15.0 to ?0.6) and Mesoproterozoic two-stage model ages, suggesting that the early Paleozoic magmatism resulted mainly from the melting of ancient crust, which played an important role in crustal evolution in the southern CAOB.     

新疆东部卡瓦布拉克地区古生代岩浆活动对中天山地块构造归属的指示意义

卡瓦布拉克地区位于中天山地块南缘。该区古生代侵入岩类广泛发育,是探究中天山构造演化及地壳生长历史的重要窗口。本文获得该区两件二长花岗岩样品的LA-ICP-MS锆石U-Pb定年结果分别为447.4±4.9Ma、422.6±5Ma。LA-MC-ICP-MS锆石Hf同位素原位分析结果显示,其εHf(t)值分别为7.1～11.9、5.8～11.8,对应的二阶段模式年龄为674～963 Ma、514～1043 Ma。侵入于晚古生代花岗岩中的中—基性岩脉携带多期捕获锆石,其εHf(t)介于-7.4～4.8,对应的模式年龄变化范围为1.47～2.54Ga。卡瓦布拉克地区古生代花岗岩及中—基性岩脉中捕获锆石所反映的基底信息表明,中天山与塔里木在中元古代(～1.4Ga)、新元古代(～800Ma)以及古生代(～400Ma)期间岩浆活动具有截然不同的源区特征。结合前人研究成果,认为中天山与塔里木不具有构造亲缘性。     

Zircon ages and Hf isotopic compositions of plutonic rocks from the Central Tianshan (Xinjiang,northwest China) and their significance for early to mid-Palaeozoic crustal evolution

We present new zircon ages and Hf-in-zircon isotopic data for plutonic rocks and review the crustal evolution of the Chinese Central Tianshan (Xinjiang, northwest China) in the early to mid-Palaeozoic. The Early Ordovician (ca. 475–473 Ma) granitoid rocks have zircon ε_Hf(t) values either positive (+0.3 to +9.5) or negative (?6.0 to ?12.9). This suggests significant addition of juvenile material to, and coeval crustal reworking of, the pre-existing continental crust that is fingerprinted by numerous Precambrian zircon xenocrysts. The Late Ordovician–Silurian (ca. 458–425 Ma) rocks can be assigned to two sub-episodes of magmatism: zircon from rocks of an earlier event (ca. 458–442 Ma) has negative zircon ε_Hf(t) values (?6.3 to ?13.1), indicating a predominantly crustal source; zircon from later events (ca. 434–425 Ma) has positive zircon ε_Hf(t) values (+2.6 to +8.9) that reveal a predominantly juvenile magma source. The Early Devonian (ca. 410–404 Ma) rocks have near-zero zircon ε_Hf(t) values, either slightly negative or positive (?1.4 to +3.5), whereas the Mid-Devonian rocks (ca. 393 Ma) have negative values (?11.2 to ?14.8). The Late Devonian (ca. 368–361 Ma) granites are undeformed and are chemically similar to adakite but have relatively low negative whole-rock ε_Nd(t)values (?2.4 to ?5.3). We interpret the Early Ordovician to Mid-Devonian magmatic event to reflect combined juvenile crustal growth and crustal reworking processes via episodic mafic underplating and mantle–crust interaction. The Late Devonian episode may signify delamination of the over-thickened Chinese Central Tianshan crust.     

