Zircon U–Pb geochronology and geochemistry of the Maoliger quartz monzodiorites,Inner Mongolia,China: implications for Carboniferous arc magmatism and closure of the Palaeo-Asian Ocean

Recent research has identified an early to late Carboniferous magmatic arc that extends from Suzuo Qi to Xiwu Qi in Inner Mongolia, China, but the eastern extension of this arc is unknown. Understanding the relationship between this arc and the Hegenshan ophiolite belt and Xilamulun Solonker suture zone is important to our understanding of the tectonic evolution of the late Palaeozoic Palaeo-Asian Ocean. Here, we present new zircon laser ablation–inductively coupled plasma mass spectrometry U–Pb and geochemical data for the Maoliger quartz monzodiorites within the Jalaid Qi area. The Maoliger quartz monzodiorites formed at 329 ± 2 Ma, are low-K and tholeiitic, and have geochemical signatures indicative of formation within a magmatic arc. These rocks are large-ion lithophile element (e.g. Rb, Ba, and Sr)-enriched and high-field-strength element (e.g. Nb and Ta)-depleted. Combined with previously published researches, it is suggested that the quartz monzodiorites within the Jalaid Qi area formed contemporaneously with and are geochemically similar to quartz diorites of the Xiwu Qi area and the Baolidao pluton in the Suzuo Qi area. This indicates that the early to late Carboniferous magmatic arc in this region extends eastward to the Jalaid Qi area. This arc is located in an area parallel to a southerly early Permian magmatic arc, suggesting that the Palaeo-Asian Ocean subduction zone migrated south between the early Carboniferous and early Permian. The new data show that the Palaeo-Asian Ocean closed after the late Carboniferous.     

Deciphering the geochronology of a large granitoid pluton (Karkonosze Granite,SW Poland): an assessment of U–Pb zircon SIMS and Rb–Sr whole-rock dates relative to U–Pb zircon CA-ID-TIMS

Granitoid plutons are often difficult to radiometrically date precisely due to the possible effects of protracted and complex magmatic evolution, crustal inheritance, and/or partial re-setting of radiogenic clocks. However, apart from natural/geological issues, methodological and analytical problems may also contribute to blurring geochronological data. This may be exemplified by the Variscan Karkonosze Pluton (SW Poland). High-precision chemical abrasion (CA) ID-TIMS zircon data indicate that the two main rock types, porphyritic and equigranular, of this igneous body were both emplaced at ca. 312 Ma, while field evidence points to a younger age for the latter. This is in contrast to the earlier reported SIMS (SHRIMP) zircon dates that scattered mainly between ca. 322 and 302 Ma. In an attempt to overcome this dispersion, at least in part caused by radiogenic lead loss, the CA technique was used before SHRIMP analysis. The ²⁰⁶Pb/²³⁸U age obtained in this way from a sample of porphyritic granite is 322 ± 3 Ma, ~16 Ma older than the untreated zircons; another porphyritic sample yielded a mean age of 319 ± 3 Ma, and the mean age was 318 ± 4 Ma for an equigranular granite sample – all three somewhat older than the age obtained by ID-TIMS. Older SIMS dates of ca. 318–322 Ma might indicate either faint inheritance or that zircon domains crystallized during earlier stages of Karkonosze igneous evolution. The ID-TIMS results have been used to re-assess the whole-rock Rb–Sr data. Excluding a porphyritic granite with excess radiogenic ⁸⁷Sr, it appears that isotopic homogeneity was achieved for most samples during the 312 Ma event, as shown by a pooled 21-point isochron with an age of 311 ± 3 Ma and an initial ⁸⁶Sr/⁸⁶Sr of 0.7067 ± 4. Local crustal contamination by stopping of metapelitic material might account for the more radiogenic Sr isotope signature observed in biotite-rich schlieren. A critical re-evaluation of all available SHRIMP data using the ID-TIMS age of 312 Ma as a benchmark suggests that the observed scatter may be partly attributed to analytical and methodological problems, in particular failing to distinguish subtly discordant spots from truly concordant ones, which is a serious limitation of the microbeam analytical approach. Other likely pitfalls contributing to geochronological scatter are identified in the published Re–Os ages on molybdenite and the ⁴⁰Ar/³⁹Ar data on micas. A scenario postulating a 15–20 milliion year evolution of the Karkonosze Pluton cannot be established on the basis of available geochronological data, which rather supports a brief igneous event, although a more protracted pre-emplacement evolution is possible. A short timescale for crystallization of large igneous bodies, as suggested by the ID-TIMS data from the Karkonosze Granite, is in line with models of transport of granitic magmas through dikes to form large plutons.     

Gold Deposits in the Sanandaj–Sirjan Zone: Orogenic Gold Deposits or Intrusion‐Related Gold Systems?

