Palaeoproterozoic granitic magmatism in the northern segment of the Jiao-Liao-Ji Belt: implications for orogenesis along the Eastern Block of the North China Craton

As the northern segment of the Jiao-Liao-Ji Belt (JLJB), the Palaeoproterozoic Liaoji Belt is a key region for deciphering the formation and evolution of the North China Craton (NCC). In this study, we present the geochronology, geochemical, and isotopic studies on the monzogranitic gneiss, which is one of the major lithotectonic elements of the Liaoji Belt. LA-ICP-MS zircon U–Pb dating reveals that the studied monzogranitic gneisses were formed in the period of 2213–2178 Ma. They are in tectonic contact with the Palaeoproterozoic volcano-sedimentary rocks in the field. The monzogranitic gneisses belong to the high-K calc-alkaline series, and are metaluminous to peraluminous. They have 10,000 Ga/Al ratios of 2.63–3.14 with an average of 2.90, and are thus classified as aluminous A-type granites. Their ε_Nd(t) values vary from ?3.4 to +2.5, indicating heterogeneous source region. The monzogranitic gneisses are characterized by enrichment in LREE and LILE (e.g. Rb, Ba, Th, and K) and depletion in HREE and HFSE (such as Nb, Ta, and Ti), and are typical to magmatism in active continental margins formed in a subduction-related tectonic setting. Taking into account their A-type affinity and regional geological data, we suggest that the monzogranitic gneisses were most probably generated in a local extensional back-arc environment during subduction.     

Os水吸收液ICP-MS测量信号强度衰减原因研究

蒸馏法能从样品中有效分离出OsO_4,吸收液直接用于ICP-MS测定,是辉钼矿Re-Os定年的关键技术环节。但实验发现,长时间放置的吸收液中Os信号强度显著降低。根据OsO_4化学性质推测原因在于一是挥发使吸收液Os含量减少,二是还原使+8价Os变成低价态,气态比例降低,若雾化效率不变,进入质谱仪的Os减少,两者都会导致信号降低,但具体影响情况不明,需深入研究。本文利用辉钼矿标准物质制备不同放置时间、酸度和温度的吸收液,对比上述条件对ICP-MS信号强度的影响。实验时将残余吸收液与稀释剂、氧化剂封入Carius管加热蒸馏,测定Os含量。结果表明:吸收液放置时间越长,酸度越低,温度越高,信号降幅越大,幅度达到3.2%~68.6%。室温下放置相同时间,低酸度吸收液的Os保存率高于高酸度吸收液,但Os信号强度低于后者,证明了挥发和还原共同导致信号衰减,且还原是主导原因。本文提出,冷冻(-18℃)可抑制OsO_4挥发,提高酸度(约3.5 mol/L)可减弱OsO_4还原,两者结合抑制信号衰减,提高了蒸馏法的灵活性和适用性。     

准噶尔盆地腹部地区生烃增压定量化评价——东道海子北凹陷为例

目前准噶尔盆地腹部地区超压演化过程仅提供了相对时间、概念、定性的认识,并未达到定量化。本文以东道海子北凹陷为例,基于流体包裹体、单井一维和剖面二维烃源岩成熟生烃史模拟技术,采用生烃增压模型定量化评价了侏罗纪八道湾组顶部和底部烃源岩的生烃增压演化过程。研究结果表明侏罗纪八道湾组为东道海子北凹陷主力烃源岩,具有幕式排烃的特点。八道湾组底部烃源岩经历了3 次超压增加和两次超压释放的过程,顶部烃源岩经历了两次超压增加和一次超压释放的过程。八道湾底部烃源岩3 次超压增加的时间分别为距今170～70 Ma、55～23 Ma、10～0 Ma,对应最大压力系数均为2.0,最大剩余流体压力50 MPa,两次超压释放的时间分别为70～55 Ma、23～10 Ma;八道湾组顶部烃源岩两次超压增加的时间分别为130～40 Ma、23～0 Ma,对应流体最大压力系数最大亦可达2.0 左右,最大剩余流体压力44 MPa,超压释放的时间为40～23 Ma。     

