Large amounts of magnesite, talc and brucite deposits are hosted within Paleoproterozoic magnesium carbonate formations on the Liaodong Peninsula, northeast China. To clarify the genetic relationships of these Mg-rich nonmetallic ore deposits, this study reviewed existing geological, geochemical and isotopic data of magnesite and talc deposits, and supplemented geochemical and magnesium isotope analyses on brucite deposit. The Veitsch-type magnesite deposits on the Liaodong Peninsula occur as stratabound monoclinal orebodies within the Dashiqiao Formation and exhibit inherited marine stable isotopic characteristics (delta Mg-26: between -1.53 parts per thousand and -0.49 parts per thousand; delta C-13: between -2.7 parts per thousand and + 1.6 parts per thousand). The talc ore bodies are clearly controlled by regional folds and fault structures formed during the Lvliangian movement(1.9 Ga similar to 1.8 Ga). Interlayer faults are the most favorable sites for the formation of talc ore bodies, which result from reactions between metamorphic-related siliceous hydrothermal fluids and dolomitic magnesite, whose magnesium isotopic composition (delta Mg-26: between -0.48 parts per thousand and + 1.06 parts per thousand) no longer reflects marine geochemical characteristics. Brucite ore bodies occur as lenticular forms within carbonate strata in skarn-type external contact zones of granitic rocks that formed during the Phanerozoic era. These ore bodies are formed through the heating of atmospheric precipitation by magmatic bodies that subsequently reacts with carbonate rocks, and they still retain a marine-like REE distribution pattern and magnesium isotope characteristics (range from -1.33 parts per thousand to -1.13 parts per thousand). Therefore, the nonmetallic magnesite, talc, and brucite deposits belong to a typical metallogenic series of Paleoproterozoic magnesium carbonate formations, which formed via metamorphic recrystallization, siliceous hydrothermal metasomatism, and late magmatic-hydrothermal mineralization, respectively.

Granitic gneisses have been widely observed from gneiss domes within the Tethyan Himalaya Sequence and from the Higher Himalayan Crystalline, but whether these granitic gneisses were involved in crustal anatexis is not well constrained. In this paper, sensitive high resolution ion micro-probe (SHRIMP) zircon U-Pb and Sr-Nd isotopic analysis and geochemical studies were performed on granitic gneiss and muscovite granite from the Gurla Mandhata dome to investigate the potential of granitic gneiss to have participated in the crustal anatexis of the Himalayan orogen. Zircon U-Pb dating of the granitic gneiss reveals Proterozoic cores and oscillatory zoning rims with concordant 206Pb/238U ages of 483.7 +/- 4.8 Ma, which indicate an Early Palaeozoic magmatism event. Zircon U-Pb dating of the muscovite granite reveals Proterozoic cores, oscillatory zoning mantles with 206Pb/238U ages of 466.8 +/- 5.0 Ma. The zircon rims of muscovite granite yield a weighted mean age of 16.0 +/- 0.2 Ma, representing the time of the anatectic event. The Sr-Nd isotopic compositions and geochemical data of the muscovite granite indicate that the muscovite granite may have been derived from fluid-fluxed melting of muscovite from the Higher Himalayan Crystalline (including metasedimentary rocks and granitic gneisses). Thus, we believe that the Early Palaeozoic granitic gneiss participated in the crustal anatexis of the Himalayan orogen.

