晚白垩世以来川东北地区的剥蚀历史——多类低温热年代学数据综合剖面的制约

低温热年代学数据是一个与热历史过程紧密相关的资料类型,与高温年代学不同,低温热年代学表观年龄本身在很多情况下没有直接的地质意义.当且仅当样品线性持续冷却的情况下,表观年龄才可以被直接解释为样品经过其封闭温度的大致时间.因此,只有结合地质约束通过对低温热年代学数据进行热历史模拟才能更好地揭示其所蕴含的地质信息.对川东北地...     

The denudation history of the Argentera Alpine External Crystalline Massif (Western Alps,France-Italy): an overview from the analysis of fission tracks in apatites and zircons

Apatite/zircon fission track (FT) records of the Argentera external crystalline massif (Western Alps) show three tectonic pulses, respectively at 22 Ma (zircons), 6 and 3.5 Ma (apatites). The first pulse is consistent with the basement exhumation and initiation of the major deformation recorded in the foreland of the belt from Middle to early Upper Miocene. The two others might be respectively local expressions of the syncollisional extension mainly controlled by a westward sedimentary cover detachment and a Plio-Quaternary uplift acceleration. Zircon ages of 50-80 Ma in a limited NW area and evidence of an uplift elsewhere show that in a large fraction of the massif, temperatures in post-Variscan times never reached 320°C. Finally, FT data show that the Argentera massif did not behave as a single block during its denudation. First, in the NW of the massif, a small fault-limited block was already separated since the Cretaceous and later on recorded the 6 Ma denudation event, the 22 Ma pulse being recorded only in the remaining part of the massif. Second, less than 3.5 Ma ago, the northeastern part of the massif overthrust the southwestern block along the Bersézio-Veillos fault zone.     

花岗岩体高温热年代学研究的新思路、方法及计算实例

对国内外花岗岩体723 对锆石U-Pb 年龄（t _Zr）和全岩Rb-Sr 等时线年龄（t _Rb）进行的相关分析, 拟合出相关系数很高
（Ｒ =0.997）, 回归系数接近l 的线性回归方程（t _Zr=1.0005×t _Rb+0.493041）。 Δt _Zr-Rb（t _Zr-t _Rb）频数统计分析表明: Δt _Zr-Rb呈对
称正态分布（偏度系数C _SK=0.193; 峰度系数C _KU=6.722）, 其均值为0.624 Ma, 众数值为1.0 Ma。这表明花岗岩体锆石U-Pb 定
年的测定结果与全岩Rb-Sr 等时线定年测定结果在允许的误差范围内是一致的。不存在花岗岩体锆石U-Pb 年龄必定大于全
岩Rb-Sr 等时线年龄的规律表明,同位素热年代学方法只适用于研究花岗岩结晶固结后的低温热演化史。 前人根据锆石U-Pb
年龄和全岩Rb-Sr 等时线年龄差值及相应同位素体系封闭温度研究的10 个花岗岩体的冷却速率（CR Zr-Rb）表明,它们与岩
体体积尺度不相关,这有悖于“热物体的体积（质量）愈大,则在相同热物理条件下其冷却速率愈小”的热物理学基本定律。
根据热传导理论及本文作者（2010）提出的侵位结晶时差概念我们得出“在相同热物理学条件下,体积尺度是决定花岗岩
体冷却速率最主要因素”的结论。以上述10 个花岗岩体为例,本文计算得出它们在结晶固结前高温阶段的冷却速率（CR _ECTD）
并拟合出冷却速率与岩体体积尺度呈幂函数关系：CR _ECTD=7544.7×D -2.1686, 计算结果符合热物理学基本定律。     

Late Miocene to present-day exhumation and uplift of the Internal Zone of the Rif chain: Insights from low temperature thermochronometry and basin analysis

