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2019 Vol. 30, No. 6

2019, 30(6): .
Metamorphism and Orogenic Belts—Response from Micro- to Macro-Scale
Preface: Metamorphism and Orogenic Belts-Response from Micro- to Macro-Scale
Xu-Ping Li, Hans-Peter Schertl, Jürgen Reinhardt
2019, 30(6): 1075-1083. doi: 10.1007/s12583-019-1269-y
The geological toolbox for the analysis of orogenic processes has seen substantial additions over the recent decades. Major advances have been made in the ability to simulate geological conditions and processes by computer modeling, we have a much improved knowledge of geochemical processes (trace elements and isotopes in particular), and, last but not least, the range and versatility of micro-analytical methods and instrumentation available to us has been expanded dramatically. The latter aspect has had a particular impact on metamorphic petrology as the conventional tools to determine pressure-temperature-time paths via rock and mineral analysis combined with isotope geochronology have generally gained in precision and accuracy through a much improved resolution. Geochronology has moved from whole-grain analysis to spot analyses on zoned single grains while analyzing trace elements and isotopes at the same time. It is therefore possible to recognize complex multi-stage orogenic events in single samples or single grains. Diffusion profiles in minerals provide us with time-scales of metamorphic and magmatic processes. Major and trace elements as well as isotope profiles of mineral grains give us insight into changing ambient conditions during mineral growth. This special issue focuses on pressure-temperature conditions and geochronology of metamorphic rocks, isotope studies of magmatic rocks, partial melting and metasomatic processes, all with a view at tectonic implications and orogeny. Much of the evidence has been gained from small-scale observation and analysis. Diligent field work and detailed microscopic examination remain indispensable, though, as demonstrated clearly by the "expansion" of the P-T space as applicable to crustal metamorphic processes towards extreme pressures and temperatures. As a consequence, much interest has thus focused on UHP and UHT rocks and the orogenic processes that generate them. There is petrological evidence for subduction to, and subsequent exhumation from, depths in excess of 250 km. While this impacts substantially on the large-scale geodynamic models of orogenic processes, the evidence is gathered primarily from small-scale petrological observation. The same applies in principle to UHT granulites. To generate temperatures in the 900 to 1 100 ℃ range within the sillimanite stability field in orogenic heat budget models remains a serious challenge, however. The large overlap of solid-state metamorphism, partial anatexis and magmatic crystallization in P-T space suggests close interrelationships, and the role and contribution of the diverse magmatic activities in forming orogenic belts, from the onset of subduction to late-orogenic delamination or slab-break-off is crucial for our understanding of geodynamics, with focus on geochemistry and geochronology. Aspects of metasomatism in the framework of orogeny are given some special consideration in this issue. The topics include the formation of sagvandite, pyrope quartzite (or whiteschist), jadeitite and rodingite. One of the key questions addressed is the source and the nature of the fluids that triggered the different types of metasomatic events. Finally, it is shown how small-scale methods contribute to a better understanding of the formation of deep-seated mantle xenoliths.
Interaction of Mantle Rocks with Crustal Fluids: Sagvandites of the Scandinavian Caledonides
Kurt Bucher, Ingrid Stober
2019, 30(6): 1084-1094. doi: 10.1007/s12583-019-1257-2
Sagvandite is an enstatite+magnesite rock formed from dunite or harzburgite bodies occurring as tectonically emplaced fragments from the upper mantle in many orogenic belts by interaction with CO2-bearing crustal fluids at upper amphibolite facies P-T conditions. Sagvandite bodies occur widespread in distinct nappes in the Scandinavian Caledonides in Norway. Common to all of the many sagvandite outcrops is their general structure of radial bundles of very coarse cm-sized enstatite crystals and interstitial magnesite. Often some strongly resorbed primary olivine is preserved, in addition to minor accessory Cr-spinel and chromite. The dunite to sagvandite conversion is governed by three metasomatic reactions:(1) carbonatization of peridotite by CO2-bearing fluids;(2) interaction with external fluids containing dissolved silica;(3) loss of Mg by dissolution of forsterite in NaCl-rich deep fluids. Simultaneous progress ξoverall of all three reactions in proportions that conserve the volume of the original dunite can explain the observed structure and mode of sagvandite. The relationship among the progress ξ of the three reactions suggests that loss of Mg by the ultramafic rock is the dominating process in the iso-volume conversion of dunite to sagvandite.
