Emplacement Of Granitic Rocks Research Articles

Fluid Evolution and Ore Genesis of the Juyuan Tungsten Deposit, Beishan, NW China

The newly discovered Juyuan tungsten deposit is hosted in Triassic granite in the Beishan Orogen, NW China. The tungsten mineralization occurred as quartz veins, and the main ore minerals included wolframite and scheelite. The age, origin, and tectonic setting of the Juyuan tungsten deposit, however, remain poorly understood. According to the mineralogical assemblages and crosscutting relationships, three hydrothermal stages can be identified, i.e., the early stage of quartz veins with scheelite and wolframite, the intermediate stage of quartz veinlets with sulfides, and the late stage of carbonate-quartz veinlets with tungsten being mainly introduced in the early stage. Quartz formed in the two earlier stages contained four compositional types of fluid inclusions, i.e., pure CO2, CO2-H2O, daughter mineral-bearing, and NaCl-H2O, but the late-stage quartz only contained the NaCl-H2O inclusions. The inclusions in quartz formed in the early, intermediate, and late stages had total homogenization temperatures of 230–344 °C, 241−295 °C, and 184−234 °C, respectively, with salinities no higher than 7.2 wt.% NaCl equiv (equivalent). Trapping pressures estimated from the CO2-H2O inclusions were 33−256 MPa and 36−214 MPa in the early and intermediate stages, corresponding to mineralization depths of 3–8 km. Fluid boiling and mixing caused rapid precipitation of wolframite, scheelite, and sulfides. Through boiling and inflow of meteoric water, the ore-forming fluid system evolved from CO2-rich to CO2-poor in composition and from magmatic to meteoric, as indicated by decreasing δ18Owater values from early to late stages. The sulfur and lead isotope compositions in the intermediate-stage suggest that the Triassic granite was a significant source of ore metals. The biotite 40Ar/39Ar age from the W-bearing quartz shows that the Juyuan tungsten system was formed at 240.0 ± 1.0 Ma, coeval with the emplacement of granitic rocks at the deposit. Integrating the data obtained from the studies including regional geology, ore geology, biotite Ar-Ar geochronology, fluid inclusion, and C-H-O-S-Pb isotope geochemistry, we conclude that the Juyuan tungsten deposit was a quartz-vein type system that originated from the emplacement of the granites, which was induced by collision between the Tarim and Kazakhstan–Ili plates. A comparison of the characteristics of tungsten mineralization in East Tianshan and Beishan suggests that the Triassic tungsten metallogenic belt in East Tianshan extends to the Beishan orogenic belt and that the west of the orogenic belt also has potential for the discovery of further quartz-vein-type tungsten deposits.

Zircon Ages from the Baydrag Block and the Bayankhongor Ophiolite Zone: Time Constraints on Late Neoproterozoic to Cambrian Subduction‐ and Accretion‐Related Magmatism in Central Mongolia

Central Mongolia represents a heterogeneous crustal domain of the Central Asian Orogenic Belt and is composed of contrasting lithotectonic units with distinct preorogenic histories. We report single‐zircon evaporation and SHRIMP ages for high‐grade rocks of the Neoarchean‐Paleoproterozoic Baydrag block and for metaigneous rocks of the junction between the late Neoproterozoic Bayankhongor ophiolite zone (BOZ) and the Baydrag block. Zircon ages for metamorphic rocks of the Baydrag block indicate a major tectonothermal event between 1840 and 1826 Ma, coeval with the emplacement of granitic rocks at middle‐crustal level dated at 1839 Ma. A granite‐gneiss yielded a much younger crystallization age of 1051 Ma, the first Grenvillian age reported for this region. Together with predominantly Mesoproterozoic detrital zircon ages for a quartzite lens from the Burd Gol accretionary complex, these data attest to the heterogeneity and long Precambrian history of the Baydrag block. Crystallization ages for granite‐gneisses from the northeastern margin of the Baydrag block indicate prolonged plutonic activity between 579 and 537 Ma, probably related to southward subduction of the Bayankhongor oceanic crust. A syntectonic granite vein yielded a crystallization age of 519 Ma, probably linked to accretion of the BOZ onto the northeastern active margin of the Baydrag block. Lastly, a felsic metavolcanic rock from the southeastern termination of the BOZ yielded a crystallization age of 472 Ma and suggests that punctuated volcanic centers developed during the early Ordovician in response to protracted convergence.