青藏高原北缘前寒武纪地质演化：进展与讨论

青藏高原北缘前寒武纪块体主要出露于塔里木盆地南缘的铁克里克和阿尔金、祁连山及柴达木盆地周缘等地区。这些古老块体分布于相对年轻的古生代秦祁昆造山带之中,大多经历了古生代造山事件的改造叠加。近10年来,对该地区前寒武纪地层时代格架、物质组成和构造属性研究取得了许多进展：1）揭示铁克里克、北阿尔金、全吉和阿拉善地块具有相似的2.5～2.2 Ga、2.1～1.7 Ga的基底演化和1.7 Ga之后的盖层沉积记录,反映塔里木克拉通、全吉地块和华北克拉通在Columbia 超大陆中具有相关和相似性。2）一系列地层时代被重新厘定,为建立新的前寒武纪地层划分方案提供了依据;3）厘定出铁克里克新元古代裂谷火山—沉积盆地,其可以与华北克拉通南缘1 000～830 Ma的裂解事件对比,它们在新元古代早期可能构成同一个克拉通裂解边缘;4）在南阿尔金与祁连、柴达木等地块识别出性质相似的新元古代岩浆作用和变质作用,它们可能共同代表一个新元古代早期活动大陆边缘的构造杂岩,为古生代汇聚、增生于塔里木克拉通或华北克拉通南缘的外来地块,存在于秦祁昆造山带之中。目前关于青藏高原北缘前寒武纪块体的物质组成、时代格架、构造属性和古环境变化研究还存在许多问题,仍需要开展进一步的大量工作。     

基于GIPL2模型的青藏高原活动层土壤热状况模拟研究

青藏高原活动层土壤热状况,对深入了解高原活动层的厚度变化特征、下垫面的热力作用以及对气候变化预测均有重要意义。利用GIPL2模型模拟青藏高原多年冻土区不同植被状况下活动层土壤热状况。模拟结果表明：模型在高寒草原（QT06）试验点模拟效果较好,高寒沼泽草甸（QT03）试验点的模拟效果较差,高寒草甸（QT01）、高寒荒漠草原（QT05）和高寒草原化草甸（QT04）试验点的模拟效果介于高寒草原试验点和高寒沼泽草甸试验点之间。QT01、QT03、QT04、QT05和QT06的土壤温度模拟值与观测值相比,均方根误差分别为0.67、1.29、0.73、0.7和0.56℃;相关系数分别为0.99、0.87、0.98、0.98和0.96;平均误差分别为0.37、0.61、0.31、0.45和0.16℃。QT06模拟结果较好,原因在于此点土壤质地变化不大,模型的分层与所取的参数更加接近此点的实际状况。QT03模拟结果较差,可能由于此地区土壤中存在砾石,在导热率参数化方案中没有考虑砾石含量,导致模拟结果偏差较大。总体而言,GIPL2模型对青藏高原活动层土壤热状况的模拟具有一定的优势,是一种模拟多年冻土区活动层土壤热状况较为理想的模型。     

华北地台北缘集宁地区古元古代片麻状石榴花岗岩的深熔成因及地质意义

本文对华北克拉通北缘集宁地区空间上密切共生的片麻状石榴花岗岩和孔兹岩系富铝片麻岩的岩相学、地球化学及年代学特征进行了对比研究。SHRIMP锆石U-Pb定年方面,在富铝片麻岩中获得了1910±10Ma和1839±13Ma变质锆石年龄,在片麻状石榴花岗岩中获得了1919±17Ma的变质重结晶锆石年龄。在石榴花岗岩的石榴石包裹体中识别出与富铝片麻岩相对应的进变质阶段(M1)和峰期阶段(M2)的矿物组合,由此确认富铝片麻岩的变质作用和导致石榴花岗岩形成的深熔作用是同一构造热事件的产物。通过对二者变质作用演化及特征变质矿物的对比,认为深熔作用主要发生在峰期后等温降压阶段(M3),石榴花岗岩中的石榴石为深熔作用过程中的残留矿物相或转熔矿物相,而石榴花岗岩则是混合有大量残留矿物相的熔体结晶的产物。对片麻状石榴花岗岩和富铝片麻岩的地球化学组成特征进行了对比分析,片麻状石榴花岗岩既有一定的继承性,又有十分明显的变异性。变异性表现为:1)石榴花岗岩主量和微量元素含量分布极不均匀,微量元素含量普遍低于源岩(Cs、Rb、Th、U、Nb、Ta、Zr、Hf等);2)大离子亲石元素Cs和生热元素U、Th亏损明显,Sr相对富集;3)高场强元素Nb、Ta、P、Ti的明显亏损;4)铕异常变化大,存在铕富集型、铕平坦型和铕亏损型共存的稀土配分曲线的岩石,这是深熔成因石榴花岗岩最突出的表现,也可能是原地-半原地深熔花岗岩的主要地球化学标志。综合区域上的地质资料,认为深熔作用与碰撞后伸展构造背景下基性岩浆底侵事件有关。     