Cathodoluminescence Microscopy of Zircon in HP- and UHP- Metamorphic Rocks: A Fundamental Technique for Assessing the Problem of Inclusions versus Pseudo-Inclusions
Hans-Peter Schertl, Andreas Hertwig, Walter V. Maresch
2019, 30(6): 1095-1107. doi: 10.1007/s12583-019-1246-5
This paper shows how a faulty approach to the study of mineral inclusions in zircon can lead to misleading interpretations of the geological context. We present and discuss two well-documented ex-amples. Zircon grains separated from HP metamorphic jadeitite of the Rio San Juan Complex, Dominican Republic, and from UHP pyrope quartzite of the Dora Maira Massif, northern Italy, were studied using cathodoluminescence (CL) techniques, in combination with mineral inclusion and age data. In general, zircon from both localities shows inherited magmatic core domains with oscillatory zoning and metamorphic rims. The magmatic cores of zircon from the jadeitite yield ages of 115-117 Ma and host jadeite and omphacite which are of metamorphic origin and formed at about 78 Ma. Zircon from lawsonite blueschist, representing the country rock of the jadeitite, contains domains with oscillatory zoning that are nearly identical in age to the zircon cores from the adjacent jadeitite, and also contains younger metamorphic minerals such as lawsonite, albite, phengite (Si3.68), chlorite, and omphacite. Similar observations were made on the magmatic cores of zircon from the pyrope quartzite. These are about 275 Ma in age and host pyrope, phengite (Si3.55), talc, and kyanite, all of which formed during UHP metamorphism at about 35 Ma. Zircon from the biotite-phengite-gneiss country rock (metagranite) shows oscillatory zoning and yields ages that are identical to those of the magmatic cores of zircon from pyrope quartzite, which thus reflect granitic intrusion ages. The country-rock zircon also encloses metamorphic minerals with ages of about 35 Ma. Such minerals are, for example, garnet and phengite, as well as a polymineralic assemblage of clinopyroxene+garnet+phengite+quartz, that point to formation at UHP metamorphic conditions around 40 kbar/750℃. Based on these examples we suggest an effective approach centered on key evidence from CL studies to show that magmatic domains of zircon may actually contain pseudo-inclusions which were not entrapped during an early stage of formation, but were instead introduced during later metamorphic or metasomatic events along microcracks representing pathways for fluid influx. Cathodoluminescence microscopy is thus an excellent tool for avoiding such pitfalls by allowing distinction between true inclusions and pseudo-inclusions in zircon.
Record of Early-Stage Rodingitization from the Purang Ophi-olite Complex, Western Tibet
Songjie Wang, Xu-Ping Li, Wenyong Duan, Fanmei Kong, Zeli Wang
2019, 30(6): 1108-1124. doi: 10.1007/s12583-019-1244-7
Rodingitization, commonly coupled with serpentinization of ultramafic rocks, bears significant information for fluid-rock interactions and element transfer from sea-floor to subduction zone envi-ronments. Numerous outcrops of rodingites are exposed along the Yarlung Zangbo suture zone (YZSZ) of southern Tibet, providing us an excellent opportunity to probe the petrogenetic processes, and unravel their implications for regional tectonic evolution. Several studies have been performed on rodingites from the eastern to central portions of the YZSZ, whereas limited work has ever been conducted on rodingitized rocks from the western segment of the YZSZ, precluding a comprehensive understanding of this lithological type. In this paper, we present detailed studies of petrology, mineral, whole-rock geochemistry and phase equilibrium modeling on a suite of newly recognized rodingites within the Purang ophiolite massif in the southwestern part of the YZSZ. The rodingites have a major metasomatic mineral association of chlorite, clinozoisite, amphibole and minor amounts of plagioclase, representing products of an early-stage rodingitization. They generally present compositions of low SiO2 (48.89 wt.%-53.57 wt.%), Fe2O3T (3.77 wt.%-5.56 wt.%), Na2O (1.31 wt.%-1.93 wt.%), Al2O3 (4.78 wt.%-8.84 wt.%), moderate CaO (9.69 wt.%-11.23 wt.%), and high MgO (24.11 wt.%-26.08 wt.%) concentrations with extremely high Mg# values[Mg#=100×Mg/(Mg+Fe2+) molar] of 89-92. Bulk-rock recalculation reveals that the rodingites have a protolith of mantle-derived olivine gabbro or gabbronorite. They have low rare earth element compositions (∑REE=2.4 ppm-6.5 ppm) and are characterized by flat LREE and slightly enriched HREE patterns with positive Eu anomalies; they also exhibit positive anomalies in Sr, U and Pb and negative anomalies in high-field strength elements, including Nb, P and Ti, suggesting for a subduction-zone imprinting. Phase equilibrium modeling shows that the rodingitization did take place at P < 2 kbar and T=~350-400℃, consistent with low greenschist facies conditions. Taking into account of all these petrological and geochemical features, we propose that the rodingites record evidence of early-stage fluid-rock interactions between olivine gabbroic rocks and Ca-rich fluids, which may have derived from weakly serpentinized ultramafic country rocks. Although this process may initially have occurred in a mid-ocean ridge setting, an obvious overprinting by supra-subduction zone fluids in a fore-arc environment is recognized.
