Journal articles: 'Potassic and Ultrapotassic rocks'

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Che, Dong, Mianping Zheng, Yuanyi Zhao, Zhaozhi Zhang, Chuanyong Ye, Enyuan Xing, Xuefei Zhang, and Mingming Li. "High Degree of Differentiation and Enrichment of Li, Rb and Cs in Potassic-Ultrapotassic Volcanic Rocks: An Example from the Lhasa Block, Tibet." Minerals 13, no. 3 (February 28, 2023): 342. http://dx.doi.org/10.3390/min13030342.

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Post-collisional potassic-ultrapotassic volcanic rocks are widely developed in the Lhasa block, Qinghai-Tibet region. In this paper, it was observed for the first time that dilute alkali elements–Li, Rb, and Cs–exhibit supernormal enrichment in the research data of numerous potassic-ultrapotassic volcanic rocks in the Lhasa block. At the same time, there are few studies on the genesis of enrichment. Currently, 568 sets of published volcanic rock data and 8 sets of measured data in the Lhasa block are sorted in detail, and the genesis of dilute alkali element enrichment is explained by means of geochemical research methods. It is believed that the high degree of magmatic fractionation of potassic-ultrapotassic volcanic rocks in the Lhasa block is the main reason for the abnormal enrichment of dilute alkali elements such as Li, Rb, and Cs. The abnormal enrichment area is mainly located in the central and western parts of the Lhasa block with an age range of 25–13 Ma. The discrimination range of Zr/Hf and Nb/Ta with a high degree of differentiation of potassic-ultrapotassic volcanic rocks in the Lhasa block is divided by analogy with the research results of highly fractionated granites, which provides a reference for the study of the supernormal enrichment of dilute alkali elements in potassic-ultrapotassic volcanic rocks in this area.

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Förster, Michael W., Stephan Buhre, Bo Xu, Dejan Prelević, Regina Mertz-Kraus, and Stephen F. Foley. "Two-Stage Origin of K-Enrichment in Ultrapotassic Magmatism Simulated by Melting of Experimentally Metasomatized Mantle." Minerals 10, no. 1 (December 31, 2019): 41. http://dx.doi.org/10.3390/min10010041.

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The generation of strongly potassic melts in the mantle requires the presence of phlogopite in the melting assemblage, while isotopic and trace element analyses of ultrapotassic rocks frequently indicate the involvement of subducted crustal lithologies in the source. However, phlogopite-free experiments that focus on melting of sedimentary rocks and subsequent hybridization with mantle rocks at pressures of 1–3 GPa have not successfully produced melts with K2O >5 wt%–6 wt%, while ultrapotassic igneous rocks reach up to 12 wt% K2O. Accordingly, a two-stage process that enriches K2O and increases K/Na in intermediary assemblages in the source prior to ultrapotassic magmatism seems likely. Here, we simulate this two-stage formation of ultrapotassic magmas using an experimental approach that involves re-melting of parts of an experimental product in a second experiment. In the first stage, reaction experiments containing layered sediment and dunite produced a modally metasomatized reaction zone at the border of a depleted peridotite. For the second-stage experiment, the metasomatized dunite was separated from the residue of the sedimentary rock and transferred to a smaller capsule, and melts were produced with 8 wt%–8.5 wt% K2O and K/Na of 6–7. This is the first time that extremely K-enriched ultrapotassic melts have been generated experimentally from sediments at low pressure applicable to a post-collisional setting.

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Goodfellow, Wayne D., Mike P. Cecile, and Matthew I. Leybourne. "Geochemistry, petrogenesis, and tectonic setting of lower Paleozoic alkalic and potassic volcanic rocks, Northern Canadian Cordilleran Miogeocline." Canadian Journal of Earth Sciences 32, no. 8 (August 1, 1995): 1236–54. http://dx.doi.org/10.1139/e95-101.

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The Northern Canadian Cordilleran Miogeocline developed intermittently during the early Paleozoic and hosts alkalic and ultrapotassic volcanic rocks that are spatially restricted in thin beds and lenses and isolated volcanic piles. On the basis of geochemistry and geographic location, these volcanic rocks are subdivided into five main groups. Group I rocks (Porter Puddle and Macmillan rocks) are potassic basanites characterized by high Nb, Ce, and Nb/Y and low Zr/Nb. They are chemically similar to the Mountain Diatreme, indicating a genetic link. Group II rocks (Porter Puddle, Niddery, and Macmillan rocks) are also potassic but have lower abundances of Nb and Ce, higher Zr/Nb, and lower Nb/Y. Group III rocks (Vulcan and Itsi Lakes) are also potassic but are chemically variable, have lower contents of high field strength elements (HFSE) than the groups I and II rocks, and contain elevated Ba contents. Groups I–III are characterized by mica (biotite and phlogopite) phenocrysts, sanidine, augite, and Ba-feldspar, a mineral assemblage typical of ultrapotassic lavas. Group IV (Whale Mountain) alkali basalts are the least enriched in the large ion lithophile elements and have relatively low contents of HFSE compared with Groups I and II basalts. Groups I–III are consistent with partial melting of a previously metasomatized lithospheric mantle that was variably enriched in Ba, Nb, and Ce, whereas the group IV rocks are more typical of asthenospherically derived oceanic island basalt partial melts. The geochemistry of the volcanic rocks is consistent with paleotectonic models of the Selwyn Basin. The Selwyn Basin is a passive continental rift that underwent episodic extension and associated subsidence throughout the lower Paleozoic. Alkalic volcanism, and spatially and temporally associated Ba and base metal mineralization, is concentrated along rift-parallel normal faults, particularly where these faults are offset by transform faults.

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Melluso, L., R. K. Srivastava, C. M. Petrone, V. Guarino, and A. K. Sinha. "Mineralogy and magmatic affinity of the Jasra intrusive complex, Shillong Plateau, India." Mineralogical Magazine 76, no. 5 (October 2012): 1099–117. http://dx.doi.org/10.1180/minmag.2012.076.5.03.

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AbstractThe rocks of the Jasra intrusive complex (Shillong Plateau, northeastern India) include phlogopite clinopyroxenites (with olivine or perovskite relics), alkali gabbros/monzodiorites, syenites and nepheline syenites. They have a potassic affinity (Na2O/K2O ∼1), and their mineralogy is dominated by clinopyroxene with which phlogopite, olivine, amphibole, feldspars, feldspathoids, oxides, orthopyroxenes, perovskite, titanite and other accessory phases are variably associated. The Jasra intrusive rocks are cumulates derived from at least two distinct magmatic liquids. The potassic affinity of the Jasra rocks differs from the nearby Sung Valley ijolitic-carbonatitic complex and from the ultrapotassic lamproitic rocks of the Damodar Valley, which are of approximately the same age. This suggests major variability in the mantle sources of small-volume alkaline volcanism in the Early Cretaceous of northeastern India.

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Plá Cid, Jorge, Cristiani S. Campos, Lauro V. S. Nardi, and Luana Florisbal. "Petrology of Gameleira potassic lamprophyres, São Francisco Craton." Anais da Academia Brasileira de Ciências 84, no. 2 (May 8, 2012): 377–98. http://dx.doi.org/10.1590/s0001-37652012005000030.

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Gameleira lamprophyres are dykes and mafic microgranular enclaves associated with the shoshonitic Gameleira monzonite. This association belongs to the Paleoproterozoic alkaline magmatism from Serrinha nucleus, northeast Brazil. The liquidus paragenesis is diopside, pargasite, apatite and mica. Reverse zoning was identified in the groundmass alkali feldspar and was related to the undercooling of lamprophyric magma during the emplacement, with high growth rate of pargasite/edenite inducing disequilibrium between feldspars and liquid. Chemical data indicate that the lamprophyres are basic rocks (SiO2 < 48 wt%), with alkaline character (Na2O + K2O > 3 wt%) and potassic signature (K2O/Na2O ≈ 2). High contents of MgO and Cr are consistent with a signature of a primary liquid, and such concentrations, as well as Al, K, P, Ba, Ni- and light rare earth elements, are consistent with an olivine-free metasomatic mantle source enriched in amphibole, clinopyroxene and apatite. By contrast, the ultrapotassic lamprophyres from Morro do Afonso, contemporaneous alkaline ultrapotassic magmatism in Serrinha nucleus, were probably produced by melting of a clinopyroxene-phlogopite-apatite enriched-source. The identification of different mineral paragenesis in the source of potassic and ultrapotassic lamprophyres from Serrinha nucleus can contribute to the understanding of the mantle heterogeneities and tectonic evolution of this region.

