Effects of igneous intrusions on coalbed methane potential, Gunnedah Basin, Australia

The Gunnedah Basin, NSW, Australia, contains more than 500 Gt of coal, and has been the subject of recent coalbed methane exploration. Large areas of the basin contain igneous intrusions and large areas of coal have been heat-affected as a consequence. A detailed study has been undertaken of coal seams intersected in a cored coalbed methane exploration drillhole in which two sill-form igneous intrusions are present. Comparisons are made between coals that are unaltered and coals that have been heat-affected, using petrographic and chemical data, coal seam gas desorption data, and gas chemical analysis data.Results demonstrate that the two igneous intrusions have had a very positive effect on coalbed methane development. The gas content in a number of heat-affected coal seams within thermal aureoles above and below the sills is substantially higher than in adjacent unaffected coal seams. In addition, the intrusions have had little effect on gas quality. The coals in the heat-affected zone were found to contain gas with approximately 95% methane. The coals in the thermal aureoles were found, under the microscope, to contain characteristic micropores and slits, which collectively may serve to enhance gas adsorption capacity, permeability, and gas desorption. Gas contents below each of the sills is substantially higher than above the sill, confirming earlier results that the sills appear to have acted as a reservoir seal, during and for some time after intrusion. The background coal rank in ACM Yannergee DDH 1 is in the high-volatile bituminous range. The igneous intrusions have resulted in an increase in rank such that large areas of coal have moved into the optimal thermogenic gas generation window. This rank increase has affected a major part of the coal-bearing sequence.     

Composition and quality of coals in the Huaibei Coalfield, Anhui, China

The Huaibei Coalfield, Anhui Province, China, is one of the largest coalfields in China. The coals of Permian age are used mainly for power generation. Coal compositions and 47 trace elements of the No. 10 Coal of the Shanxi Formation, the No. 7, 5, and 4 Coals of the Lower Shihezi Formation, and the No. 3 Coal of the Upper Shihezi Formation from the Huaibei Coalfield were studied. The results indicate that the Huaibei coals have low ash, moisture, and sulfur contents, but high volatile matter and calorific value. The ash yield increases stratigraphically upwards, but the volatile matter and total sulfur contents show a slight decrease from the lower to upper seams. Magmatic intrusion into the No. 5 Coal resulted in high ash, volatile matter, and calorific value, but low moisture value in the coal. Among the studied 47 trace elements, Ba, Co, Cr, Cu, Hg, Mo, Ni, Pb, Sb, Th, U, V, and Zn are of environmental concerns. Four elements Hg, Mo, Zn, and Sb are clearly enriched in the coals as compared with the upper continental crust.     

岩浆侵入煤层中锑的赋存特征——以淮北卧龙湖矿为例

为探讨岩浆蚀变作用对煤层中锑赋存特征的影响,系统采集安徽淮北煤田卧龙湖煤矿岩浆侵入煤层侵入岩和全煤层样品共12个,利用原子荧光光谱法（AFS）测定样品中Sb含量,并对煤质参数进行分析。结果表明：卧龙湖煤矿岩浆侵入区煤表现为超低挥发分,中等灰分,特低硫的特点,煤中的硫主要以有机硫和黄铁矿硫存在。受岩浆热液影响,煤中灰分增加,挥发分减少;岩浆蚀变煤层中锑明显富集,算术平均值达到10.48 mg/kg,且侵入岩上方煤中Sb的平均含量明显增高,煤岩接触带位置Sb的含量达到最高值（13.93 mg/kg）;岩浆蚀变煤中的锑主要以无机结合态形式存在（相关系数r为0.74）,有机硫与煤中Sb呈显著负相关（相关系数r为-0.60）。岩浆侵入作用导致卧龙湖煤矿煤的煤质特征及煤层中锑的赋存方式受到不同程度的影响,研究结果可为特殊地质作用下煤中锑的环境地球化学特征提供参考。     