Tectonic Implications and Petrogenesis of the Various Types of Magmatic Rocks from the Zedang Area in Southern Tibet
Yuanku Meng, Fahui Xiong, Jingsui Yang, Zhao Liu, Kieran A. Iles, Paul T. Robinson, Xiangzhen Xu
2019, 30(6): 1125-1143. doi: 10.1007/s12583-019-1248-3
In this study, we report systematically field observations, geochronology, whole-rock geochemistry and Sr-Nd-Hf isotopic dataset on the various types of magmatic rocks collected from the Zedang area. Chemically, the diabase and gabbro have a low-K calc-alkaline affinity, whereas the basalt and plagiogranite have medium to high-K calc-alkaline characteristics. In addition, the basalts are highly enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE), but strongly depleted in high strength field elements (HFSE), indicating that their magma source probably was derived from a subduction- or arc-related setting. In contrast, both the gabbro and diabase mainly demonstrate an N-MORB-like affinity consistent with normal mid-oceanic ridge basalt (N-MORB) origin. The zircon U-Pb dating results suggest that the basalts were crystallized earlier at ca. 158-161 Ma (Oxfordian stage), but the gabbro was crystallized at ca. 131 Ma (Hauterivian stage of Early Cre-taceous). The zircon U-Pb dating results correspond with the field observations that the veins of gabbro intruded basalt. Furthermore, the plagiogranite has a weighted mean age of ca. 160 Ma (MSWD=2.1) consistent with the basalt within the uncertainty. The basalt and the plagiogranite have significantly positive εHf(t) values (+5.8 to +15.6 and +8.6 to +16.1, respectively), suggesting that they were originated from partial melting of a depleted source. However, basalt and plagiogranite are characterized by the wide variations of εHf(t) values indicating minor amounts of exotic crustal material input during the later magma evolution. Additionally, the basalt shows duplex geochemical features of island-arc and mid-oceanic ridge basalt, corresponding to the supra-subduction zone-(SSZ) type affinity. To sum up, two distinct magmatic events identified in this study probably suggest an intra-oceanic arc system ex-isting in the Zedang area during the Late Jurassic, but the intra-oceanic arc subduction extinguished in the Early Cretaceous as suggested by the N-MORB-like gabbro and diabase. Integrated with regional background and different rock types, as well as geochemical features, we conclude that intra-oceanic arc subduction setting developed during the Late Jurassic in the Zedang area, southern Tibet.
Metamorphism and Orogenic BeltsjResponse from Micro- to Macro-Scale
Timanide (Ediacaran-Early Cambrian) Metamorphism at the Transition from Eclogite to Amphibolite Facies in the Beloretsk Complex, SW-Urals, Russia
Arne P. Willner, Michael Gopon, Johannes Glodny, Victor N. Puchkov, Hans-Peter Schertl
2019, 30(6): 1144-1165. doi: 10.1007/s12583-019-1249-2
The Beloretsk Metamorphic Complex in the SW Urals formed at a convergent eastern margin of Baltica during the Neoproterozoic-Early Cambrian Timanide orogeny. It comprises three major units with lenses of facies-critical metabasites within metasedimentary rocks:A lowermost eclogite unit, an intermediate garnet amphibolite unit and an upper amphibolite-greenschist unit. Pressure (P)-temperature (T)-paths of four rocks from the two lowermost units were determined mainly by PT pseudosection techniques showing similar clockwise loops at different peak metamorphic, water-satu-rated conditions:A phengite-bearing eclogite shows peak PT conditions of 16.5-18.5 kbar/525-550℃ (stage Ⅰ) followed by stage Ⅱ at 11.5-13.0 kbar/585-615℃. A garnet amphibolite from the intermediate unit yields lower peak conditions of 11.7-14.5 kbar/480-510℃ (stage Ⅰ) followed by stage Ⅱ at 9.5-11.0 kbar/535-560℃. However, a granite gneiss in the eclogite unit shows similar maximum pressures as the eclogite, but higher temperatures at 15.6-16.2 kbar/660-675℃, whereas a garnet micaschist contains comparable high pressure relicts, but underwent an advanced midcrustal reequilibration at 7.5-9.0 kbar/555-610℃. We dated the eclogite by a 7-point Rb/Sr mineral isochron (phengite, omphacite, apa-tite) at 532.2±9.1 Ma interpreted as age of crystallisation of the eclogitic peak PT assemblage. This age is the youngest compared to the known Timanide metamorphic and magmatic ages.
