Evolution of Tectonic Uplift, Hydrocarbon Migration, and Uranium Mineralization in the NW Junggar Basin: An Apatite Fission-Track Thermochronology Study

The Mesozoic–Cenozoic tectonic movement largely controls the northwest region of the Junggar Basin (NWJB), which is a significant area for the exploration of petroleum and sandstone-type uranium deposits in China. This work collected six samples from this sedimentary basin and surrounding mountains to conduct apatite fission track (AFT) dating, and utilized the dating results for thermochronological modeling to reconstruct the uplift history of the NWJB and its response to hydrocarbon migration and uranium mineralization. The results indicate that a single continuous uplift event has occurred since the Early Cretaceous, showing spatiotemporal variation in the uplift and exhumation patterns throughout the NWJB. Uplift and exhumation initiated in the northwest and then proceeded to the southeast, suggesting that the fault system induced a post spread-thrust nappe into the basin during the Late Yanshanian. Modeling results indicate that the NWJB mountains have undergone three distinct stages of rapid cooling: Early Cretaceous (ca. 140–115 Ma), Late Cretaceous (ca. 80–60 Ma), and Miocene–present (since ca. 20 Ma). These three stages regionally correspond to the Lhasa-Eurasian collision during the Late Jurassic–Early Cretaceous (ca. 140–125 Ma), the Lhasa-Gandise collision during the Late Cretaceous (ca. 80–70 Ma), and a remote response to the India-Asian collision since ca. 55 Ma, respectively. These tectonic events also resulted in several regional unconformities between the J3/K1, K2/E, and E/N, and three large-scale hydrocarbon injection events in the Piedmont Thrust Belt (PTB). Particularly, the hydrocarbon charge event during the Early Cretaceous resulted in the initial inundation and protection of paleo-uranium ore bodies that were formed during the Middle–Late Jurassic. The uplift and denudation of the PTB was extremely slow from 40 Ma onward due to a slight influence from the Himalayan orogeny. However, the uplift of the PTB was faster after the Miocene, which led to re-uplift and exposure at the surface during the Quaternary, resulting in its oxidation and the formation of small uranium ore bodies.     

Seismic Hazard Assessment of District Mansehra,Khyber Pakhtoonkhawa,Pakistan

The site of Mansehra is located seismically in an active regime, known as the Crystalline Nappe Zone and Hazara-Kashmir Syntaxis in NW Himalayas, Pakistan. Seismic Hazard Assessment （SHA） for the site has been carried out by considering the earthquake source zones, selection of appropriate attenuation equations, near fault effects and maximum potential magnitude estimation. The Mansehra Thrust, Oghi Fault, Banna Thrust, Balakot Shear Zone, Main Boundary Thrust, Panjal Thrust, Jhelum Fault and Muzaffarabad Fault and, further to the south, the Sanghargali, Nathiagali, and Thandiani Thrusts are the most critical tectonic features within the 50 km radius of Mansehra. Using the available instrumental seismological data from 1904 to 2007, SHA has been carried out. Other reactivated critical tectonic features in the area have been investigated. Among them the Balakot-Bagh fault, with the fault length of 120 km from Balakot to Poonch, has been considered as the most critical tectonic feature on the basis of geological/structural/seismological data. The potential earthquake of maximum magnitude 7.8 has been assigned to the Balakot-Bagh fault using four regression relations. The peak ground acceleration value of 0.25 g （10% probability of exceedance for 50 years） and 0.5 g has been calculated with the help of the attenuation equation using probabilistic and deterministic approaches.     