中天山巴仑台地区花岗质岩石的Hf同位素研究：对构造演化及大陆生长的约束

中国中天山地块位于天山造山带的核心部位,对研究中亚造山带西南段构造演化、块体起源和陆壳生长等科学问题具有重要意义。本次研究围绕中天山地块西段巴仑台一带出露的古生代花岗质岩石展开,报道了部分代表性岩体的LA-ICP-MS锆石U-Pb年龄和MC-ICP-MS锆石Lu-Hf同位素特征。同时还系统总结前人发表的研究区内花岗质岩石的锆石U-Pb年龄和Lu-Hf同位素资料。本次研究的7个花岗质侵入体的锆石LA-ICPMS年龄分别为435±5 Ma、432±4 Ma、359±4 Ma、312±4 Ma、346±2 Ma、306±5 Ma和362±5 Ma。它们在成因类型上均属于I型花岗岩,起源于深部不同性质地壳物质的部分熔融,部分岩体具有壳幔混合成因。研究表明,巴仑台一带的岩浆事件主要发生在早志留世—早泥盆世(435~408 Ma)、晚泥盆世—早石炭世(370~339 Ma)和晚石炭世—中二叠世(313~263 Ma)三个阶段,第一期岩浆事件是古天山洋闭合形成的后碰撞体制以及古南天山洋俯冲导致的大陆岛弧环境共同作用的结果。而古南天山洋俯冲活动的暂停和新一轮的洋盆扩张是导致区内中、晚泥盆世岩浆活动暂停的原因。第二期花岗质侵入体是古南天山洋第二期北向俯冲所导致的大陆岛弧岩浆作用的产物,而第三期花岗质侵入体形成于古南天山洋最终闭合之后的后碰撞环境中。通过总结区内古生代花岗质岩体的锆石的Hf同位素特征,我们认为巴伦台地区前寒武基底主要形成于三个阶段:1~2.47Ga至~2.26Ga,为研究区对全球陆核生长事件的响应;2~1.47Ga至~1.25Ga,对应于哥伦比亚超大陆的裂解;3~1.20Ga至~0.90Ga,很可能是研究区对导致罗迪尼亚超大陆聚合的"Grenville运动"的响应。     

中天山卡瓦布拉克地区彩霞山花岗岩体年龄及成因

彩霞山花岗岩体位于中天山南缘的卡瓦布拉克地区,由糜棱岩化二长花岗岩和斑状钾长花岗岩组成,其LA-ICP-MS锆石U-Pb年龄分别为(330.0±3.6)Ma、(333.3±3.6)Ma;其锆石εHf(t)分别为5.23~0.87和10.85^-5.81,tDM2分别为1.28~1.00Ga和1.7~0.65Ga。地球化学分析结果显示,二长花岗岩和斑状钾长花岗岩的A/CNK、Na2O+K2O值分别为6.40、45.91和4.17、33.19,均属于高钾钙碱性过铝质I型花岗岩。富集轻稀土元素,具有强烈的铕负异常(δEu=2.76~4.14)。糜棱岩化二长花岗岩同构造侵位的显微构造特征揭示卡瓦布拉克韧性剪切带至少在早石炭世晚期处于活动状态。结合区域地质资料,认为彩霞山花岗岩体形成于南天山洋向北俯冲的活动大陆边缘环境,代表中天山南缘晚古生代岩浆弧的一部分。     

东天山沙泉子铁铜矿区火山岩地球化学特征、锆石U-Pb年龄及地质意义

沙泉子铁铜矿床是东天山地区赋存于火山岩中的矿床之一。矿体产于底坎尔组玄武岩与英安岩接触部位,在闪长玢岩与围岩接触带上也可见不规则铁矿化。对火山岩的形成时代以及构造地质背景的研究是重建成矿过程的关键。LA-ICP-MS锆石U-Pb定年结果表明,沙泉子铁铜矿区底坎尔组流纹岩和闪长玢岩的206Pb/238U加权平均年龄分别为(321.7±1.7)Ma和(322.2±1.7)Ma,是早石炭世末岩浆活动的产物。元素地球化学和Hf同位素特征表明,底坎尔组火山岩属钙碱性系列,富集轻稀土元素(LREE)和大离子亲石元素(LILE),亏损高场强元素(Nb、Ta、Ti),具有岛弧火山岩地球化学特征。基性岩来源于受俯冲板片流体交代的亏损地幔,中性岩为基性岩分离结晶的产物,流纹岩是新生地壳物质部分熔融形成。综合前人研究成果表明,沙泉子铁铜矿床形成于早石炭世末陆缘弧环境,铁矿化不早于322 Ma。     

