A red bole zircon record of cryptic silicic volcanism in the Deccan Traps, India

Silicic magmas within large igneous provinces (LIPs) are understudied relative to volumetrically dominant mafic magmas despite their prevalence and possible contribution to LIP-induced environmental degradation. In the 66 Ma Deccan LIP (India), evolved magmatism is documented, but its geographic distribution, duration, and significance remain poorly understood. Zircons deposited in weathered Deccan lava flow tops (“red boles”) offer a means of indirectly studying potentially widespread, silicic, explosive volcanism spanning the entire period of flood basalt eruptions. We explored this record through analysis of trace elements and Hf isotopes in zircon crystals previously dated by U–Pb geochronology. Our results show that zircon populations within individual red boles fingerprint distinct volcanic sources that likely developed in an intraplate setting on cratonic Indian lithosphere. However, our red bole zircon geochemical and isotopic characteristics do not match those from previously studied silicic magmatic centers, indicating that they must derive from yet undiscovered or understudied volcanic centers associated with the Deccan LIP.

Spatiotemporal evolution of large igneous provinces and their related rifts in North China craton: Role in craton breakup and destruction

The North China craton is encircled by four successive triple-conjugated rifts, which are respectively centers of large igneous provinces (LIPs) of bimodal compositions, i.e., Xiong'er rift (south, ca. 1.78 Ga Taihang LIP), Yanliao rift (north, ca. 1.32 Ga Yanliao LIP), Xuhuai rift (east, ca. 1.23 Ga Licheng and ca. 0.92 Ga Dashigou LIPs), and Langshan rift (west, ca. 0.82 Ga Qianlishan LIP). These rifts are genetically related with their contemporaneous LIPs based on their consistent geometry. Spatial migration of these rifts and LIPs indicates their propagation from along one marginal side to the opposite side of the craton, which may results in the sequential breakup of the proto-North China craton from one side to another during 1.8-0.8 Ga. However, the observation that the lithosphere under the LIP-associated rift regions is less destructed (decratonized) in the Mesozoic indicates a possible role of LIPs in strengthening intracratonic steady state. This study shows that LIPs may change craton stability in either direction.

Platinum Group Elements in the South Transbaikalian Basanites (First Data)

—Study of the behavior and distribution of platinum group elements (PGE), along with other data, is necessary for geodynamic reconstructions. There are almost no PGE data for Transbaikalia, one of the large regions of Russia. This work presents the first data on the contents and behavior of PGE in the Cenozoic intraplate alkali basaltoids of southern Transbaikalia. The total PGE contents are 20–40 ppb. The PGE pattern of the studied basanites is similar to those of mafic OIB, including the Hawaiian ones, and rocks of large igneous provinces: tholeiitic basalts of the Siberian Platform and basaltoids of the West Siberian Plate. Based on this similarity and on the intraplate location of the South Transbaikalian basanites, we have concluded that the basanitic melts formed under mantle plume impact.

Oceanic and super-deep continental diamonds share a transition zone origin and mantle plume transportation

Rare oceanic diamonds are believed to have a mantle transition zone origin like super-deep continental diamonds. However, oceanic diamonds have a homogeneous and organic-like light carbon isotope signature (δ13C − 28 to − 20‰) instead of the extremely variable organic to lithospheric mantle signature of super-deep continental diamonds (δ13C − 25‰ to + 3.5‰). Here, we show that with rare exceptions, oceanic diamonds and the isotopically lighter cores of super-deep continental diamonds share a common organic δ13C composition reflecting carbon brought down to the transition zone by subduction, whereas the rims of such super-deep continental diamonds have the same δ13C as peridotitic diamonds from the lithospheric mantle. Like lithospheric continental diamonds, almost all the known occurrences of oceanic diamonds are linked to plume-induced large igneous provinces or ocean islands, suggesting a common connection to mantle plumes. We argue that mantle plumes bring the transition zone diamonds to shallower levels, where only those emplaced at the base of the continental lithosphere might grow rims with lithospheric mantle carbon isotope signatures.

Existence of the DHArwar-BAstar-SInghbhum (DHABASI) megacraton since 3.35 Ga: Constraints from the Precambrian Large Igneous Province record

We propose a Precambrian megacraton (consisting of two or more ancient cratons) ‘DHABASI’ in the Indian Shield that includes the Dharwar, Bastar and Singhbhum cratons. This interpretation is mainly based on seven large igneous provinces (LIPs) that are identified in these three cratons over the age range of ca. 3.35-1.77 Ga, a period of at least 1.6 Gyr. The absence of any subsequent breakup of ‘DHABASI’ since 1.77 Ga suggests that this megacraton has existed for the past 3.35 Gyr.In addition to their use in recognizing this megacraton, these LIP events may also provide likely targets for Cu-Ni-Cr-Co-PGE deposits. We suggest that the megacraton ‘DHABASI’ was an integral part of supercontinents/supercratons through Earth's history, and that it should be utilized as a distinct building block for paleocontinental reconstructions rather than using the individual Dharwar, Bastar and Singhbhum cratons.