Lacustrine strata-bound magnesite deposits associated with Alpine-type ultramafic rocks are hydrothermal in origin. The magnesite ores of the Kamado deposit are unconformably underlain by mid-Jurassic marine carbonate and ultramafic rocks of the Bangong-Nujiang ophiolite suite and are in fault contact with hanging wall rocks composed of siliceous sinter. Three types of cryptocrystalline magnesite ores can be identified in Kamado: (1) strata-bound massive magnesites, representing the main ore type in the upper part; (2) banded ores in the lower part; and (3) some vein and stockwork ore in the ultramafic wall rocks. Integrated scanning electron microscopy, C–O isotope analysis, and geochemical analyses were carried out on the Kamado deposit. The results indicate that: (1) the orebody is composed of magnesite, with accessory minerals of aragonite, opal, and chromite; (2) the siliceous sinter and relatively high B (32.0–68.1 ppm) and Li (14.7–23.4 ppm) contents of the magnesite ores reflect long-term spring activity in Kamado; (3) the light carbon (δ13CV-PDB: −4.7 ± 0.3‰ to −4.1 ± 0.6‰) and oxygen isotopic compositions (δ18OV-SMOW: +12.3 ± 0.3 to +16.3 ± 0.1‰) of the stockwork ores in the foot wall rocks indicated that the carbon in fractures in the ultramafic rocks is from a mixture of marine carbonate and oxidized organic-rich sedimentary rocks, reflecting a typical “Kraubath-type” magnesite deposit; and (4) the relatively heavy carbon isotopic (δ13CV-PDB: +8.7 ± 0.4‰ to +8.8 ± 0.3‰) composition of the banded magnesite ores in the lower segment may have formed from heavy CO2 generated by anaerobic fermentation in the lakebed. Additionally, the carbon isotopic (δ13CV-PDB: +7.3 ± 0.3‰ to +7.7 ± 0.7‰) composition of the massive magnesite ores in the upper segment indicates a decline in the participation of anaerobic fermentation. As this economically valuable deposit is of the strata-bound massive ore type, Kamado can be classified as a lacustrine hydrothermal-sedimentary magnesite deposit, formed by continuous spring activities under salt lakes on the Tibetan Plateau, with the Mg mainly being contributed by nearby ultramafic rocks and the carbon mainly being sourced from atmosphere-lake water exchange, with minor amounts from marine carbonate strata.

The large magma reservoirs underlying world-class porphyry deposits are one of the key factors in their formation, which thus led to the present study focusing on the unmineralized intrusive rocks underlying the porphyry molybdenum-copper orebody of the post-collisional Jiama porphyry-skarn copper-polymetallic deposit in southern Tibet. The Jiama porphyry intrusion comprises intermediate-silica quartz diorite, monzogranite, and granodiorite porphyries, as well a high-silica granite porphyry. The intrusive rocks suite exhibits similar whole-rock Sr-Nd isotopic compositions [εNd(t) = −3.9 to −0.8], suggesting a common, non-radiogenic magma source. Yet, these rocks have distinct geochemical characteristics. The intermediate-silica rocks are relatively enriched in Ba and Sr with minor Eu anomalies, and show adakite-like geochemical characteristics. In contrast, the high-silica granite porphyry is strongly depleted in Ba, Sr, and Eu, and lacks adakite-like geochemical characteristics. We propose that the high-silica granite porphyry represents highly fractionated melt extracted from a silicic mush reservoir (crystallinity of ∼40%−65%), and that the monzogranite and granodiorite porphyries constitute the complementary residual silicic cumulates. High crystallinity facilitates the formation of connected fluid pathways, allowing the efficient removal of volatiles from the remaining silicic melt and a rapid flux of the ore-forming fluids toward the apical parts of the large magma reservoir. Less-evolved mafic melt is believed to have repeatedly intruded the base of the magma reservoir, thereby releasing volatiles and water into the silicic mush systems. The volatiles migrated upward through the fluid channels and accumulated in the apical part of the magma reservoir, subsequently, as a result of the overpressure in the roof zone, ore-forming fluids and successive batches of magma were expelled together, thereby forming the Jiama porphyry-skarn deposit.