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Peccerillo, Angelo. "Potassic and ultrapotassic rocks : Compositional characteristics, petrogenesis, and geologic significance." Episodes 15, no. 4 (December 1, 1992): 243–51. http://dx.doi.org/10.18814/epiiugs/1992/v15i4/002.

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Palmer, M. R., E. Y. Ersoy, C. Akal, İ. Uysal, Ş. C. Genç, L. A. Banks, M. J. Cooper, J. A. Milton, and K. D. Zhao. "A short, sharp pulse of potassium-rich volcanism during continental collision and subduction." Geology 47, no. 11 (September 23, 2019): 1079–82. http://dx.doi.org/10.1130/g45836.1.

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Abstract Potassic volcanic rocks are characteristic of collisional tectonic zones, with recycling of continental crust playing an important role in their generation. Potassium-rich partial melts and/or fluids derived from subducted continental material initiate and/or mix with mantle-derived melts and then erupt at the surface with varying degrees of interaction with the overlying lithosphere. The details of how continental material incorporates into mantle melts are, however, uncertain. In particular, the depths from which the potassium-rich fluids and/or melts are released from the continental material and then react with the mantle-derived melts remain a subject of debate. We have measured the boron isotope composition of volcanic rocks from Western Anatolia (Turkey) that erupted between 52 and 0.1 Ma, and span the lifetime of collisional events from initial arc-type eruptions to post-collisional volcanism. These data and other geochemical indices show that ultrapotassic volcanism was mainly confined to a narrow window between ca. 20 and 15 Ma, consistent with recycling of high-pressure phengite, with the timing of the potassic volcanism coincident with slab rollback and breakoff.

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Carlier, G., J. P. Lorand, J. P. Liégeois, M. Fornari, P. Soler, V. Carlotto, and J. Cárdenas. "Potassic-ultrapotassic mafic rocks delineate two lithospheric mantle blocks beneath the southern Peruvian Altiplano." Geology 33, no. 7 (2005): 601. http://dx.doi.org/10.1130/g21643.1.

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Mitchell, Roger H. "Igneous Rock Associations 26. Lamproites, Exotic Potassic Alkaline Rocks: A Review of their Nomenclature, Characterization and Origins." Geoscience Canada 47, no. 3 (September 28, 2020): 119–42. http://dx.doi.org/10.12789/geocanj.2020.47.162.

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Lamproite is a rare ultrapotassic alkaline rock of petrological importance as it is considered to be derived from metasomatized lithospheric mantle, and of economic significance, being the host of major diamond deposits. A review of the nomenclature of lamproite results in the recommendation that members of the lamproite petrological clan be named using mineralogical-genetic classifications to distinguish them from other genetically unrelated potassic alkaline rocks, kimberlite, and diverse lamprophyres. The names “Group 2 kimberlite” and “orangeite” must be abandoned as these rock types are varieties of bona fide lamproite restricted to the Kaapvaal Craton. Lamproites exhibit extreme diversity in their mineralogy which ranges from olivine phlogopite lamproite, through phlogopite leucite lamproite and potassic titanian richterite-diopside lamproite, to leucite sanidine lamproite. Diamondiferous olivine lamproites are hybrid rocks extensively contaminated by mantle-derived xenocrystic olivine. Currently, lamproites are divided into cratonic (e.g. Leucite Hills, USA; Baifen, China) and orogenic (Mediterranean) varieties (e.g. Murcia-Almeria, Spain; Afyon, Turkey; Xungba, Tibet). Each cratonic and orogenic lamproite province differs significantly in tectonic setting and Sr–Nd–Pb–Hf isotopic compositions. Isotopic compositions indicate derivation from enriched mantle sources, having long-term low Sm/Nd and high Rb/Sr ratios, relative to bulk earth and depleted asthenospheric mantle. All lamproites are considered, on the basis of their geochemistry, to be derived from ancient mineralogically complex K–Ti–Ba–REE-rich veins, or metasomes, in the lithospheric mantle with, or without, subsequent contributions from recent asthenospheric or subducted components at the time of genesis. Lamproite primary magmas are considered to be relatively silica-rich (~50–60 wt.% SiO2), MgO-poor (3–12 wt.%), and ultrapotassic (~8–12 wt.% K2O) as exemplified by hyalo-phlogopite lamproites from the Leucite Hills (Wyoming) or Smoky Butte (Montana). Brief descriptions are given of the most important phreatomagmatic diamondiferous lamproite vents. The tectonic processes which lead to partial melting of metasomes, and/or initiation of magmatism, are described for examples of cratonic and orogenic lamproites. As each lamproite province differs with respect to its mineralogy, geochemical evolution, and tectonic setting there is no simple or common petrogenetic model for their genesis. Each province must be considered as the unique expression of the times and vagaries of ancient mantle metasomatism, coupled with diverse and complex partial melting processes, together with mixing of younger asthenospheric and lithospheric material, and, in the case of many orogenic lamproites, with Paleogene to Recent subducted material.

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Cellai, Daniela, Sandro Conticelli, and Silvio Menchetti. "Crystal-chemistry of clinopyroxenes from potassic and ultrapotassic rocks in central Italy: implications on their genesis." Contributions to Mineralogy and Petrology 116, no. 3 (April 1994): 301–15. http://dx.doi.org/10.1007/bf00306499.

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Ayer, John A., and Jaroslav Dostal. "Nd and Pb isotopes from the Lake of the Woods greenstone belt, northwestern Ontario: implications for mantle evolution and the formation of crust in the southern Superior Province." Canadian Journal of Earth Sciences 37, no. 12 (December 1, 2000): 1677–89. http://dx.doi.org/10.1139/e00-067.

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Nd and Pb isotopes from the Lake of the Woods greenstone belt indicate the presence of three distinct reservoir sources: old enriched crust (>3.0 Ga); pre-2.7 Ga, homogeneous depleted mantle; and post-2.70 Ga heterogeneous mantle. EpsilonNd values of +1.1 to +2.3 for ultramafic to felsic metavolcanic rocks (2.742.72 Ga) indicate derivation from depleted mantle. The εNd value of 0.9 for younger turbidite (2.71 Ga), in conjunction with detrital zircon ages ranging from 2.72 to 3.0 Ga, indicates detritus from local greenstone belt sources (depleted mantle) mixed with an older crustal source. Post-2.70 Ga heterogeneity is demonstrated by εNd values ranging from 0.4 to +0.4 in shoshonitic to calc-alkaline metavolcanic rocks and +2.1 in a coeval ultrapotassic pluton. Pb isotopes from the pluton indicate derivation from a depleted mantle reservoir with an initial 207Pb/204Pb of 14.52, an initial 206Pb/204Pb of 13.29, and µ1 of 7.86. Isotopic comparison with post-2.70 Ga potassic suites from across the Superior Province indicates widespread mixing between depleted mantle and enriched end members. The enriched end member has isotopic characteristics of rocks derived from old crustal terrains, such as the Winnipeg River and Opatica subprovinces. This type of isotopic heterogeneity could be the result of crustal contamination or derivation from metasomatized mantle. Contamination of the mantle wedge by influx of fluids derived from partial melting of isotopically evolved, subducted sediments is favoured for the Superior Province potassic suite, because elevated concentration of Sr, Nd, and Pb in conjunction with primitive Mg#s suggest only limited crustal contamination has occurred.

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Jia, Xiaohui, Xiaodi Wang, and Wenqiang Yang. "Petrogenesis and geodynamic implications of the early Paleozoic potassic and ultrapotassic rocks in the South China Block." Journal of Asian Earth Sciences 135 (March 2017): 80–94. http://dx.doi.org/10.1016/j.jseaes.2016.12.013.

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Marchev, Peter, Raya Raicheva, Stoyan Georgiev, Ivan P. Savov, and Danko Jelev. "Formation of ultrapotassic magma via crustal contamination and hybridization of mafic magma: an example from the Stomanovo monzonite, Central Rhodope Massif, Bulgaria." Geological Magazine 159, no. 1 (October 18, 2021): 81–96. http://dx.doi.org/10.1017/s0016756821000868.