Metamorphism and Orogenic Belts—esponse from Micro- to Macro-Scale
Reconstruction the Process of Partial Melting of the Retrograde Eclogite from the North Qaidam, Western China: Constraints from Titanite U-Pb Dating and Mineral Chemistry
Yuting Cao, Liang Liu, Wenqiang Yang, Yuan Gao, Xiaohui Zhu
2019, 30(6): 1166-1177. doi: 10.1007/s12583-019-1253-6
Retrograde eclogite and garnet amphibolite of the Lüliangshan unit of the Shenglikou area, North Qaidam, were studied with emphasis on rutile and titanite. A special focus is on the formation of rutile and its corona of titanite (Ttn1) in retrograde eclogite and on coarse-grained titanite (Ttn2) from the garnet amphibolite. Using zirconium (Zr)-in-rutile and Zr-in-titanite thermometers, the temperatures estimated for the formation of an early generation of rutile are 823-884 ℃ at 2.5-2.8 GPa, while 812-894 ℃ at 1.3-1.5 GPa are derived for the formation of coronitic Ttn1 in the retrograde eclogite. Therefore, isothermal decompression must have occurred during exhumation, which also has triggered the partial melting of the retrograde eclogite. Ttn2 of the garnet amphibolite has high REE contents and high Th/U ratios, indicating that it is newly grown from a Ti, Ca, and LREE enriched anatectic melt derived from the partial melting of retrograde eclogite. LA-ICP MS U-Pb dating yields a lower intercept age of 423±4 Ma for Ttn2, which is consistent with the granulite-facies metamorphic age of the retrograde eclogite. Moreover, a temperature of 781-823℃ at 1.0-1.2 GPa is obtained for Ttn2, which fits the P-T conditions of the HP granulite-facies metamorphic stage (P=1.07-1.24 GPa and T=774-814℃), and documents that the crystallization of the melt occurred at the granulite-facies stage at 423 Ma. The high amount of REE of the garnet amphibolite is a consequence of the formation of Ttn2 from the melt. The contents and ratios of Zr and Hf in rutile and Ttn2 differ from those in the garnet amphibolite, and the whole rock Zr/Hf ratios of retrograde eclogite and garnet amphibolite are both higher than the respective ratios in rutile and Ttn2, suggesting that rutile and titanite cannot be the major carriers of Zr and Hf accounting for the high whole rock Zr/Hf ratios.
Metamorphism and Orogenic Belts—Response from Micro- to Macro-Scale
Ultrahigh Temperature Metamorphic Record of Pelitic Granulites in the Huangtuyao Area of the Huai'an Complex, North China Craton
Shaoting Ma, Xu-Ping Li, Hao Liu, Fanmei Kong, Han Wang
2019, 30(6): 1178-1196. doi: 10.1007/s12583-019-1245-6
Pelitic granulite from the Huangtuyao area, occurrs in the Huai'an Complex, is located in the Trans-North China Orogen of the North China Craton. On the basis of petrolography, mineral com-ponent, and phase equilibrium modeling studies, the P-T conditions and mineral assemblages of pelitic granulites can be divided into four metamorphic stages:the prograde metamorphic stage M1 defined by the stable mineral assemblage of Grt1 (garnet core)+Pl+Bt+Kfs+Qz+Rt, the peak pressure Pmax stage M2 indicated by Grt2 (garnet mantle)+Kfs±(Ky)+Rt+Qz+Liq (melt), peak temperature Tmax stage M3 characterized by Grt3 (garnet rim)+Sill+Pl+Kfs+Qz+Ilm+Liq, and retrograde stage M4 represented by Grt (in matrix)+Kfs+ Sill+Bt+Pl+Qz+Ilm. By using the THERMOCALC V340, the P-T conditions are estimated at ~13.8-14.1 kbar and ~840-850℃ at stage M2, and 7-7.2 kbar and 909-915℃ for the Tmax stage M3, indicating an ultra-high temperature (UHT) metamorphic overprinting during decompression and heating process after high pressure granulite facies metamorphism. The mineral assemblages and their P-T conditions presented a clockwise P-T trajectory for the Huangtuyao pelitic granulites. The major metamorphic events at ~1.95 and ~1.88 Ga obtained by the zircon U-Pb dating suggest that pelitic granulites from the Huangtuyao area has undergone HP granulite metamorphism which probably occurred in the prograde metamorphism and related to the collision between the Ordos and the Yinshan blocks, and afterwards UHT metamorphism is related to crustal extension after continental-continental collision.