中天山天湖东铁钼矿含矿片麻状花岗岩年代学、地球化学和锆石Hf同位素-对于中天山早古生代构造演化的启示

以中天山东段的天湖东铁钼矿含矿花岗岩为例,在LA-ICP-MS锆石U-Pb年代学测定其为早古生代花岗岩（（445.3±4.6） Ma）基础上,通过岩相学、地球化学及锆石原位Hf同位素组成等多方面研究,探讨该岩体的成岩作用及其构造背景。天湖东含矿片麻状花岗岩的主要矿物为斜长石、石英、钾长石,并含少量黑云母和角闪石等。全岩地球化学分析结果表明,该片麻状花岗岩高硅、弱富铝、富钙、富钠而贫钾,ASI值为0.68~0.82,属于准铝质钙碱性花岗岩,总体上富集大离子亲石元素（LILE）Rb、Ba等和轻稀土元素La、Ce、Nd等,而亏损高场强元素Nb、Ta、Ti、Yb等,轻重稀土分异明显,轻稀土分异较为明显,而重稀土分异不明显,表现出典型岛弧岩浆岩的地球化学特征。锆石的ε_Hf(445 Ma)值为-6.31~-1.77,二阶段Hf模式年龄（T_DM2）为1.538~1.825 Ga,表明该花岗岩的源区主要为壳源物质。综合分析上述资料,认为天湖东铁钼矿片麻状花岗岩是由俯冲过程中地壳物质重熔的产物。结合前人的研究和本课题组的新近研究成果认为,在早古生代时,中天山为岩浆弧构造环境,形成一系列的钙碱性岩浆岩,而该岩浆弧的形成可能是受到介于吐哈陆块和塔里木板块之间的古天山大洋在早古生代时期向南俯冲而形成的。     

The petrogenesis and tectonic implications of the granitoid gneisses from Xingxingxia in the eastern segment of Central Tianshan

As part of Central Asian Orogenic Belt (CAOB), the Central Tianshan zone plays a crucial role in the reconstruction of the tectonic evolution of the CAOB. Furthermore, it is bordered by the Tarim Craton to the south, and the comparable evolutionary history between them enables the Central Tianshan zone to provide essential information on the crustal evolution of the Tarim Craton. The eastern segment of the Central Tianshan tectonic zone is characterized by the presence of numerous Precambrian metamorphic rocks, among which the Xingxingxia Group is the most representative one. The granitoids gneisses, intruded into the Xingxingxia Group, consist of two major lithological assemblages: (1) biotite-monzonitic gneisses and (2) biotite-plagioclase gneisses. These metamorphosed granitoid rocks are characterized by enrichment in SiO₂, Al₂O₃ and K₂O and depletion in MgO and FeO_T. The Rittmann index (σ) spreads between 1.44 and 2.21 and ACNK (Al₂O₃/(CaO + Na₂O + K₂O)) ranges from 1.03 to 1.08, indicating that these granitoid gneisses are high-K calc-alkaline and peraluminous. Trace element data indicate that the studied samples are enriched in LREE with moderate REE fractionated patterns ((La/Yb)_N = 10.5–75.3). The concentrations of HREE of the garnet-bearing gneisses are significantly higher than those of garnet-free gneisses. The former show pronounced negative Eu anomalies (Eu/Eu^* = 0.32–0.57), while the latter are characterized by negligible negative Eu anomalies to moderate positive Eu anomalies (Eu/Eu^* = 0.80–1.35). In addition, the enrichment of LILE (Rb, Th, K, Pb) and depletion of HFSE (Ta, Nb, P, Ti) of the examined granitoid gneisses are similar to typical volcanic-arc granites. Zircons U–Pb dating on the biotite monzonitic gneiss yields a weighted mean ²⁰⁶Pb/²³⁸U age of 942.4 ± 5.1 Ma, suggesting their protoliths were formed in the early Neoproterozoic, which is compatible with the time of the assembly of supercontinent Rodinia. The zircons have a large ε_Hf(t) variation from −5.6 to +3.2, suggesting that both old crust-derived magmas and mantle-derived juvenile materials contributed to the formation of their protoliths. Based on field observation, and petrological, geochemical and geochronological investigations, we infer that the granitoid gneisses from Xingxingxia were probably formed on a continental arc that resulted from the interaction of Australia and the Tarim Craton during the assembly of the Rodinia supercontinent, and that the Central Tianshan zone was a part of the Tarim Craton during that time. Besides, the Grenvillian orogenic events may have developed better in the Tarim Craton than previously expected.     