冀北北岔沟门地区中生代侵入岩地质年代学和地球化学特征研究

北岔沟门地区广泛分布中生代侵入岩体.本文选取了该地区有代表性的8个岩体进行地质年代学和地球化学研究,旨在建立其年代格架并探讨岩石的成因演化.主要岩石类型为闪长玢岩、花岗闪长岩、石英二长岩、二长花岗岩、钾长花岗岩等.颗粒级锆石的U-Pb同位素测年数据表明所研究的岩体主要有三期早三叠世(245～250Ma)、晚侏罗世(140～147Ma)和早白垩世(125～137Ma).地球化学数据表明岩石普遍具有较高的钾含量、准铝质,主要属高钾钙碱性系列,部分为橄榄玄粗岩系列.岩石不同程度地显示轻稀土元素富集、高场强元素(HFSE)和大离子亲石性元素(LILE)解偶等特点.进一步的岩石地球化学研究表明区内侵入岩可划分为高BaSr和低BaSr两种类型,其中高BaSr型具有高Al2O3(≥15%)、Sr(≥400×10-6) 和低Y(≤18×10-6)、Yb(≤1.9×10-6),高的Na2O/K2O(>1), Sr/Y(>20)、La/Yb(≥10)比值;较高的Mg#(38.47～57.78)、具正的或弱的铕负异常等地球化学特征,这些特征与埃达克岩具有某些相似性;而低BaSr型岩石SiO2、K2O、Y、Yb含量相对较高、Al2O3、Sr、Ba含量相对较低、具明显的铕负异常等地球化学特征.尽管两类岩石在时空上密切共生,但可能具有不同的源区和成因机制.综合研究表明本区中生代侵入岩总体形成在加厚地壳的构造背景下,与底侵作用或壳幔相互作用有关.     

华北克拉通南缘蚌埠隆起古元古代侵入体地质地球化学特征

华北陆块是世界上最古老、最大的克拉通地块之一。蚌埠隆起作为华北陆块的组成部分,其初始陆壳的形成时限为中太古代晚期,随着扬子陆块与华北陆块碰撞、拼接,经历了较为复杂的演化过程。为了深入探讨蚌埠隆起带古元古代岩浆活动,更新补充年代学及岩石地球化学分析数据,本次通过对区内古元古代侵入体的野外观察、年代学和岩石地球化学研究,在庄子里岩体和磨盘山岩体中分别获得锆石U-Pb年龄为(2089±44)Ma、(2133±27)Ma。地球化学研究显示两岩体明显富钠贫钾,总体铝碱比偏高,钙碱比偏低,属准铝—铝过饱和类型;轻稀土相对富集,具明显的铕负异常,铈异常不明显或无异常;K、Nb、Sr、P和Ti有较明显的亏损,Rb、Th、U、Nd、Zr和Sm相对富集,成因类型具备造山后A型花岗岩特征。ε_(Nd)(t)值介于-3.87～+3.20,暗示侵入体可能来源于同一源区,Nd两阶段模式年龄(2.37～2.84 Ga)与华北克拉通主体形成于太古宙,并以2.40～2.50 Ga为主体相一致。ε_(Hf)(t)值介于-9.77～+9.59,且差别较大,说明其具物质起源的复杂性,古老的两阶段Hf模式年龄(2.27～2.96 Ga)说明其物质起源主要为新太古宙,与蚌埠隆起拉张背景时间上具有一致性。构造环境判别属板内花岗岩范畴,表现为非造山构造环境,暗示其伸展构造背景。     

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.     