Marsh benthic Foraminifera response to estuarine hydrological balance driven by climate variability over the last 2000 yr (Minho estuary,NW Portugal)

A high-resolution study of a marsh sedimentary sequence from the Minho estuary provides a new palaeoenvironmental reconstruction from NW Iberian based on geological proxies supported by historical and instrumental climatic records. A low-salinity tidal flat, dominated by Trochamminita salsa, Haplophragmoides spp. and Cribrostomoides spp., prevailed from AD 140–1360 (Roman Warm Period, Dark Ages, Medieval Climatic Anomaly). This sheltered environment was affected by high hydrodynamic episodes, marked by the increase in silt/clay ratio, decrease of organic matter, and poor and weakly preserved foraminiferal assemblages, suggesting enhanced river runoff. The establishment of low marsh began at AD 1380. This low-salinity environment, marked by colder and wet conditions, persisted from AD 1410–1770 (Little Ice Age), when foraminiferal density increased significantly. Haplophragmoides manilaensis and Trochamminita salsa mark the transition from low to high marsh at AD 1730. Since AD 1780 the abundances of salt marsh species (Jadammina macrescens, Trochammina inflata) increased, accompanied by a decrease in foraminiferal density, reflecting climate instability, when droughts alternate with severe floods. SW Europe marsh foraminifera respond to the hydrological balance, controlled by climatic variability modes (e.g., NAO) and solar activity, thus contributing to the understanding of NE Atlantic climate dynamics.     

滇西北三叠系铅锌铁铜多金属矿含矿层位

滇西北德钦—维西一带有一类重要的铁铜铅锌多金属矿,含矿岩石为一套夹中酸性—基性火山岩的沉积岩系。目前的地质文献中,该沉积岩系的时代和名称争论颇多。笔者研究后认为应是中三叠统攀天阁组、中—上三叠统崔衣比组。建议以巍山地区歪古村组、三合洞组、挖鲁八组及麦初箐组作为兰坪—思茅中、新生代上叠陆内盆地的上三叠统地层名称;而攀天阁组、崔衣比组及石钟山组则为金沙江构造带维西陆缘弧带的三叠系地层名称,便于两个不同大地构造单元三叠系地层的对比。     

Qiarbahete Sanukitoids and adakitic rocks in NW Tianshan: age and geochemical constraints on their petrogenesis and tectonic settings

The Qiarbahete complex in NW China consists of gabbroic diorite, granodiorite, and late-stage quartz diorite porphyry veins. Zircon sensitive high-resolution ion microprobe (SHRIMP) U–Pb analyses show that the gabbroic diorite and granodiorite formed at 368 ± 5.2 Ma and 354 ± 4.1 Ma, respectively, indicating that the complex was emplaced in the Late Devonian–Early Carboniferous. The gabbroic diorites, characteristic of Sanukitoids, exhibit high Mg^# (62 average), MgO (6.84% average), Cr (195 ppm average), and Ni (61.4 ppm average) contents. The rocks show moderately fractionated rare earth element (REEs) patterns and weak negative Eu anomalies (δEu: 0.83–0.89), enrichment of large ion lithophile elements (LILEs), and depletion of high field strength elements (HFSEs), with low ?_Nd(t) values (1.46–1.73). The gabbroic diorites originated from partial melting of a hydrous mantle wedge followed by assimilation of crust during ascent. The granodiorites show a geochemical affinity with adakitic rocks, e.g. SiO₂ (64.95–67.87%) > 56%, Al₂O₃ (15.88–16.56%) > 15%, MgO (1.79–2.31%) < 3%, Sr (315–375 ppm) > 300 ppm, and Yb (1.84–2.06 ppm). They are enriched in light rare earth elements (LREEs) and LILEs and depleted in HFSEs, with weak negative Eu anomalies (δEu: 0.78–0.87). The granodiorites were mainly derived by the partial melting of a subducted oceanic slab, followed by subsequent melt–mantle interaction and crustal rocks contamination. All these indicate that the Qiarbahete complex was emplaced in a continental arc setting attending the southward subduction of the Junggar Ocean during the Late Devonian–early Carboniferous, generating the lateral accretion of continental crust in NW Tianshan.     