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AbstractGenerally all orogenic ultrapotassic rocks are formed after melting of metasomatized sub-continental lithospheric mantle via subducted crustal mica-bearing lithologies. Here we present another possible model, based on the study of the small Stomanovo ultrapotassic monzonite porphyry intrusion in the Central Rhodope Massif, Bulgaria. The monzonite dated at 30.50 ± 0.46 Ma is intruded into the voluminous Oligocene (31.63 ± 0.40 Ma) Bratsigovo–Dospat ignimbrite. The monzonite hosts both normally and reversely zoned clinopyroxene phenocrysts. The normally zoned clinopyroxene is characterized by gradually diminishing core-to-rim Mg no. (89–74), whereas the reversely zoned clinopyroxene has green Fe-rich cores (Mg no. 71–55) mantled by normally zoned clinopyroxene (Mg no. 87–74). Neither the core of the normally zoned clinopyroxene nor the Fe-rich green cores are in equilibrium with the host monzonite. This ultrapotassic monzonite shows more radiogenic Sr isotopes ((87Sr/86Sr)i = 0.71066) and ϵNd(t) = −7.8 to −8.0 that are distinct from the host ignimbrites with (87Sr/86Sr)i = 0.70917–0.70927 and ϵNd(t) = −4.6 to −6.5. The Sr–Nd isotopic data and the presence of copious zircon xenocrysts from the underlying metamorphic basement suggest extensive crustal assimilation. Our observations indicate that the Stomanovo ultrapotassic monzonite formed after extensive lower or middle crustal fractional crystallization from an evolved magma producing cumulates. The process was followed by hybridization with primitive mantle-derived magma and subsequent continuous crustal contamination. We suggest that instead of inheriting their high K2O and large-ion lithophile element enrichments from slab-derived/metasomatic fluids, the Stomanovo ultrapotassic monzonite may owe some of its unusually high alkalinity to the assimilation of potassium-rich phases from the Rhodope Massif basement rocks.

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Huang, X. L., Y. Niu, Y. G. Xu, L. L. Chen, and Q. J. Yang. "Mineralogical and Geochemical Constraints on the Petrogenesis of Post-collisional Potassic and Ultrapotassic Rocks from Western Yunnan, SW China." Journal of Petrology 51, no. 8 (June 11, 2010): 1617–54. http://dx.doi.org/10.1093/petrology/egq032.

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Coulson, Ian M., James K. Russell, and Gregory M. Dipple. "Origins of the Zippa Mountain pluton: a Late Triassic, arc-derived, ultrapotassic magma from the Canadian Cordillera." Canadian Journal of Earth Sciences 36, no. 9 (September 1, 1999): 1415–34. http://dx.doi.org/10.1139/e99-045.

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The Zippa Mountain intrusion is of Late Triassic age and is situated in the Iskut River area of northwest British Columbia. The pluton is elliptical in shape and 3.5 by 5 km in diameter. The pluton intrudes Palaeozoic and Triassic rocks within Stikinia and is compositionally zoned from clinopyroxenite at the pluton margins to a core of syenite. The Zippa Mountain pluton comprises aegirine-augite, potassium feldspar, and minor biotite, hornblende, nepheline, vishnevite, titanian andradite, titanite, and apatite. Based on new field, petrographic, and chemical data this intrusion is shown to be silica-undersaturated, strongly alkaline, and ultrapotassic. We interpret the pluton as a single pulse of magma, which entered a shallow-level crustal magma chamber. The potassic nature is a characteristic of the parental magma, but is enhanced by fractional crystallization and crystal sorting processes. The parental magma has affinities with arc-type magmas related to subduction (shoshonitic magma series), as is evidenced by high LILE/LREE ratio, and select depletion of HFSE. Upon emplacement, crystallization of clinopyroxene and then K-feldspar, and efficient physical sorting within the magma chamber, resulted in sidewall, marginal pyroxenite and roof-zone syenites, respectively. Continued fractionation in the core of the intrusion increased volatile contents and led to the crystallization of feldspathoids. Potentially, a mass of residual melt, and crystals of K-feldspar and feldspathoid, was buoyant relative to the surrounding pyroxenite, which allowed it it to rise and partly intrude the syenites.

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Chayka, Ivan F., Alexander V. Sobolev, Andrey E. Izokh, Valentina G. Batanova, Stepan P. Krasheninnikov, Maria V. Chervyakovskaya, Alkiviadis Kontonikas-Charos, Anton V. Kutyrev, Boris M. Lobastov, and Vasiliy S. Chervyakovskiy. "Fingerprints of Kamafugite-Like Magmas in Mesozoic Lamproites of the Aldan Shield: Evidence from Olivine and Olivine-Hosted Inclusions." Minerals 10, no. 4 (April 9, 2020): 337. http://dx.doi.org/10.3390/min10040337.

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Mesozoic (125–135 Ma) cratonic low-Ti lamproites from the northern part of the Aldan Shield do not conform to typical classification schemes of ultrapotassic anorogenic rocks. Here we investigate their origins by analyzing olivine and olivine-hosted inclusions from the Ryabinoviy pipe, a well preserved lamproite intrusion within the Aldan Shield. Four types of olivine are identified: (1) zoned phenocrysts, (2) high-Mg, high-Ni homogeneous macrocrysts, (3) high-Ca and low-Ni olivine and (4) mantle xenocrysts. Olivine compositions are comparable to those from the Mediterranean Belt lamproites (Olivine-1 and -2), kamafugites (Olivine-3) and leucitites. Homogenized melt inclusions (MIs) within olivine-1 phenocrysts have lamproitic compositions and are similar to the host rocks, whereas kamafugite-like compositions are obtained for melt inclusions within olivine-3. Estimates of redox conditions indicate that “lamproitic” olivine crystallized from anomalously oxidized magma (∆NNO +3 to +4 log units.). Crystallization of “kamafugitic” olivine occurred under even more oxidized conditions, supported by low V/Sc ratios. We consider high-Ca olivine (3) to be a fingerprint of kamafugite-like magmatism, which also occurred during the Mesozoic and slightly preceded lamproitic magmatism. Our preliminary genetic model suggests that low-temperature, extension-triggered melting of mica- and carbonate-rich veined subcontitental lithospheric mantle (SCLM) generated the kamafugite-like melts. This process exhausted carbonate and affected the silicate assemblage of the veins. Subsequent and more extensive melting of the modified SCLM produced volumetrically larger lamproitic magmas. This newly recognized kamafugitic “fingerprint” further highlights similarities between the Aldan Shield potassic province and the Mediterranean Belt, and provides evidence of an overlap between “orogenic” and “anorogenic” varieties of low-Ti potassic magmatism. Moreover, our study also demonstrates that recycled subduction components are not an essential factor in the petrogenesis of low-Ti lamproites, kamafugites and leucitites.

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Liu, Dong, Zhidan Zhao, Di-Cheng Zhu, Yaoling Niu, Donald J. DePaolo, T. Mark Harrison, Xuanxue Mo, et al. "Postcollisional potassic and ultrapotassic rocks in southern Tibet: Mantle and crustal origins in response to India–Asia collision and convergence." Geochimica et Cosmochimica Acta 143 (October 2014): 207–31. http://dx.doi.org/10.1016/j.gca.2014.03.031.

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Tian, Shi-Hong, Zhu-Sen Yang, Zeng-Qian Hou, Xuan-Xue Mo, Wen-Jie Hu, Yue Zhao, and Xiao-Yan Zhao. "Subduction of the Indian lower crust beneath southern Tibet revealed by the post-collisional potassic and ultrapotassic rocks in SW Tibet." Gondwana Research 41 (January 2017): 29–50. http://dx.doi.org/10.1016/j.gr.2015.09.005.

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Castorina, F., F. Stoppa, A. Cundari, and M. Barbieri. "An enriched mantle source for Italy's melilitite-carbonatite association as inferred by its Nd-Sr isotope signature." Mineralogical Magazine 64, no. 4 (August 2000): 625–39. http://dx.doi.org/10.1180/002646100549652.

