Tectonothermal events in the Olympic IOCG Province constrained by apatite and REE-phosphate geochronology

The Olympic iron oxide–copper–gold province in South Australia contains numerous deposits and prospects, including the Olympic Dam Cu–U–Au–Ag deposit and the Acropolis prospect. The Acropolis prospect comprises massive, coarse-grained magnetite–apatite veins partly replaced by a hematite-stable assemblage. The apatite grains in the veins contain zones with abundant inclusions of other minerals (including monazite and xenotime) and low trace-element concentrations relative to the inclusion-free zones. The inclusion-rich apatite zones are interpreted to be formed from the recrystallisation of the inclusion-free apatite and remobilisation of U, Th and rare earth element (REE) from apatite into monazite and xenotime. Apatite, monazite and xenotime are all established U–Th–Pb geochronometers and offer the potential to constrain the alteration history of the Acropolis prospect. The LA-ICPMS U–Pb age of inclusion-free apatite is within error of the age of the host volcanic units (ca 1.59 Ga). Inclusion-rich apatite yields both near-concordant analyses that are within error of the inclusion-free apatite as well as highly disturbed (discordant) analyses. The most concordant analyses of monazite (Th–Pb) inclusions and xenotime (U–Pb) inclusions and rim grains indicate an alteration event occurred at ca 1.37 Ga and possibly also at ca 500 Ma. The disparity in age of the inclusion-rich apatite and the REE-phosphate inclusions (and rim grains) is suggested to be owing to the apatite being initially recrystallised at ca 1.59 Ga and modified again by a later event that also formed (or coarsened) most of the inclusions. Partial resetting of the majority of the monazite inclusions as well as the presence of significant amounts of common Pb has complicated the interpretation of the monazite results. In contrast, xenotime is a more robust geochronometer in this setting. The ages of the two post-1.59 Ga events that appear to have affected the Acropolis prospect do not correspond to any events known to have occurred in the Gawler Craton. The earlier (ca 1.37 Ga) age instead corresponds best with metamorphic–magmatic–hydrothermal activity in Laurentia, consistent with the proximity of Laurentia and the Gawler Craton inferred from palaeogeographic reconstructions. The later (ca 500 Ma) event corresponds to the Delamerian Orogeny and has been shown by prior studies to have also affected the Olympic Dam deposit.     

中新生代南北天山差异性抬升历史的磷灰石裂变径迹证据

堆积于天山山前坳陷内部的巨厚新生代地层不仅记录所在沉积区的热历史信息,还记录了物源区的信息。本文选择天山南北两侧山前坳陷中3条地质剖面进行了大量的磷灰石裂变径迹测试和部分样品的热历史模拟分析,来揭示上新世以来天山在南北方向上隆升过程的差异性。采样剖面的选取较前人更加靠近前陆盆地方向,样品所在地层年代更新。结果显示,东秋里塔格背斜剖面中的样品记录了中天山、南天山和背斜区分别在55~65Ma、20~25Ma和5Ma经历了构造隆升。玛纳斯背斜剖面中的样品记录了北天山的三次构造隆升事件分别发生于55~65Ma、20~25Ma和5Ma,其中距今5Ma为玛纳斯背斜带起始隆升的时代。结合前人在相同区域的研究成果,分析得出天山的不同部分经历了不同的构造演化历史,自150Ma以来经历了三期差异性隆升。中生代时期(150~125Ma)表现为山体整体抬升,中生代晚期-新生代早期(100~50Ma)北天山明显早于南天山开始构造隆升,新生代以来(~50Ma)的构造运动以向前陆盆地方向扩展为特征,而隆升起始时间南北差异变小。虽然在南北方向上天山山体隆起时间上存在明显的差异,但是中新生代以来山体物源区的剥蚀速率大体相同。因此,隆升起始时间与隆升量之间并不存在必然的定量关系。天山的不同块体具有不同的构造演化历史的事实提示在研究大范围构造隆升作用时,应将构造作用作为一个过程来对待。变形在传递的过程中,在时间和空间上存在一定的滞后现象。     