Stratigraphy and tectonic evolution of the Kazdağı Massif (NW Anatolia) based on field studies and radiometric ages

The Kazda?? Massif was previously considered as the metamorphic basement of the Sakarya Zone, a microcontinental fragment in NW Anatolia. Our new field mapping, geochemical investigations, and radiometric dating lead to a re-evaluation of previous suggested models of the massif. The Kazda?? metamorphic succession is subdivided into two major units separated by a pronounced unconformity. The lower unit (the Tozlu metaophiolite) is a typical oceanic crust assemblage consisting of ultramafic rocks and cumulate gabbros. It is unconformably overlain by a thick platform sequence of the upper group (the Sar?k?z unit). The basement ophiolites and overlying platform strata were subjected to a single stage of high-temperature metamorphism under progressive compression during the Alpine orogeny, accompanied by migmatitic metagranite emplacement. Radiometric age data obtained from the Kazda?? metamorphic succession reveal a wide range of ages. Metagranites of the Kazda?? metamorphic succession define a U–Pb discordia upper intercept age of ca. 230 Ma and a lower intercept age of 24.8 ± 4.6 Ma. This younger age agrees with ²⁰⁷Pb/²⁰⁶Pb single-zircon evaporation ages of 28.2 ± 4.1 to 26 ± 5.6 Ma. Moreover, a lower intercept age of 28 ± 10 Ma from a leucocratic metagranite supports the Alpine ages of the massif within error limits. Reconnaissance detrital zircon ages constrain a wide range of possible transport and deposition ages of the metasediments in the Sar?k?z unit from ca. 120 to 420 Ma. Following high-temperature metamorphism and metagranite emplacement, the Kazda?? sequence was internally imbricated by Alpine compression, and the lowermost Tozlu ophiolite thrust southward onto the Sar?k?z unit. Field mapping, internal stratigraphy, and new radiometric age data show that the Sar?k?z unit is the metamorphic equivalent of the Mesozoic platform succession of the Sakarya Zone. The underlying metaophiolites are remnants of the Palaeo tethys Ocean, which closed during the early Alpine orogeny. After strong deformation attending nappe emplacement, the unmetamorphosed Miocene Evciler and Kavlaklar granites intruded the tectonic packages of the Kazda?? Massif. During Pleistocene time, the Kazda?? Massif was elevated by EW trending high-angle normal faults dipping to Edremit Gulf, and attained its present structural and topographic position. Tectonic imbrication, erosion and younger E–W-trending faulting were the main cause of the exhumation of the massif.     

Early Cambrian alkaline volcanism on the southern margin of Laurentia: evidence in the volcaniclastic units from the Puerto Blanco Formation in the Caborca block,NW Mexico

ABSTRACT

Volcaniclastic units are exposed at the base of the Puerto Blanco Formation in the Caborca region, northwestern Mexico. The lower unit reveals the presence of Early Cambrian mafic volcanism in this region. It consists of a volcano-sedimentary sequence represented by tuffaceous conglomerates, agglomerates, lapillistones, tuffs, and altered mafic volcanic flows. Petrographic analysis classified the volcanic clasts as albite-sphene-calcite-actinolite granofels, with a moderate to intense hydrothermal alteration, precisely characterized by EPMA analysis. Albite-actinolite geothermometry indicates temperatures from 400 to 500°C, suggesting metamorphic conditions in the upper temperature greenschist facies. Geochemistry analysis shows a high TiO₂ basic–ultrabasic volcanism that originated the volcanic clasts. Rock protoliths were studied using immobile trace elements, which classified them as OIB-type alkaline basalts with the characteristic spider hump-shaped pattern, situated in an anorogenic intracontinental tectonic setting with enriched mantle signatures. ⁴⁰Ar/³⁹Ar geochronology shows metamorphic ages of 52.58 ± 2.0 and 91.67 ± 0.55 Ma, consistent with the emplacement of Laramidic granitoids identified in the region. Possible correlations of this alkaline volcanism include the Southern Oklahoma Aulacogen and the late stages of the rifting of north western Laurentia represented in western United States.     

