Plio-Quaternary development of the Baklan–Dinar graben: implications for cross-graben formation in SW Turkey     

《International Geology Review》2012,54(1):33-50

In the Dnepr-Donets trough, salt domes having their origin in Devonian rocks were formed by four stages of cyclic tectonic activity from Late Devonian through Cretaceous. Three types of domes were formed: open piercement core, crypto-diapir, and crypto-diapiroid. - M. Russell.  相似文献   

Geochronologic and isotope geochemical constraints on magmatism and associated W–Mo mineralization of the Jitoushan W–Mo deposit,middle–lower Yangtze Valley     

《International Geology Review》2012,54(13):1532-1547

The Jitoushan W–Mo ore body is a typical skarn-type deposit with the potential for porphyry Mo mineralization at depth. As it is newly discovered, only a few studies have been conducted on the geochronology and ore genesis of this deposit. The ore district consists of Cambrian to Silurian sedimentary and low-grade metasedimentary strata, intruded by granodiorite, diorite porphyry, granite porphyry, and quartz porphyry. Skarn W–Mo ore bodies are hosted in the contact zone between the granodiorite and Cambrian limestone strata. Within the granodiorite near the contact zone, quartz vein type and disseminated sulphide mineralization are well developed. The Mo-bearing granite porphyry has been traced at depth by drilling. Our results reveal two discrete magmatic events at ca. 138 and ca. 127 Ma in the study area. The molybdenite Re–Os isochronal age of 136.6 ± 1.5 million years is consistent with the first magmatic event. The zircon Hf isotope (?_Hf(t) =??12.55?3.91), sulphide isotopes (δ³⁴S = 3.32–5.59‰), and Re content of molybdenite (Re_content = 6.424–19.07 μg) indicate that the ore-forming materials were mainly derived from the deep crust. The regional tectonic system switched from a Late Jurassic transpressive regime to an earliest Cretaceous extensional regime at ca. 145 Ma, and at ca. 138 Ma, the Jitoushan W–Mo deposit formed in an extensional setting.  相似文献   

Zircon U–Pb ages and Hf isotopic compositions from the Sin Quyen Formation: the Precambrian crustal evolution of northwest Vietnam     

《International Geology Review》2012,54(13):1548-1561

The location of the suture zone between the South China and Indochina blocks in northwest Vietnam has been under debate for decades. Generally, the boundary between these blocks has been placed along (1) the Ailaoshan–Red River zone or (2) the Song Ma zone. The Sin Quyen Formation, lying between these zones, was previously regarded as a Palaeo- and Mesoproterozoic sequence. It comprises its provenance and tectonic affinity. We analysed detrital zircons from two paragneisses and one migmatite of the Sin Quyen Formation employing laser ablation inductively coupled plasma mass spectrometry U–Pb dating techniques. U–Pb ages of these zircons show three main periods of zircon formation: ～2.7–3.0, ～2.2–2.5, and ～1.8 Ga, suggesting that Sin Quyen rocks were mainly derived from Palaeoproterozoic and Archaean basement units. Inasmuch as the South China basement comprises rocks of similar ages, we conclude that the Sin Quyen Formation belongs to that block. Our new data strengthen the view that the suture between the South China and Indochina blocks is located within the Song Ma zone. In addition, zircons with U–Pb ages >3.0 thousand million years represent the oldest minerals reported in northwest Vietnam so far, indicating the existence of Mesoarchaean crustal remnants in this region.  相似文献   

Zeolite Parageneses in the North Atlantic Igneous Province: Implications for Geotectonics and Groundwater Quality of Basaltic Crust     

《International Geology Review》2012,54(1):15-44

Zeolites are among the most common products of chemical interaction between groundwaters and the Earth's crust during diagenesis and low-grade metamorphism. The unique crystal structures of zeolites result in large molar volumes, high cation-exchange capacities, and reversible dehydration. These properties influence both the stability and chemistry of zeolites in geologic systems, leading to complex parageneses and compositional relationships that provide sensitive indicators of physicochemical conditions in the crust. Observations of zeolite occurrence in Tertiary basaltic lavas in the North Atlantic region indicate that individual zeolite minerals are distributed in distinct, depth-controlled zones that parallel the paleosurface of the plateau basalts and transgress the lava stratigraphy. The zeolite zones are interpreted to have formed at the end of burial metamorphism of the lavas. Relative timing relations between various mineral parageneses and crustal-scale deformal features indicate that the minerals indicative of the zeolite zones formed within 1 million years after cessation of volcanism. Empirical correlation between the depth distribution of zeolite zones and the temperatures of formation of zeolites in geothermal systems provides estimates of regional thermal gradients and heat flow in flood-basalt provinces. Similarly, the orientations of zeolite zones can be used to distinguish synvolcanic and post-volcanic crustal deformation. Because zeolites that characterize the individual zones display different ion-exchange selectivities for various cations, reactions between groundwaters and zeolites in basaltic aquifers can result in depth-controlled zones where individual elements are concentrated in the crust. This is established for Sr, which is concentrated by at least an order of magnitude in heulandite, resulting in an overall Sr enrichment of lavas in the heulandite-stilbite zeolite zone.  相似文献   