淮北煤田煤中镧系元素和钇的地球化学——“岩浆侵入对淮北花沟西煤中稀土元素分布的影响”的商榷

"岩浆侵入对淮北花沟西煤中稀土元素分布的影响"(高校地质学报,2013,19(4):671-676页)和"岩浆侵入对袁店二井煤矿72煤中稀土元素的影响"(煤炭工程,2014,46(5):119-122页)两文均表明"岩浆侵入致使煤中稀土元素含量增加,使煤中稀土元素发生了二次迁移与富集,且岩浆组分对煤中稀土元素的迁移富集具有一定程度的影响",而经重新整理原作者数据,并对其中镧系元素和钇(REY)的含量特征、上陆壳标准化分配模式的分析后,则得出完全不同的结论:淮北煤田煤中REY平均118mg/kg,天然焦中REY平均128mg/kg,侵入岩中REY平均326mg/kg;煤层侵入岩REY含量高于煤和天然焦,而煤和天然焦中REY含量无显著差别。煤层侵入岩上陆壳标准化的REY分配模式均显著富集LREY,且明显与煤和天然焦的REY分配模式不同,这表明岩浆侵入对煤中镧系元素和钇的影响甚微,且煤中的HREY较LREY和MREY富集。总结得出:对煤中稀土元素地球化学的研究须将钇元素一并分析,且将REY三分(LREY,MREY和HREY)便于更细致的对比;稀土元素分配模式标准化的参考应该尽量选择与煤近似的地质体(如北美页岩、上陆壳、中国煤等),不应均以球粒陨石为标准,方可更准确地解析稀土元素的来源及其在成煤及变质过程中的分异等。     

滇西龙陵地区三叠纪蚌东花岗岩体LA-ICP-MS锆石U-Pb年龄、地球化学特征及其构造意义

保山地块是滇西特提斯多岛洋的重要组成部分,属滇-缅-马-泰微大陆的北端。出露于保山地块西部的蚌东花岗岩体的LA-ICP-MS锆石U-Pb年龄为228.3±1.7Ma,记录了特提斯洋关闭后的弧-陆碰撞过程。该岩体以正长花岗岩为主,岩石具有高硅、富碱、低镁、低钙、富铬、富镍的特点;在B-A图解上显示了堇青石过铝花岗岩的演化特征;总体上表现为富集大离子亲石元素、亏损高强场元素的特点,可划归后碰撞-后造山花岗岩。但是,该岩体远离昌宁-孟连主特提斯弧-陆碰撞带,可能是主造山过程晚期,滇-缅-马-泰微大陆内部各微小陆块相互作用导致地幔岩石圈发生拆沉作用的产物,或是昌宁-孟连洋盆闭合过程中俯冲板块的拖拽在后缘的岩石圈伸展作用的产物。     

Apatite fission-track study on the thermo-tectonic history of the Huainan Coalfield in Anhui Province, China： Tectonic implications for the potential coalbed methane resource

Coalbed methane (CBM) is a kind of burgeoning and enormously potential clean energy resource, and the temperature of the thermogenic CBM generation is close to that of the partial annealing zone (PAZ) of apatite fission tracks (AFT). In this study the thermo-tectonic history of the Huainan Coalfield and the potential CBM resource were studied and discussed by using the AFT method. The AFT data indicate that the apparent ages of AFT vary from 45.5 to 199.1 Ma. They are younger than the ages of their host strata (255–1800 Ma) except one sample, and the single-grain ages of AFT can be classified as a single age group for each sample. In combination with the geological setting, modeling results of the AFT ages, average lengths, and the thermal history based on the AFT single-grain ages and length distributions, some preliminary conclusions can be drawn as follows: (1) at least three thermo-tectonic events (in the periods of ∼240, 140 and 80 Ma, respectively) have occurred in the study area since the Late Paleozoic. The occurrence of both the first (during 240–220 Ma) and second (during 160–120 Ma) thermo-tectonic events is possibly responsible for the establishment of the patterns of gas generation and reservoir formation. The second thermo-tectonic event also led to slight accumulation of hydrocarbons and generation of thermogenic gas; (2) the AFT ages of most coal-bearing strata lie between 50 and 70 Ma. They should represent the cooling ages and the ages of inferred uplift and denudation, as well as the possible CBM release history. Therefore, the maximum burial depth of coal-bearing strata and the denudation thickness of the overlying strata are over 3000 and 2000 m in the Upper Cretaceous and Paleogene series, respectively; and (3) subsequently, a spot of secondary biogenic and scarcely thermogenic gas generation occurred due to negligible sedimentation during the Neogene and Quaternary periods. Thus, it can be presumed that subsequent tectonism would destroy the CBM reservoir after its formation in the Huainan Coalfield, especially in its structural development region. These AFT data may be helpful for a better understanding of the thermo-tectonic history of the Huainan Coalfield, as well as of CBM generation, storage and release in the Huainan Coalfield.     