西天山昭苏北部石炭纪火山岩的岩石地球化学特征、成因及形成环境

西天山昭苏北部早石炭纪大哈拉军山组火山岩由碱性橄榄玄武岩和少量的拉斑玄武岩组成。火山岩TiO2（1．10～1．99％）和P2O5（0．22～0．70％）含量较高,富集大离子亲石元素（Rb,Ba,K）并强烈亏损高场强元素（Nb,Ta,Ti）（（Nb／La）N=0．20～0．36）,轻重稀土分异,其地球化学特征总体上与美国盆岭地区新生代（中新世中期之前）火山岩以及中美洲和南美洲的弧后“过渡型”基性火山岩相似,但与典型火山弧岩浆岩有些不同。大量元古代继承锆石的出现以及主量、微量元素和Nd同位素地球化学特征均表明火山岩经历了相当程度的结晶分异和陆壳混染（AFC）。与碱性玄武岩相比,拉斑玄武岩的SiO2含量和K2O／Na2O比值较高,而εNd（t）,MgO和Mg^#值较低,可能由碱性玄武岩浆经AFC演化形成。碱性橄榄玄武岩中含富Fe,Ti贫Si的火山岩夹层（Fe-Ti玄武岩）,是碱性玄武质岩浆依Fenner趋势发生较高程度结晶分异的产物。火山岩的元素地球化学特征指示岩浆源区可能为俯冲流体交代富集的岩石圈地幔,然而,Fe-Ti玄武岩的出现以及地球化学特征随时间的规律性变化均指示它们形成于拉张的构造环境。我们提出,昭苏北部大哈拉军山组火山岩可能形成于具有元古代陆壳基底的活动大陆边缘弧后拉张环境。这一认识与前人提出的大哈拉军山组火山岩为地幔柱活动影响的大陆裂谷岩浆岩的认识有所不同。     

东天山晚古生代构造转折: 红山南-天木东地区岩浆岩年代学与地球化学的约束

东天山是中亚造山带的重要组成部分, 区内晚古生代岩浆活动与成矿作用强烈, 是理解中亚造山带构造演化与成矿作用的关键地区。然而, 前人对东天山构造带由俯冲向碰撞转变的时间和过程仍存在较大争议。本文对东天山红山南-天木东地区广泛出露的晚古生代岩浆岩开展了野外考察和岩相学鉴定, 进行了年代学和岩石地球化学分析, 以限定其形成时代、岩石成因和构造背景, 进而探讨晚古生代构造演化过程。红山南-天木东地区岩浆岩主要为早石炭世火山岩和侵入岩, 次为早二叠世侵入岩。早石炭世火山岩主要为安山岩(328.8±2.0Ma)和英安岩, 侵入岩主要为辉长闪长岩(328.7±1.8Ma); 早二叠世侵入岩为黑云母二长花岗岩(290.3±2.1Ma)和石英闪长岩(290.0±1.6Ma)。早石炭世岩浆岩富含角闪石和斜长石, 为钙碱性, 准铝质系列, 富Rb、Ba、Th、U和Pb等大离子亲石元素, 亏损Nb、Ta和Ti等高场强元素和Sr-Nd-Hf同位素, 具有岛弧岩浆岩特征, 是交代地幔楔部分熔融的产物。相对于早石炭世岩浆岩, 早二叠世侵入岩富含黑云母和碱性长石, 富集SiO₂、Na₂O和K₂O, 贫Al₂O₃、MgO、Fe₂O₃^T及CaO, 同位素更亏损, 为碰撞后背景下新生加厚地壳部分熔融的产物。总之, 红山南-天木东地区的早石炭世与早二叠世岩浆岩地球化学差异显著, 指示东天山构造背景从早石炭世大洋俯冲体制转变为早二叠世碰撞后造山体制, 即其构造转折时间为晚石炭世-早二叠世。