Petrogenesis of the Palaeoproterozoic Xishankou pluton,northern Tarim block,northwest China: implications for assembly of the supercontinent Columbia     

《International Geology Review》2012,54(15):1829-1842

The Tarim block, one of the largest cratons in China, records an important part of the Proterozoic crustal evolution of the Earth. Many previous studies have focused on the Neoproterozoic magmatism and tectonic evolution of this block in relation to the break-up of Rodinia, although relatively little is known about its earlier tectono-magmatic history. In this article, we present detailed petrographic, geochronologic, whole-rock geochemical, and in situ zircon Hf isotope data for the pre-Neoproterozoic Xishankou granitoid pluton (XBP), one of several blue quartz-bearing granitoid intrusions well exposed in the Quruqtagh area, and discuss these intrusions in terms of their tectonic environment. Zircon LA-ICP-MS dating indicates that gneissic quartz diorite and granodiorite of the XBP crystallized at 1934 ± 13 and 1944 ± 19 Ma, respectively. Both underwent metamorphism essentially coeval with emplacement, a time that is compatible with the globally distributed 2.1–1.8 Ga crustal amalgamation during formation of the supercontinent Columbia. Petrographic and geochemical evidence suggest that the XBP is a continental-arc-type granite and may have been generated by the partial melting of Archaean thickened lower crust; this would suggest that the northern Tarim block was a continental-type arc at ca. 1940 Ma. Our new data, together with previous regional geological studies, indicate that a series of Palaeoproterozoic (ca. 2.0–1.8 Ga) tectono-magmatic events occurred in the northern Tarim attending the assembly of Columbia.  相似文献   

Constraints on timing and origin of the Dayinjian intrusion and associated molybdenum mineralization,western Dabie orogen,central China     

《International Geology Review》2012,54(13):1579-1596

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Petrogenesis of Ordovician magmatic rocks in the southern Chiapas Massif Complex: relations with the early Palaeozoic magmatic belts of northwestern Gondwana     

《International Geology Review》2012,54(16):1918-1943

The recent discovery of Early Ordovician S-type granites in the southwest of the Chiapas Massif Complex adds a new perspective to the Palaeozoic history of the Maya block, inasmuch as no rocks of such age had previously been reported in this region. New geologic mapping west of Motozintla, Chiapas, revealed pelitic to psammitic metasedimentary successions (Jocote Unit) intruded by granitoids and metabasites. The Jocote Unit is unconformably underlain by the newly defined Candelaria Unit, which comprises deformed calc-silicate rocks and interlayered folded amphibolites. The Candelaria Unit is the oldest rock succession so far recognized in the southern Maya block. We used laser-ablation multicollector inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb dating to determine the ages of the rock, yielding Early Ordovician (ca. 470 Ma) and Late Ordovician (ca. 450 Ma) ages.

Major and trace element geochemistry, as well as Nd and Sr isotope data, suggest that folded amphibolites of the Candelaria Unit are mantle-derived and are probably related to rifting. The Early Ordovician bimodal magmatism of the Jocote Unit is more strongly differentiated; it reflects crustal contamination and volcanic-arc chemical signatures. A granitic stock (Motozintla pluton) intruded the area in the Late Ordovician. Its geochemical composition indicates less crustal contamination and a mixed signature between volcanic-arc and within-plate settings. Magmatic rocks analogous in age and chemical character crop out in the Rabinal and the Altos Cuchumatanes areas of Guatemala, suggesting the existence of a semi-continuous Ordovician magmatic belt from Chiapas to central Guatemala. Similar but somewhat younger granites also occur in the Maya Mountains of Belize, suggesting that magmatism migrated in the Silurian from the Chiapas–Guatemala belt towards the Maya Mountains.  相似文献   

Occurrence and significance of a quartz–amphibole schist xenolith within a mafic microgranular enclave in the Xiangshan volcanic-intrusive complex,SE China     

