西秦岭印支期高Sr/Y花岗岩类的成因及动力学背景——以同仁地区舍哈力吉岩体为例

西秦岭印支期花岗岩类分布十分广泛,形成时代集中于248~234Ma和224~211Ma两个阶段.其中,夏河岩体(248~238Ma)和温泉岩体(223~216Ma)的部分样品被厘定为埃达克岩(Sr>400×10^-6,Yb<2×10^-6),指示陆壳厚度大于50km.本文对西秦岭同仁地区舍哈力吉岩体进行了锆石U-Pb定年、岩石学、地球化学和Sr-Nd同位素研究.舍哈力吉岩体主要由石英二长岩组成,同时含有许多暗色镁铁质微粒包体(MME).寄主岩中发育少量的钾长石巨晶,并且部分巨晶具有环斑结构.舍哈力吉石英二长岩化学成分比较均一,而且也显示出类似埃达克岩的一些地球化学特点,如富SiO₂(66.07%~67.52%)和Al₂O₃(14.85%~15.95%),高Sr(560×10^-6~692×10^-6),低Y(11.4×10^-6~12.9×10^-6)和Yb(0.99×10^-6~1.09×10^-6),并具有较高的(La/Yb)_N比值(27.8~34.3)和微弱的负Eu异常(δEu=0.77~0.95).锆石U-Pb测年结果为234.1±0.5Ma,表明其形成于印支早期.岩石为偏铝质、高钾钙碱性系列且K₂O/Na₂O>1,高Mg^#(59~60)、Cr(69.1×10^-6~81.2×10^-6)和Ni(31.6×10^-6~36.1×10^-6),以富集大离子亲石元素(Rb、Ba、Th、U)而相对亏损高场强元素(Nb、Ti、P)为特征,(⁸⁷Sr/⁸⁶Sr)_i=0.7075~0.7077,ε_Nd(t)=-6.3~-6.1,亏损地幔模式年龄为1.25~1.33Ga.舍哈力吉石英二长岩起源于石榴角闪岩相古老下地壳的部分熔融,之后经历了壳幔岩浆混合作用和以斜长石为主的分离结晶作用.寄主岩的环斑结构和相对一致的地球化学特征,很可能是高温幔源熔体对壳源富钾高黏度岩浆改造所导致的晶粥快速再活化的结果.西秦岭在印支早期可能并未经历显著的地壳加厚过程.西秦岭印支早期花岗岩类形成于活动大陆边缘局部伸展环境,可能与古特提斯洋壳俯冲极性的改变有关.     

陕西小秦岭地区熊耳群火山岩型铁(钛)矿及资源潜力

对小秦岭地区熊耳群地层的分布作了概述。在熊耳群地层分布区划出了坝源—洛源(A区)、三岔—石门(B区)和西峪河—梧桐河(C区)三个火山岩型铁矿资源潜力区。阐述了各潜力区的铁矿成矿条件,对潜在资源量作了测算。预测全区300 m以上铁矿潜在资源量为≥9.4亿吨,钛铁矿≥300万吨。     

辽西中生代燕鸟化石新材料的补充研究

本文记述了一件产自辽宁锦州义县早白垩世九佛堂组燕鸟 (Yanornis)化石的新标本。研究标本不但自身保存非常精美 ,而且其嘴里还完整地保存了它捕获的最后一件猎物——吉南鱼 (Jinanichthys longi-cephalus)。该标本的研究 ,不仅对燕鸟的生存环境、生活习性、捕食类型等研究提供了直接的证据 ,而且对于探讨辽西热河生物群中脊椎动物的“集群死亡”的原因也具有重要的意义     

Structural geometry and controls on basement‐involved deformation in the northern Flinders Ranges,Adelaide Fold Belt,South Australia