淮北杨柳矿区煤系构造热演化对页岩气生成与保存的影响

在“双碳”目标背景下,大力发展以页岩气为代表的低碳清洁能源是实现“碳减排”的重要途径。华北南部淮北地区蕴藏着丰富的煤系页岩气资源,但受复杂构造热演化影响,区域内页岩气生成与保存机理尚不清晰。因此,本文采用镜质组反射率、岩石热解、裂变径迹和盆地模拟技术研究了华北南部淮北地区晚古生代以来的构造热演化与生烃过程,讨论了复杂构造热作用下煤系页岩气的生成和保存机理。结果表明,淮北地区煤系页岩气生成过程受到燕山期构造热事件的显著控制,晚侏罗世基性岩浆侵入煤系使得下石盒子组和山西组页岩经历最高古温度达~172℃,对应热流峰值124 mW/m2。煤系页岩Ro值在0. 87%~1. 74%,最高热解温度（Tmax）在437~563 ℃,表明有机质进入轻质油—湿气生成阶段。研究区二叠系山西组砂岩磷灰石裂变径迹年龄（60~42 Ma）明显小于所在地层年龄（298~272 Ma）,部分锆石裂变径迹年龄略低于地层年龄,证实了研究区发生了强烈的岩浆热活动,导致地温梯度达到峰值~65 ℃/km。燕山期岩浆热效应促使区域煤系页岩高效生烃成藏,太平洋板块俯冲后撤引起的伸展断裂使得强构造变形区页岩气藏破坏逸散。因此,在淮北地区,弱构造变形区并伴有适度岩浆活动的区域具备页岩气保存的良好条件,具有良好的油气勘探前景。     

新疆坡北杂岩体西端镁铁-超镁铁质岩体成因的稀有气体同位素制约

新疆坡北镁铁-超镁铁质杂岩体由一个辉长岩体以及二十多个超镁铁质侵入体组成,其中坡一超镁铁质岩体稀有气体同位素组成揭示存在地幔柱的贡献。坡北杂岩体西端的坡一、坡四、坡十和坡十四等几个超镁铁质岩体的稀有气体同位素对比分析结果表明,岩浆矿物的³He/⁴He值（0.26~2.79Ra）分布于地壳与地幔值之间,较高的²⁰Ne/²²Ne和较低的²¹Ne/²²Ne值分布于Ne质量分馏线（MFL）和L-K线之间,⁴⁰Ar/³⁶Ar=295~598。³He/⁴He与⁴⁰Ar/³⁶Ar比值揭示坡北杂岩体西端不同超镁铁质岩体形成过程中地幔（柱）、地壳和大气组分的贡献不同,岩体成因也可能不同。其中,坡一岩体具有地幔柱作用的贡献,其他三个岩体的岩石圈地幔及地壳流体组分的贡献较大。岩浆地幔源区由深部地幔柱物质叠加俯冲流体交代的岩石圈地幔物质所组成,大气与地壳物质组分可能由俯冲再循环洋壳带入到岩浆地幔源区以及围岩物质的混入。     

Geochronology and geochemistry of Early Devonian intrusions in the Qimantagh area,Northwest China: evidence for post-collisional slab break-off