Petrology, Metamorphic P-T Paths and Zircon U-Pb Ages for Paleoproterozoic Mafic Granulites from Xuanhua, North China Craton
Guidong Wei, Fanmei Kong, Hao Liu, Xiaoman Wang, Yancheng Zhang, Xiaohan Liu
2019, 30(6): 1197-1214. doi: 10.1007/s12583-019-1251-8
The studied mafic granulites are located at Xiwangshan, Xuanhua region in the north of the Trans-North China Orogen (TNCO), occurring as lens within tonalite-trondhjemite-granodiorite (TTG) gneisses in the eastern part of the Xiwangshan area. The rocks contain the representative granulite-facies minerals such as garnet, clinopyroxene, orthopyroxene, plagioclase, amphibolite, rutile and quartz, and also well-developed melt pseudomorph and antiperthite. Although the prograde metamorphic stage (M1) cannot be retrieved due to rare preservation of pre-peak-stage mineral associations, three distinct mineral assemblages that formed in different metamorphic stages can be identified, based on petrography and mineralogy characteristics. The peak stage (M2) is characterized by Grt2+Cpx2+Amp2+Pl2+Rt+melt pseudomorphs, and a post-peak decompression stage (M3) contains a mineral assemblage of Grt3+Opx3+ Cpx3+Amp3+Pl3, while a later-retrogression stage (M4) is featured by coronas of Amp4+Pl4 surrounding garnet. By calculating metamorphic P-T conditions using THERMOCALC, stage M2 was constrained to be 13.2-14.8 kbar and 1 050-1 080℃, and M3 recorded P-T conditions of 5.7-7.3 kbar and 825-875℃, while M4 yielded P of~5 kbar and T of~660℃, consistent with amphibolite facies metamorphism. Taking into account of all these petrological data, we propose that the mafic granulite experienced a high-pressure (HP) and ultra-high temperature (UHT) granulite-facies metamorphism during the peak metamorphism, which was accompanied with a clockwise P-T path. U-Pb dating of metamorphic zircons in the granulites yields two groups of ages at 1 853±14 and 1 744±44 Ma, respectively. We suggest that the older age corresponded to the HP-UHT metamorphism, while the younger age represented an retrograde metamorphic event during cooling.
Metamorphism and Zircon Geochronological Studies of Metagabbro Vein in the Yushugou Granulite-Peridotite Complex from South Tianshan, China
Lu Zhang, Jianjiang Zhu, Bin Xia, Cong Zhang, Lifei Zhang
2019, 30(6): 1215-1229. doi: 10.1007/s12583-019-1254-5
Yushugou granulite-peridotite complex, located at the east part of the northern margin of South Tianshan, may represent an ophiolitic slice subducted to 40-50 km depth with high-pressure granulite facies metamorphism. Although a lot of studies have been conducted on rocks in this belt, the rock as-sociation and tectonic background of the ophiolitic slice are still in dispute. A detailed study on petrology, phase equilibrium modeling and U-Pb zircon ages have been performed on the metagabbro vein in peridotite unit to constrain the tectonic evolution of the Yushugou granulite-peridotite complex. Three stages of mineral assemblage in the metagabbro were defined as stage Ⅰ:CpxA+OpxA+PlA, which represents the original minerals of the metagabbro vein; stage Ⅱ:CpxB+OpxB+PlB+Spl, which represents the mineral assemblage of granulite facies metamorphism with peak P-T conditions of 4.2-6.9 kbar and 940-1 070℃; stage Ⅲ is characterized by the existence of prehnite, thomsonite and amphibole in the matrix, indicating that the metagabbro vein may be influenced by fluids during retrograde metamorphism. Combined with the crosscut relationship, it can be deduced that the metagabbro vein, together with the peridotite in Yushugou granulite-peridotite complex has experienced similar high-temperature granulite facies metamorphism. The zircon chronological data shows that the protolith age of the metagabbro vein is 400.5±6.2 Ma, reflecting Devonian magmatism event and the granulite facies metamorphism occurred at~270 Ma which may be related to the post-collisional magmatism.
Zircon U-Pb Ages and Hf Isotopes of Neoproterozoic Me-ta-Igneous Rocks in the Liansandao Area, Northern Sulu Orogen, Eastern China, and the Tectonic Implications
Zhaojun Song, Huimin Liu, Fanxue Meng, Xingyu Yuan, Qiao Feng, Dingwu Zhou, Juan Ramon Vidal Romaní, Hongbo Yan
2019, 30(6): 1230-1242. doi: 10.1007/s12583-019-1252-7
The Sulu Orogen preserves the Neoproterozoic tectonic-magmatic events, corresponding to the breaking up of the Rodinia supercontinent. The ages and petrogenesis of meta-igneous rocks in the Liansandao area in the northern Sulu Orogen are not well-constrained. This study reports zircon U-Pb ages and Hf isotopes of these rocks from the Liansandao area. Three meta-igneous rock samples give similar weighted mean 206Pb/238U ages of 744±11, 767±12, and 762±15 Ma, respectively, indicating the Neoproterozoic crystallization ages. These rocks formed coevally with the Wulian and Yangkou intrusions that located along the Yantai-Qingdao-Wulian fault zone. The Neoproterozoic ages indicate that the meta-igneous rocks from the Liansandao area have affinity to the Yangtze Block. The three samples have εHf(t) values of -7.2- -10.5, -6.0- -17.5, and -6.8- -12.0, respectively. These negative εHf(t) values indicate a primarily crustal source. However, the widely various εHf(t) values that are higher than the continental crust, suggesting magma mixing between mantle-derived materials and the continental crust or source heterogeneity. Combined with the Hf model ages and geochemical characteristics, the monzodiorite (sample LSD-2) is most likely to be mantle-derived magma then interacted with ancient continental crust, and the granitic protolith (samples LSD-1 and LSD-3) in the Liansandao area might derive from the re-melting of a Paleoproterozoic continental crust at ~750 Ma, resulting from the upwelling and underplating of mantle-derived magma formed in an extensional setting due to the break- up of the Rodinia supercontinent.
