华北克拉通南部地区现今地温场特征及其地质意义

在系统分析华北克拉通南部地区现今地温场数据的基础上,对该区现今地温场特征进行了系统的研究,对其控制因素及其油气地质意义进行了探讨。该区现今地温梯度平均为2.69℃/100m,大地热流平均为56.54mW/m2,地温场特征表现为北高南低,东高西低,与中国东部热盆、西部冷盆相比,华北克拉通南部地区属于一种过渡类型。现今地温场主要受岩石圈厚度、构造特征和地下水活动的影响。华北克拉通南部不同地区热演化过程及其结果不同,开封坳陷、周口坳陷中部局部凹陷带现今地温场代表了该区最高的热演化状态并影响着古生界烃源岩成烃。其他地区现今地温则小于古地温,古地温决定了这些区域古生界烃源岩成烃。

初论造山带古地理学

造山带古地理学属构造古地理学 ,是造山带地层学的姐妹学科 ,其核心是活动论构造观。简述了造山带古地理学的形成和内涵 ,重点讨论了地质记录已发生移位、歪曲和混杂的造山带地区 (或经造山作用改造的克拉通地区 )正确地进行构造—古地理重建的三个问题 :一是不能用“将今论古”的方法恢复地史期间的隆起区和堆积区 ,地史期间的物源区并非一成不变 ,要充分认识物源供应的多样性和多重性 ;二是沉积相带的展布受区域构造应力场及基底构造格局控制 ,要特别重视边缘相及其物源区的研究 ;三是辨析原生沉积盆地与构造盆地 ,对盆地进行正确的构造复位是古地理重建的基础。

Mantle olivine xenocrysts entrained in Mesozoic basalts from the North China craton: Implication for replacement process of lithospheric mantle

Mesozoic (125 Ma) Fangcheng basalts from Shandong Province contain clearly zoned olivines that are rare in terrestrial samples and provide first evidence for the replacement of lithospheric mantle from high-Mg peridotites to low-Mg per-idotites through peridotite-melt reaction.Zoned olivines have compositions in the core (Mg#=87.2—90.7) similar to those olivines from the mantle peridotitic xenoliths entrained in Ceno-zoic basalts from the North China craton and in the rim (Mg#=76.8—83.9) close to olivine henocrysts of the host basalts (75.7—79.0). These compositional features as well as rounded crystal shapes and smaller grain sizes (30—800 μm) demon-strate that these zoned olivines are mantle xenocrysts, i.e. disag-gregates of mantle peridotites. Their core compositions can represent those of olivines of mantle peridotites. The zoned texture of olivines was formed through rapid reaction between the olivine xenocryst and the host basalt. This olivine-basaltic melt reaction could have been ubiquitous in the Mesozoic lithospheric mantle beneath the North China craton, i.e. an important type of the replacement of lithospheric mantle. The reaction resulted in the transformation of the Paleozoic refractory (high-Mg) peridotites to the late Mesozoic fertile (Iow-Mg) and radiogenic isotope-enriched peridotites, leading to the loss of old lithospheric mantle.

Discovery of Late Paleozoic retrograded eclogites from the middle part of the northern margin of North China Craton

The retrograded eclogites have been discovered in the middle part of the northern margin of the North China Craton, which occur as lens or boudin within bio-tite-plagioclase gneisses in Paleoproterozoic Hongqiyingzi Group. The peak eclogite facies (P > 1.40—1.50 GPa, T = 680—730℃) mineral assemblage is composed of garnet, ompha-cite and rutile (±quartz), which was overprinted by the granulite facies mineral assemblage of vermicular symplec-tite of sodic clinopyroxene and plagioclase which replaced the precursory omphacite, and then amphibolite facies ret-rograded minerals with characterization of Amp+Pl ke-lyphitic rim and symplectite, and amphibole replaced clino-pyroxene. The protolith of retrograded eclogites is oceanic basalt formed at 438±11 Ma.The peak eclogite facies meta-morphic age of the retrograded eclogite is 325±4 Ma. These relict eclogites may be formed by the subduction of Pa-leo-Asian oceanic crust beneath the North China Craton during Late Paleozoic. The discovery of relict eclogite in this paper provides a new insight into farther understanding of tectonic evolution of the northern margin of the North China Craton, and the relationship between the Paleo-Asian Ocean and the North China Craton.

Geochemical characteristics and petrogenesis of Mesozoic basalts from the North China Craton: A case study in Fuxin, Liaoning Province

Occurrence of Cretaceous basalts in Fuxin County, Liaoning Province provides us an opportunity to understand Mesozoic mantle processes beneath the northern margin of the North China Craton (NNCC). Fuxin Jianguo basalts occur as volcanic channel phases with well-developed columnar jointings and contain few spinel lherzolite and pyroxenite xenoliths. They are poor in silica and rich in alkalis, Ti and Al, belonging to alkaline basalts. In trace element compositions, Jianguo basalts are moderately enriched in LREE and LILE, but not depleted in HFSE. They have low Sr and high Nd and Pb isotopic ratios. These geochemical characteristics suggest that Jianguo basalts originated from the depleted asthenosphere, representing an undifferentiated and uncontaminated primitive magma. Presence of these basalts indicates that the lithosphere beneath the region had thickness less than 65 km at the time of basalt eruption and was mainly composed of fertile pargasite-bearing spinel lherzolite and plagioclase pyroxenite. The voluminous basaltic-andesitic magmatism during the early Jurassic-late Cretaceous time indicates that the commencement and accomplishment of lithosphere thinning in the NNCC was much earlier than that in the southern margin, since the mafic-intermediate volcanism only occurred at the Cretaceous time in the southern margin and the basalts with an asthenosphere isotopic signature at the Tertiary. This shows that highly spatial and temporal heterogeneity existed in the Mesozoic lithosphere evolution.

Layering of subcontinental lithospheric mantle

Recent seismic studies reveal a sharp velocity drop mostly at^70–100 km depth within the thick mantle keel beneath cratons, termed the mid-lithosphere discontinuity(MLD). The common presence of the MLD in cratonic regions indicates structural and property layering of the subcontinental lithospheric mantle(SCLM). The nature and origin of the MLD, and many issues associated with the layering of the SCLM are essential to understand the formation and evolution of continents, and have become frontier subjects in the Earth sciences.

地下温度是成熟盆地的勘探钥匙：热背斜——油气发现的关键

美国中陆地区和其它克拉通地区均存在与产油构造伴生的温度异常，可以有效地用作成熟油气区的勘探钥匙，因此热背斜的概念对油气发现十分关键。通过对过去几十年积累资料的分析，可以了解热背斜问题的实质。Roberts的温度差模型和Walters的流体流动规则可以解释油气运移和圈集的一种机理。如果Roberts模型确实有效，那么浅层较高的温度、温度梯度或热流就有可能指示深部的油气聚集。