湖北蕲春烈马咀花岗岩成因及与钼成矿的关系

湖北蕲春烈马咀钼矿位于大别山南坡,已探明的大型钼矿鲜有报道,对该矿区的深入研究甚少,缺少对成岩成矿时代、成因和构造背景的准确厘定。对烈马咀钼矿及与成矿有关的花岗岩进行了岩相学、岩石地球化学研究和Re−Os同位素测年。结果表明:与成矿有关的岩石为斑状二长花岗岩或二长花岗斑岩,矿区成矿规模小,矿石为浸染状或细脉浸染状展布;辉钼矿等时线年龄为119±8 Ma,年龄加权平均值为118.9±0.98 Ma,指示烈马咀钼矿为早白垩世热液产物;岩石地球化学数据表明其为高硅、高钾钙碱性系列A型花岗岩;稀土元素的总含量高,轻稀土元素含量相对富集,重稀土元素含量相对亏损。烈马咀钼矿区与成矿有关的岩石形成于大别造山带伸展环境,与燕山晚期岩石圈减薄有关。

基于HSB颜色空间的南红玛瑙颜色特征及定量分级研究

近些年,南红玛瑙在珠宝市场上,价格不断上升。颜色作为影响南红玛瑙质量评价的最主要因素,南红玛瑙市场价格的高低与其密切相关,但目前国家尚未出台南红玛瑙相关的分级标准。为了使南红玛瑙颜色的评定过程更加客观、科学和规范,开展了南红玛瑙颜色分级的相关研究。利用灯箱和相机获取样品颜色图片,基于HSB颜色空间,对采集到的南红玛瑙颜色图片进行颜色量化。利用Origin和SPSS软件,对所得颜色量化数据的色调、饱和度和明度(HSB)参数进行统计分析。结果表明,在95%置信区间内红色系南红玛瑙的色调(H)主要分布于[3.20°,17.52°]区间内;饱和度(S)主要分布在[63.82%,92.69%]区间内;明度(B)主要分布在[42.97%,75.37%]区间内,统计结果与南红玛瑙颜色的肉眼观察特征一致。结合肉眼观察特征,借助二阶聚类分析,对红色系南红玛瑙的颜色分级进行了尝试:将色调分为红(R)、橙红(oR)、红橙(rO)3个类别;将饱和度分为浓(S1)、中(S2)、浅(S3)3级;将明度分为亮(B1)、中(B2)、暗(B3)3个级别。对于不同颜色品种,在饱和度方面,柿子红、水红、锦红大于其他品种,冰红和玫瑰红为中等,冰粉的为最低;在明度方面,冰橘和水红最高,柿子红、冰红和冰粉中等,锦红和玫瑰红最低。以上述数据分布特征为基础,结合颜色分级结果,对市场中出现的南红玛瑙的不同颜色名称进行科学的区分并给出推荐的HSB数值参考范围。

广西中更新世喀斯特洞穴堆积物矿物与元素组成特征及其古气候环境意义

通过对广西感仙洞洞穴堆积物粘土矿物和元素丰度的分析,探讨了其垂向变化的古气候环境意义。结果表明,根据粘土矿物组成变化大致可将洞穴堆积物划分为以较高含量蛭石为特征的无分层的上部层段、以高岭石含量较高为特征且有较明显分层的下部层段以及底部砾石段。堆积物元素丰度存在剖面变化,但微量元素和稀土元素配分模式显示洞穴堆积物(除砾石层外)物源基本一致。堆积物化学蚀变指数垂向变化不大,平均值为95.56,显示物源区风化强烈。总体来看该洞穴堆积物代表了古老基地形成的风化壳经侵蚀并在洞穴中再堆积的产物,这些堆积物主要形成于3个时间段,即700 ka底部砾石沉积阶段、700—500 ka间多期次堆积阶段和500—150 ka间快速堆积阶段。最后,粘土矿物与元素含量垂向变化不同步应与物源区剥蚀再堆积及洞穴风化淋滤等有关。

Clay Mineralogy and its Paleoclimatic Significance of the OligoceneMiocene Sediments in the Gerze Basin, Tibet

This study collected the early Oligocene to middle Miocene sediments from the Gerze Basin of Tibet, and used X-Ray diffraction （XRD） and Scanning Electron Microscope （SEM） to discuss their clay mineralolgy, clay indices, better understand the clay mineralogy and its paleoclimatic significance. The results show that clay minerals of the Gerze Basin sediments are mainly composed of iilite and chlorite, with minor amounts of smectite and kaolinite, and their relative content varies along the section. Variations of relative contents and clay indices suggest that the Gerze Basin has experienced three-stage evolution of paleoclimate： I ） high ilUte and chlorite contents, with fluctuant smectite and low （I＋Ch）/（K＋S） ratio, indicative of a dominant seasonal arid climate from the early Oligoeene to late Oligocene; Ⅱ） higher illite and chlorite contents and larger （I＋Ch）/（K＋S） ratio but absence of kaolinite, indicating a colder and drier climate from the late Oligocene to early Miocene; Ⅲ） high iilite and chlorite contents with fluctuant （I＋Ch）/（K＋S） ratios and occasional occurrence of kaolinite, suggesting that the climate became warmer and more humid compared with that of stage Ⅱ in the mid-Miocene. These conclusions were also reinforced by the clay morphology, which suggests that physical weathering dominated in stage Ⅱ, while relatively strong chemical weathering was dominant in stages Ⅰ and Ⅲ Clay minerals of the sediments mainly consist of illite and chlorite, indicating that the source rock played a significant role in clay origin. It is inferred that global cooling and the enhancement of denudation and obstruction of northward moisture due to the uplift of the Qinghai-Tibet Plateau were responsible for the provenance of iUite and chlorite under weak chemical weathering. Though the Qinghai-Tibet Plateau reached a certain elevation by the mid-Miocene, yet the mid-Miocene widespread warming might have largely impacted the Gerze climate.