Petrogenesis and Geodynamic Implications of the Carboniferous Granitoids in the Dananhu Belt, Eastern Tianshan Orogenic Belt
Long Du, Chao Yuan, Xu-Ping Li, Yunying Zhang, Zongying Huang, Xiaoping Long
2019, 30(6): 1243-1252. doi: 10.1007/s12583-019-1256-3
This paper presents new LA-ICP-MS zircon U-Pb geochronology, whole-rock major and trace element geochemistry, and Sr-Nd isotopes systematically on porphyritic granitic and K-feldspar granitic intrusions from the Dananhu belt, eastern Tianshan orogenic belt (ETOB). Zircon U-Pb dating indicates that the porphyritic granitic and K-feldspar granitic plutons were formed at 357±3 and 311±3 Ma, respectively. The porphyritic granites show geochemical and isotopic characteristics (high SiO2, low MgO and Mg#, depleted Sr-Nd isotopic values (about 0.703 4 and 6.13, respectively), with Nb/Ta (13.3-14.7) and Zr/Hf (31.0-33.9) ratios) similar to those of the crustal-derived magmas. The above characteristics suggest they were probably originated from juvenile lower crustal materials. The K-feldspar granites also have high SiO2, low MgO and Mg#, depleted Sr-Nd isotopic values (0.703 3-0.704 6 and 4.41-5.67, respectively). But some trace elements contents vary widely, with variable Nb/Ta (12.7-22.7), Zr/Hf (21.3-36.1) and Nb/La (0.38-1.07) ratios, indicating that the K-feldspar granites were formed by partial melting of juvenile lower crustal materials with old crustal materials. Combined with previous data on Carboniferous granitoids in the Dananhu belt, we infer that all the Carboniferous granitic plutons in the Dananhu belt were most likely emplaced in an island arc environment (Dananhu arc). Subsequently, a tectonic transition from oceanic subduction to post-collisional extension probably occurred in the ETOB.
Survived Seamount Reveals an in situ Origin for the Central Qiangtang Metamorphic Belt in the Tibetan Plateau
Deliang Liu, Rendeng Shi, Lin Ding, Shao-Yong Jiang
2019, 30(6): 1253-1265. doi: 10.1007/s12583-019-1250-9
The origin of the central Qiangtang metamorphic belt (CQMB) has long been in debate, which is not clear whether this belt is the exhumed Jinsha oceanic plate that had been subducted and underthrusted beneath the Qiangtang Block, or the in situ Longmu Co-Shuanghu suture that separated the south and north Qiangtang blocks. Here we report field observations, zircon U-Pb ages and Lu-Hf isotopes, as well as whole rock geochemistry and Sr-Nd isotopes of the Late Triassic volcanic rocks near the Chabo Co within the southern margin of the CQMB. The ca. 229 Ma Chabo Co volcanic rocks and limestones possess characteristic lithologies of a seamount. Their geochemical and isotopic compositions are similar to OIB-type lavas. Unlike other metabasalts (eclogites and blueschists) in the CQMB, the Chabo Co volcanic rocks are OIB-type lavas that did not experience high-grade metamorphism; this is likely because that the Chabo Co seamount was detached from the subducting Longmu Co-Shuanghu oceanic slab. This work provides new solid evidences for an in situ origin of the CQMB.