Boron isotope composition of tourmalinite and vein tourmalines associated with gold mineralization, Serra do Itaberaba Group, central Ribeira Belt, SE Brazil

Important concentrations of tourmaline occur as gold-bearing stratiform tourmalinites and in mineralized quartz–tourmaline veins at the Tapera Grande and Quartzito gold prospects in the Mesoproterozoic Serra do Itaberaba Group, central Ribeira Belt (São Paulo State, SE Brazil). The main rock types in both prospects constitute the volcanic–sedimentary Morro da Pedra Preta Formation, which formed in a submarine back-arc setting. At Tapera Grande, the volcanic–sedimentary sequence is composed of metabasic and metavolcaniclastic rocks, graphitic and sulfur-rich metapelites, banded iron formation, metandesite, metarhyolite, calc-silicates, tourmalinites and metahydrothermalites derived from mafic and felsic rocks. The Mesoproterozoic rocks at Quartzito prospect are lithologically similar but they have been affected by Neoproterozoic faulting and shearing and by the emplacement of granitic rocks, resulting in the formation of tourmaline-rich quartz–carbonate veins with gold and base metal mineralization. We conducted a chemical and B-isotope study of tourmalines in order to better understand the origin of the stratiform tourmalinites in the Morro da Pedra Preta Formation and their relationship with gold mineralization. The overall range of δ 11B values obtained for the tourmalinite and vein tourmalines is between − 15‰ and − 5‰, with the tourmalinites falling at the low end of this range (− 15 to − 8‰). Such values are typical for continental crust and inconsistent with a primary marine boron signature as expected from the submarine-exhalative model for the gold prospects. We conclude from this that tourmaline formed or recrystallized from crustal fluids related to the amphibolite-grade metamorphism which affected the Serra do Itaberaba Group and that gold deposition occurred syn- to post-peak metamorphism by phase immiscibility, as attested by fluid inclusions in Tapera Grande tourmalinite tourmaline and quartz. The vein-hosted tourmalines at Quartzito have isotopically variable boron signatures, with heavier δ 11B values of − 5‰ to − 8‰ for acicular green tourmalines and lighter values (− 15‰ to − 7‰ for light blue, Ti-free tourmaline from quartz–carbonate veins). We attribute the heavier boron to fluids derived from the volcano-sedimentary rocks of marine affinity whereas the lighter boron was contributed by crustal fluids related to the granitoids or metasediments in the continental crust.

U–Pb constraints on the thermotectonic evolution of the Vernon antiform and the age of the Aberdeen gneiss complex, southeastern Canadian Cordillera

The Aberdeen gneiss complex is composed of complexly deformed migmatitic orthogneiss and paragneiss situated within the core of the Vernon antiform, a structure defined by a series of subparallel reflectors visible at upper to middle crustal depths (6–18 km) in seismic reflection data from the Vernon area of the Shuswap metamorphic complex. The Vernon antiform and the Aberdeen gneiss complex lie within the footwall of the gently west dipping (top to the west) Kalamalka Lake shear zone. Migmatitic gneiss exposed within the antiform records evidence (recorded as age domains in complexly zoned zircon grains) of three metamorphic events, occurring at 155–150, 90, and 66–51 Ma. The timing of magmatic events within the antiform includes emplacement of diorite at ~232 Ma, tonalite at ~151 Ma, granodiorite at 102 Ma, and monzonite at 52 Ma. Middle to Late Jurassic metamorphism resulted in widespread migmatization. Early Tertiary metamorphism (66–51 Ma) was coeval with the emplacement of granitic rocks and exhumation typical of other areas of the Shuswap metamorphic complex. Highly deformed orthogneiss situated within the hanging wall of the Kalamalka Lake shear zone, comprising the superstructure, was emplaced at ~171 Ma. Ductile deformation had ceased by 162 Ma. The complex metamorphic and magmatic evolution of the Vernon antiform, which is similar to other areas of the southern Canadian Cordillera including the Nicola horst, Mount Lytton – Eagle plutonic complex, Cariboo Mountains, and Mica Creek area, may reflect episodic tectonic activity at the plate margin.