Landslides seriously threaten human life and property. The rapid and accurate prediction of landslide geological hazard susceptibility is the key to disaster prevention and mitigation. Traditional landslide susceptibility evaluation methods have disadvantages in terms of factor classification and subjective weight determination. Based on this, this paper uses a random forest model built using Python language to predict the landslide susceptibility of Muli County in western Sichuan and outputs the factor weight and model accuracy. The results show that (1) the three most important factors are elevation, distance from the road, and average annual rainfall, and the sum of their weights is 67.54%; (2) the model’s performance is good, with ACC = 99.43%, precision = 99.3%, recall = 99.48%, and F1 = 99.39%; (3) the landslide development and susceptibility zoning factors are basically the same. Therefore, this model can effectively and accurately evaluate regional landslide susceptibility. However, there are some limitations: (1) the landslide information statistical table is incomplete; (2) there are demanding requirements in terms of training concentration relating to the definition of landslide and non-landslide point sets, and the landslide range should be accurately delineated according to field surveys.

Jinan is an important city in eastern China, with rich groundwater in the region. There are four famous springs in the urban area and an abundance of geothermal water in the northern part, which makes the migration of groundwater in this area a very important issue. To study the shallow shear wave velocity structure and groundwater migration in Jinan, we utilized almost a month of continuous waveform data from 175 short period seismometers deployed by the Chinese Academy of Geological Sciences, in order to calculate the cross-correlation function. We picked 7749 group dispersion curves and 6117 phase dispersion curves with a period range of 0.2-2 s. Through inversion, we obtained the fine three-dimensional shear wave velocity and azimuthal anisotropy structure (0-2.4 km). Combining the results with local geological and hydrological data, the following conclusions were reached. (1) There are widespread high velocity anomalies in the region between the Qianfoshan and Wenhuaqiao faults, as well as to the east of the Wenhuaqiao Fault, which may be related to the intrusive gabbro known as the Jinan Intrusive Rock. (2) The two distinct high velocity anomalies in our model (referred to as west and east Jinan Intrusive Rock in this paper) may indicate that the Jinan Intrusive Rock was broken through crustal movement. (3) There is an obvious low velocity layer under the intrusive rock, which could be the channel of groundwater migration. The precipitation in the southern mountain region seeps down into the ground, then is blocked by the Jinan Intrusive Rock and can only progress downwards to a deeper part, where the groundwater is heated by the geothermal gradient. The heated water finally arrives at the northern part and forms geothermal water. (4) The depth of the low velocity layer beneath the Jinan Intrusive Rock varies laterally, which may indicate that the depth of the groundwater migration is different beneath the west and east Jinan Intrusive Rock. (5) There is strong azimuthal anisotropy in southern Jinan, with nearly E-W fast orientation, which may be related to the tilt limestone layering structure.