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AbstractNew Sr-Nd isotope data were obtained from Late Pleistocene carbonatite-kamafugite associations from the Umbria-Latium Ultra-Alkaline District of Italy (ULUD) with the aim of constraining their origin and possible mantle source(s). This is relevant to the origin and evolution of ultrapotassic (K/Na ≫2) and associated rocks generally, notably the occurrences from Ugandan kamafugites,Western Australian lamproites and South African orangeites. The selected ULUD samples yielded 87Sr/86Sr and 143Nd/144Nd ranging from 0.7100 to 0.7112 and from 0.5119 to 0.5121 respectively, similar to cratonic potassic volcanic rocks with higher Rb/Sr and lower Sm/Nd ratios than Bulk Earth. Silicate and carbonate fractions separated from melilitite are in isotopic equilibrium, supporting the view that they are cogenetic. The ULUD carbonatites yielded the highest radiogenic Sr so far reported for carbonatites. In contrast, sedimentary limestones from ULUD basement formations are lower in radiogenic Sr, i.e. 87Sr/86Sr = 0.70745–0.70735. The variation trend of ULUD isotopic compositions is similar to that reported for Ugandan kamafugites and Western Australian lamproites and overlaps the values for South African orangeites in the εSr-εNd diagram. A poor correlation between Sr/Nd and 87Sr/86Sr ratios in ULUD rocks is inconsistent with a mantle source generated by subduction-driven processes, while the negligible Sr and LREE in sedimentary limestones from the ULUD region fail to account for a hypothetical limestone assimilation process. The Nd model ages of 1.5–1.9 Ga have been inferred for a possible metasomatic event, allowing further radiogenic evolution of the source, a process which may have occurred in isolation until eruption time. While the origin of this component remains speculative, the Sr-Nd isotope trend is consistent with a simple mixing process involving an OIB-type mantle and a component with low εNd and high εSr.

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AKAL, CÜNEYT. "K-richterite–olivine–phlogopite–diopside–sanidine lamproites from the Afyon volcanic province, Turkey." Geological Magazine 145, no. 4 (April 24, 2008): 570–85. http://dx.doi.org/10.1017/s0016756808004536.

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AbstractMiddle Miocene volcanic activity in the Afyon volcanic province (eastern part of Western Anatolia) is characterized by multistage potassic and ultrapotassic alkaline volcanic successions. The volcanism is generally related to the northward subduction of the African plate beneath the Eurasian Plate. In Afyon, the Middle Miocene volcanic products consist of melilite leucitite, tephriphonolite, trachyte, basaltic–trachyandesite, phonolite, phonotephrite, tephriphonolite and lamproite rocks. Near-surface emplacement and relatively quiescent subaerial eruptions of lamproitic magma produced different emplacement forms such as dome/plug-shaped bodies and lava flows, showing variation in volume and texture. The mineralogical constituents of the lamproites are sanidine, olivine (77 < Mg no. < 81), phlogopite (74 < Mg no. < 78), K-richterite, clinopyroxene (74 < Mg no. < 78), with accessory apatite, calcite and opaque minerals. Afyon lamproites resemble Mediterranean-type Si-rich lamproites. Their compositional range is 50–52 wt% SiO2, 4–8 wt% MgO, and they display a typical lamproitic affinity. Chondrite-normalized REE patterns exhibit enrichment in LREE relative to HREE ((La/Yb)CN=15.3–17.0). They show extreme enrichment in LILE relative to primitive mantle values and troughs of Nb and Ti. The lamproites give a range of high initial87Sr/86Sr ratios and low143Nd/144Nd ratios. The geochemical and isotopic characteristics suggest that lamproitic magma is derived from highly metasomatized mantle. The enrichment history may include metasomatic events related to subduction, as in other active orogenic areas of the Mediterranean.

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Varol, Elif. "The derivation of potassic and ultrapotassic alkaline volcanic rocks from an orogenic lithospheric mantle source: the case of the Kalecik district, Ankara, Central Anatolia, Turkey." Neues Jahrbuch f??r Mineralogie - Abhandlungen: Journal of Mineralogy and Geoche 191, no. 1 (November 1, 2013): 55–73. http://dx.doi.org/10.1127/0077-7757/2013/0247.

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Conticelli, S., M. D'Antonio, L. Pinarelli, and L. Civetta. "Source contamination and mantle heterogeneity in the genesis of Italian potassic and ultrapotassic volcanic rocks: Sr-Nd-Pb isotope data from Roman Province and Southern Tuscany." Mineralogy and Petrology 74, no. 2-4 (March 1, 2002): 189–222. http://dx.doi.org/10.1007/s007100200004.

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Oberti, R., M. Boiocchi, F. C. Hawthorne, and P. Robinson. "Crystal structure and crystal chemistry of fluoro-potassic-magnesio-arfvedsonite from Monte Metocha, Xixano region, Mozambique, and discussion of the holotype from Quebec, Canada." Mineralogical Magazine 74, no. 6 (December 2010): 951–60. http://dx.doi.org/10.1180/minmag.2010.074.6.951.

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AbstractFluoro-potassic-magnesio-arfvedsonite, ideally AKBNa2c(Mg4Fe3+)TSi8O22wF2, has been found in a dyke ∼25 km southwest of Monte Metocha, Xixano region, northeastern Mozambique. Fluoro-potassic-magnesio-arfvedsonite and low sanidine form a fine-grained mafic, ultrapotassic, peralkaline igneous rock without visible phenocrysts. The amphibole is brittle, has a Mohs hardness of 6 and a splintery fracture; it is non-fluorescent with perfect {110} cleavage and no observable parting, and has a calculated density of 3.174 gcm−3. In plane-polarized light, it is pleochroic, X= pale grey-green, Y = blue-green, Z = pale grey; X ^ c = 23.6° (in β obtuse), Y ‖ b, Z ^ c = 66.4° (in β acute). Fluoro-potassic-magnesio-arfvedsonite is biaxial negative, α = 1.652(2), β = 1.658(2), γ = 1.660(2); 2Vobs = 22.5(7)°, 2Vcalc = 30.2°. The unit-cell dimensions are a = 9.9591(4), b = 17.9529(7), c = 5.2867(2) Å, β = 104.340(1)°, V = 919.73(10) Å3, Z = 2. The nine strongest X-ray diffraction lines in the experimental powder pattern are: [d in Å(I)(hkl)]: 2.716(100)(151), 3.410(70)(131), 8.475(50)(110), 3.178(50)(310), 3.309(30)(240), 2.762(20)(31), 2.549(20)(260), 2.351(10)(51), 2.269(10)(331). Electron microprobe analysis gave: SiO2 54.25, A12O3 0.03, TiO2 1.08, FeO 6.69, Fe2O3 8.07, MgO 13.99, MnO 0.32, ZnO 0.05, CaO 1.16, Na2O 6.33, K2O 5.20, F 2.20, H2Ocalc 0.74, sum 99.18 wt.%. The formula unit, calculated on the basis of 24 (O,OH,F) with (OH+F) = 2−(2 Ti), is AKa0.98B(Na1.18Ca0.18)∑1.99C(Mg3.07Fe0.832+Mn0.04Al0.01Fe0.903+Ti0.12Zn0.01)∑=4.98TSi8O22W[Fi.o3(OH)0.73O0.24]∑2.00 and confirms the usual pattern of cation order in the amphibole structure. The presence of a significant oxo component (locally balanced by Ti at the M(1) site) is related to the crystallization conditions. The presence of Fe3+ at the T sites, originally suggested for the holotype specimen, is discounted for this amphibole composition.

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Efremov, S. V. "Geochemistry and genesis of ultrapotassic and potassic magmatic rocks on the eastern shore of Chaun Bay in Chukotka and their role in the metallogenic specialization of tin-bearing granitoids." Russian Journal of Pacific Geology 3, no. 1 (February 2009): 80–90. http://dx.doi.org/10.1134/s1819714009010084.

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Chen, Huan, Qun-ke Xia, and Jannick Ingrin. "Water content of the Xiaogulihe ultrapotassic volcanic rocks, NE China: implications for the source of the potassium-rich component." Science Bulletin 60, no. 16 (August 2015): 1468–70. http://dx.doi.org/10.1007/s11434-015-0862-4.