Large Igneous Provinces of the Amazonian Craton and their Metallogenic Potential in Proterozoic Times

This paper overviews the Proterozoic Large Igneous Provinces of the Amazonian Craton, characterized by large volumes of extrusive and intrusive magmatic rocks. We reassess the geologic, geochronologic and geochemical information to stablish three intracontinental felsic volcanic-plutonic igneous belts (i.e., SLIPs), namely: Orocaima (1.98-1.96 Ga), Uatumã (1.88-1.87 Ga) and Alta Floresta (1.80-1.79 Ga). The Avanavero LIP (1.79-1.78 Ga), as well as the Rincón del Tigre-Huanchaca LIP (1.11 Ga) are also revisited. The relationships of these events with intraplate settings through time and space are apparent. We examine the main characteristics of each magmatic event in light of the U-Pb zircon and baddeleyite ages and coupled isotopic-geochemical constraints, the geodynamic significance, and metallogenetic potential. The Uatumã and Alta Floresta SLIPs host the most important mineral resources within the Amazonian Craton. Global barcode matches of the Proterozoic SLIPS/LIP events of Amazonia are also addressed, as well as their possible links with geologic time-scale periods: the Orosirian, Statherian and Stenian boundaries. We also evaluate the available paleomagnetic data to address issues related to the barcode match of such SLIP/LIP events in the context of supercontinent cycles.

Sub-lithospheric mantle sources for overlapping southern African Large Igneous Provinces

At least four spatially overlapping Large Igneous Provinces, each of which generated ∼1 x 106 km3 or more of basaltic magmas over short time intervals (<5 m.y.), were emplaced onto and into the Kaapvaal Craton between 2.7 and 0.18 Ga: Ventersdorp (2 720 Ma, ∼0.7 x 106 km3), Bushveld (2 056 Ma, ∼1.5 x 106 km3), Umkondo (1 105 Ma, ∼2 x 106 km3) and Karoo (182 Ma, ∼3 x 106 km3). Each of these has been suggested to have been derived from melting of sub-continental lithospheric mantle (SCLM) sources, but this is precluded because: (1) each widespread heating event sufficient to generate 1 to 2 x 106 km3 of basalt from the Kaapvaal SCLM (volume = 122 to 152 x 106 km3) would increase residual Mg# by 0.5 to 2 units, depending on degree of melting, and source and melt composition, causing significant depletion in already-depleted mantle, (2) repeated refertilization of the Kaapvaal SCLM would necessarily increase its bulk density, compromising its long-term buoyancy and stability, and (3) raising SCLM temperatures to the peridotite solidus would also have repeatedly destroyed lithospheric diamonds by heating and oxidation, which clearly did not happen. It is far more likely, therefore, that the Kaapvaal LIPs were generated from sub-lithospheric sources, and that their diverse geochemical and isotopic signatures represent variable assimilation of continental crustal components. Combined Sr and Nd isotopic data (n = 641) for the vast volumetric majority of Karoo low-Ti tholeiitic magmatic products can be successfully modelled as an AFC mixing array between a plume-derived parental basalt, with <10% of a granitic component derived from 1.1 Ga Namaqua-Natal crust. Archaean crustal materials are far too evolved (εNd ∼ -35) to represent viable contaminants. However, a very minor volume of geographically-restricted (and over-analysed) Karoo magmas, including picrites, nephelinites, meimechites and other unusual rocks may represent low-degree melting products of small, ancient, enriched domains in the Kaapvaal SCLM, generated locally during the ascent of large-volume, plume-derived melts. The SCLM-derived rocks comprise the well-known high-Ti (>2 to 3 wt.% TiO2) magma group, have εNd, 182 values between +10.5 and -20.9, and are characteristically enriched in Sr (up to 1 500 ppm), suggesting a possible connection to kimberlite, lamproite and carbonatite magmatism. These arguments may apply to continental LIPs in general, although at present, there are insufficient combined Sr + Nd isotopic data with which to robustly assess the genesis of other southern African LIPs, including Ventersdorp (n = 0), Bushveld (n = 55) and Umkondo (n = 18).