Decoupling of Lu-Hf and Sm-Nd Isotopic System in Deep-Seated Xenoliths from the Xuzhou-Suzhou Area, China: Differences in Element Mobility during Metamorphism
Fanxue Meng, Wenliang Xu, Qinglin Xu, Jingliang Guo, Yu Zhang
2019, 30(6): 1266-1279. doi: 10.1007/s12583-019-1255-4
This paper presents whole-rock Hf isotopic data for a suite of eclogite and garnet clinopyroxenite xenoliths hosted in the Early Cretaceous dioritic intrusions from the Xuzhou-Suzhou area along the southeastern margin of the Eastern Block of the North China Craton (NCC). Six of the eight studied xenolith samples plot significantly above the terrestrial Hf-Nd isotopic array and have εHf(0) value up to +60. All the samples define a well correlated 147Sm/144Nd-143Nd/144Nd age of 2 081 Ma, which is considered to record the granulite-facies metamorphism. In contrast, the Lu-Hf isotope system faithfully records the protolith information. The mineralogical assemblage, especially garnet and/or zircon (rutile to some extent) mainly controlled the decoupling of Hf-Nd isotope. The metamorphic modification on protolith characteristics and the differences in element mobility during metamorphism may also reinforce the observed decoupling between the Sm-Nd and Lu-Hf isotope systems; i.e., the absence of the correlations in εNd-εHf and also 87Sr/86Sr-143Nd/144Nd diagram. The Lu/Hf isochron age of 2 424 Ma is similar to the zircon age peak of the studied xenoliths and the dominant age of NCC basement, indicating that the igneous protolith has an affinity to the Archean basement of the NCC. Furthermore, the positive εHf(t) values at 2 500 Ma indicate a crustal growth event of 2 500 Ma in the NCC.
Petrology and Metamorphic P-T Paths of Metamorphic Zones in the Huangyuan Group, Central Qilian Block, NW China
Zhuoyang Li, Yilong Li, Limin Zhao, Jianping Zheng, Fraukje M. Brouwer
2019, 30(6): 1280-1292. doi: 10.1007/s12583-018-0879-0
The Central Qilian Block is a Precambrian block in the Qilian Orogen,which has long drawn international attention for the study of orogeny and continental dynamics. The Huangyuan Group in the Datong area is one of the Precambrian metamorphic basement units in the Central Qilian Block and reflects metamorphism in the Barrovian garnet zone and sillimanite zone from south to north. Based on detailed fieldwork,this study presents a systematic study of petrography,mineral chemistry and phase equilibria of schists and gneisses from the two metamorphic zones. The garnet metamorphic zone is composed of micaschist,garnet-bearing micaschist and felsic leptynite,with in-terlayered plagioclase amphibolite. The sillimanite metamorphic zone consists of garnet-bearing biotite micaschist,sillimanite-bearing biotite-plagioclase gneiss and felsic leptynite. Garnet from the garnet metamorphic zone shows growth zoning with increasing almandine and pyrope and decreasing spessartine from core to rim. Garnet from the sillimanite metamorphic zone is almost homogeneous. Towards the outer rim,the contents of almandine and pyrope slightly decrease and grossular slightly increase. Biotite in both metamorphic zones is ferro-biotite. Plagioclase is oligoclase in garnet metamorphic zone and andesine in sillimanite metamorphic zone. Phase equilibrium modeling of a sample from garnet metamorphic zone resulted in a clockwise P-T path with a prograde stage (4.5-5.0 kbar,520-530℃),a peak P stage (9.8-10.2 kbar,560-570℃),a stage of thermal relaxation (8.0-8.5 kbar,580-590℃) and finally a retrograde stage (6.8-7.0 kbar,560-580℃). Thermodynamic modeling of a sample from the sillimanite metamorphic zone indicates a prograde stage (5.5-6.0 kbar,540-550℃) and a peak stage (7.8-8.5 kbar,660-690℃). The results indicate that the Huangyuan Group experienced medium-pressure amphibolite-facies metamorphism,which resulted from continental-continental collision between the Qaidam Block and the Central Qilian Block.
Elasticity and Anisotropy of the Pyrite-Type FeO2H-FeO2 System in Earth's Lowermost Mantle
Shengxuan Huang, Shan Qin, Xiang Wu
2019, 30(6): 1293-1301. doi: 10.1007/s12583-018-0836-y
The pyrite-type FeO2H-FeO2 system has been experimentally confirmed to be stable in Earth's lowermost mantle but there is limited information about its physical properties at high pressures constraining our understanding of its potential geophysical implications for the deep Earth. Here,static calculations demonstrate that the pyrite-type FeO2H-FeO2 system has a high density and Poisson's ratio and ultra-low seismic velocities at conditions of Earth's lowermost mantle. It provides a plausible mechanism for the origin of ultra-low velocity zones at Earth's D″ layer. The incorporation of hydrogen in the pyrite-type FeO2H-FeO2 system tends to decrease the S wave velocity (VS) but increase the bulk sound velocity (VΦ),and can potentially explain the observed anti-correlation of VS and VΦ in the lowermost mantle. Additionally,FeO2H exhibits nearly isotropic whereas FeO2 is highly anisotropic,which may help understand some seismic anisotropies at the core-mantle boundary.