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Molnár, Kata, Pierre Lahitte, Stéphane Dibacto, Zsolt Benkó, Samuele Agostini, Boglárka Döncző, Artur Ionescu, et al. "The westernmost Late Miocene–Pliocene volcanic activity in the Vardar zone (North Macedonia)." International Journal of Earth Sciences 111, no. 3 (December 24, 2021): 749–66. http://dx.doi.org/10.1007/s00531-021-02153-2.

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AbstractLate Miocene to Pleistocene volcanism within the Vardar zone (North Macedonia) covers a large area, has a wide range in composition, and is largely connected to the tectonic evolution of the South Balkan extensional system, the northern part of the Aegean extensional regime. The onset of the scattered potassic to ultrapotassic volcanism south from the Scutari-Peć transverse zone occurred at ca. 8.0 Ma based on this study. Here, we focused on three volcanic centers located on deep structures or thrust faults along the western part of the Vardar zone, for which there is none to very little geochronological and geochemical data available. Pakoševo and Debrište localities are represented as small remnants of lava flows cropping out at the southern edge of Skopje basin and at the western edge of Tikveš basin, respectively. Šumovit Greben center is considered as part of the Kožuf-Voras volcanic system, and it is located on its westernmost side, at the southern edge of Mariovo basin, which is largely composed of volcaniclastic sediments. We present new eruption ages applying the unspiked Cassignol-Gillot K–Ar technique on groundmass, as well as petrological and geochemical data, supplemented with Sr and Nd isotopes to complement and better understand the Neogene-Pleistocene volcanism in the region. Eruption ages on these rocks interlayered between sedimentary formations allow to better constrain the evolution of those sedimentary basins. Rocks from the three volcanic centers belong to the high-K calc-alkaline–shoshonitic series based on their elevated K content. The oldest center amongst these three localities, as well as other Late Miocene centers within the region, is the trachyandesitic Debrište, which formed at ca. 8.0 Ma, and exhibits the highest Nd and lowest Sr isotopic ratios (0.512441–0.512535 and 0.706759–0.706753, respectively). The basaltic trachyandesite Pakoševo center formed at ca. 3.8 Ma and its Nd and Sr isotopic ratios (0.512260 and 0.709593, respectively) bear the strongest signature of crustal contamination. The rhyolitic Šumovit Greben center is a composite volcanic structure formed at ca. 3.0–2.7 Ma. Its youngest eruption unit has a slightly higher Nd and lower Sr isotopic ratios (0.512382 and 0.709208, respectively) representing a magma with a lesser extent of crustal assimilation than the other samples from this center. The overall trend through time in the Sr and Nd isotopic ratios of the Late Miocene to Pleistocene mafic volcanic centers in the region implies an increasing rate of metasomatism of the lithospheric mantle.

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Foley, Stephen, and Angelo Peccerillo. "Potassic and ultrapotassic magmas and their origin." Lithos 28, no. 3-6 (November 1992): 181–85. http://dx.doi.org/10.1016/0024-4937(92)90005-j.

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Rios, D. C., H. Conceição, D. W. Davis, J. Plá Cid, M. L. S. Rosa, M. J. B. Macambira, I. McReath, M. M. Marinho, and W. J. Davis. "Paleoproterozoic potassic–ultrapotassic magmatism: Morro do Afonso Syenite Pluton, Bahia, Brazil." Precambrian Research 154, no. 1-2 (March 2007): 1–30. http://dx.doi.org/10.1016/j.precamres.2006.11.015.

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Efremov, S. V., and A. V. Travin. "Isotopic age and paleogeodynamic position of ultrapotassic magmatism of Central Chukotka." Geodynamics & Tectonophysics 12, no. 1 (March 21, 2021): 76–83. http://dx.doi.org/10.5800/gt-2021-12-1-0513.

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The 40Ar/39Ar dating of ultrapotassic rocks from Central Chukotka shows that these rocks are Early Cretaceous, and yields a narrow range of age variations (109 to 107 Ma), which correlates fairly well with the range of age variations of granitoids typical of the study area (117–105 Ma). There are thus grounds to suggest that the ultrapotassic magmas and granitoids resulted from the same geological process that can be identified from the material characteristics of the ultrapotassic magmas.In the modern concepts of the regional geological development, the formation of the granitoid and ultrapotassic magmas can be related to the continental lithosphere extension due to the collision of Eurasian plate and the Chukotka – Arctic Alaska continental block.Using modern genetic models based on the interpretations of the material characteristics of ultrapotassic magmas, it is possible to limit the number of genetic hypotheses and to relate the continental lithosphere extension to the processes that took place in the upper mantle of the study area.

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Prouteau, Gaelle, Rene C. Maury, Manuel Pubellier, Joseph Cotten, and Herve Bellon. "Le magmatisme post-collisionnel du Nord-Ouest de Borneo, produit de la fusion d'un fragment de croute oceanique ancre dans le manteau superieur." Bulletin de la Société Géologique de France 172, no. 3 (May 1, 2001): 319–32. http://dx.doi.org/10.2113/172.3.319.

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Abstract Magmatic activity linked to syn- or post-collisional zones leads to the emplacement of remarkably heterogeneous rocks: calc-alkaline, high-K calc-alkaline or shoshonitic series variably contaminated by continental crust; anatectic granites and ignimbrites derived from the latter; and finally alkali potassic to ultrapotassic basalts [Harris et al., 1990; Pearce et al., 1984, 1990; Arnaud et al., 1992; Benito et al., 1999]. The main sources of these magmas are either the upper mantle (sub-oceanic or subcontinental) frequently metasomatized by hydrous fluid originating from the subducted slab; or the continental crust, which can act as a contaminant [Benito et al., 1999; Miller et al., 1999] or melt directly [Harris et al., 1990; Zingg et al., 1990]. The purpose of the present paper is to document the role of a third source: the subducted oceanic crust, as evidenced by the occurrence of Miocene adakites in Sarawak (NW Borneo). The studied rocks have been sampled from western Sarawak (fig. 1), and their location is shown on the geological map [Tan, 1982] of figure 2. They mostly occur as stocks, dykes and sills which crosscut the Paleozoic to Miocene sedimentary units. Two kinds of intrusions can be distinguished. High-K calc-alkaline to medium-K calc-alkaline diorites and microdiorites occur in the northern part of the studied area, in Salak Island and Santubong Peninsula. Microtonalites and dacites occur near Kuching and in the southern part of Sarawak (Kuap and Bau areas). Whole-rock K-Ar data (table I) demonstrate that these two associations are of different ages: high-K calc-alkaline diorites were emplaced during the Lower Miocene (22.3 to 23.7 Ma), whereas the microtonalites and dacites are younger by ca. 8 Ma or more (Middle to Upper Miocene, 14.6 to 6.4 Ma). Major and trace element data (table II) show that the Lower Miocene diorites display all the usual characteristics of subduction-related magmas. The Middle to Upper Miocene microtonalites and dacites share some of these characteristics, but in addition they display typical adakitic features: SiO 2 -rich (65.5-70%) and sodic (Na 2 O/K 2 O>2) character (table II and figure 3); lack or rare occurrence of pyroxenes, usually replaced by early-crystallized (near-liquidus) amphiboles (table III); very low Y and HREE contents, consistent with the presence of residual garnet in their source, and leading to characteristically high La/Yb and Sr/Y ratios (fig. 4, 5). Their titanomagnetite-hemoilmenite associations reflect equilibrium features [Bacon and Hirschman, 1988] indicating moderate temperatures (<900 degrees C) and highly oxidizing (NNO+1) crystallization conditions [Ghiorso and Sack, 1991]. The Lower Miocene Sarawak diorites are typically subduction-related from a geochemical point of view. They likely derive from the evolution of island-arc basaltic magmas, which themselves originated from the partial melting of upper mantle peridotites previously metasomatized by hydrous fluids expelled from the subducting oceanic slab [Tatsumi et al., 1986; Tatsumi, 1989]. The origin of the Middle-Upper Miocene adakitic microtonalites and dacites is different. According to previous studies, they likely derive from the partial melting of metabasalts (garnet amphibolites or eclogites) from subducted oceanic crust [Defant and Drummond, 1990; Defant et al., 1991, 1992; Drummond et al., 1996; Maury et al., 1996; Martin, 1993, 1999]. Their position in the hybrid tonalite+peridotite system [Caroll and Wyllie, 1989] shows that they crystallized within the garnet stability field and likely interacted with the upper mantle during their ascent (fig. 7). This feature is not consistent with their genesis through melting of metabasalts accreted at the base of the Borneo continental crust. In addition, the less evolved Sarawak adakites display mineralogical and geochemical features remarkably similar to those of the 1991 Mt Pinatubo dacite, the experimental petrology of which has been extensively studied at low [2 kbar; Scaillet and Evans, 1999; Rutherford and Devine, 1996] to medium pressures [4 to 20 kbar; Prouteau et al., 1999]. Such dacitic magmas are not in equilibrium with garnet at pressures lower than or equal to 20 kbar, which rules out their derivation from metabasalts tectonically or magmatically accreted to the base of the North Borneo continental crust. We propose, instead, that they originated from the partial melting of basalts from a fragment of oceanic lithosphere within the upper mantle. Like the adakites of Central Mindanao, Philippines [Sajona et al., 1994, 1997 and 2000; Maury et al., 1996] and those from Aird Hills, Papua-New Guinea [Smith et al., 1979; Defant and Drummond, 1990] the Sarawak adakites represent potential markers of the occurrence at depth of oceanic crust slivers, which could be much more common in collision zones than previously thought.