前陆盆地异常流体压力: 地质作用及其增压效率

在前陆盆地形成过程中,强烈挤压构造应力场和特殊的盆-山关系造成极为复杂的沉积环境和构造形变,多种地质作用都可能对地层内异常流体压力的产生及演化起到十分重要的作用。通过对准噶尔盆地南缘地区中段的地质条件及压力分布的分析,利用数值盆地模型方法,模拟分析了在前陆盆地构造挤压和盆地沉降过程中压实作用、断裂开启、褶皱、剥蚀等地质过程对流体压力的作用和影响,定量讨论了压力异常的成因机制及其效率。模拟分析结果表明,构造应力在水平方向上派生的侧向压实作用、强烈的褶皱作用及伴随的快速沉积-剥蚀作用等是前陆盆地中特有的增压作用,都可造成较高压力异常。准噶尔盆地南缘中新生界地层中广泛分布的高异常压力是新生代以来,特别是第四纪以来,在快速的压实作用、构造挤压作用所形成的高地层压力背景下,叠加了近期因断裂活动和背斜构造快速形成所引起的他源高压而形成的。     

塔里木盆地西北缘柯坪冲断带构造变形特征

柯坪冲断带位于塔里木盆地西北缘,是新生代南天山褶皱冲断系的一部分.本文根据野外实际考察和地震剖面解释,总结了该冲断带的构造变形特征.它是发育于古生界中且以中寒武统膏盐层为主滑脱面的薄皮构造,是内部结构相对简单的叠瓦状冲断,因更新世才定型而具暴露式冲断前锋,有断层传播褶皱发育但已遭强烈剥蚀,前展式冲断.上新世晚期的冲断曾控制了磨拉石盆地发育（西域组砾岩）,但该盆地已遭更新世的冲断推覆作用破坏.根据平衡剖面恢复,柯坪冲断带南部3排冲断层的总构造缩短量为29.1%-40.7%.     

Muglad盆地Sufyan凹陷下白垩统AG组2段沉积特征与成因模式

下白垩统AG组2段(后简称AG2段)是苏丹Muglad盆地Sufyan凹陷的主力烃源岩和最重要的含油层系。本文基于岩石学、测井相、地震相和地震属性研究,对Sufyan凹陷下白垩统AG2段沉积体系进行精细研究,结合其沉积期构造特征、古地貌特征、古气候环境及内物源和外物源发育特征,建立了其断陷期沉积模式。Sufyan凹陷AG组断陷初期为双断模式,南北两侧高陡断层发育规模相当,随着盆地的演化和湖平面的变化,到AG2段进入高水位期,凹陷北部逐渐演变为缓坡沉积环境,南部仍然为陡坡沉积环境。凹陷北部为Babanusa凸起和中非走滑带,为Muglad盆地的盆外物源,凹陷南部以Tomat凸起与Nugara凹陷分割,发育内物源。从钻井和岩心资料来看,凹陷北部以分选较好、细粒沉积为主,在断层下降盘发现中粗粒重力流沉积,反映了北部物源长距离搬运和长期供应的特点,据此建立了断陷后期AG2段北部曲流河三角洲沉积模式,北部物源为主力物源区;南部临近凹陷断裂带钻井揭示其发育较高砂地比的细粒沉积,显示物源供给的周期性和近源性,研究认为发育辨状河三角洲,沉积模式类似于扇三角洲,总体物源供给能力较弱,具有近源水下搬运特征。南部物源和西部物源一起,构成凹陷的次物源。本文综合编制了Sufyan凹陷AG2段沉积期的两期沉积相图,建立了立体沉积模式,认为盆地优质储层应以凹陷中部近烃源岩的区带为目标进行寻找。