Illite-smectite Mixed-layer Minerals in the Alteration Volcanic Ashes under Submarine Environment

The clay mineralogy of the clay intervals interbedded with siliceous mudstones across the Permian-Triassic boundary (PTB) in Pengda, Guiyang, Guizhou province, was investigated by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). The clay mineral assemblages of the sediments are mainly I/S clays and minor smectite, kaolinite, and illite as reveled by XRD analyses. The peak-shape parameters BB1 and BB2 of I/S clays of the representative clay bed PL-01 are 4.7° and 4.4°, and the peak position of the low angle reflection is at 6.8° 2θ (13.6 ), suggesting that the I/S clays has a IS type of ordering. However, the presence of multi-order reflections and their intensities are different from those of completely ordered 1∶1 mixed-layer I/S clay rectorite, indicating that I/S clays of the Pengda section have partially ordered IS structures. HRTEM observations show that most of the I/S clays exhibit an IS stacking ordering. However, in some areas within a IS particle, smectite layer is observed in doublets, triplets, and quartets, which are interstratified by various amounts of illite layers, suggesting the presence of other irregular stacking in addition to the major 1∶1 IS ordered stacking. Transformation of smectite layer into illite layers is also observed in the I/S clays, suggesting that the Pengda I/S clays are derived from smectite illitization, in good agreement with the clay mineral assemblage. The I/S clays of the Pengda section contain up to 45% to 95% smectite layer, the notably higher contents of smectite layer relative to those of other PTB stratigraphic sets in south China can be attributed to difference in alteration and smectite illitization processes due to different sedimentary environments.

Relations Between Paleoclimatological Conditions and Mineralogical Characteristics of Clays in Miocene Sediments at Linxia Basin, China

Linxia Basin is a late Cenozoic fault-block basin along the border between the Tibet plateau and the Loess plateau in Northwestern China. Its formation and sediments record may be directly affected by the structural dynamics and the uplift of the Tibet Plateau. For this reason, we studied the mineral characteristics of the Maogou formation of Miocene sediments using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD results showed that quartz, chlorite, illite, calcite, plagioclase, orthoclase, kaolinite, and trace palygorskite are present throughout the sequence of the cross-section in Linxia basin. In contrast, gypsum and ankerite occur occasionally in the upper portion of the Miocene deposits. The content of calcite varied with layers in the profile and was relatively concentrated in mudstone. Chlorite and illite were observed transforming into palygorskite under SEM observation. Based on the mineral characteristics and the change of mineral composition, especially the clay minerals, it could be inferred that an arid environment prevailed in the region with warm and cold intervals during Miocene time.

Cenozoic sedimentary records and geochronological constraints of differential uplift of the Qinghai-Tibet Plateau

Geological mapping data (1:250000) in the Qinghai-Tibet Plateau and its adjacent regions reveal the sediment sequences, distribution and tectonic evolution of the 92 Tertiary remnant basins. Southern Tibet and the Yecheng area in Xinjiang, located at southern and northwestern margins of the Qinghai-Tibet Plateau, respectively, were parts of the Neo-Tethys remnant sea in the Paleogene. In southern Tibet, both the subabyssal and abyssal sequences occur at the Gyangze, Saga, Guoyala, and Sangmai areas. The deep-water facies successions outcrop in the west, whereas the shallow-water facies sequences in the east, indicating the east to the west retreat of the Neo-Tethys Ocean. The retreat of the Neo-Tethys Ocean in the east was contributed to the earlier tectonic uplift of the eastern Qinghai-Tibet Plateau. The uplift process of the Plateau from the Late Cretaceous to Pliocene is described as follows: During the Late Cretaceous, tectonic uplift of the Qinghai-Tibet Plateau occurred in the northeastern part and the configuration of the Qinghai-Tibet Plateau was characterized by rise in the northeast and depression in the west. In the Paleocene-Eocene interval, the Tengchong-Baingoin and Kuyake-Golmud areas experienced local tectonic uplifting, the West Kunlun uplift zone broadened easterly, the Qilian uplift zone broadened southerly, and the Songpan-Garzê uplift zone shrank easterly. The Oligocene configuration of the Qinghai-Tibet Plateau was characterized by mountain chains rising along its margins and sedimentary basins in the central part because of tectonic uplifts of the Gangdisê and the Himalaya blocks. Meanwhile, the Kunlun-Altyn-Qilian uplift zones have also broadened southerly and northerly. In contrast, the great uplift zones of the Gangdisê, the Himalaya, the Karakorum, and the Kunlun blocks characterize the paleogeographic contours of the Qinghai-Tibet Plateau during the Miocene-Pliocene. Additionally, the thermochronological data on tectonic uplift events in southern Tibet, West Kunlun Mountains, Altyn Tagh, eastern Tibet, and western Sichuan all suggest that the most intense deformation occurred at 13-8 Ma and since 5 Ma, respectively, corresponding to two great uplift periods in Neogene. As a result, turnover of paleogeographic configuration of the Qinghai-Tibet Plateau occurred during the Neogene, experiencing a change from high contours in the east in the pre-Oligocene to high contours in the west at the end-Pliocene. The uplift of the Qinghai-Tibet Plateau during the Cenozoic was episodic, and the uplifts of various blocks within the Plateau were spatially and chronologically different.