Phanerozoic crustal growth: U–Pb and Sr–Nd isotopic evidence from the granites in northeastern China

Northeastern China (NE China) is an eastern part of the Central Asian Orogenic Belt (CAOB). Its geology is distinguished by extensive distribution of Phanerozoic granitic and acid volcanic rocks. The granitoids comprise mainly I- (especially the highly fractionated felsic I-) and A-type granites; S-type granites are conspicuously absent. New zircon U–Pb and Rb–Sr mineral isochron ages, together with previously published results, indicate that these granites were emplaced in Late Paleozoic to Late Mesozoic times. Most of the granites are characterized by low initial 87Sr/ 86Sr ratios (0.705±0.001), positive ε Nd( T) values (+4 to 0) and fairly young T DM model ages (500–1300 Ma), suggesting that a significant proportion of the granites is of juvenile origin. In contrast, some granites emplaced within Precambrian terranes (or microcontinents) in this area show negative ε Nd( T) values of 0 to −8, and higher T DM ages of 1500–2000 Ma. This suggests that the Precambrian basement rocks have exerted a significant role in the generation of these granites. Sr–Nd isotopic modeling shows that these granites are likely to have been produced by partial melting of mixed sources, mostly probably of Phanerozoic underplated basaltic and lower crustal rocks. The generation of the granites with negative ε Nd( T) values involved a smaller proportion of basaltic component (≈40%), whereas the dominant granites with positive ε Nd( T) values require a much greater amount of basaltic material (55–85%). The emplacement of granitic rocks with such a large proportion of mantle-derived component indicates a massive addition of juvenile continental crust in NE China. We propose that the granites were formed in an anorogenic tectonic setting and that underplating of basaltic liquid as a result of extension is an important mechanism for the continental growth.

Isotopic structure and tectonics of the central Transantarctic mountains

Regional patterns of Nd, Sr, and O isotopic ratios of ∼500 Ma granitic rocks are used to identify the ages and areal extents of three crustal provinces in the central Transantarctic Mountains. One of the provinces is the edge of the East Antarctic Craton, which isotopic analyses show is composed of Archean rocks thrust over Proterozoic rocks. The other two provinces compose the Beardmore microcontinent, which we deduce was allochthonous to East Antarctica and was emplaced in late Precambrian or early Paleozoic time. Evidence for a former ocean basin between the Beardmore microcontinent and East Antarctica is provided by basalt and gabbro of mid‐ocean ridge character, dated by Sm‐Nd at ∼760 Ma, associated with marine sediments now located at the suture. The granitic rocks formed over a westward‐dipping subduction zone that was active at ∼500 Ma. The East Antarctic Craton is exposed in the Miller Range, which is a tectonic composite of reworked Archean and early Proterozoic material containing ∼500 Ma peraluminous granites with model ages (TDM) of 2.0 Ga, high δ18O (+11 to +12‰) and high initial 87Sr/86Sr (0.7324 to 0.7417). East of the Marsh Glacier the granitic rocks are metaluminous to weakly peraluminous with model ages of 1.3 to 1.8 Ga, high δ18O (+9 to +13‰) and lower 87Sr/86Sr (0.7068 to 0.7191). East of the Shackleton Glacier, gabbro, tonalite, diorite, and granodiorite have low δ18O (+6 to +7‰), low initial 87Sr/86Sr (0.7045 to 0.7059) and high ϵNd (+0.4 to +1.7). These isotopic provinces correspond to differences in age and composition of the middle and lower crust at the time of formation of the granitic magmas. The boundaries of the isotopic provinces also correspond to discontinuities in provenance, lithology, structural style, and grade of metamorphism of prebatholithic metasedimentary rocks. The isotopic data indicate that the granitic magmas were formed mostly by crustal anatexis in the areas west of the Shackleton Glacier. This is typical of early Paleozoic granitic batholiths elsewhere in the world and has led to speculation that subduction was not involved in granitic magmatism at that time of earth history. However, the granitic rocks located west of the Shackleton Glacier, by virtue of their mantle‐like isotopic compositions and their association with metavolcanic rocks, appear to be subduction‐related. The tectonic history deduced for the Gondwana margin, as represented in the central Transantarctic Mountains, began with deposition of sediments on an Atlantic‐type rifted margin at ∼760 Ma. The Beardmore microcontinent was most likely accreted in association with folding of the clastic sedimentary rocks before middle Early Cambrian time (550 Ma). Carbonate sedimentation and volcanism along the eastern margin of the Beardmore microcontinent commenced in Cambrian time. Folding and metamorphism of all older units occurred in late Cambrian time followed by emplacement of granitic rocks at ∼500 Ma.