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Nardi, Lauro V. S., Jorge Plá-Cid, Maria de Fátima Bitencourt, and Larissa Z. Stabel. "Geochemistry and petrogenesis of post-collisional ultrapotassic syenites and granites from southernmost Brazil: the Piquiri Syenite Massif." Anais da Academia Brasileira de Ciências 80, no. 2 (June 2008): 353–71. http://dx.doi.org/10.1590/s0001-37652008000200014.

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The Piquiri Syenite Massif, southernmost Brazil, is part of the post-collisional magmatism related to the Neoproterozoic Brasiliano-Pan-African Orogenic Cycle. The massif is about 12 km in diameter and is composed of syenites, granites, monzonitic rocks and lamprophyres. Diopside-phlogopite, diopside-biotite-augite-calcic-amphibole, are the main ferro-magnesian paragenesis in the syenitic rocks. Syenitic and granitic rocks are co-magmatic and related to an ultrapotassic, silica-saturated magmatism. Their trace element patterns indicate a probable mantle source modified by previous, subduction-related metasomatism. The ultrapotassic granites of this massif were produced by fractional crystallization of syenitic magmas, and may be considered as a particular group of hypersolvus and subsolvus A-type granites. Based upon textural, structural and geochemical data most of the syenitic rocks, particularly the fine-grained types, are considered as crystallized liquids, in spite of the abundance of cumulatic layers, schlieren, and compositional banding. Most of the studied samples are metaluminous, with K2O/Na2O ratios higher than 2. The ultrapotassic syenitic and lamprophyric rocks in the Piquiri massif are interpreted to have been produced from enriched mantle sources, OIB-type, like most of the post-collisional shoshonitic, sodic alkaline and high-K tholeiitic magmatism in southernmost Brazil. The source of the ultrapotassic and lamprophyric magmas is probably the same veined mantle, with abundant phlogopite + apatite + amphibole that reflects a previous subduction-related metasomatism.

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Prelević, D., S. F. Foley, V. Cvetković, and R. L. Romer. "The analcime problem and its impact on the geochemistry of ultrapotassic rocks from Serbia." Mineralogical Magazine 68, no. 4 (August 2004): 633–48. http://dx.doi.org/10.1180/0026461046840209.

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AbstractTertiary ultrapotassic volcanic rocks from Serbia occasionally display low levels of K2O and K2O/ Na2O. In these rocks, analcime regularly appears as pseudomorphs after pre-existing leucite microphenocrysts. The process ofleucite transformation in Serbian ultrapotassic rocks is very thorough: fresh leucite survives only in ugandites from the Koritnik lava flows as well as in rare inclusions in Cpx. This paper focuses on the impact of ‘analcimization’ on the mineralogy and geochemistry ofthe Serbian ultrapotassic rocks, using the samples where leucite survived as a monitor for the process.Analcimization has had a great impact on the geochemistry of the rocks, but affects only a restricted number of chemical parameters. These are the falsification of the original K2O/Na2O ratio, the decoupling oflarge-ion lithophile elements resulting in considerable depletion of Rb and K2O, but not ofBa, and sporadic, but extreme enrichment ofCs in some analcime-bearing samples (up to 900 ppm). Analcimization is also recognized by an increase in whole-rock δ18O values of ∼3% compared to fresh rocks, which correlates with the level of whole-rock hydration. Finally, the 87Sr/86Sr enrichment at nearly constant 143Nd/144Nd demonstrated by some rocks can also be explained by the analcimization ofleucite. For samples with variable 87Sr/86Sr from the same lava flow, 87Sr/86Sr values correlate with modal analcime abundance (ex-leucite), loss on ignition of whole-rock and whole-rock δ18O values. The extreme depletion in K and enrichment in Na, together with modification of other geochemical parameters, may have led to the misinterpretation of the origin and geodynamic affiliations of the Serbian ultrapotassic rocks, had the effects of analcimization not been taken into account.

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Leat, P. T., R. N. Thompson, M. A. Morrison, G. L. Hendry, and S. C. Trayhorn. "Geodynamic significance of post-Variscan intrusive and extrusive potassic magmatism in SW England." Transactions of the Royal Society of Edinburgh: Earth Sciences 77, no. 4 (1987): 349–60. http://dx.doi.org/10.1017/s0263593300023221.

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ABSTRACTPost-Variscan magmatism in SW England involved the synchronous emplacement of basaltic and potassic lavas, minette dykes and the Cornubian granite batholith at c. 290 Ma. The basaltic and potassic rocks have high contents of Ni and Cr, which suggest that both are not excessively fractionated. The basaltic lavas are moderately enriched in LREE and LIL elements relative to HREE, whereas the chemically-varied potassic lavas are more strongly enriched in LREE and LIL elements, with notable depletions in Nb, Ta and Ti relative to LREE. These features are consistent with the view that these rocks are subduction-related. Possibly the potassic rocks were derived from an ultimate source in lithosphere subducted or downthrust during the Variscan orogeny. The source of the basaltic rocks was probably in the asthenosphere. The minette dykes are chemically similar to the potassic lavas, suggesting that they are genetically related. Most dykes occur in a zone up to 25 km wide around the margin of the granite batholith, in a “shadow-zone” relationship. The granite batholith (c. 48,000 km3) is moderately enriched in Th and HFS elements, but is strongly enriched in Rb. Rb-Th relationships indicate an origin for the granite by fractionation from potassic magma in addition to melting of crust.

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Valério, Cristóvão da Silva, Moacir José Buenano Macambira, Valmir da Silva Souza, and Elton Luiz Dantas. "SiO2-saturated potassic alkaline magmatism in the central Amazonian Craton, southernmost Uatumã-Anauá Domain, NE Amazonas, Brazil." Brazilian Journal of Geology 47, no. 3 (September 2017): 441–46. http://dx.doi.org/10.1590/2317-4889201720170044.

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ABSTRACT: This paper approaches the record of SiO2-saturated potassic alkaline magmatism of Castanhal Quartz Monzonite, Mapuera Suite, and Ladeira da Vovó Quartz Syenite. These samples are located near the Northern border of the Amazon Basin. Such rocks show K2O + 2 > Na2O and K2O/Na2O < 2 values that confirm the potassic or shoshonitic character of these rocks. The Castanhal Quartz Monzonite contains less than 20% volume of quartz, which is also a characteristic of the shoshonitic or SiO2-satured potassic alkaline A-type magma signature observed on geochemical plots. Listric faults, representing the rifting phase of Amazon Basin formation, emplaced and reworked Ladeira da Vovó Quartz Syenite, which caused its granophyric texture, probably during the Tonian period. A group of 21 zircon crystals was extracted from a hornblende quartz monzonite and yields an average age of 1872 ± 6 Ma (MSWD = 2.4). However, an additional zircon crystal yielded a Trans-Amazonian age of 2062 ± 17 Ma. These potassic alkaline rocks of Orosirian (1872 Ma) age may correspond to a post-collisional setting. Dominantly negative εHft values and Hf TDM ages reveal a large contribution of a mafic crustal component from Mesoarchean to Neoarchean age (2.95 - 2.66 Ga), and a felsic crustal component from Neoarchean to later Siderian ages (2.51 - 2.34 Ga).

