黑龙江省塔河绿林林场一带兴华渡口群岩石地球化学特征

黑龙江省塔河西北绿林林场一带原划分的兴华渡口群的岩石地球化学成分可与太古宙绿岩带对比,该区的兴华渡口群为低级地体（火山沉积盆地）,ＳｍＮｄ模式年龄及单阶段演化年龄为（１２５２±２８～１４６３±２０）Ｍａ。     

复合点坝构型样式分类方案及分布概率统计*

复合点坝储集层内部非均质性分析是曲流河研究的难点,仅靠地震和测井资料难以解释清楚。关于复合点坝储层构型表征也较缺乏定量化指导标准。本研究选取了13条曲流河河段的260个复合点坝作为数据样本,进行参数分类统计,形成曲流河复合点坝地质知识库。将复合点坝分为4大类、25个亚类;将侧积体分为8大类、22个亚类。统计不同类型复合点坝和侧积体构型样式的分布概率关系。以此为基础,充分利用定量分布概率关系,达到在资料较少情况下分析复合点坝储集层平面非均质性的目的。     

Differences in grain growth of calcite: a field-based modeling approach

Normal grain growth of calcite was investigated by combining grain size analysis of calcite across the contact aureole of the Adamello pluton, and grain growth modeling based on a thermal model of the surroundings of the pluton. In an unbiased model system, i.e., location dependent variations in temperature-time path, 2/3 and 1/3 of grain growth occurs during pro- and retrograde metamorphism at all locations, respectively. In contrast to this idealized situation, in the field example three groups can be distinguished, which are characterized by variations in their grain size versus temperature relationships: Group I occurs at low temperatures and the grain size remains constant because nano-scale second phase particles of organic origin inhibit grain growth in the calcite aggregates under these conditions. In the presence of an aqueous fluid, these second phases decay at a temperature of about 350 °C enabling the onset of grain growth in calcite. In the following growth period, fluid-enhanced group II and slower group III growth occurs. For group II a continuous and intense grain size increase with T is typical while the grain growth decreases with T for group III. None of the observed trends correlate with experimentally based grain growth kinetics, probably due to differences between nature and experiment which have not yet been investigated (e.g., porosity, second phases). Therefore, grain growth modeling was used to iteratively improve the correlation between measured and modeled grain sizes by optimizing activation energy (Q), pre-exponential factor (k₀) and grain size exponent (n). For n=2, Q of 350 kJ/mol, k₀ of 1.7×10²¹ mⁿs^–1 and Q of 35 kJ/mol, k₀ of 2.5×10^-5 mⁿs^–1 were obtained for group II and III, respectively. With respect to future work, field-data based grain growth modeling might be a promising tool for investigating the influences of secondary effects like porosity and second phases on grain growth in nature, and to unravel differences between nature and experiment.Editorial responsibility: J. Hoefs     

Cognate clinopyroxene from Paleogene mantle xenolith-bearing basanite lavas (East Serbia, SE Europe): the role of dissolution of mantle orthopyroxene

The study focuses on clinopyroxene from mantle xenolith-bearing East Serbian basanites and suggests that dissolution of mantle orthopyroxene played an important role in at least some stages of the crystallization of these alkaline magmas. Five compositional types of clinopyroxene are distinguished, some of them having different textural forms: megacrysts (Type-A), green/colourless-cored phenocrysts (Type-B), overgrowths and sieve-textured cores (Type-C), rims and matrix clinopyroxene (Type-D), and clinopyroxene from the reaction rims around orthopyroxene xenocrysts (Type-E). Type-A is high-Al diopside that probably crystallized at near-liquidus conditions either directly from the host basanite or from compositionally similar magmas in previous magmatic episodes. Type-B cores show high ^VIAl/^IVAl≥1 and low Mg# of mostly <75 and are interpreted as typical xenocrysts. Type-C, D and E are interpreted as typical cognate clinopyroxene. Type-D has Mg#<78, Al₂O₃?=?6–13?wt.%, TiO₂?=?1.5–4.5?wt.%, and Na₂O?=?0.4–0.8?wt.% and compositionally similar clinopyroxene is calculated by MELTS as a phase in equilibrium with the last 30?% of melt starting from the average host lava composition. Type-C has Mg#?=?72–89, Al₂O₃?=?4.5–9.5?wt.%, TiO₂?=?1–2.5?wt.%, Na₂O?=?0.35–1?wt.% and Cr₂O₃?=?0.1–1.5?wt.%. This clinopyroxene has some compositional similarities to Type-E occurring exclusively around mantle orthopyroxene. Cr/Al vs Al/Ti and Cr/Al vs Na/Ti plots revealed that Type-C clinopyroxene can crystallize from a mixture of the host basanite magma and 2–20?wt.% mantle orthopyroxene. Sieve-textured Type-C crystals show characteristics of experimentally produced skeletal clinopyroxene formed by orthopyroxene dissolution suggesting that crystallization of Type-C was both texturally and compositionally controlled by orthopyroxene breakdown. According to FeO/MgO^cpx/melt modelling the first clinopyroxene precipitating from the host basanite was Type-A (T?~?1250?°C, p?~?1.5?GPa). Dissolution of orthopyroxene produced decreasing FeO/MgO^melt and crystallization of Type-E and sieve-textured Type-C clinopyroxene (0.3–0.8?GPa and 1200–1050?°C). The melt composition gradually shifted towards higher FeO/MgO^melt ratios precipitating more evolved Type-C and Type-D approaching near-solidus conditions (<0.3?GPa; ~950?°C).     