     

东昆仑祁漫塔格地区晚三叠世正长花岗岩岩石成因及构造意义

青海省东昆仑祁漫塔格地区肯德可克矿区外围东部发育一正长花岗岩体,主要矿物组合为正长石(50%~60%)+石英(20%~30%)+斜长石(10%~20%)+黑云母(1%~5%)。其LA-ICP-MS锆石U-Pb加权平均年龄为217.9±1.7 Ma(MSWD=0.74,n=20),形成时代为晚三叠世,与祁漫塔格地区铁多金属矿床基本同时形成。岩石地球化学组成具有高硅(Si O2=74.53%~75.28%)、富碱(K2O+Na2O=8.81%~8.95%)、富铁贫镁(Fe OT/Mg O=18.02~31.48)的特征,并具强烈的负Eu异常(δEu=0.04~0.05),富集Rb、Th、U、K、Ga,亏损Sr、Ba、Ta、P、Ti,显示其为准铝质A型花岗岩。正长花岗岩锆石εHf(t)为2.0~12.4,平均6.4,显示其源区具有壳幔混合作用的特征,壳幔物质交换为区内铁多金属矿化提供了大量成矿物质。该正长花岗岩属A2型花岗岩,暗示其形成于造山后的伸展构造体制,反映了祁漫塔格地区晚华力西-印支期造山旋回于晚三叠世由造山后期转为伸展阶段。     

中天山卡瓦布拉克杂岩带中闪长岩的锆石U-Pb年龄及Hf同位素特征

卡瓦布拉克杂岩带出露于中天山地块东段卡瓦布拉克—阿克塔格地区,沿卡瓦布拉克断裂呈东西向展布。笔者选择构成该杂岩带的中—基性岩石主体闪长岩,开展了LA-ICP-MS锆石U-Pb年代学和LA-MC-ICP-MS锆石Hf同位素研究。结果表明:闪长岩中锆石呈自形—半自形,发育典型的岩浆锆石振荡生长环带,Th/U值较高(均大于0.40),且Th、U含量呈现较好的正相关关系,为典型的岩浆成因锆石;这些锆石的206Pb/238 U年龄加权平均值为(375±1)Ma,MSWD=0.081,属晚泥盆世,可代表其结晶年龄;锆石具有较均一的Hf同位素组成,初始比值为0.282 655~0.282 747、εHf(t)值为4.0~7.2,其对应的亏损地幔模式年龄为714~842Ma。结合区域地质资料认为,卡瓦布拉克杂岩带中的闪长岩由亏损岩石圈地幔发生部分熔融而形成。     

Petrogenesis and tectonic implications of early Palaeozoic igneous rocks of the western South Qilian Belt,central China

Early Palaeozoic granitoids in the South Qilian Belt, central China, record details of the tectonic evolution and crustal growth of the Qilian orogenic belt. Five representative granitoids from the western South Qilian Belt were sampled for zircon LA-ICPMS U–Pb dating, Lu–Hf isotopes, and whole-rock geochemical analyses. Zircon U–Pb dating of two porphyritic granodiorites and a porphyritic monzogranite yielded ages of 442.7 ± 3.5, 441.8 ± 4.3, and 435.4 ± 3.5 Ma, respectively. These granitoids exhibit a geochemical affinity to I-type granite, are metaluminous with a low aluminium saturation index (A/CNK = 0.75–1.15), have moderate Al₂O₃ and low MgO contents, high La/Yb and low Sr/Y ratios, and are depleted in Nb, Ta, P, and Ti, which suggests a subduction zone magmatic arc affinity, with mixing between a primary mantle-derived magma with lesser continental crustal material. The syenogranite and monzogranite from the South Qilian Belt, which yield U–Pb zircon ages of 440.4 ± 9.0 and 442.3 ± 1.2 Ma, respectively, have pronounced S-type geochemical affinities, are peraluminous with A/CNK values of 1.07–1.16, have relatively high SiO₂, Al₂O₃, K₂O, and Rb contents, low Y and Yb, low Sr/Y and La/Yb ratios, positive Th, U, and light Rare Earth Element (REE) anomalies, and depletions in Nb, Ta, Sr, and Ti. Their geochemical signature suggests derivation from partial melting of continental crust in a syn-collisional setting. The Hf isotopic data of zircons from the granitoids show a significant input of Paleoproterozoic crust in the crustal formation of the western South Qilian Belt in Palaeozoic. Compare the ε_Hf(t) value of S-type granite with that of I-type granite, the former may have a comparatively homogeneous source. Together with regional evidence, it is proposed that a collisional event occurred between the South Qilian Belt and the Central Qilian Belt at ca. 442–435 Ma.     