渤海湾盆地济阳坳陷碎屑锆石裂变径迹年龄记录的构造抬升事件

对采自渤海湾盆地东南部济阳坳陷的碎屑岩进行测年研究,目的是通过碎屑锆石裂变径迹年龄揭示源区及其抬升剥露史和构造热事件,为华北克拉通构造演化特别是元古宙构造演化提供新的热年代学约束。14件上白垩统-上新统砂岩/粉砂岩岩心样品测年结果显示,锆石裂变径迹年龄分布在308±35Ma~145±19Ma之间,且所有单颗粒锆石径迹年龄均大于其沉积年龄,表明这些锆石为碎屑锆石。除1件样品外,其余13件样品的单颗粒年龄的,可以用来识别源区及其构造抬升。未通过χ2检验的锆石二项式最佳拟合峰值年龄集中分为9组:P1(1187Ma)、P2(720~548Ma)、P3(526Ma)、P4(330~319Ma)、P5(296~274Ma)、P6(213~201Ma)、P7(195~177Ma、162Ma)、P8(134~102Ma)和P9(94Ma),加上通过χ2检验的三叠纪(230Ma),指示源区中元古代-晚白垩世经历的9期构造抬升/岩浆活动。它们分别是发生在中元古代的芹峪运动、新元古代的构造抬升(约720~575Ma)、~548Ma的蓟县运动;古生代~526Ma早寒武世末构造运动、海西期构造抬升;晚三叠世印支期挤压构造抬升、早-中侏罗世印支期弱挤压抬升、早白垩世燕山期强烈岩浆活动及晚白垩世燕山晚期的抬升。华北克拉通北缘、克拉通内部古陆和盆地内部是渤海湾盆地上白垩统-上新统的主要物源区,古生代以来剥露速率逐渐增大,古生代、三叠纪、早-中侏罗世和白垩纪分别为0.020~0.033mm/y,0.033~0.042mm/y,0.034~0.049mm/y和0.041~0.097mm/y,反映源区白垩纪构造/岩浆活动最强烈。锆石裂变径迹年龄记录的中元古代-晚白垩世构造运动对探讨华北克拉通的构造演化特别是元古宙的演化提供了年代学证据,综合分析推断华北克拉通可能参与了Rodinia超大陆的形成与裂解。     

云南中甸地区晚白垩世斑岩型Mo-Cu矿床磷灰石、锆石裂变径迹年代学研究

云南中甸地区位于西南三江铜钼铅锌金多金属矿集区的南端,是一个独具特色的Cu-Mo多金属复合叠加成矿带.本文采用裂变径迹低温热年代学技术对区内晚白垩世铜厂沟、休瓦促、热林成矿斑岩体,进行了锆石、磷灰石裂变径迹分析测试,开展了晚白垩世以来的构造热史演化模拟,揭示了区内构造-岩浆成矿事件及热史演化过程.研究表明,锆石裂变径迹年龄值变化于52±2～96±5 Ma;磷灰石裂变径迹的年龄值变化于15±1～48±3 Ma,总体变化幅度不大,中心年龄与池年龄在误差范围也基本一致.通过锆石、磷灰石的裂变径迹分析,揭示出云南中甸地区自晚白垩世以来主要经历了三个阶段的构造热事件.第一阶段(96～60 Ma),主要为岩浆侵位后快速降温的热史演化阶段;第二阶段(52～39 Ma),为缓慢的降温作用过程;第三阶段(16～15 Ma),揭示了受中新世以来青藏高原隆升造山作用的影响,该区经历了快速降温的地质演化过程.综合锆石裂变径迹、磷灰石裂变径迹的热史反演结果,表明区内晚白垩世典型成矿斑岩体具有相似的隆升过程和剥蚀历史,并获得了剥蚀量与剥蚀速率的定量计算结果,为区内矿床的资源潜力评价及勘查工作提供了科学参考.     

1961—2019年青藏高原中东部夏季强降水与大尺度环流的关系

采用一元线性回归、合成分析等方法对1961—2019年青藏高原中东部71个站点夏季强降水与大尺度环流进行了分析,研究结果表明,近年来青藏高原中东部强降水呈增加趋势。在强降水高值年时,青藏高原中东部水汽辐合加强,中纬度西风和热带地区东风带向极移动加强,高层辐散流场、水汽输送以及上升运动条件,共同作用导致了强降水的产生。在强降水低值年时,青藏高原中东部大部水汽异常辐散,区域内的季风水汽输送减弱,西风带和东风带均向赤道移动减弱,高层为气旋式环流异常。通过风暴轴、波作用通量和E-P通量进一步分析发现,当北大西洋地区风暴轴偏强（偏弱）时,瞬变扰动作用加强（减弱）,使得北大西洋地区高纬度西风加速（减弱）,急流出口区的不稳定能量激发了欧洲西北部的异常反气旋（异常气旋）,并通过Rossby波列调控季风输送,导致了青藏高原中东部地区强降水的变化。     

Inter‐laboratory Characterisation of Apatite Reference Materials for Chlorine Isotope Analysis

Here we report on a set of six apatite reference materials (chlorapatites MGMH#133648, TUBAF#38 and fluorapatites MGMH#128441A, TUBAF#37, 40, 50) which we have characterised for their chlorine isotope ratios; these RMs span a range of Cl mass fractions within the apatite Ca₁₀(PO₄)₆(F,Cl,OH)₂ solid solution series. Numerous apatite specimens, obtained from mineralogical collections, were initially screened for ³⁷Cl/³⁵Cl homogeneity using SIMS followed by δ³⁷Cl characterisation by gas source mass spectrometry using both dual‐inlet and continuous‐flow modes. We also report major and key trace element compositions as determined by EPMA. The repeatability of our SIMS results was better than ± 0.10‰ (1s) for the five samples with > 0.5 % m/m Cl and ± 0.19‰ (1s) for the low Cl abundance material (0.27% m/m). We also observed a small, but significant crystal orientation effect of 0.38‰ between the mean ³⁷Cl/³⁵Cl ratios measured on three oriented apatite fragments. Furthermore, the results of GS‐IRMS analyses show small but systematic offset of δ³⁷Cl_SMOC values between the three laboratories. Nonetheless, all studied samples have comparable chlorine isotope compositions, with mean 10³δ³⁷Cl_SMOC values between +0.09 and +0.42 and in all cases with 1s ≤ ± 0.25.     