Dauphiné twinning and texture memory in polycrystalline quartz. Part 3: texture memory during phase transformation

Samples of quartz-bearing rocks were heated above the α (trigonal)–β (hexagonal) phase transformation of quartz (625–950°C) to explore changes in preferred orientation patterns. Textures were measured both in situ and ex situ with neutron, synchrotron X-ray and electron backscatter diffraction. The trigonal–hexagonal phase transformation does not change the orientation of c- and a-axes, but positive and negative rhombs become equal in the hexagonal β-phase. In naturally deformed quartzites measured by neutron diffraction a perfect texture memory was observed, i.e. crystals returned to the same trigonal orientation they started from, with no evidence of twin boundaries. Samples measured by electron back-scattered diffraction on surfaces show considerable twinning and memory loss after the phase transformation. In experimentally deformed quartz rocks, where twinning was induced mechanically before heating, the orientation memory is lost. A mechanical model can explain the memory loss but so far it does not account for the persistence of the memory in quartzites. Stresses imposed by neighboring grains remain a likely cause of texture memory in this mineral with a very high elastic anisotropy. If stresses are imposed experimentally the internal stresses are released during the phase transformation and the material returns to its original state prior to deformation. Similarly, on surfaces there are no tractions and thus texture memory is partially lost.     

The formation of porphyry copper deposits

Copper is a moderately incompatible chalcophile element. Its behavior is strongly controlled by sulfides. The speciation of sulfur is controlled by oxygen fugacity. Therefore, porphyry Cu deposits are usually oxidized (with oxygen fugacities > ΔFMQ +2) (Mungall 2002; Sun et al. 2015). The problem is that while most of the magmas at convergent margins are highly oxidized, porphyry Cu deposits are very rare, suggesting that high oxygen fugacity alone is not sufficient. Partial melting of mantle peridotite even at very high oxygen fugacities forms arc magmas with initial Cu contents too low to form porphyry Cu deposits directly (Lee et al. 2012; Wilkinson 2013). Here we show that partial melting of subducted young oceanic slabs at high oxygen fugacity (>ΔFMQ +2) may form magmas with initial Cu contents up to >500 ppm, favorable for porphyry mineralization. Pre-enrichment of Cu through sulfide saturation and accumulation is not necessarily beneficial to porphyry Cu mineralization. In contrast, re-melting of porphyritic hydrothermal sulfide associated with iron oxides may have major contributions to porphyry deposits. Thick overriding continental crust reduces the “leakage” of hydrothermal fluids, thereby promoting porphyry mineralization. Nevertheless, it is also more difficult for ore forming fluids to penetrate the thick continental crust to reach the depths of 2–4 km where porphyry deposits form.     

A subsidiary fast-diffusing substitution mechanism of Al in forsterite investigated using diffusion experiments under controlled thermodynamic conditions