东天山中天山构造带喀拉塔格地区早石炭世岛弧火山岩的厘定及其构造意义

本研究以东天山中天山中段喀拉塔格地区的火山岩为研究对象,前人通过区域对比将其时代定为前寒武纪,本文通过锆石SIMS U-Pb定年获得其成岩年龄为347.5±5.9 Ma,同时还发现了一些前寒武纪捕获锆石,显示中天山存在老基底。地球化学研究显示这套火山岩具有相对较低TiO2(0.85%~1.21%)含量,高Mg#(46~64);富集大离子亲石元素(LILE:Rb、Ba、Th、U)、LREE和Pb元素,亏损髙场强元素(HFSE:Nb、Ta、Ti)特征;具明显Eu负异常;具相对较低εNd(t)值(-4.4~-5.7)和高初始Sr比值[(87Sr/86Sr)i=0.70884~0.70920];具有相对高的Th和Pb含量,较低的Ce/Th、Ce/Pb和Ba/Th比值,具俯冲带岛弧钙碱性岩浆特征;同时样品具较低Nb/U和Ce/Pb值,且发育捕获锆石,显示存在陆壳混染作用。这一工作在中天山前寒武地层中分解出古生代岛弧火山岩,综合的区域地质资料分析显示中天山岛弧带在早石炭世时期是类似于现在日本岛弧的岛弧带。     

东天山石炭纪雅满苏组火山岩特征及地质意义

雅满苏组火山岩是东天山石炭纪火山岩的重要组成部分,也是东天山地区海相火山岩型铁多金属矿床的赋矿地层。其年代学及地球化学研究对探讨该区古生代构造演化和火山岩型铁多金属矿床成因具有重要意义。本文对东天山地区雅满苏组火山岩的岩石学、地球化学和同位素年代学进行了系统研究。结果显示:雅满苏组是一套海相火山岩夹碳酸盐岩建造,其上亚组英安岩的LA-ICP-MS锆石U-Pb年龄为334.4±1.7 Ma(MSWD=0.67),代表了雅满苏上亚组火山岩形成时代,切穿雅满苏铁矿区矽卡岩及矿体的正长岩的LA-ICP-MS锆石U-Pb年龄为325.5±1.7 Ma(MSWD=0.34),表明雅满苏铁矿床形成不晚于325 Ma。雅满苏上亚组英安岩和玄武岩显示了富集LREE、U、Sr,相对亏损Nb、Ta等元素的特征,且英安岩锆石的(176Hf/177Hf)i比值介于0.282 644~0.282 802之间,εHf(334 Ma)为3.0~8.0,表明它们是活动大陆边缘弧环境的产物,英安岩是新生地壳物质部分熔融的结果,玄武岩是软流圈地幔与受俯冲板片流体交代地幔的混合熔体演化的产物。结合前人研究成果,认为雅满苏组火山岩是早石炭世中期古亚洲洋俯冲作用的产物,石炭纪时期古亚洲洋尚未闭合,雅满苏铁矿床形成介于334~325 Ma之间,是与石炭纪火山岩有成因联系的铁矿床。     