Structural setting and geochemistry of Archaean I-type granites in the Bardoc-Coolgardie area of the Norseman-Wiluna belt, Western Australia

Abstract Regional structures in the Bardoc-Coolgardie area of the Archaean Norseman-Wiluna greenstone belt in Western Australia developed during early, large-scale thrusting followed by a transpressional regime characterized by ENEWSW shortening and large-scale sinistral strike-slip faults. Structural relationships between granites and greenstone successions indicate emplacement of granitic rocks throughout this deformation history. Emplacement mechanisms include solid- or liquid-state diapirism, forceful dilation of country rocks, and passive stoping. I-type granites are common, and include early- and late-tectonic intrusions. The widespread occurrence of I-type granodiorite and monzogranite, probably derived by partial melting of lower continental crust or subducted oceanic crust, suggests a continental margin setting for the belt. Alkalic quartz-diorite occurs as rounded enclaves in granodiorite, and is enriched in Ba, Rb, Sr, Ce, La, P and F, which suggests a mantle-derived volatile component. These quartz-diorite melts may have formed by partial melting of metasomatized mantle or, alternatively, mantle degassing may have lowered solidus temperatures in the source region, and thus induced melting. Emplacement of hot, volatilerich quartz-diorite melts into the lower crust may have lowered solidus temperatures in the source rocks for granodiorite and monzogranite. Recent models for Archaean gold mineralization suggest that auriferous fluids contained CO 2 derived from lower crustal or mantle sources. In the Bardoc-Coolgardie area, CO 2 may have been flushed out during partial melting of the lower continental crust. However, the origin of the gold in the mineralizing fluids requires some other explanation because gold mineralization is generally a late-stage event, and took place over a considerably shorter time interval than the formation and emplacement of I-type granites.

Emplacement of Granitic Rocks in the Outer Zone of Southwest Japan and Geological Significance

With respect to the modes of occurrence, petrographical and chemical characteristics, and the responses during tectonic movements, the Southwestern Outer Zone-type Miocene granitic rocks, which are mainly within the Shimanto major belt in the outer zone of Southwest Japan, have characteristics different from either the synkinematic granitic rocks of the Hidaka major belt in northern Japan or the trondhjemitic rocks of the green tuff region in northeastern Japan, though the developmental stages of the Shimanto, Hidaka and Green Tuff orogenies are about contemporaneous with Alpine orogeny in relation to tectonic events on a world-wide basis. The Southwestern Outer Zone-type granitic rocks have not been affected either by significant regional metamorphism or by post-emplacement deformation. The kinds of xenoliths that occur in the granitic rocks, and the contamination-trends of the rocks, considered in the light of experimental studies on rock melting make it likely that the magmas were generated by early partial melting of felsic materials or geo-synclinal sediments plus later assimilation and contamination. The granitic rocks of the Southwestern Outer Zone-type were formed by post-kinematic acid plutonism of the Shimanto orogeny, and represent one of a series of products of the Alpine orogenic movement in the Circum-Pacific regions.