Diffusion of Al in synthetic forsterite was studied at atmospheric pressure from 1100 to 1500 °C in air along [100] with activities of SiO₂, MgO and Al₂O₃ (a_SiO2, a_MgO and a_Al2O3) buffered. At low a_SiO2, the buffer was forsterite + spinel + periclase (fo + sp + per) at all temperatures, while at high a_SiO2 and subsolidus conditions a variety of three-phase assemblages containing forsterite and two other phases from spinel, cordierite, protoenstatite or sapphirine were used at 1100–1350 °C. Experiments at high a_SiO2 and 1400 °C used forsterite + protoenstatite + melt (fo + en + melt), and at 1500 °C, fo + melt. The resulting diffusion profiles were analysed by LA–ICP–MS in scanning mode. Diffusion profiles in the high a_SiO2 experiments were generally several hundred microns in length, but diffusion at low a_SiO2 was three orders of magnitude slower than in high a_SiO2 experiments carried out at the same temperature, producing short profiles only a few microns in length and close to the spatial resolution of the analytical method. Interface concentrations of Al in the forsterite, obtained by extrapolating the diffusion profiles to the crystal/buffer interface, were only a fraction of those expected at equilibrium, and varied among the differing buffer assemblages according to (a_Al2O3)^1/2 and (a_SiO2)^3/4, pointing to the substitution of Al in forsterite by an octahedral-site, vacancy-coupled (OSVC) component with the stoichiometry Al _4/3 ³⁺ vac_2/3SiO₄, whereas the main substitution expected from previous equilibrium studies would be the coupled substitution of 2 Al for Mg + Si, giving the stoichiometry MgAl₂O₄. It is proposed that this latter substitution is not seen on the length scales of the present experiments because it requires replacement of Si by Al on tetrahedral sites, and is accordingly rate-limited by the slow diffusivity of Si. Instead, diffusion of Al by the OSVC mechanism is relatively fast, and at high a_SiO2, even faster than Fe–Mg interdiffusion.     

Maastrichtian Charophyte Flora from the Jiankou Section of the Jiaolai Basin

The latest Cretaceous strata of the Jiaolai Basin were studied in two scientific cores,including LK-1 drilled by the Institute of Geology,Chinese Academy of Geological Sciences(Li et al.,2018;Li et al.,2020),and JK-1 drilled by the Shandong Institute of the Geological Survey and Institute of Geology,Chinese Academy of Geological Sciences(Xu et al.,2017).However,outcrop sections were poorly studied,and the latest Cretaceous charophyte flora in particular had not previously been adequately documented from outcrops in the Jiaolai area.     

山东郭城牧牛山二长花岗岩的岩石成因:地球化学和锆石U—Pb年代学制约

山东胶莱盆地东北缘郭城牧牛山二长花岗岩的锆石LA--ICP--MS U--Pb年代学及岩石地球化学特征表明,牧牛山花岗岩为古元古代(2 138±15 Ma)岩浆侵入产物,是一套钾玄岩系列岩石,A/CNK为1.07~1.13。稀土配分曲线表现为右倾模式,轻稀土和重稀土分异明显,Eu/Eu*值为0.59~0.71。蛛网图表明明显富集大离子亲石元素(Rb、K),相对亏损高场强元素(Th、U、Nb、Ta、Ti、P)。岩石10 000 Ga/Al值(2.73~2.85),为A型花岗岩。岩石的Mg~#值为12~28,Nd/Th值为1.62~1.96,Rb/Sr值为4.70~9.71,显示壳源特征。综合分析认为,古元古代胶辽地块向西俯冲引发幔源岩浆底侵,导致地壳物质部分熔融形成牧牛山花岗岩。     

鄂尔多斯盆地及周缘地区下二叠统沉积特征*

通过大量的野外剖面观察和盆地内钻井岩心的详细描述,综合测井资料,从岩石类型、结构、沉积构造、古生物化石及测井曲线响应特征等方面对鄂尔多斯盆地及周缘地区下二叠统太原组和山西组沉积相特征进行了全面分析研究。结果表明,太原组主要发育陆棚、海岸、冲积扇和三角洲等沉积相,海岸沉积相包括障壁岛、潟湖和潮坪沉积,三角洲沉积相可划分为三角洲平原、三角洲前缘和前三角洲沉积。山西组主要发育冲积扇、河流、曲流河三角洲、湖泊和海岸沉积相,其中河流沉积相包括辫状河和曲流河沉积,曲流河三角洲沉积相可划分为曲流河三角洲平原、曲流河三角洲前缘和前三角洲沉积,而湖泊沉积相以浅湖沉积为主,海岸沉积主要为潟湖沉积。太原期,海相沉积占主导,主要分布于银川—榆林北部一线以南广大地区,并且从东西两侧至中部地区由浅海陆棚沉积和滨浅海过渡为潟湖沉积和潮坪沉积,其间发育障壁岛。盆地西北缘发育冲积扇和扇三角洲沉积,北部广大地区以三角洲沉积为主,自北向南依次为三角洲平原和三角洲前缘沉积。山西期,海水从盆地东南部退却,整体演变为海陆过渡相沉积,盆地北部乌达—杭锦旗—鄂尔多斯一线发育冲积扇沉积,向南至靖边一带依次发育辫状河和曲流河沉积,靖边以南至延安以北地区以三角洲平原沉积为主,向南至同心—庆阳一线发育三角洲前缘沉积,盆地南部彭阳—泾阳地区主要为浅湖沉积,再向南发育物源来自南部的三角洲沉积,在东南部武乡—义马一带为潟湖沉积。