Granitic gneiss (orthogneiss) and Himalayan leucogranite are widely distributed in the Himalayan orogen, but whether or not the granitic gneiss made a contribution to the Himalayan leucogranite remains unclear. In this study, we present the petrological, geochronological and geochemical results for orthogneisses and leucogranites from the Zhada area, Western Himalayas. Zhada orthogneiss is composed mainly of quartz, plagioclase, K‐feldspar, biotite and muscovite, with accessory zircon and apatite. Orthogneiss zircon cathodoluminescence (CL) images show that most grains contain a core with oscillatory zoning, which indicates an igneous origin. Sensitive high‐resolution ion microprobe (SHRIMP) U‐Pb dating of the zircon cores in the orthogneiss shows a weighted 206 Pb/ 238 U age of 515 ± 4 Ma (early Paleozoic), with spongelike zircon rims of 17.9 ± 0.5 Ma (Miocene). Zhada leucogranite shows 206 Pb/ 238 U ages ranging from 19.0 ± 0.4 Ma to 12.4 ± 0.2 Ma, the weighted average age being 16.2 ± 0.4 Ma. The leucogranites have a low Ca content (<1 wt%), FeO t content (<1 wt%), Rb content (67.0–402 ppm), Sr content (<56.6 ppm), Ba content (3.35–238 ppm) and Rb/Sr ratio (0.5–14.7), which are similar to the geochemical characteristics of the Himalayan leucogranite derived from muscovite dehydration partial melting of metasediments and representative of most Himalayan leucogranites. The highly variable Na 2 O + K 2 O (4.33 wt%–9.13 wt%), Al 2 O 3 (8.44 wt%–13.51 wt%), ∑REE (40.2–191.0 ppm), Rb (67.0–402 ppm) and Nb (8.23–26.4 ppm) contents, 87 Sr/ 86 Sr( t ) ratios (0.7445–0.8605) and ε Nd ( t ) values (–3.6 to –8.2) indicate that the leucogranite is derived from a heterogenetic source. The nonradiogenic Nd isotope values of the studied Zhada leucogranite and orthogneiss range from –8.2 to –3.6 and from –8.7 to –4.1, respectively. Therefore, the general mixing equation was used to perform the Sr and Nd isotope mixing calculations. The results indicate that the heterogenetic source was the Tethyan Himalayan Sequence (THS)/Higher Himalayan Crystalline (HHC) metasediments and Zhada orthogneiss. The Zhada area experienced crustal anatexis during the Miocene and the heterogenetic source of the orthogneiss and metasediment may have experienced crustal anatexis controlled by muscovite dehydration. The Zhada leucogranite inherited not only the geochemical characteristics of the Himalayan metasediment (muscovite dehydration melting), but also the trace elements and Sr‐Nd isotopic characteristics of the Zhada orthogneiss. These results indicate that the Paleozoic Zhada orthogneiss was involved in crustal anatexis at 17.9 ± 0.5 Ma (Miocene) and that the muscovite dehydration of the metasediments in the heterogenetic source produced fluid, which may have caused the orthogneiss solidus lines to decline, triggering a partial melting of the Zhada orthogneiss. It is therefore proposed that Himalayan leucogranite is a crust‐derived granite rather than a S‐type granite, as previously hypothesized.

The extensive production of Miocene high-to ultrahigh-K basaltic rocks and high-Sr/Y granites across southern Tibet might be related to mantle geodynamics, but there is a lack of direct petrological evidence for the exact mechanism involved in this igneous activity. This study reports a study of silicocarbonatite dikes that intrude sedimentary rocks of the Tethyan Himalayan Sequence, with the aim of elucidating the geodynamic mechanism that led to this magmatism. These dikes are composed mainly of ferro-and magnesio-dolomite (55-65 vol%) and quartz (25-30 vol%), with accessory minerals of anatase, titanite, chrome spinel, apatite, monazite, pyrite, and zircon. The carbon (delta 13C =-6.3%o to-6.0%o) and initial Nd [epsilon Nd(18.4 Ma) = +0.2 to +0.4] isotopic compo-sitions, as well as the relatively high whole-rock contents of Cr (218-956 ppm), Ni (84.1-974 ppm), and Co (28.1-96.3 ppm), indicate that these carbonatitic magmas were sourced from a mantle region. Sensitive high -resolution ion microprobe zircon U-Pb analysis results showed that these carbonatitic igneous rocks have inherited single-grain 206Pb/238U ages of 2394.2-28.5 Ma and a weighted mean 206Pb /238U age for the ten youngest zircon grains of 18.4 +/- 0.2 Ma, which represents the age of magmatic crystallization. Low-viscosity carbonatitic magma is inferred to have ascended rapidly, mixing with high-viscosity silicate melts at mid-dle-lower crustal levels, ultimately forming silicocarbonatitic (SiO2 = 30.17-37.67 wt%) dikes that intruded shales and sandstones of the Tethyan Himalayan Sequence. Tearing of subducted Indian lithosphere might have occurred beneath the eastern Tibet-Himalayan Orogen, allowing magma to upwell and generate linearly distributed Miocene igneous rocks along the N-S-trending Cona rift.