An Effective Oxide Interference Correction on Sc and REE for Routine Analyses of Geological Samples by Inductively Coupled Plasma-Mass Spectrometry
Wei Zhao, Keqing Zong, Yongsheng Liu, Zhaochu Hu, Haihong Chen, Ming Li
2019, 30(6): 1302-1310. doi: 10.1007/s12583-019-0898-5
Oxide interference correction plays a vital role in the accurate determination of trace element compositions of geological samples by inductively coupled plasma-mass spectrometry (ICP-MS). In this study,we found that the oxide production is mainly controlled by the gas flow of the ICP-MS and a constant oxide correction factor (OCF) can be measured during a routine analysis. Thus,we can obtain the oxide production by just investigating the gas flow for a fixed ICP-MS system with monitoring of OCF. Si,Ba and LREE oxide interferences on the Sc,Eu and Gd of four geological standard samples GSP-2,JP-1,GBW03112 and GBW03113 were corrected by such method and the results were in good agreement with the recommended values. Therefore,the present study provides a simple and fast correction method for the oxide interferences of the geological samples during the routine analyses. Furthermore,a Microsoft Excel spreadsheet template integrating the correction equations was devel-oped in an in-house software (ICPMSDataCal) for effective calibration.
Waste-to-Fuel Technology in Albania——How to Implement a Renewable Energy System in Europe's Largest Onshore Oilfield
Besmir Buranaj Hoxha, Dael Dervishi, Kyle Sweeney
2019, 30(6): 1311-1325. doi: 10.1007/s12583-017-0782-0
Albania has historically been known to have an active but challenging drilling activity that demands the most innovative technology to develop,predominantly,medium-heavy oil reservoirs. Although recent efforts have been made by the government to stimulate and expand the largest onshore European oil-field,technical and economical obstacles are prevalent. These obstacles make it difficult to fully develop reliable and profitable hydrocarbon bearing zones in a downturn economy,especially since Albanian oil can be costly to produce and refine. Due to these typical issues that affect many local energy sectors,many developed countries diversify their energy production to avoid strict dependency on crude oil. An emblematic and modern option that is extensively gaining popularity in Europe focuses on renewable energy from sophisticated recycling programs. Although Albania is a relatively "green" country when it pertains to its electricity production (97% hydropower and 3% fossil fuels),it has yet to develop energy-recycling programs that it can salvage for self-sustainable energy sources. The past years have seen a conscious revitalization and stimulation in the mentality of green economy in Albania. But,in comparison to the rest of "western Europe" that are leading world examples in efficient recycling,it is significantly lagging with initial strides just now focusing on aligning national legislations with current EU models. Furthermore,two crucial reasons that should motivate Albania to investigate new applications for energy recycling are:(1) alternatives to crude oil and petroleum products that can be supplemental and provide stable access to fossil fuels; (2) industrial and municipal recycling via waste management to reprocess waste and produce industrial raw material-spawning the emergence of a "circular economy" to develop the backbone needed to strengthen the industrial and manufacturing markets for a self-sustaining economy. Accordingly,in this paper,the topic that will be addressed,given the recent decrease in oil & gas prices,focuses on the Albanian energy sector's capability to sustain and develop a supplementary recycling program via "waste-to-fuel" (WTF) technology (biofuels and/or in-organic waste). With the intent that it could function cooperatively with Albania's active drilling pro-gram to mitigate dependency on a single fuel source and produce enough fossil fuel in an effective and sustainable manner.
Evolution of Low-Angle Normal Faults in the Enping Sag, the Northern South China Sea: Lateral Growth and Vertical Rotation
Zhichao Zhou, Lianfu Mei, Hesheng Shi, Yu Shu
2019, 30(6): 1326-1340. doi: 10.1007/s12583-019-0899-4
Low-angle normal faults (dip < 30°,LANFs) are widespread in the northern margin of the South China Sea where the maximum crust thickness is approximately 30.0 km. Based on 3D seismic survey data and drilling wells in the Enping sag,evidences for LANFs that initially formed at high-angles are discussed. After a detailed investigation of extensional fault system and description of 3D fault geometry,the initial fault dips under the model of distributed vertical simple shear are also calculated. The results indicate that the present-day dip angles of the LANFs are in the range of 12° to 29°,and the initial fault dip angles are in the range of 39° to 49°. Deep seismic imaging suggests that the upper crust in the footwall block of the LANFs was tilted at an angle of~14° to 22° due to the isostatic rebound during rifting. Moreover,the temporal and spatial sequences of the lateral growth of the LANFs have been investigated by the seismic interpretation of four isochronous stratigraphic interfaces,which demonstrates that two individual fault segments propagated towards each other and subsequently,were hard-linked during the Early Eocene.