In the northern Flinders Ranges, Neoproterozoic and Cambrian sedimentary rocks were deformed and variably metamorphosed during the ca 500 Ma Cambro‐Ordovician Delamerian Orogeny. Balanced and restored structural sections across the northern Flinders Ranges show shortening of about 10–20%. Despite the presence of suitable evaporitic detachment horizons at the basement‐cover interface, the structural style is best interpreted to be thick‐skinned involving basement with only a minor proportion of the overall shortening accommodated along stratigraphically controlled detachments. Much of the contractional deformation was localised by the inversion of former extensional faults such as the Norwest and Paralana Faults, which both controlled the deposition of Neoproterozoic cover successions. As such, both faults represent major, long‐lived structures which effectively define the present boundaries of the northern Flinders Ranges with the Gawler Craton to the west and the Curnamona Craton to the east. The most intense deformation, which resulted in exhumation of the basement along the Paralana Fault to form the Mt Painter and Babbage Inliers, coincides with extremely high heat flows related to extraordinarily high heat‐production rates in the basement rocks. High heat flow in the northern Flinders Ranges suggests that the structural style not only reflects the pre‐Delamerian basin architecture but is also a consequence of the reactivation of thermally perturbed, weakened basement.     

Syngenetic gold in western Victoria: occurrence,age and dimensions

In western Victoria, a widespread stratiform style of gold enrichment in Palaeozoic black mudstone and chert—clearly different from the classic mesothermal quartz vein deposits of the Victorian goldfields—has been confirmed by whole-rock geochemistry and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS). This enrichment pre-dates compaction, deformation and low-grade metamorphism of the sedimentary host-rocks, and therefore possibly developed diagenetically during slow deposition of the thin carbonaceous black mudstone beds and the thinner layers of chert. These paired strata have been documented at many locations in three regional outcrop areas of chevron-folded Cambrian and Lower Ordovician metasediments in the Stawell and Bendigo Zones, where they are interbedded with quartz-rich turbidites. The layers were named ‘indicators’ by the early miners, who found locally rich nuggety gold deposits at intersections between these layers and mesothermal quartz veins. Gold is present in euhedral pyrite crystals in both black shale and chert. LA-ICPMS analysis of individual pyrite crystals in the indicator beds shows that pyrite is enriched in Au, As, Sb, Se, Te and Bi. The Au content of pyrite varies from 0.03 to 2.69 ppm with a mean of 0.58 ppm and shows a positive correlation with As, which varies from 1000 to 6000 ppm. Many pyrite crystals show enrichment of gold in their cores and depletion in their rims, confirming the likely syngenetic or syndiagenetic accumulation of gold during pyrite formation in the sediments. Prior to regional metamorphism, folding and faulting, the many indicator strata in the outcrop areas were parts of an extensive marine sequence of Late Cambrian and Early Ordovician age. The former primary source of this mineralisation is considered to have been one or more contemporaneously exhalative submarine hydrothermal systems. Thus, the older Palaeozoic sediments of the western Lachlan Fold Belt were significantly enriched in syngenetic gold in the Early Palaeozoic, at least 40 million years before emplacement of the quartz – gold vein deposits of the goldfields.     

伊朗北部阿哈尔地区土地利用信息的遥感分类与制图

遥感作为目前快速实现全球或大区域对地观测的最佳方法,在“一带一路”沿线地区地表信息获取方面具有重要的作用。总结了遥感技术在伊朗北部土地利用分类与制图的流程和方法,在土地利用分类体系、遥感分类方法和成果制图3个方面进行了研究。通过土地利用信息遥感分类标志,建立非接触的土地利用信息分类工作方法,保证了良好的工作精度。进行了伊朗北部地区土地利用信息的遥感制图,获取了该地区土地利用状况,为我国矿业企业与地质调查部门开展“一带一路”区域合作提供了技术支撑和决策依据,为开展境外土地利用信息的提取与制图工作提供了案例。     

Taphonomy of large marine vertebrates in the Upper Cretaceous (Cenomanian-Turonian) Tropic Shale of southern Utah