泽当岛弧位于藏南乃东县境内,主要由英云闪长岩、花岗闪长岩、奥长花岗岩和角闪石岩组成,是晚侏罗世洋壳俯冲的产物.本文对该地区出露的角闪石岩开展了野外地质调查,通过室内SHRIMP锆石U-Pb定年、全岩地球化学和Sr-Nd同位素等研究,探讨了泽当角闪石岩的成因、源区及其与花岗岩的成因关系,获得以下认识:角闪石岩成岩年龄为159.1±7.2 Ma;角闪石岩具有较低Sr含量、较高的Y含量和较低的Sr/Y值,富集MREE;角闪石岩与花岗岩Sr-Nd同位素特征一致,角闪石岩87 Sr/86 Sr(t)值(0.704 0～0.704 5)较低,εNd(t)值变化范围为+5.5～+6.1.结合前人研究认为,泽当岛弧的英云闪长岩、花岗闪长岩、奥长花岗岩和角闪石岩均来自地幔楔部分熔融作用.英云闪长岩为相对原始的岩浆,在角闪石分离结晶作用未结束前,先从岩浆房中分离出来;残余岩浆继续发生角闪石分离结晶作用,导致Sr/Y值进一步升高和Cr、 Ni、MREE含量进一步降低.因此,角闪石的分离结晶作用是泽当岛弧高Sr/Y花岗岩形成的关键因素.

The Himalayan orogen is featured by widespread S-type leucogranites (ca. 45 to 9 Ma) formed primarily from the partial melting of metapelites (800-480 Ma), and minor from the partial melting of amphibolite with subordinate metapelites. The Ama Drime gneiss and Mabja leucogranite pluton are both located at the footwall of the NS-trending Xainza-Dinggye normal fault in the central part of the Himalayan orogen, with published epsilon(Nd)(t) values of -21.0 to -19.6 and -19.3 to -18.3 and Sr-87/Sr-86(t) values of 0.90954-0.92574 and 0,84853-0.85474, respectively. In this study, we presented new SHRIMP zircon U-Pb ages and laser ablation multi-collector-inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) tourmaline boron isotope data on the metamorphic rocks and leucogranites of the Himalayan orogen. The weighted mean (207)pb/(206)pb age of the zircon cores of the Ama Drime gneiss (T0446-2-3) is 1854 +/- 4 Ma. The tourmaline delta B-11 values of the Ama Drime gneiss (T0446-1-6) are -17.6 to -14.3 parts per thousand, similar to those of the Mabja leucogranite (T0436-4, -18.9 to -17.4 parts per thousand). In contrast, the tourmaline delta B-11 values of the Quedang metapelite (T0389-18) and its partial melting product - Malashan leucogranite (T0659-12A-3) are substantially higher, i.e., -15.3 to -12.5%. and -16.2 to -8.0%., respectively. The tourmaline delta B-11 values of the Yadoi leucogranite (T0321-4), derived from partial melting of amphibolite, range from -8.4 to -5.4 parts per thousand. Therefore, the tourmaline B-isotopes and Sr-Nd-isotopes results are consistent, and may have reflected an E-W extension along the southern Tibetan rift system, indicating a late Miocene anatexis in the North Himalaya region. The melts derived from the partial melting of metapelites and mature crustal materials (e.g., Paleoproterozoic Ama Drime gneiss) ascended along the N-S-trending Xainza-Dinggye normal fault, and were subsequently emplaced in the Tethyan Himalaya sequence. (C) 2018 Elsevier B.V. All rights reserved.