The Qimantagh area of Northwest China lies in the western part of the East Kunlun Orogenic Belt and is characterized by extensive magmatism, particularly in the Triassic. However, recent research has shown that Devonian magmatism was also widespread in this area and has a genetic relationship with mineralization. This article presents a detailed study of three types of Early Devonian intrusions: high-K calc-alkaline granites, A-type granites, and mafic intrusions, all from the Qimantagh region. These rocks were subjected to precise zircon U–Pb dating, major and trace element analyses, and Sr–Nd isotope measurements, focusing on the Lalingzaohuo (eastern Qimantagh) and Yemaquan (central Qimantagh) monzogranites, as well as the coeval Tanbeixuefeng (western Qimantagh) mafic dike swarm. To better understand the Early Devonian igneous activity in the Eastern Kunlun, data for other coeval granitoids were compared with our data. The Yemaquan monzogranite yielded a mean zircon U–Pb age of 400.5 ± 1.4 Ma. These rocks are metaluminous to slightly peraluminous, with Al₂O₃ contents of 13.10–14.16 wt.%, high alkali contents (total K₂O + Na₂O) of 6.89–7.68 wt.%, relatively low Sr contents (79–192 ppm), and high (La/Yb)_N ratios, all of which indicate an I-type granite affinity. The Lalingzaohuo monzogranites yielded mean zircon U–Pb ages of 396.2–402.2 Ma. These rocks have higher SiO₂ and alkali contents than the Yemaquan monzogranite, with high 10,000 Ga/Al ratios, high Zr + Nb + Ce + Y contents, high Fe₂O₃^T/MgO ratios, and high Y contents, indicating an A-type granite affinity. These two monzogranites have initial ⁸⁷Sr/⁸⁶Sr ratios of 0.703–0.706 and εNd(t) values of –0.1 to –0.7. The Sr–Nd isotopic data require a significant input of a mantle component in the petrogenesis of these granites. The Tanbeixuefeng diabase dikes formed at ~396 Ma and have a continental tholeiitic affinity, as evident from small Ti–Nb–Ta anomalies and high contents of light rare earth and large-ion lithophile elements. We propose that post-collisional slab break-off was responsible for the generation of these Early Devonian intrusions in the Qimantagh area.     

Petrogenesis of mid-Carboniferous volcanics and granitic intrusions from western Junggar Basin boreholes: geodynamic implications for the Central Asian Orogenic Belt in Northwest China

The western Junggar Basin is located on the southeastern margin of the West Junggar terrane, Northwest China. Its sedimentary fill, magma petrogenesis, tectonic setting, and formation ages are important for understanding the Carboniferous tectonic evolution and continental growth of the Junggar terrane and the Central Asian Orogenic Belt. This paper documents a set of new zircon secondary ion mass spectrometry U–Pb geochronological and Hf isotopic data and whole-rock elemental and Sr–Nd isotopic analytical results for the Carboniferous strata and associated intrusions obtained from boreholes in the western Junggar Basin. The Carboniferous strata comprise basaltic andesite, andesite, and dacite with minor pyroclastic rocks, intruded by granitic intrusions with zircon secondary ion mass spectrometry U–Pb ages of 327–324 Ma. The volcanic rocks are calc-alkaline and show low high ε_Nd(t) values (5.3–5.6) and initial ⁸⁷Sr/⁸⁶Sr (0.703561–0.703931), strong enrichment in LREEs, and some LILEs and depletion in Nb, Ta, and Ti. Furthermore, they also display high (La/Sm)_N (1.36–1.63), Zr/Nb, and La/Yb, variable Ba/La and Ba/Th and constant Th/Yb ratios. These geochemical data, together with low Sm/Yb (1.18–1.38) and La/Sm (2.11–2.53) ratios, suggest that these volcanic rocks were derived from a 5–8% partial melting of a mainly spinel Iherzolite-depleted mantle metasomatized by slab-derived fluids and melts of some sediments in an island-arc setting. In contrast, the granitic intrusions represent typical adakite geochemical features of high Sr and low Y and Yb contents, with no significant Eu anomalies, high Mg#, and depleted ε_Nd(t) (5.6–6.4) and ε_Hf(t) (13.7–16.2) isotopic compositions, suggesting their derivation from partial melting of hot subducted oceanic crust. In combination with the previous work, the West Junggar terrane and adjacent western Junggar Basin are interpreted as a Mariana-type arc system driven by northwestward subduction of the Junggar Ocean, possibly with a tectonic transition from normal to ridge subduction commencing ca. at 331–327 Ma.     

Leaching behavior of Li and Ga from granitic rocks and sorption on kaolinite: Implications for their enrichment in the Jungar Coalfield,Ordos Basin

The granite collected from the Yinshan Mountain and kaolinite has been selected for the leaching and adsorption experiment,respectively,aiming to clarify the enrichment processes of Li and Ga during the deposition.Results suggest both Li and Ga could be leached out from granite by using different acid solutions of different p H and kaolinite can adsorb Li and Ga with varying degrees.Lithium and Ga had the highest leaching ratio when p H=1.Special geological events(e.g.volcanic eruptions and wildfires),which could result in very low p H values of water in peatland,may have accelerated the release of Li and Ga from the source rocks.Kaolinite has the highest adsorption fraction was obtained at p H=8.The different characteristics of Li and Ga displayed in the leaching and adsorption experiments probably result from the different occurrences and enrichment processes of Li and Ga in the coals.Lithium was probably enriched before the Li carriers(e.g.kaolinite)had been transported into paleomires because of its high leaching ratio and high adsorption fraction under neutral and alkaline conditions,whereas Ga was more likely concentrated by kaolinite and other carriers after it had been transported into the peat mires.     