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Rajesh, V. J., S. Arai, M. Santosh, and A. Tamura. "LREE-rich hibonite in ultrapotassic rocks in southern India." Lithos 115, no. 1-4 (March 2010): 40–50. http://dx.doi.org/10.1016/j.lithos.2009.11.004.

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Chung, Sun-Lin, Kuo-Lung Wang, Anthony J. Crawford, V. S. Kamenetsky, Cheng-Hong Chen, Ching-Ying Lan, and Chang-Hwa Chen. "High-Mg potassic rocks from Taiwan: implications for the genesis of orogenic potassic lavas." Lithos 59, no. 4 (December 2001): 153–70. http://dx.doi.org/10.1016/s0024-4937(01)00067-6.

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Poli, Giampiero. "Potassic igneous rocks and associated gold–copper mineralization." Lithos 56, no. 2-3 (March 2001): 265–66. http://dx.doi.org/10.1016/s0024-4937(00)00067-0.

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Valverde Cardenas, Carolina, Aphrodite Indares, and George Jenner. "Mafic and ultrapotassic rocks from the Canyon domain (central Grenville Province): geochemistry and tectonic implications." Canadian Journal of Earth Sciences 49, no. 2 (February 2012): 412–33. http://dx.doi.org/10.1139/e11-065.

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The Canyon domain and the Banded complex in the Manicouagan area of the Grenville Province preserve a record of magmatic activity from ∼1.4 to 1 Ga. This study focuses on 1.4–1.2 Ga mafic rocks and 1 Ga ultrapotassic dykes. Geochemistry and Sm–Nd isotopic signatures were used to constrain the origin of these rocks and evaluate the changing role of the mantle with time and tectonic setting from the late evolution of the Laurentian margin to the Grenvillian orogeny, in the Manicouagan area. The mafic rocks include layers inferred to represent flows, homogeneous bodies in mafic migmatite, and deformed dykes, all of which were recrystallized under granulite-facies conditions during the Grenvillian orogeny. In spite of the complexities inherent in these deformed and metamorphosed mafic rocks, we were able to recognize suites with distinctive geochemical and isotopic signatures. Integration of this data along with available ages is consistent with a 1.4 Ga continental arc cut by 1.2 Ga non-arc basalts derived from depleted asthenospheric mantle, with varied degrees of crustal contamination and inferred to represent magmatism in an extensional environment. The 1 Ga ultrapotassic dykes postdate the Grenvillian metamorphism. They are extremely enriched in incompatible elements, have negative Nb anomalies, relatively unradiogenic Sr-isotopic compositions (initial 87Sr/86Sr ~ 0.7040) and εNd –3 to –15. Some dykes have compositional characteristics consistent with derivation from the mantle, ruling out crustal contamination as a major process in their petrogenesis. The most likely source region for the ultrapotassic dykes is a metasomatized subcontinental lithospheric mantle, with thermal input from the asthenosphere in association with post-orogenic delamination.

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Wang, Yu, Stephen F. Foley, Stephan Buhre, Jeremie Soldner, and Yigang Xu. "Origin of potassic postcollisional volcanic rocks in young, shallow, blueschist-rich lithosphere." Science Advances 7, no. 29 (July 2021): eabc0291. http://dx.doi.org/10.1126/sciadv.abc0291.

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Potassium-rich volcanism occurring throughout the Alpine-Himalayan belt from Spain to Tibet is characterized by unusually high Th/La ratios, for which several hypotheses have brought no convincing solution. Here, we combine geochemical datasets from potassic postcollisional volcanic rocks and lawsonite blueschists to explain the high Th/La. Source regions of the volcanic melts consist of imbricated packages of blueschist facies mélanges and depleted peridotites, constituting a new mantle lithosphere formed only 20 to 50 million years earlier during the accretionary convergence of small continental blocks and oceans. This takes place entirely at shallow depths (<80 km) without any deep subduction of continental materials. High Th/La in potassic rocks may indicate shallow sources in accretionary settings even where later obscured by continental collision as in Tibet. This mechanism is consistent with a temporal trend in Th/La in potassic postcollisional magmas: The high Th/La signature first becomes prominent in the Phanerozoic, when blueschists became widespread.

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Diguim Kepnamou, Amadou, Naimou Seguem, Ntoumbé Mama, Amaya Adama Adama Dairou, Bello Bienvenu, Haskandi Kalaza Josue, Awé Wangmene Salomon 5, Ngounouno Ismaila, and Ngounouno Ismaila. "Petrographic and geochemical study of Doua granitoids (adamawa-yade domain, center Cameroon): Petrogenesis and geodynamic implication." International Journal of Advanced Geosciences 9, no. 2 (January 2, 2022): 99. http://dx.doi.org/10.14419/ijag.v9i2.31702.

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The region Doua is located in the central area or Adamawa-Yade domain of the Pan-African fold belt in Cameroon. This work focuses on the petrography and geochemistry of granitoids in this region. The study area is made up of plutonic rocks (amphibole and biotite granite, biotite and muscovite granite, syeno-diorite, syenite. The geochemical study of the granitoids in the area shows that the rocks are magnesian and slightly iron-bearing, potassic to hyper-potassic calc - alkaline, metaluminous and belongs to type I granitoids. The profiles of the rare earths (REE) show a negative anomaly in Eu. The multi-element spectra show positive anomalies, or negative anomalies for some samples in Ba and Negative anomalies in Nb-Ta, Sr and Ti. The process which led to the formation of these rocks is fractional crystallization. These rocks are setup in a syn-collisional subduction environment (volcanic arc granitoids).

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Pope, Alasdaire J., and Matthew F. Thirlwall. "Tectonic setting, age, and regional correlation of ultrabasic–ultrapotassic dykes in the northern Purcell Mountains, southeast British Columbia." Canadian Journal of Earth Sciences 29, no. 3 (March 1, 1992): 523–30. http://dx.doi.org/10.1139/e92-045.

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Ultrabasic–ultrapotassic dykes have been identified in the Toby–Horsethief Creek area of the Purcell Mountains, in southeast British Columbia. The dykes intrude Helikian and Hadrynian strata of the Purcell Anticlinorium, a parautochthonous terrane of folded and faulted sub-lower greenschist-facies metasediments of the ancestral Cordilleran Miogeocline. Structural–stratigraphic relationships indicate that the loci of the dykes are controlled by Helikian to Upper Paleozoic extensional fault systems associated with rifting of the ancestral passive margin.Two dyke types have been distinguished. Group A dykes are typically light green and xenolithic. They may be phlogopitephyric, and consist dominantly of carbonate (commonly pseudomorphing olivine). These dykes are transitional between group II and group III ultrapotassic rocks (rift to active orogen). Group B dykes are dark green, phlogopite- and apatitephyric, with a carbonate, apatite, chlorite, and phlogopite matrix. They are classified as group II (continental rift) ultrapotassic rocks, with kimberlitic affinities.One of the group B dykes yielded a 245 ± 2.4 Ma Rb–Sr phlogopite–apatite mineral-pair age of emplacement, which is contemporaneous with the petrogenetically and tectonically similar Cross kimberlite, in Paleozoic miogeoclinal sediments of the adjacent Rocky Mountain terrane. The presence of these group II ultrapotassic intrusives in the Purcell Mountains suggests that Helikian through Paleozoic rifting of the passive margin continued into the Permo-Triassic. Palinspastic separation of the Cross kimberlite and the Toby–Horsethief Creek dykes indicates a belt of continental rifting at least 150 km wide. An initial 87Sr/86Sr ratio of 0.70707 for the dated group B dyke suggests a (palinspatically restored) stabilized continental lithosphere source approximately 50 km to the west, and supports geophysical evidence that the Hudsonian basement extends west, below the Kootenay Arc.