《International Geology Review》2012,54(7):894-903

The Xiangshan volcanic-intrusive complex is composed of rhyolitic crystal tuffs, welded tuffs, rhyodacite, porphyroclastic rhyolitic lava, subvolcanic rocks such as granite porphyry, and late quartz monzonitic porphyry and lamprophyre dikes. We report the first occurrence of a quartz–amphibole schist (QAS) xenolith enclosed within a mafic microgranular enclave (MME) in the Xiangshan volcanic-intrusive complex. The mineralogy of this xenolith consists of amphibole, biotite, quartz, and minor plagioclase. Petrographic and mineral composition studies indicate that the protolith of this xenolith likely originated from the metamorphic basement beneath Xiangshan. The amphibole (actinolite and magnesiohorblende) has been partially replaced by orthopyroxene at 800–1000°C and by diopside at <700°C, according to mineral thermometers; this replacement process may have taken place after the xenolith was trapped by the mafic magma host (now an MME). Studies of the QAS xenolith provide new information on the emplacement history of the mafic magma. The peak metamorphic temperature for amphibole replaced by pyroxene is higher than the crystallization temperature of the subvolcanic magma, which indicates that the heat of pyroxene formation must have been provided by the engulfing mafic melt. This magma must have emplaced to crustal level and trapped the QAS as a xenolith and then injected into the felsic magma. We suggested that the hybridization processes for the major elements of the pristine mafic magma may have been contaminated by crustal rocks to form its present composition of MME before mafic magma injection. However, the hybridization process appears not to have been formed via a single-stage process because various types of MMEs are presented in the Mesozoic magmatic rocks of SE China.  相似文献   

Palaeozoic porphyry Cu–Au and ultramafic Cu–Ni deposits in the eastern Tianshan orogenic belt: temporal constraints from U–Pb geochronology     

《International Geology Review》2012,54(7):842-862

During late Palaeozoic time, extensive magmatism and associated ore deposits were developed in the eastern Tianshan orogenic belt (ETOB), Northwest China, which is part of the Central Asian Orogenic Belt. To understand the petrogenesis of the intrusions in this area, we performed in situ zircon U–Pb and Hf isotopic analyses on the Tuwu–Yandong (TW–YD) stocks and the Xianshan, Hulu, Luodong, and Poshi batholiths. Two major suites of intrusive rocks have been recognized in the ETOB: (1) 338–339 Ma plagiogranite porphyries and 265–300 Ma ultramafic and mafic rocks, of which the former are associated with 323 Ma porphyry Cu–Mo deposits and have enriched radiogenic Hf isotopic compositions (?_Hf(t) = +11.5 to +15.6), which were derived from a depleted mantle source, whereas the latter are associated with 265–300 Ma magmatic Ni–Cu deposits and have variable Hf isotopic compositions (?_Hf(t) = ?10.3 to +14.3), indicating an origin via the hybridization of depleted mantle magma and variable amounts of ancient lower-crustal components. The proposed magma sources, combined with the geochemical differences between these two suites of intrusive rocks, indicate that in the lower to middle Carboniferous, a N-dipping subduction zone beneath the Dananhu arc triggered the emplacement of granitic porphyries in the Tousuquan and Dananhu island arc belt in the east Tianshan, leading to the formation of the TW and YD porphyry Cu–Mo deposits. In the Upper Carboniferous to Lower Permian, large mafic–ultramafic complexes were emplaced during the closure of the ancient Tianshan Ocean, resulting in the formation of several magmatic Cu–Ni sulphide deposits.  相似文献   

Geochemistry and zircon U–Pb chronology of charnockites in the Yinshan Block,North China Craton: tectonic evolution involving Neoarchaean ridge subduction     

《International Geology Review》2012,54(13):1688-1704

The Yinshan Block, part of the Neoarchaean basement of the Western Block of the North China Craton, is composed of granite–greenstone and granulite–charnockite complexes. We report research on a suite of charnockites from the granulite–charnockite complex and characterize their geochemistry, zircon U–Pb geochronology, and Hf isotopic composition. The charnockites can be divided into intermediate (SiO₂ = 59–63 wt.%) and silicic (SiO₂ = 69–71 wt.%) groups. U–Pb zircon data yield protolith formation ages of 2524 ± 4 Ma, 2533 ± 15 Ma, followed by metamorphism at 2498 ± 3 Ma, 2490 ± 11 Ma, respectively, for these groups. Although the intermediate charnockites are characterized by higher Al₂O₃, TiO₂, Fe₂O₃^T, MnO, MgO, CaO, P₂O₅, K₂O, Sr, and ΣREE content than the silicic charnockites, the ages and Hf isotopic composition of zircons and REE patterns of both intermediate and silicic charnockites are remarkably consistent, which indicates that they are genetically related. These charnockites are predominantly metaluminous to slightly peraluminous, calc-alkalic to calcic, and magnesian – characteristics generally related to a subduction setting. High-Sr + Ba granites with low K₂O/Na₂O characteristics, shown by these charnockites, imply a mixture of mafic and felsic magmas generated from an enriched mantle + lower crust. High MgO, Ni, Cr and Mg#, low K₂O/Na₂O, and metaluminous to slightly peraluminous natures imply that the source rocks most likely were amphibolites. Coeval calc-alkaline magmatism and high-T granulite-facies metamorphism under low-H₂O activity in the area lead us to propose a model involving mid-ocean ridge subduction within a Neoarchaean convergent margin. The arc-related rocks accreted along the continent margin, and became a barrier when the lithospheric mantle ascended through the slab window. Melt derived from the decompressing mantle mixed with melt derived from the overlying, juvenile lower crust melt, which was warmed and metamorphosed by the ascending lithospheric mantle.  相似文献