西藏拉萨地块南部啊扎侵入体锆石U-Pb年龄、地球化学特征及其对新特提斯洋演化历史的指示

拉萨地块南缘广泛出露的岩浆岩是研究新特提斯洋沿该区域北向俯冲演化历史的良好对象。为研究新特提斯洋俯冲及演化机制, 对西藏山南地区啊扎侵入体进行了系统的岩石学、年代学和地球化学研究。结果表明,其为一套形成于晚白垩世(95.0±1.4 Ma、100.2±1.4 Ma)的石英二长闪长岩;地球化学组成显示其高硅、富钠(Na2O>K2O),属于高钾钙碱性岩;微量元素具有高Sr(588.47×10-6、649.65×10-6),低Y(8.66×10-6、9.03×10-6)和Yb(0.87×10-6、0.92×10-6)及高的Sr/Y值(65.17、75.02),显示典型的埃达克岩地球化学特征。同时富集Rb、Sr等大离子亲石元素,亏损Nb、Ta、Ti等高场强元素,稀土元素配分曲线呈右倾模式,具正Eu异常;显示低的(87Sr/86Sr)i(0.703825、0.703836),高的143Nd/144Nd(0.512790、0.512798)及正的εNd(t)值(4.08和4.25)。结合前人的研究成果,认为啊扎岩体是新特提斯洋洋脊俯冲消减背景下洋壳部分熔融的产物。     

Characteristics of faults and their implications for oil and gas enrichment in the Liaoxi Depression,Bohai Bay Basin,eastern China

The faults that developed in the Liaoxi Depression can be classified into three types according to their extent and connectivity with the source and reservoir rocks (i.e. type I faults, type II faults and type III faults). These faults played different roles in controlling the basin geomorphology; the formation and evolution of the source rocks, reservoir rocks, cap rocks and traps; and the migration and accumulation of hydrocarbons in the Liaoxi Depression. Extending from the basement to the Neogene strata, type I faults, which are the largest in the basin, mainly controlled the development and basin-scale geomorphology; type II faults mainly controlled the sub-tectonic zones; and type III faults mainly controlled the formation and evolution of the traps. The movements of type I and type II faults during the hydrocarbon expulsion period were closely related to oil and gas migration. The rates of fault activity varied among the different sags of the Liaoxi Depression. Type I faults in both the northern and southern sags appear to have moved considerably during the hydrocarbon generation and expulsion stages, which strongly promoted hydrocarbon migration, whereas weakly active type I faults in the central sag made limited contributions to hydrocarbon migration. The sealing behaviour of the faults controlled the hydrocarbon migration directions and locations, and the good lateral sealing ability of the type I faults in the northern and southern sags confined the accumulation of hydrocarbons within the sags independently. However, the type I faults in the central sag partially opened laterally, which increased the likelihood of hydrocarbon migration from the sag centre to the uplift and reduced the likelihood of hydrocarbon accumulation within the sag centre. Therefore, the oil- and gas-enrichment patterns in the Liaoxi Depression are closely related to the characteristics of the faults, with traps near types I and II faults showing an increased likelihood of oil- and gas-field formation, as observed with the JZ9-3, LD4-2 and LD5-2 wells, and traps located in the sags remote from types I and II faults showing a reduced likelihood of oil and gas accumulation.     