南阿尔金泥盆纪中基性杂岩体的成因及其地质意义研究

出露于南阿尔金西段的塔什萨依辉长岩和闪长岩及其内花岗质细脉是古生代多期岩浆活动的产物,它们构成了南阿尔金俯冲碰撞杂岩带的一部分,是深入探讨该地区构造演化过程的良好材料。本文通过对这些地质体野外地质特征、岩石学、地球化学特征、锆石U-Pb年代学和锆石Hf同位素特征的系统研究,以期确定其形成时代、源区性质和岩石成因,为深入探讨南阿尔金俯冲碰撞杂岩带的演化过程提供进一步约束。本文研究表明:辉长岩和闪长岩具相对较高的SiO_2含量(50.4%~53.5%)和Mg#(57~80),低的K_2O/Na_2O比值(0.17~0.67),为钙碱性系列岩石;辉长岩的∑REE偏低(36.9×10~(-6)~83.1×10~(-6)),Eu正异常(δEu=1.17~1.85);闪长岩∑REE稍高(182×10~(-6)~190×10~(-6)),Eu负异常(δEu=0.85~0.86);二者相对富集LREE和LILE,亏损HFSE。其主量元素特征、微量元素(高Nb、Zr含量,低Zr/Y比值)、锆石Hf同位素和Sr-Nd同位素组成表明二者应为大陆板内伸展背景下软流圈交代的岩石圈地幔部分熔融的产物,并在其岩浆演化过程中经历了地壳混染和分离结晶作用。花岗质细脉具高的Si O2含量(72.4%～75.5%)和K_2O/Na_2O比值(2.33～2.56),属于钾玄岩系列岩石;与闪长岩相比,两者微量元素蛛网图相似,但花岗质细脉轻重稀土分馏程度较大,Eu负异常(δEu=0.55～0.61)和P、Ti的亏损更加显著。锆石U-Pb定年结果显示,辉长岩形成时代约为400～420Ma;闪长岩和其内花岗质细脉的形成时代基本一致,约为400Ma,并具有相似的锆石Hf同位素组成和Sr-Nd同位素组成,结合地球化学特征及野外产状,推测花岗质细脉为闪长岩分异的产物。结合南阿尔金区域地质背景综合分析,塔什萨依辉长岩和闪长岩起源于造山后伸展背景下软流圈交代的岩石圈地幔的部分熔融,并经历了地壳混染和分离结晶作用;而闪长岩进一步分异形成花岗质细脉,并在其形成过程中可能伴随少量壳源熔融物质的加入。     

A model for the representation of emergency cases

The aim of this paper is to propose a location model of earthquake emergency service depot on the basis of hybrid multi-attribute decision-making method. The advantage of the proposed method is that practical mixed uncertainty of location decision information is considered, and the corresponding factors that affect the location of transfer stations are contained. To solve the location problem, a hybrid multi-attribute decision procedure without information transformation is developed. Besides, a novel weighting method and aggregation process is given. Finally, a numerical example is provided to show the feasibility and validity of the proposed method.     

长春地区粉质黏土导热系数与其物性参数相关性研究

为研究导热系数与影响因素之间的相关关系,建立导热系数的推算公式,以长春地区粉质黏土为研究对象,对原状土样的导热系数与其物理参数之间的相关性进行回归分析。制作9个重塑土样,测其相关的参数值,以验证回归方程的适用性。结果表明,回归分析建立导热系数与2个物理参数之间的关系式不成立;考虑天然密度、含水率和孔隙度为自变量,其分别对应的相关性系数T检验显著值(Sig)都0. 05,复决定系数为0. 886,建立的回归方程成立,自变量能准确解释因变量的变化,且含水率与导热系数呈负相关,天然密度和孔隙度呈正相关。重塑土样相关参数代入回归方程得到的导热系数值与实验实测值之间相对误差低于4%,验证了该回归方程的普遍性和适用性。     

Late Quaternary Slip Rate of the Xiugou Segment,Eastern Kunlun Fault Zone

The Eastern Kunlun fault zone (EKLF) is a large left-lateral strike-slip fault, whose slip rate is meaningful to seismic hazard assessment and geodynamics of the Tibetan Plateau. Previous studies suggested that the late Quaternary average slip rate was stable and uniform (10~13 mm/a) in the central and western segment of the EKLF. But there were a few researches of accurate slip rate in the central segment on the EKLF. Therefore, we focused on an offset and well preserved alluvial fan from Xiugou basin, located in the east of Xidatan-Dongdatan, to make it clear. Moreover, we used high-resolution satellite images and digital elevation model extracted from SPOT7 stereo image pairs to restore the offset alluvial fan, and combined terrestrial cosmogenic nuclides method, including 13 quartz-rich samples from this fan surface, 1 quartz-rich sample from the main active channel bed and 1 ¹⁰Be depth profile from this fan edge to eliminate the ¹⁰Be concentration of inheritance accurately, with 1 optically stimulated luminescence sample to obtain the reliable age of this alluvial fan together. Referring to field observations, this alluvial fan was offset left-laterally by (1 862±103) m, and its age is (76.55±3.20)~(106.37±3.38) ka which can be determined through the actual geologic setting and improving chi-square test. Thus, we used the Monte Carlo method to obtain a left-lateral slip rate of (20.3+3.5/-2.3) mm/a with 68% confidence envelopes since the late Pleistocene in the Xiugou basin. As a result, combining with the results of previous studies, the left-lateral slip rate indicated that the obviously decreasing activity transferred from late Pleistocene to Holocene on the central segment of the EKLF.