Most of the known large gold deposits in Iran are located along the Sanandaj–Sirjan Zone, western Iran, which hosts a wide range of gold deposit types. Gold deposits in the belt, hosted in upper Paleozoic to upper Mesozoic volcano‐sedimentary sequences of lower greenschist to lower amphibolite metamorphic grade, appear to represent mainly orogenic and intrusion‐related gold deposit types. The largest resource occurs at Muteh, with smaller deposits/occurrences at Zartorosht, Qolqoleh, Kervian, Qabaqloujeh, Kharapeh, and Astaneh. Although a major part of the gold deposits in the Sanandaj–Sirjan Zone are related to metamorphic devolatilization, some deposits including Muteh and Astaneh are related to short‐lived disruptions in an extensional tectonic regime and are associated with magma generation and emplacement. The age of gold ore formation in the orogenic gold deposits is Late Cretaceous to Tertiary, reflecting peak‐metamorphism during regional Cretaceous–Paleocene convergence and compression. The Oligocene to Pliocene age of most intrusion‐related gold systems is consistent with the young structural setting of the gold ore bodies; these deposits are sequestered along normal faults, correlated with Middle to Late Tertiary extensional tectonic events. This relationship is comparable to the magmatic‐metallogenetic evolution of the Urumieh‐Dokhtar magmatic arc, where the number of different types of gold‐copper deposits and the magnitude of the larger ones followed development of a magmatic arc. The appropriate explanation may be related to two different stages of gold mineralization consisting of a first compressional phase during the Late Cretaceous to Early‐Middle Tertiary, which is related to orogenic gold mineralization in the Qolqoleh, Kervian, Qabaqloujeh, Kharapeh, and Zartorosht deposits, and the extensional phase during the Eocene to Pliocene that is recognized by young intrusion‐related gold mineralization in the Muteh and Astaneh deposits.     

滇西大理至瑞丽铁路沿线地温场特征及其 工程地质意义

在整理、分析云南大理至瑞丽拟建铁路沿线及其邻区现今地温场分布特征的基础上,进一步总结前人的资料,综合研究、探讨了该区地温场与岩浆活动、活动构造、地震活动、区域深部构造的关系。结果表明,该区中高温温泉（中高地温场）的空间分布与地表岩浆岩的出露、地表主要活动断裂带的分布都具有较好的对应关系。综合研究后认为,该区的中高温温泉可归结为岩浆热源型、断裂深循环型和岩浆热源叠加断裂深循环作用型3种基本成因类型。同时还发现,该区的温泉分布与区域地震活动空间上也存在密切的关系,并据此将区内划分为4个地震区带。研究结果表明,本区地表温泉分布所反映出的地温场特征对本区的工程稳定性评价具有重要的指示意义。     

全球地表覆盖高分辨率遥感制图

全球地表覆盖分布及变化是气候变化研究、生态环境评估、地理国情监测、宏观调控分析等不可或缺的重要基础信息。国际上现有全球五套地表覆盖数据产品的空间分辨率为1km或300m,数据精度、分类体系、时空分辨率等均存在不足。为了满足全球变化研究与地球模式模拟的需求,应该研制具有较高时空分辨率、更符合全球变化需要、精度较好的全球地表覆盖数据产品。本文简要介绍了全球地表覆盖遥感制图的情况和数据产品的不足,讨论了对新一代地表覆盖数据产品的需求,介绍了我国研制全球30m地表覆盖数据产品的863重点项目。     

浅谈厦门市大比例尺数字栅格地图的生产方法

为了满足厦门市城市规划、设计和建设的需要,2009年厦门市国土资源与房产管理局组织实施了厦门市1∶2000比例尺地形图测绘及空间数据库建设Ⅱ期项目。该项目涵盖了多坐标系、多比例尺、多类别的共计17种产品。本文主要就厦门市1∶2000比例尺数字栅格图的生产方法做一些技术上的探讨。     

测绘产品质量管理

首先简要论述了测绘产品质量的重要性,提出了测绘产品质量管理的要求,然后结合工作中的实际情况,详细阐述了加强测绘产品质量管理的一些方法与措施。     

厦门市基础测绘后续产品关键技术探讨

介绍了在厦门市全要素1∶500数字地形图基础测绘的基础上进行后续产品生产,经过必要的数据处理,完成数字高程模型、路网数据、地理要素、地理对象等专题信息的制作,实现一图多用,充分提高了地形图的使用效率,提高了基础测绘成果的经济价值和社会价值。     

利用MODIS/LST产品分析基准气候站环境代表性

该文基于2001-2007年地表温度遥感反演产品(MOD11A2),以基准气候站对其周围不同大小窗口内地表温度距平序列的解释方差作为度量,评估了我国142个基准气候站的环境代表性,并将代表性与土地覆盖和高程状况进行相关研究.结果显示:以解释方差大于0.75作为区分是否具有代表性的阈值,约41%的站点代表性较好,代表区域范围可超过51×51 km2,多分布于北方地区;约21%的站点代表性较差,代表区域范围不足7×7 km2,多分布于南方地区;其他代表区域范围居中的站点在南、北方均有分布;站点周围的土地覆盖多样性和地形起伏度与站点代表性存在负相关,且相关性随窗口的增大而加强.文中还评估了基准气候站对所属气候区的代表性,发现在气候特征复杂的西南地区和新疆部分地区,站点对气候区的代表性较差.     

利用MODIS/LST产品分析基准气候站环境代表性

该文基于2001—2007年地表温度遥感反演产品 (MOD11A2),以基准气候站对其周围不同大小窗口内地表温度距平序列的解释方差作为度量,评估了我国142个基准气候站的环境代表性,并将代表性与土地覆盖和高程状况进行相关研究。结果显示:以解释方差大于0.75作为区分是否具有代表性的阈值,约41%的站点代表性较好,代表区域范围可超过51×51 km2,多分布于北方地区;约21%的站点代表性较差,代表区域范围不足7×7 km2,多分布于南方地区;其他代表区域范围居中的站点在南、北方均有分布;站点周围的土地覆盖多样性和地形起伏度与站点代表性存在负相关,且相关性随窗口的增大而加强。文中还评估了基准气候站对所属气候区的代表性,发现在气候特征复杂的西南地区和新疆部分地区,站点对气候区的代表性较差。