西南天山二叠纪中酸性侵入岩的地质学和地球化学：岩石成因和构造背景

选择3个典型岩体,即位于西南天山东段的拜城县英买来岩体和位于西段阔克萨岭区的川乌鲁岩体、巴雷公岩体（为了对比,也选择了位于塔里木盆地西北缘的麻扎山岩体）,进行了岩石学和地球化学研究。结果表明,这些岩体具有不同的特点。英买来岩体为黑云母花岗岩和二云母花岗岩,具有高的SiO2含量,弱过铝,高的Sr同位素初始值（约0.710）和负的εNd(t)值（-4～-6）,属于S—A型之间的过渡类型。麻扎山岩体由正长岩组成,属于碱性岩,微量元素标准化图解和其他岩体明显不同的是没有明显的Nb和Ta的负异常。川乌鲁岩体是一个由3个不同期次岩石组成的杂岩体,主体为正长岩-二长岩,地球化学特征显示是由基性岩浆和酸性岩浆不同程度混合形成的。位于同一构造区的巴雷公岩体则与川乌鲁岩体中的花岗斑岩的地球化学特征相似。综合岩石学和地球化学特征推测,南天山东段的英买来岩体是地壳熔融的结果,没有任何地幔物质加入的地球化学信息,西段的阔克萨岭地区酸性岩浆的形成则可能是来自于幔源底侵的基性岩浆导致薄的地壳发生熔融的结果。麻扎山岩体则完全是不同构造背景的产物,有可能与发生在塔里木盆地的二叠纪大规模的岩浆活动有关。因此,二叠纪岩浆活动的性质主要受地壳成分和结构的控制。     

华北克拉通南缘大纸房和嵖岈山花岗岩的锆石U-Pb定年、地球化学特征及成因启示

伏牛山余脉是华北克拉通南缘早白垩世花岗岩的集中出露区之一,其内花岗岩成因认识能为深入理解华北南缘燕山期岩浆活动规律和深部过程提供重要支撑。大纸房和嵖岈山岩株是伏牛山余脉花岗岩的典型代表,它们的U-Pb年龄分别为119.5±1.6 Ma和116.8±1.3 Ma,形成于早白垩世阿普特期。此外,它们的定年结果形成了锆石年龄谱,大纸房U-Pb年龄形成142 Ma和135 Ma两个峰值,嵖岈山U-Pb年龄形成135 Ma一个峰值。大纸房和嵖岈山花岗岩样品属高钾钙碱性系列,均具有富硅、碱和贫钙、镁的特征,分别属于弱过铝质和准铝质—弱过铝质花岗岩。大纸房和嵖岈山花岗岩样品均显示了Rb、Th、Zr、Hf的异常峰和Ba、Sr、P、Ti的异常谷。大纸房花岗岩样品的稀土总量介于176×10^-6~217×10^-6之间,（La/Yb）_N比值范围是43.0~55.5,它的稀土配分模式以轻稀土富集、重稀土亏损和负Eu异常不明显为特征。嵖岈山花岗岩样品的稀土总量介于230×10^-6~316×10^-6之间,（La/Yb）_N比值范围是15.8~22.9,稀土配分模式具轻稀土富集、中稀土亏损和重稀土略微富集的“V”型（海鸥型）特征,负Eu异常明显。大纸房花岗岩高Sr和低Y、Yb,Sr/Y值为17.1~51.5,具有埃达克岩的特性,形成深度大于50 km,部分熔融源区残余相包括石榴子石、金红石和角闪石,且无（富钙）斜长石残留。嵖岈山花岗岩为低Sr、高Yb的南岭型（A型）花岗岩,其部分熔融源区残余相主要为角闪石和斜长石及金红石,无石榴子石残余,形成深度30 km以浅。大纸房和嵖岈山花岗岩形成于板内环境,经历了岩浆/流体体系混合再活化作用,是~120 Ma区域岩石圈拆沉作用的岩浆响应。

     