Sierra Nevada Plutonic Cycle: Part I, Origin of Composite Granitic Batholiths

Research Article| April 01, 1971 Sierra Nevada Plutonic Cycle: Part I, Origin of Composite Granitic Batholiths R. W KISTLER; R. W KISTLER U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar J. F EVERNDEN; J. F EVERNDEN Nuclear Monitoring Research Office, ARPA, Washington, D.C. 20301 Search for other works by this author on: GSW Google Scholar H. R SHAW H. R SHAW U.S. Geological Survey, Washington, D.C. 20242 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1971) 82 (4): 853–868. https://doi.org/10.1130/0016-7606(1971)82[853:SNPCPI]2.0.CO;2 Article history received: 09 Feb 1970 rev-recd: 08 Dec 1970 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation R. W KISTLER, J. F EVERNDEN, H. R SHAW; Sierra Nevada Plutonic Cycle: Part I, Origin of Composite Granitic Batholiths. GSA Bulletin 1971;; 82 (4): 853–868. doi: https://doi.org/10.1130/0016-7606(1971)82[853:SNPCPI]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Intrusion of Mesozoic batholiths in California and the western North America Cordillera began in the Late Triassic 210 m.y. ago and ended in the Late Cretaceous 80 m.y. ago. Emplacement of granitic rocks was apparently not continuous but was accomplished during five major epochs of intrusion at approximately 30 m.y. intervals, each epoch taking 10 to 20 m.y. to complete. A progressive transgression of epicontinental seas onto the midcontinent occurred during the same interval of time as the batholithic emplacement to the west. A penecontemporaneous deformation near the loci of granitic emplacement and a temporary regression during the major progressive transgression of seas onto the midcontinent are correlated with each intrusive epoch. The locus of Mesozoic granitic rocks was a source of sediments during most of the period of time required to emplace the batholiths; the origin of the batholithic magmas cannot be related only to localized down-warping of geosynclines. The source of the major proportion of the mobile granodioritic magmas of the Sierra Nevada was within the mantle, as is indicated by Sr isotope data. All plutons now exposed in the Sierra Nevada, whether of Cretaceous age or older, were emplaced at depths of a very few kilometers, the shallowest having been emplaced at depths of 4 km or less. The spatial relationships among these synchronous geologic phenomena and the geochemical and geophysical data from the same region are accounted for by a northwestward drift of North America in the region of the western Cordillera of the United States onto and across a Mesozoic feature that had characteristics like present-day oceanic rises. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Permian volcanism and its relation to the tectonic development of Sumatra

The Permian volcanic deposits covering an extensive area southeast of Lake Singkarak, Central Sumatra, have been mapped in detail and studied in relation to the structural development of the pre-Tertiary Sumatra orogene. During the Permian time, Central Sumatra was occupied by an elongated sea basin in which thick sequence of bathyal and neritic sediments were deposited. Pelitic sediments dominated, but at the same time volcanic activity started in this area. The volcanic products comprise mainly flow of hornblende and augite andesites with their tuffs. In some parts of Southern Sumatra the volcanic activity lasted till Cretaceous time. The main phase of folding took place about 120 m.y. ago accompanied by an emplacement of granitic rocks. After an uplift in younger Cretaceous time, the area was strongly attacked by erosion. The regional geologic history of Sumatra revealed clearly a divergent behaviour from the classical concept of magmatic evolution in an orogenic belt as demonstrated by the dominantly andesitic character of the geosynclinal volcanism. Other examples of volcanism associated with geosynclinal subsidence, possessing an andesitic rather than a basaltic character, could also be observed in the Tertiary Sunda mountain system of Sumatra. The Indonesian examples and similar occurrences of andesitic volcanism during a geosynclinal subsidence in other parts of the world, show that much work still will have to be done in order to gain a better undestanding regarding the relationship between volcanism and orogenesis.

Zircon Ages of Precambrian Granitic Rocks, Northeastern Wisconsin

U-Pb isotopic analyses of cogenetic zircon fractions from four granitic bodies in northeastern Wisconsin yielded the following concordia intercept ages: Amberg Granite and Newingham Granodiorite, ; Hoskin Lake Granite, ; Dunbar Gneiss, Emplacement of granitic rocks in this area therefore appears to have occurred during a time interval extending over and not exceeding a few tens of millions of years, presumably as part of the Penokean orogeny. Moreover, the sequence of ages agrees with geologic evidence, with the possible exception of the problematical Dunbar Gneiss. Slight differences in slopes and intercepts of the chords defined by the zircon data indicate that no single simple mechanism can explain the observed isotopic disturbance patterns.