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Boehnke, Patrick, Elizabeth A. Bell, Thomas Stephan, Reto Trappitsch, C. Brenhin Keller, Olivia S. Pardo, Andrew M. Davis, T. Mark Harrison, and Michael J. Pellin. "Potassic, high-silica Hadean crust." Proceedings of the National Academy of Sciences 115, no. 25 (June 4, 2018): 6353–56. http://dx.doi.org/10.1073/pnas.1720880115.

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Understanding Hadean (>4 Ga) Earth requires knowledge of its crust. The composition of the crust and volatiles migrating through it directly influence the makeup of the atmosphere, the composition of seawater, and nutrient availability. Despite its importance, there is little known and less agreed upon regarding the nature of the Hadean crust. By analyzing the 87Sr/86Sr ratio of apatite inclusions in Archean zircons from Nuvvuagittuq, Canada, we show that its protolith had formed a high (>1) Rb/Sr ratio reservoir by at least 4.2 Ga. This result implies that the early crust had a broad range of igneous rocks, extending from mafic to highly silicic compositions.

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Foley, S. F., G. Venturelli, D. H. Green, and L. Toscani. "The ultrapotassic rocks: Characteristics, classification, and constraints for petrogenetic models." Earth-Science Reviews 24, no. 2 (April 1987): 81–134. http://dx.doi.org/10.1016/0012-8252(87)90001-8.

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Edgar, A. D., and D. Vukadinovic. "Implications of experimental petrology to the evolution of ultrapotassic rocks." Lithos 28, no. 3-6 (November 1992): 205–20. http://dx.doi.org/10.1016/0024-4937(92)90007-l.

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Thompson, R. N., D. Velde, P. T. Leat, M. A. Morrison, J. G. Mitchell, A. P. Dickin, and S. A. Gibson. "Oligocene lamproite containing an Al-poor, Ti-rich biotite, Middle Park, northwest Colorado, USA." Mineralogical Magazine 61, no. 407 (August 1997): 557–72. http://dx.doi.org/10.1180/minmag.1997.061.407.08.

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AbstractA small 33 ± 0.8 Ma lamproite pluton is exposed in the midst of a 23–26 Ma basalt-rhyolite province in Middle Park, NW Colorado. It contains abundant phlogopite phenocrysts in a fine-grained groundmass of analcime pseudomorphs after leucite, biotite, potassic richterite, apatite, ilmenite and accessory diopside. The phlogopite phenocryst cores contain ∼4 wt.% TiO2, 1% Cr2O3 and 0.2% BaO. The smallest groundmass biotites have normal pleochroism but compositions unlike any previously reported, with ∼2% Al2O3, ∼8% TiO2 and F <1.5%. Apart from those elements affected by leucite alteration, both the elemental and isotopic composition of this lamproite are close to those of the Leucite Hills, Wyoming. Its Nd-isotopic model age (TDM = 1.6 Ga) is outside the Leucite Hills range but within that of other Tertiary strongly potassic magmatism in the region underlain by the Wyoming craton. Evidence from both teleseismic tomography and the mantle xenoliths within other western USA mafic ultrapotassic igneous suites shows that the total lithospheric thickness beneath NW Colorado was probably ∼150–200 km at 33 Ma, when the Middle Park lamproite was emplaced. This is an important constraint on tectonomagmatic models for the Cenozoic evolution of this northernmost part of the Rio Grande rift system.

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Dyulgerov, Momchil. "Potassic syenite from Shipka, Central Balkan Mts, Bulgaria: characterization and insight into the source." Geologica Balcanica 40, no. 1-3 (December 2011): 3–12. http://dx.doi.org/10.52321/geolbalc.40.1-3.3.

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Petrographic, mineralogical and whole-rock chemistry data from a new outcrop of peralkaline potassic syenite of presumed Variscan age near the town of Shipka, are presented here. The syenites exhibit peralkaline chemistry and very potassic character which markedly differs from nearby situated potassic monzonites, known as Shipka pluton. In spite of the close spatial association of these two bodies, genetic link between them can hardly be supposed. The syenites are composed of K-feldspar, diopside, mica and late interstitial amphibole. Mineral composition reflects the agpaitic conditions of crystallization with formation of sodic amphibole and K-feldspars with important Sr and Ba contents. These rocks have peralkaline wholerock chemistry, very high potassic content and extreme enrichment in LILE, LREE, Th and U. Their trace element signature and isotope characteristics are in favour of derivation from metasomaticaly enriched mantle source.

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Soder, Christian G., and Rolf L. Romer. "Post-collisional Potassic–Ultrapotassic Magmatism of the Variscan Orogen: Implications for Mantle Metasomatism during Continental Subduction." Journal of Petrology 59, no. 6 (June 1, 2018): 1007–34. http://dx.doi.org/10.1093/petrology/egy053.

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Melfos, Vasilios, Panagiotis Voudouris, Margarita Melfou, Matías G. Sánchez, Lambrini Papadopoulou, Anestis Filippidis, Paul G. Spry, et al. "Mineralogical Constraints on the Potassic and Sodic-Calcic Hydrothermal Alteration and Vein-Type Mineralization of the Maronia Porphyry Cu-Mo ± Re ± Au Deposit in NE Greece." Minerals 10, no. 2 (February 18, 2020): 182. http://dx.doi.org/10.3390/min10020182.

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The Maronia Cu-Mo ± Re ± Au deposit is spatially related to a microgranite porphyry that intruded an Oligocene monzonite along the Mesozoic Circum-Rhodope belt in Thrace, NE Greece. The magmatic rocks and associated metallic mineralization show plastic and cataclastic features at the south-eastern margin of the deposit that implies emplacement at the ductile-brittle transition, adjacent to a shear zone at the footwall of the Maronia detachment fault. The conversion from ductile to brittle deformation caused a rapid upward magmatic fluid flow and increased the volume of water that interacted with the host rocks through high permeable zones, which produced extensive zones of potassic and sodic-calcic alteration. Potassic alteration is characterized by secondary biotite + K-feldspar (orthoclase) + magnetite + rutile + quartz ± apatite and commonly contains sulfides (pyrite, chalcopyrite, pyrrhotite). Sodic-calcic alteration consists of actinolite + sodic-calcic plagioclase (albite/oligoclase/andesine) + titanite + magnetite + chlorite + quartz ± calcite ± epidote-allanite. The high-oxidation state of the magmas and the hydrothermal fluid circulation were responsible for the metal and sulfur enrichments of the aqueous fluid phase, an increase in O2 gas content, the breakdown of the magmatic silicates and the production of the extensive potassic and sodic-calcic alterations. Brittle deformation also promoted the rapid upward fluid flow and caused interactions with the surrounding host rocks along the high temperature M-, EB-, A- and B-type veins.

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Dyulgerov, Momchil. "Dating of Variscan magmatism in Kraishte and Balkan Mts." Review of the Bulgarian Geological Society 83, no. 3 (December 2022): 73–76. http://dx.doi.org/10.52215/rev.bgs.2022.83.3.73.

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New age determinations by in-situ zircon and titanite LA-ICP-MS analysis for Variscan magmatic activity from Kraishte and Balkan Mts. are reported. The results confirm the presumed Variscan age of the magmatic rocks. For the Sedemte Prestola potassic granitoids, titanite dating reveal an age of 308.7±9.1 Ma. The zircon dating of potassic syenites, cropping out west of Shipka town gave less consistent results – 355±89 Ma. For potassic-alkaline syenite porphyries from the Lutskan pluton, Variscan 206Pb/238U ages cluster in 328–308 Ma interval. Zircons dating of potassic quartzdiorite porphyry from the Lutskan pluton display important inheritance with single 206Pb/238U age of 316 Ma, whereas results of titanite dating range between 350 and 315 Ma, defining poor isochrone of 301±91 Ma and MSWD of 5.6. Zircons from gabbro-diorite porphyries, cutting the Lutskan granitoids plotted on Terra-Wasserburg diagram yield Variscan age of 312±21 Ma and Concordia age of 296±4.6 Ma.

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Castor, S. B. "THE MOUNTAIN PASS RARE-EARTH CARBONATITE AND ASSOCIATED ULTRAPOTASSIC ROCKS, CALIFORNIA." Canadian Mineralogist 46, no. 4 (August 1, 2008): 779–806. http://dx.doi.org/10.3749/canmin.46.4.779.

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Journal articles on the topic 'Potassic and Ultrapotassic rocks'

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