Sediments from the Upper Cretaceous (Cenomanian-Turonian) Tropic Shale were deposited along the western margin of the Western Interior Seaway, in present-day southern Utah. Marine vertebrates from this formation include plesiosaurs, mosasaurs, bony fish, sharks, and turtles. They are concentrated in the lower portion of the Tropic Shale, mostly between Bentonites B and D. Study of the taphonomic condition of these vertebrates has contributed to an understanding of how they were preserved as well as a detailed paleoenvironment for the Tropic Shale. Physical factors played the dominant role in their preservation, with robust and durable skeletal elements, such as teeth and vertebrae, being most common within the shale. Isolated bones and teeth are also relatively common within the formation, while complete and nearly complete skeletons are more rare. Biological factors played a less dominant role, with no evidence of epifaunal or infaunal activity preserved with any of the skeletal remains. In addition, scavenging marks (both bite and gnaw marks) are relatively uncommon, typically only being found on more complete specimens. A signature of post-burial alteration can be recognized as low levels of abrasion, weathering, and compression and high levels of fracturing of vertebrate skeletal material. Slightly higher levels of abrasion and weathering occur to the west, closer to the ancient shoreline, suggesting some pre-burial alteration. The preservation of marine vertebrates in the Tropic Shale suggests a low energy marine environment with some weak bottom currents and low levels of benthic oxygen. The substrate ranged from soft and soupy to firm, with moderate sedimentation rates resulting in relatively rapid burial.     

Geochronology and geochemistry of the Hekoulinchang Sn-Pb-Zn-Ag polymetallic deposit (73240 t) in Heilongjiang Province,China

The Hekoulinchang Sn-Pb-Zn-Ag polymetallic deposit(20000 t Sn at 0.27%,236 t Ag at 122.89 g/t,15000 t Pb at 0.84%,and 38000 t Zn at 1.43%)is located in the Wandashan Terrane of the easternmost segment of the Central Asian Orogenic Belt.The timing of Sn-Pb-Zn-Ag polymetallic mineralization remains unclear due to a lack of precise isotope dating directly conducted on ore minerals.The authors herein report that the LA-ICP-MS U-Pb ages of cassiterite and zircon from the granite porphyry in the Hekoulinchang Sn-Pb-Zn-Ag polymetallic deposit are 101.4±7.9 Ma and 115.4±1.0 Ma,respectively,indicating that Sn mineralization and magmatism occurred during the Early Cretaceous.The granite porphyry belongs to the subalkaline series peraluminous I-type granites that are depleted in Nb,Ta,and Ti and enriched in Rb,Th,U,and Pb.TheεHf(t)values of the granite porphyry range from 0.9 to 7.4,with an average of about 5.6 and two-stage model ages(T_DM2)of 705–1116 Ma,with an average age of 819 Ma.The ε_Nd(t)values of the apatites are–1.60–0.45,with an average of–0.9,and two-stage model ages(T_DM2)of 872–1040 Ma,with an average age of 983 Ma.The Nd-Hf isotope data indicate that the magma may have been derived from the partial melting of juvenile crustal material.     

Huanggang Intrusive Complex in Northern Tongbai Area: Island-Arc Tectonic Environment and Its Geological Significance

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Examples of convective fractionation in high‐temperature granites from the Lachlan Fold Belt

Igneous rocks derived from high‐temperature, crystal‐poor magmas of intermediate potassic composition are widespread in the central Lachlan Fold Belt, and have been assigned to the Boggy Plain Supersuite. These rocks range in composition from 45 to 78% SiO₂, with a marked paucity of examples in the range 65–70% SiO₂, the composition dominant in most other granites of the Lachlan Fold Belt. Evidence is presented from two units of the Boggy Plain Supersuite, the Boggy Plain zoned pluton and the Nallawa complex, to demonstrate that these high‐temperature magmas solidified under a regime of convective fractionation. By this process, a magma body solidified from margin to centre as the zone of solidification moved progressively inwards. High‐temperature near‐liquidus minerals with a certain proportion of trapped interstitial differentiated melt, separated from the buoyant differentiated melt during solidification. In most cases much of this differentiated melt buoyantly rose to the top of the magma chamber to form felsic sheets that overly the solidifying main magma chamber beneath. Some of these felsic tops erupted as volcanic rocks, but they mainly form extensive high‐level intrusive bodies, the largest being the granitic part of the Yeoval complex, with an area of over 200 km². Back‐mixing of fractionated melt into the main magma chamber progressively changed the composition of the main melt, resulting in highly zoned plutons. In the more felsic part of the Boggy Plain zoned pluton back‐mixing was dominant, if not exclusive, forming an intrusive body cryptically zoned from 63% SiO₂ on the margin to 72% SiO₂ in the core. It is suggested that tonalitic bodies do not generally crystallise through convective fractionation because the differentiated melt is volumetrically small and totally trapped within the interstitial space: back‐mixing is excluded and homogeneous plutons with essentially the composition of the parental melt are formed.