Located on the margin of the west Alboran basin, the Gibraltar Arc (Betic-Rif mountain belt) displays post-Pliocene vertical movements evidenced by uplifted marine sedimentary basins and marine terraces. Quantification of vertical movements is an important clue to understand the origin of present-day relief generation in the Betic-Rif mountain chain together with the causes of the Messinian Salinity Crisis. In this paper, we present the results of a pluridisciplinary study combining an analysis of low temperature thermochronology and Pliocene basins evolution to constrain the exhumation history and surface uplift of internals units of the Rif belt (Northern Morocco). The mean (U-Th)/He apatite ages obtained from 11 samples are comprised between 14.1 and 17.8 Ma and display a wide dispersion, which could be explained by a great variability of apatite chemistries in the analyzed samples. No correlations between altitude and age have been found along altitudinal profile suggesting a rapid exhumation during this period. Thermal modeling using our (U-Th)/He apatite ages and geochronological data previously obtained in the same area (⁴⁰Ar/³⁹Ar and K/Ar data on biotite, zircon and apatite fission track) allow us to propose a cooling history. The rocks suffered a rapid cooling at 60–100 °C/Ma between 22.5 and 19 Ma, then cooled to temperatures around 40 °C between 19 and 18 Ma. They were re-heated at around 110 °C between 18 and 15 Ma then rapidly cooled and exhumed to reach the surface temperature at around 13 Ma. The re-heating could be related to a renewal in thrusting and burying of the inner zones. Between 15 and 13 Ma the cooling resumed at a rate of 50 °C/Ma indicating an exhumation rate of 0.8 mm/y considering an average 40 °C/km geothermal gradient. This exhumation may be linked to the extension in the Alboran Sea. Otherwise biostratigraphic and sedimentological analysis of Pliocene basins of the internal Rif provided informations on the more recent events and vertical movements. Pliocene deposits of the Rifian coast represent the passive infilling of palaeo-rias between 5.33 and 3.8 Ma. The whole coastal area was uplifted at slow average rates (0.01–0.03 mm/y) in relation with a northeastward tilting of 0.2–0.3° since the Lower-Pliocene. A late Pliocene to present extensional tectonics associated to uplift has been identified all along the coastal ranges of the Internal Zone of the Rif chain. This extension was coeval with the major late Pliocene to Pleistocene extensional episode of the Alboran Sea and appears to be still active nowadays. No significant late Messinian uplift was evidenced, thus calling into question the geodynamic models relating the closure of the marine gateways and the MSC to slab roll back.     

Mesoproterozoic fluid events affecting Archean crust in the northern Olympic Cu–Au Province,Gawler Craton: insights from 40Ar/39Ar thermochronology

The Olympic Cu–Au Province, Gawler Craton, is host to the Olympic Dam and Prominent Hill iron oxide–copper–gold (IOCG) deposits. Both of these deposits and the region between the two are covered by Neoproterozoic to Cenozoic sediment, making inferences about prospectivity in this portion of the Olympic Domain reliant on geophysical interpretation and sparse drill hole information. We present new U–Pb zircon sensitive high resolution ion microprobe (SHRIMP) dates from two basement intersecting drill holes in the region between Olympic Dam and Prominent Hill that show bimodal volcanism occurred at 2555 ± 5 Ma, and was followed by intrusion of tonalite at 2529 ± 6 Ma. Laser ⁴⁰Ar/³⁹Ar dating of biotite and muscovite from the tonalite yields ages around ca 2000 Ma, consistent with slow cooling trends observed in Archean rocks elsewhere in the northern Gawler Craton. Step heating experiments on K-feldspar from the same tonalite yields an age spectrum with older ages around 1740 Ma from the highest temperature steps becoming progressively younger to a minimum of 1565 Ma in the lowest temperature heating steps; this is consistent with either Paleoproterozic cooling to final closure of K-feldspar by 1565 Ma or a reheating event at ca 1565 Ma, with the latter more likely, given the evidence for sub-solidus alteration of the K-feldspar. Sericite within hematite–sericite–chlorite altered portions of the tonalite yield a poorly defined age of ca 1.6 Ga. Taken together the ⁴⁰Ar/³⁹Ar data providing evidence for a fluid event affecting this region between Olympic Dam and Prominent Hill during the early Mesoproterozoic. Low temperature quartz–carbonate–adularia veins occur in <10 cm wide fractures within basalt in one drill hole in this region. Adularia from these veins yields ⁴⁰Ar/³⁹Ar ages that span from ca 1.3–1.1 Ga. This age range is interpreted to approximate either the timing of adularia formation during a hydrothermal event or the timing of resetting of the ⁴⁰Ar/³⁹Ar systematics within the adularia as a result of fluid flow in this sample. This is evidence for a mid-Mesoproterozoic fluid event in the Gawler Craton and necessitates a reconsideration of the long-term stability of the craton, as it appears to have been affected, at least locally, by fluid flow related to a much larger event within the Australian continent, the Musgrave Orogeny.     