Integration of zircon and apatite U–Pb geochronology and geochemical mapping of the Wude basalts(Emeishan large igneous province):A tool for a better understanding of the tectonothermal and geodynamic evolution of the Emeishan LIP

Radiogenic isotopic dating and Lu–Hf isotopic composition using laser ablation-inductively coupled plasma-mass spectrometry(LA-ICP-MS)of the Wude basalt in Yunnan province from the Emeishan large igneous province(ELIP)yielded timing of formation and post-eruption tectonothermal event.Holistic lithogeochemistry and elements mapping of basaltic rocks were further reevaluated to provide insights into crustal contamination and formation of the ELIP.A zircon U–Pb age of 251.3±2.0 Ma of the Wude basalt recorded the youngest volcanic eruption event and was consistent with the age span of 251-263 Ma for the emplacement of the ELIP.Such zircons hadε_Hf(t)values ranging from7.3 to+2.2,identical to those of magmatic zircons from the intrusive rocks of the ELIP,suggesting that crust-mantle interaction occurred during magmatic emplacement,or crust-mantle mixing existed in the deep source region prior to deep melting.The apatite U–Pb age at 53.6±3.4 Ma recorded an early Eocene magmatic superimposition of a regional tectonothermal event,corresponding to the Indian–Eurasian plate collision.Negative Nb,Ta,Ti and P anomalies of the Emeishan basalt may reflect crustal contamination.The uneven Nb/La and Th/Ta values distribution throughout the ELIP supported a mantle plume model origin.Therefore,the ELIP was formed as a result of a mantle plume which was later superimposed by a regional tectonothermal event attributed to the Indian–Eurasian plate collision during early Eocene.     

CONDITIONAL NONLINEAR OPTIMAL PERTURBATIONS: APPLICATION IN TROPICAL CYCLONE FORECASTS

Considering the feature of tropical cyclones (TCs) that strong positive vorticity exists in the lower layers of troposphere, this study proposed to use vorticity at 850 hPa as cost function to find the conditional nonlinear optimal perturbation (CNOP), which was largely different from those previous studies using total energy of perturbed forecast variables. The CNOP was obtained by an ensemble-based approach. All of the sensitive areas determined by CNOP with vorticity at 850 hPa as cost function for the three cases were located over the TC core region and its vicinity. The impact of the CNOP-based adaptive observations on TC forecasts was evaluated with three cases via observational system simulation experiments (OSSEs). Results showed obvious improvements in TC intensity or track forecasts due to the CNOP-based adaptive observations, which were related to the main error source of the verification area, i.e., intensity error or location error.     

冬季北半球风暴轴的多尺度能量变化特征及其可能机制

基于1971—2016年NCEP/NCAR(美国环境预报中心和国家大气研究中心)的逐日再分析资料及NCPC(美国国家海洋和大气管理局气候预报中心)的海温、大气环流及海洋指数等资料通过多尺度能量分析(MS-EVA)等方法,把冬季北半球风暴轴看做一整体,分析了风暴轴区域多尺度的能量变化特征及其可能机制。主要结论概括如下:(1)多年气候平均状态下,风暴轴的动能来源主要表现为在风暴轴中上游先由低频尺度向天气尺度输送有效位能,随后在风暴轴主体区再由天气尺度有效位能转换为天气尺度动能,其中风暴轴西端可直接由低频尺度向天气尺度输送动能。(2)北半球三大风暴轴联合EOF结果表明:第一模态下,主要体现了北西伯利亚风暴轴与北太平洋风暴轴强度的减弱(增强),同时伴随着北大西洋风暴轴位置北抬(南压);第二模态下,主要体现了北西伯利亚风暴轴强度减弱(增强),同时北太平洋风暴轴位置北抬(南压)中东部强度增强(减弱),而北大西洋风暴轴位置南压(北抬)。(3)回归分析表明:北半球风暴轴异常在不同模态下与低频尺度环流联系密切。低频尺度波动可通过海温及西风急流等异常变化先影响风暴轴区域多尺度间的能量转换,进而影响风暴轴整体的异常变化。     

西北太平洋热带气旋路径的历史模拟

基于IBTrACS提供的热带气旋最佳路径数据集,在统计分析历史热带气旋的发生年频次、发生位置、路径移动及强度变化等的基础上,建立了西北太平洋热带气旋轨迹合成模型。模型包括生成模型、移动模型、消亡模型及强度模型4个部分,并从地理轨迹密度、年登陆率、登陆风速分布三个方面,对模拟的气旋路径与历史气旋路径进行比较,以验证模型的准确性和可靠性。结果表明,构建的西北太平洋热带气旋全路径统计模拟模型稳健可靠,可进一步应用于研究区热带气旋的定量精细化的风险评估,能提高气旋风险灾害评估的可信度。