New geological evidence of crustal thickening in the Gangdese block prior to the Indo-Asian collision

Recent mapping in the Gangdese block has revealed many leucogranites that are similar to those in the High Himalaya. These leucogranites formed at ～140 Ma as indicated by monazite Th-Pb ion-microprobe dating and cooled at ～130 Ma as indicated by muscovite ^40Ar/^39Ar dating. In conjunction with previous structural and paleogeographic studies, the new data indicate that the Gangdese block underwent crustal thickening and associated exhumation during ～140—130 Ma. In this regard, the southern margin of Eurasia continent was comparable to the modern South American Altiplano-Puna plateau, the prime example of active ocean-continent subduction and associated thickened crust. Specifically, the early stages of crustal thickening and uplifting of the Gangdese block may result from subduction of the Neo-Tethyan Ocean. If the Tibetan Plateau would form by accretion of a series of blocks with thickened crust, an elevated topographic plateau similar to the Altiplano-Puna plateau had formed before collision between the Indian and Eurasian plates. Then the Tibetan Plateau would have quickly thickened, uplifted, and begun to extend soon after onset of the collision. Thus, the deformational mechanism of the Tibetan Plateau is not distributed shortening, but rather concentrating deformation within regions of thin crust between the accreted blocks.     

Timing and history of marine hydrocarbon accumulation in Tarim craton

<正> Based on the analyses of hydrocarbon inclu-sions, K-Ar dating of authigenic illites and oil/gas-watercontact retrospection as well as other methods, the marineprimary reservoirs in the cratonic region of the Tarim Basinare found to have been formed in the late Caledonian toearly Hercynian, late Hercynian, and Himalayan, and oil andgas adjusted and redistributed in the Yanshanian (Jurassic toCretaceous) and Himalayan (Tertiary). The analyses alsoshow that the remaining primary oil accumulations aremostly formed in the late Hercynian, and the secondary oilreservoirs resulted from the adjustment and redistribution ofthe earlier accumulations during the Yanshanian and Hima-layan (especially late Himalayan), of which the Himalayan isalso the major stage of gas accumulation. The primary oilreservoirs formed in the late Hercynian mostly occur withinthe Paleozoic formation, whereas the secondary reservoirsformed in the Himalayan in the Mesozoic. The late adjust-ment and redistribution of reservoirs in the craton region ofthe Tarim Basin is ubiquitous because of the intensified tec-tonic movements since the Mesozoic, especially Cenozoic andintrusion of the high- to over-mature gas. Furthermore, thelower amplitude of reservoirs in the craton region also makesthem easier to be adjusted and redistributed. Therefore, theremaining paleo-uplift and palaeo-slope developed in rela-tively stable tectonic regions are the main potential areas forthe middle-large marine reservoirs in the Tarim Basin.     

早泥盆世古亚洲洋构造作用:来自可可托海和额济纳旗花岗岩年代学研究

古亚洲构造域内发育有大量的古生代酸性侵入岩。对阿尔泰造山带可可托海近3号脉的酸性侵入岩体进行LA-ICP-MS锆石U-Pb定年分析,以确定其岩浆作用时代及其岩浆活动的构造意义。研究区内的花岗岩包含的锆石大部分为自形-半自形晶,显示为典型的岩浆成因;测年结果发现,该岩体形成于404.4±3.2 Ma,为早泥盆世岩浆活动的产物。通过对额济纳辉森乌拉西糜棱岩化二长花岗岩中白云母⁴⁰Ar/³⁹Ar同位素年代学分析,获得白云母的坪年龄和等时线年龄分别为407.69±3.09 Ma和407.65±3.99 Ma,这暗示了拐子湖-呼和音乌苏弧形挤压带在早泥盆世活动的冷却年龄。以上事件与早泥盆世古亚洲洋的俯冲、碰撞的构造环境关系密切。     

Dating formation of natural gas pools using fluid inclusion data from reservoirs

A method has been suggested which is based on the homogenization temperatures and other data of fluid inclusions from a reservoir rock, with the combination of burial and geothermal history of the hosted rock, to date the gas reservoir formation. On the basis of this, a case study of the Carboniferous-Permiangas pools in the Ordos Basin has been conducted. The results have shown that the reservoir sandstones of the gas pool were filled by gases during 125-150 Ma, earlier in the southern area and later in the northern area, which is consistentwith the basin's geological and geochemical background under which the gas pools formed.     

U-Pb dating of detrital zircons from the Wudangshan Group in the South Qinling and its geological significance

U-Pb dating was made by the LA-ICP-MS method for detrital zircons from the Wudangshan volcanic-sedimentary succession in the South Qinling. Samples comprise quartz sandstones of the Wudangshan Group collected from the base of the Yangping Formation and an upper layer of the Shuangtai Formation overlain its volcanic sequence, and two river-sand collections from the drainage systems cutting across the two formations, respectively. The results show that the Yangping detrital zircons are dominated by 830–780 Ma grains with a minor population of ~1.0–0.84 Ga and sporadic grains of ~2.6, ~2.4 and 2.0 Ga, whereas the Shuangtai zircons yield an upper intercept age of 763±33 Ma, identical to the timing of the Wudangshan volcanism within error, with few concordant grains of 1.9 and 0.86 Ga. Age spectra for the two river-sand samples are similar to those of the Yangping and Shuangtai Formations, respectively. It thus suggests that the Wudangshan strata are less than 780 Ma, whereas their major detrital zircon populations of 1.0–0.85 Ga and 830–780 Ma are consistent with timing of the Hannan magmatic activities along the northwestern margin of the South China Block. This suggests a Hannan or adjacent area provenance for the Wudangshan strata. The Wudang area is characterized by rift-related igneous events at ~755 and ~680 Ma, respectively, pointing to a tectono- magmatic history different from the Hannan area. It is inferred that the ~755 Ma magmatism is likely to indicate a separation of the South China Block from the supercontinent Rodinia, while the ~680 Ma event suggests a further split between the South Qinling and some unknown continent.     