川西拉拉Fe-Cu矿区含矿镁铁质层状岩席的首次发现及其成岩成矿意义

尽管镁铁质层状侵入体得到了广泛关注,与其相关的成岩和成矿过程仍然存在很多疑问。文中首次报道了在川西拉拉Fe-Cu矿区发现的一种含矿镁铁质岩席,它的深入研究可能有助于理解拉拉Fe-Cu矿床的成因,以及层状侵入体的组装过程与成矿作用。野外观察表明,该岩席共由9个岩相带组成,相邻岩相带为侵入接触关系,上半部分和下半部分的岩性呈镜像对应。对该岩席上半部分的5个岩相带分别进行了显微镜观察、粉晶X-射线衍射分析和CSD分析,表明相邻岩相带的矿物组成和结构参数具有明显区别,揭示该岩席由4、5次岩浆脉动组装而成。各岩相带均具有显微斑状结构,其中1～4岩相带的斑晶矿物主要为角闪石、云母和Ti-Fe氧化物,第5岩相带的斑晶为白云母、钾长石和石英。此外,第3岩相带还含有大颗粒单斜辉石斑晶,第4岩相带含有方解石大斑晶。含水矿物呈斑晶产出表明所有岩相带都是挥发分(H2O+CO2)饱和或过饱和岩浆固结的产物,但各岩相带的岩浆具有不同的来源。根据斑晶(循环晶)矿物组合、定量化结构参数和参数变异趋势,推测拉拉岩席之下曾经存在3～5个位于不同深部水平上的岩浆房。这些岩浆房有不同成分的进化岩浆充填,可能富集了相应的成矿金属。当深部含矿流体输入该岩浆系统时,有可能引起骨牌效应,导致各种含矿流体大规模释放。拉拉矿区的这类岩席可能对成矿物质起到了屏蔽作用,使其大规模聚集形成超大型矿床。需要注意的是,拉拉岩席的富矿岩相带侵位时间最晚,类似于攀枝花铁矿。因此,拉拉岩席的成岩成矿模式有可能也适应于攀枝花式铁矿。     

Geochronological and geochemical constraints on the genesis of the Tieshan complex in the Edong district,Eastern China with implications for Fe and Cu skarn mineralization

Fe and Cu skarn deposits constitute the most important skarn type worldwide, whereas the controlling factors that lead to the difference in metal associations remain not well known. The Fe- and Cu-hosting Tieshan complex in the Edong district provides a good opportunity for comparative study on the genetic differences between Fe and Cu skarn deposits. In this study, integrated studies of geochronology, geochemistry and Sr-Nd-Hf isotope compositions were conducted on the complex. LA-ICP-MS zircon U-Pb dating results show that the Tieshan complex was emplaced in the time interval of 135 ± 3 to 144 ± 1 Ma. Multiphase rocks from the complex can be broadly subdivided into two suites. The Fe-Cu-related suite, which consists of diopside diorite, quartz diorite, quartz diorite porphyrite and porphyritic granodiorite, possesses low SiO₂ (53.5–67.1 wt.%), K₂O (2.44–3.53 wt.%) and Rb (45−83 ppm) contents, but high Sr (1132−2684 ppm), Ba (1073−1656 ppm) contents and negligible Eu anomalies, with very high Sr/Y (>90) ratios, similar to typical high Ba-Sr granitoids. The rock suite has initial ⁸⁷Sr/⁸⁶Sr values of 0.70648 to 0.70737, ε_Nd(t) values of −12.3 to −8.2 and ε_Hf(t) values of −16 to −7, comparable to values of the Early Cretaceous mafic rocks in the Edong district and adjacent areas, indicating that it might be largely derived from an enriched lithospheric mantle source, along with minor involvement of lower-crustal components. By contrast, the Fe-related suite, which is composed of quartz diorite, quartz diorite porphyrite and granodiorite porphyry, is characterized by relatively high SiO₂ (63.0–71.0 wt.%) and K₂O contents (3.36–5.53 wt.%), and a wide range of Sr (158−1135 ppm), Ba (762−1366 ppm) contents and Sr/Y (11–99) ratios. In combination with the presence of abundant inherited zircon grains, the lower ε_Nd(t) (−12.4 to −9.3) and ε_Hf(t) (−25 to −15) values indicate a greater degree of lower-crustal contribution for the Fe-related suite. In addition, the calculated zircon Ce (Ce/Ce* and Ce⁴⁺/Ce³⁺) and Eu (Eu/Eu*) anomalies suggest that the Fe-Cu-related suite has much higher oxygen fugacity (fO₂) than the Fe-related suite. This study highlights fO₂ and fractionation degree of magma as useful indicators for differentiating Fe and Cu skarn mineralization.