The Gurla Mandhata dome is located in the western Tethyan Himalaya. It consists of biotite gneiss, granitic gneiss, mylonite, migmatite, meta-sandstone, amphibolite and marble intruded by tourmaline granite and two-mica granite. An integrated petrographic, zircon U-Pb dating and geochemical study has been carried out on the migmatite, granitic gneiss, tourmaline granite and two-mica granite in Gurla Mandhata dome. The data results show that: (1) the upper intercept Pb-206/(238) U age of the migmatite (TO768-4 A-4 C) is 1873 +/- 28 Ma, with weighted Pb-207/Pb-206 age at 1877 +/- 21Ma. Meanwhile, Sr (Sr-87/Sr-86((i)) = 1. 25018 similar to 1. 44452) and Nd (epsilon(Nd) (t) = -28. 8 similar to -28. 5) isotopic compositions of the migmatite indicate that it has the same geochemical properties as those of the Lower Himalayan Sequence. (2) The upper and lower intercept Pb-206/U-238 ages of the granitic gneiss (TG-LE-11) are 1878 +/- 9Ma and 10. 9 +/- 0. 5Ma, respectively. A 13. 1 +/- 0. 3Ma magmatic crystallized zircon age was obtained in the granitic gneiss, indicated an anatexis event happened in the Mandhata Massif around 10Ma; (3) the concordant age of tourmaline granites that intruded into the Paleoproterozoic migmatite is 9.0 +/- 0. 2Ma, in accordance with the anatexis age of the granitic gniess; (4) epsilon(Nd) (t) values (18. 9 +/- -16. 1) of tourmaline granite are lower than that of the two-mica granite (epsilon(Nd) (t) = 14. 4 similar to -10. 3), indicating the contribution of mature crust materials in the source melting region of the tourmaline granitic pluton; (5) the relative lower epsilon(Nd) (t) values (-12.6) of the individual tourmaline granite may be resulted from partly dissemination of the magma druing the rising stage. This study supports the model proposed by Zhang et al. (2012) that the tectonic regime of Himalayan orogen was in a period of transition and adjustment from N-S extension to E-W extension during 19 similar to 13Ma, and further induced the transition of the melting source of the Himalayan leucogranite. During the period of the N-S extension stage, melting of the meta-pelite and meta-sandstone formed the two-mica granite (similar to 16Ma); while during the stage of the E-W extension happened along the southern Tibetan rift system, the mixing source of metapelites and Paleoproterozoic crust materials adjacent to the Main Central Thrust (MCT) began to melt, giving rise to the drawing up of the magmas along the S-N normal fault and finally forming the tourmaline-bearing leucogranitic plutons.

在北喜马拉雅萨迦片麻岩穹窿西南侧发育有麻迦淡色花岗岩体,出露于南北向申扎—定结裂谷正断层的下盘,属一处较大规模的晚中新世淡色花岗岩体.该岩体具有较均一的元素和同位素(Sr和Nd)组成,但与多数喜马拉雅淡色花岗岩相比,具有异常高的(87 Sr/86 Sr)i比值(0.85033～0.85034)和异常低的εNd(t)值(-19.26～-18.30)组成,指示其部分熔融源区有更成熟古老地壳物质的参与.麻迦淡色花岗岩SHRIMP锆石U-Pb定年结果显示:①该岩体主要记录了至少两阶段岩浆结晶作用,分别发生在11.6士0.2 Ma和9.6±0.2 Ma;②个别13.8～16.0 Ma的岩浆作用年龄;③多数锆石继承核年龄分布于泛非期,少数年龄为中元古代(1558～1584 Ma).在麻迦淡色花岗岩体南侧约40km处的日玛那穹窿,同位于申扎—定结南北向正断层的下盘,出露有大量原岩年龄为古元古代的日玛那糜棱岩,元素地球化学特征上类似于变泥质岩,显示高SiO2 (70.6％～74.6％),Al2O3(12.3％～14.0％),K2O (4.22％～4.93％),A/CNK (1.50～1.58)和K2O/Na2O (1.42～2.18),代表了部分熔融源区可能存在的古老地壳物质岩石单元.因此,以麻迦淡色花岗岩为代表的北喜马拉雅晚中新世地壳深熔作用可能与青藏高原后碰撞阶段东西向伸展作用相关,泛非期变泥质岩及少量日玛那糜棱岩所代表的更古老岩石单元在16.0 Ma开始发生部分熔融,并在11.6 Ma至9.6 Ma之间达到深熔作用峰期,熔体活动可能持续了～2 myr,以岩脉汇聚的形式延南北向正断层上升,构成侵位至北喜马拉雅特提斯沉积岩系之中的晚中新世麻迦淡色花岗岩体.