从文学和物理学到地球科学：漫谈时间*

笔者从文学、物理学、地球科学到地质年代学论及时间点和时间段的定年问题。同位素地质年代学定年起源于欧洲,已有近百年的历史相当成熟,但只能测定地质事件峰值（时间点）迄今的年龄;我们倡导的构造地质年代学速率法定年为近年的探索,可以直接测定地质事件过程（时间段）历经的年龄。同位素地质年代学定年与构造地质年代学定年两者相互补。     

Geochronology of the Hannan intrusive complex to adjoin the Qinling orogen and its rapid cooling reason

The geochronological works for the Hannan intrusive complex, cosisting of the gabbro-quartz dio-rite-plagiogranite bodies, in the north border of the Yangtze craton block, adjoining the Qinling orogen, are reported, because its age and genesis are of great importance to research of the tectonic evalutional history for the Qinling orogen and of the rifted processes for the Late Proterozoic supercontinent Rodinia. A good isochron of t=(837±26) Ma (2σ), corresponding to INd=0.51165±2(2σ), εNd(t)=+1.9, MSWD1.02, was difined by the Nd isotopic analytical results for the 21 whole-rock samples from the varied lithological complex bodies, but for the Rb-Sr isotopic aralytical data there is no isochron. The 40Ar/39Ar plateau age of the biotite, sorted from plagiogranites, is (796±20) Ma(2σ), and yet for the Rb-Sr isotopic data of the plagiogranite whole-rock samples (WR) and the sorted biotite (Bio), plagioclase (Plag) and apatite (Apt) mineral samples from the plagiogranitewhole-rock samples, an isochron of t=(824.86±3.8) Ma (2σ) with ISr=0.70393±14(2σ), MSWD2.44 is given. The U-Pb isotopic results for the single zircon, sorted from pla-giogranite samples, yielded an upper and a lower intercept ages of -876 Ma and -273 Ma. The Nd isotope data of complex indicate that it is probably the products of crystallization differentiation from the magma with 3333Nd>0 when the rapid uplift in 837-800 Ma took place in the northern border of the Yangtze craton block.     

Geologic relationships and geochronology of the Cenozoic volcanoes and interbedded weathered mantles of Yulinshan in Qiangtang, North Tibet

The Yulinshan accumulations of volcanic rocks and interbedded weathered mantles provide a unique chance for studying the processes and environment of the formation of the planation surface in central Tibetan Plateau. Geochemical,⁴⁰Ar/³⁹Ar and K/Ar geochronologic investigations of the weathered mantles and high-potassium volcanic rocks reveal that the volcano-weathered mantle accumulations formed under arid or semi-arid subtropic environment in 30–24 Ma. The sole planation surface of the Qiangtang region finally formed in about 20 Ma.     

Zircon U-Pb geochronology of basement metamorphic rocks in the Songliao Basin

Zircon LA-ICP MS U-Pb dating of six metamorphic rocks and a metagranite (breccia) from southern basement of the Songliao Basin are reported in order to constrain the formation ages of basement. The basement metamorphic rocks in the Songliao Basin mainly consist of metagabbro (L45-1), amphibolite (SN117), metarhyolitical tuff (G190), sericite (Ser) schist (N103), chlorite (Chl) schist (T5-1), biotite (Bi)-actinolite (Act)-quartz (Q) schist (Y205), and metagranite (L44-1). The cathodoluminesence (CL) images of the zircons from metagabbro (L45-1) and metagranite (L44-1) indicate that they have cores of magmatic origin and rims of metamorphic overgrowths. Their U-Pb isotopic ages are 1808±21 Ma and 1873±13 Ma, respectively. The zircons with oscillatory zoning from amphibolite (SN117) and Chl schist (T5-1), being similar to those of mafic igneous rocks, yield ages of 274 ± 3.4 Ma and 264 ± 3.2 Ma, re-spectively. The zircons from metarhyolitical tuff (G190) and Ser schist (N103) display typical magmatic growth zoning and yield ages of 424 ± 4.5 Ma and 287 ± 5.1Ma, respectively. Most of zircons from Bi-Act-Q schist (Y205) are round in shape and different in absorption degree in the CL images, implying their sedimentary detritals. U-Pb dating yield concordant ages of 427 ± 3.1Ma, 455 ± 12 Ma, 696 ± 13 Ma, 1384±62 Ma, 1649±36 Ma, 1778±18 Ma, 2450±9 Ma, 2579±10 Ma, 2793±4 Ma and 2953±14 Ma. The above-mentioned results indicate that the Precambrian crystalline basement (1808―1873 Ma) exists in the southern Songliao Basin and could be related to tectonic thrust, and that the Early Paleozoic (424―490 Ma) and Late Paleozoic magmatisms (264―292 Ma) also occur in the basin basement, which are consistent with the ages of the detrital zircons from Bi-Act-Q schist in the basement.