天山石炭-二叠纪后碰撞花岗质岩石地球化学研究

在对前人研究资料综合的基础上,重点对天山造山带不同构造单元中石炭—二叠纪后碰撞花岗岩地球化学特征进行了对比研究,认为天山石炭—二叠纪后碰撞花岗质岩石属高钾钙碱—钾玄岩系列,以钙碱系花岗质岩石类型为主。其中,发育在裂谷带中的石炭—二叠纪花岗质岩石较发育在古微地块中或其边缘的花岗质岩石富MgO、TiO2、Na2O,贫K2O、Nb、Th,两者具有不同的源区。裂谷带中的花岗质岩石多与火山岩同源,由含不同程度壳源组分的壳幔混合源岩浆形成,而古微地块花岗质岩石主要来自壳源。处于同一类构造位置但不同地区的花岗质岩石化学成分也不相同,如天山西端伊犁地块南缘的托木尔峰花岗质岩石较天山中东段南部的库鲁克塔格花岗质岩石富Fe、Mg、K、Nb、Sr,而贫Zr、Ba,它们均是壳源成因,反映了天山东、西地壳基底组分的不同。石炭—二叠纪裂谷带中的花岗质岩石在天山东、西段也有差别,东段的觉罗塔格和博格达花岗质岩石较天山西段伊犁裂谷中的花岗质岩石明显地富Nb、Th而贫Sr、Ba,反映出东、西天山石炭—二叠世花岗岩源区不同。花岗质岩石的正εNd值并不是来源于与基性、超基性岩浆活动有关的幔源组分,而是来自于幔源火山岩浆活动。     

南天山北缘榆树沟变质基性超基性岩的地球化学及其成因机制

榆树沟变质基性－超基性岩带出露于塔里木板块与哈萨克斯坦板块之间的南天山北缘，主要由变质橄榄岩和变质基性岩组成。变质橄榄岩富相容元素Cr、Co和Ni，贫不相容元素，太离子亲石元素Ba、Rb和Sr含量较低，与世界典型蛇绿岩相似，代表了地幔残留物特征。REE分布模式为LREE亏损型，REE含量小于或等于2．5倍球粒陨石，类似于阿尔卑斯型变质橄榄岩，显示榆树沟的变质橄榄岩是原始地幔岩部分熔融萃取出玄武岩后的残留物。变质基性岩绝大部分为LREE亏损型，类似于N－MORB。所有样品均以富集Nb和Ta、高场强元素不分异，以及微量元素含量低为特征，批示岩浆源区总体上类似于MORB，Nb、Ta富集可能与OIB型源区有关，Nd、Sr同位素特征也显示其具有OIB型源区特征。综合分析认为，榆对沟变质基性岩石的岩浆可能经历了两个阶段的演化过程，即上地幔底部或下地幔顶部的OIB型原始岩浆形成阶段和软流圈地幔亏损阶段。     

班韦乌卢地块中部变质表壳岩碎屑锆石U-Pb年代学、Hf同位素研究及其构造意义

通过LA-MC-ICP-MS碎屑锆石微区U-Pb定年和Hf同位素分析,对班韦乌卢地块中部地区基底变质表壳岩进行了同位素定年及物源示踪研究。结果显示,两件样品的碎屑锆石峰值年龄分布表现出较好的一致性,总体呈现出2490～2059 Ma、2044～1954 Ma、1942～1887 Ma、1865～1817 Ma以及1641～1522 Ma五个年龄组,分别与班韦乌卢地块内的构造岩浆事件相吻合。综合区域地质特征与碎屑锆石年龄谱特征分析认为:原岩蚀源区比较复杂,近源区古元古代花岗岩、花岗片麻岩及火山岩是主要的蚀源区。根据碎屑锆石最小年龄1522±23 Ma,推测表壳岩原岩形成时代上限可能为中元古代,而不是之前认为的形成于古元古代。碎屑锆石的ε_Hf(t)值介于-6.26～7.37之间(平均1.37),由负到正变化范围较大,表明它们除来自古老地壳的再循环物质外,还存在新生地壳的物质来源。t_DM2峰值年龄出现在2.40～2.50 Ga,说明班韦乌卢地块地壳增生事件主要发生于古元古代,可能与凯诺兰超大陆的聚合过程有关,其晚于全球大陆地壳主增长期,说明了地壳增...