青藏高原东缘地区隆升作用特征－低温年代学证据

通过对比研究青藏高原东缘若尔盖－泸定地区低温年代学样品(ZFT样31件、AFT样56件和 A(U­Th)/He 样37件)各参数(隆升年龄和隆升速率)特征表明,该地区中生代以来的抬升冷却过程具由北向南的递进隆升特征,南部丹巴弧形带与北部茂县弧形带产生了显著的隆升剥露“翘掀式”调整,北部弧形带隆升剥露较早、速率先快后慢,南部弧形带隆升剥露较晚、速率先慢后快; 且在早中新世研究区处于平静期,抬升剥露作用显著减缓。年龄及抬升冷却速率等值线垂向上浅部(70℃等温面)较深部(110℃等温面)弧形展布特征显著; 平面上总体向南具连续弧形变化趋势(年龄变新、隆升速率增大)。抬升冷却(剥露)特征显示出中央造山带和青藏高原的形成对该地区隆升过程的强烈影响,以及弧形构造格架对浅部地表抬升剥露的显著控制作用。     

Thermal anomaly around the Nojima Fault as detected by fission-track analysis of Ogura 500 m borehole samples

Abstract To better understand heat generation and transfer along earthquake faults, this paper presents preliminary zircon fission-track (FT) length data from the Nojima Fault, Awaji Island, Japan, which was activated during the 1995 Kobe earthquake (Hyogo-ken Nanbu earthquake). Samples were collected of Cretaceous granitic rocks from the Ogura 500 m borehole as well as at outcrops adjacent to the borehole site. The Nojima Fault plane was drilled at a depth of 389.4 m (borehole apparent depth). Fission-track lengths in zircons from localities > 60 m distance from the fault plane, as well as those from outcrops, are characterized by the mean values of ≈10–11 μm and unimodal distributions with positive skewness, which show no signs of an appreciable reduction in FT length. In contrast, those from nearby the fault at depths show significantly reduced mean track lengths of ≈6–8 μm and distributions having a peak around 6–7 μm with rather negative skewness. In conjunction with other geological constraints, these results are best interpreted by a recent thermal anomaly around the fault, which is attributable to heat transfer via focused fluids from the deep interior of the crust and/or heat dispersion via fluids associated with frictional heating by fault motion.     

Quantifying the effect of recent relief changes on age–elevation relationships

The effect that recent relief changes may have on the distribution of rock ages with elevation is investigated for a range of thermochronometers. From the solution of the heat transport equation in a crustal block undergoing uplift and surface erosion, the temperature history of rock particles that are exhumed at the Earth’s surface today is computed. These T-t paths are then used to calculate apparent isotopic ages for the (U–Th)/He system in apatite, characterized by a low (≈70°C) closure temperature. The results show that recent relief changes strongly affect the distribution of ages with elevation (notably the slope of the age–elevation relationship). The calculations presented here predict that, in most situations, regions that have undergone a steady decrease in surface relief in the recent past should be characterized by an inverted age–elevation relationship, that is older ages should be found near valley bottoms and younger ages near summit tops. It is also shown how the wavelength of the topography, the geothermal gradient, the exhumation rate and the duration of the relief reduction event affect this result.     

阿尔金山中一新生代隆升历史研究进展

阿尔金断裂左旋走滑的同时，伴随较大的逆冲分量，总体成花状构造，引起阿尔金山的垂向隆升，大量证据表明阿尔金山自中生代以来主要经历了6次快速隆升事件，即白垩纪、晚始新世一早渐新世、早中新世、中中新世、上新世、早更新世末一中更新世初。新生代的五期重要的隆升事件，与欧亚大陆拼合后的印度板块持续向北的挤压有关，俯冲引起青藏高原的阶段性快速隆升，是阿尔金山隆升的动力学机制。     

一种新的构造变形热年代学研究方法——显微构造变形热年代学

显微构造变形热年代学是一种新兴的研究构造变形热年代学方法,能够解决一些常用方法无法解决的或很困难的构造问题。显微构造变形热年代学利用因构造变形事件而产生的新生矿物结晶年龄来测定小至一般的构造变形,大至区域构造乃至造山带或碰撞带构造变形的年龄,建立构造演化时间序列,并可以计算其变形速率或隆升速率。