Elemental distribution and neodymium isotopic composition of Silurian metasediments, western Maine, USA: Redistribution of the rare earth elements

Pelitic schists from the lower garnet to lower staurolite zones from the Rangeley, Perry Mountain, and Smalls Falls formations of western Maine were analyzed for major elements, trace elements, and neodymium isotopes. These formations were derived from highlands created during the Taconian orogeny, deposited into a trough, and metamorphosed during subsequent orogenic events. Most major and trace element abundances relative to Al2O3 were statistically identical between zones of the same formation, as well as between formations. Although the average major element composition of these formations are the same, there are systematic variations in some elements. Notably, plots of SiO2 vs. Al2O3 and K2O vs. Al2O3 suggest that most of the variation could be produced by mixing of a fairly constant ratio of clay minerals and feldspar with varied amounts of quartz due to sorting in the sedimentary system. Different amounts of these minerals should not influence the shape of the REE patterns of the metapelites, but higher amounts of quartz and feldspar may dilute the REEs and most elemental abundances of the clay minerals and lead to lower elemental abundances. The major difference between the samples within the Perry Mountain Formation are different LREE and MREE abundances relative to Al2O3 which are not correlated to differences in major element or other trace element abundances relative to Al2O3. The samples in the Perry Mountain with higher LREE and MREE abundances have, for example, 42.3 ± 8.3 ppm, and those with low abundances have 5.6 ± 3.6 ppm. The samples with the high REE abundances of the Perry Mountain Formation are similar in abundances and REE patterns to those of the Rangeley and Smalls Falls formations typical of mudstones derived from granitoids. Another difference between the low and high REE abundance samples are the calculated Tdm model ages. The high REE abundance samples of the Perry Mountain Formation show Tdm similar to the samples of the Rangeley Formation, with ages of about 1.7–1.8 Ga. The Perry Mountain samples with low REE abundances, however, give unrealistically old Tdms between 2.5 and 5.3 Ga. These unrealistically old Tdms are due to the relatively high Sm/Nd ratios (compared to crustal values) which are characteristic of samples of the Perry Mountain Formation with lower REE abundances. We therefore suggest that these samples may be indicators for open system behavior of the neodymium isotopic system. The timing of this disturbance of the neodymium isotope system is difficult to determine and cannot be tied to weathering or a definite postdepositional event. The complexities of the data suggest more than one resetting event. The most likely event that could have produced much of the movement of the LREEs and MREEs could have been due to small scale migration between anoxic hemipelagites and turbidite mudstones during diagenesis, but some migration may have continued during metamorphism in order to reconcile the neodymium isotopic data

A Geologic Classification of Worldwide Seismic Sites

Broadband seismic data recorded by more than 200 stations in two permanent networks, GSN and GEOSCOPE, have been widely used to investigate a large array of problems related to the structure and dynamics of the earth\u27s interior. Yet so far there still is a lacking of a standard database of the geological setting in the vicinity of each of the stations. We are being funded by the National Science Foundation to compile such a database based on information provided by many previous studies. The geological setting in the vicinity of the stations has been classified broadly into a number of categories: Mesozoic-Cenozoic or Precambrian plateau basalts, Phanerozoic or Precambrian platform sedimentary rocks, Mesozoic-Cenozoic or Paleozoic orogenic provinces, Precambrian orogenic provinces (0.8 to 1.6 Ga, 0.6 to 0.8 Ga, 1.6 to 2.5 Ga, 2.5 to 3.5 Ga, and older than 3.5 Ga years old), and oceanic islands. In addition, these groups have been further sub-classified as to the types of rocks or environments in which the rocks are present. For instance, the oceanic islands have been classified as oceanic rise tholeiites (e.g., Iceland), ocean floor hotspot islands (either mostly tholeiiitic sequences, or mostly alkalic), continental mid-ocean islands (e.g., Seychelles Islands-mostly composed of granitoids), oceanic-oceanic subduction (e.g., Adak Island, the Aleutian arc), or oceanic-continental subduction (e.g., Kodiak Island, the Aleutian arc). The resulting comprehensive database, once completed, will become an essential resource for the study of the crust and mantle beneath the stations using various geophysical techniques, such as shear-wave splitting analysis, crustal thickness and Vp/Vs measurements, and seismic tomography and seismic wave attenuation analyses

Crustal Thickness beneath Ocean Islands

We measured the thickness of the Earth\u27s crust beneath about two dozen of the GDSN or GEOSCOPE stations located on ocean islands by stacking moveout-corrected high-quality P-to-S receiver functions (RFs). The RFs were filtered in the 0.05-0.5 Hz frequency bands to compress strong noises that are common for ocean island stations. Given the small (less than 2 s) time separation between the direct P and the P-to-S converted phase from the Moho, the PSmS phase, which has a negative polarity and can be clearly observed at almost all the stations, is used for the stacking. Preliminary resulting thickness at each of the stations is as follows: AFI (12.4 km), AIS (13.6), ASCN (9.6), BBSR (9.9), BORG (9.4), CRZF (6.6), GUMO (8.0), HNR (8.0), HOPE (19.0), KIP (13.0), MSEY (10.7), MSVF (15.1), NOUC (15.1), PAF (8.9), POHA (17.0), PPT (12.3), PTCN (10.4), RAR (12.8), RER (13.8), RPN (9.3), SEY (14.9), SHEL (17.5), TBT (14.1), XMAS (11.8). Crustal thickness at some of the stations has been measured previously, and our results are in general agreement with those measurements. Possible age-dependence of the resulting thickness and geological implications in the understanding of plume-lithosphere interactions and formation of ocean islands will be presented

Sedimentary evolution of the Mesozoic continental redbeds using geochemical and mineralogical tools: the case of Upper Triassic to Lowermost Jurassic Monte di Gioiosa mudstones (Sicily, southern Italy)

The continental redbeds from the Internal Domains of the central-western Mediterranean Chains have an important role in the palaeogeographic and palaeotectonic reconstructions of the Alpine circum-Mediterranean orogen evolution since these redbeds mark the Triassic- Jurassic rift-valley stage of Tethyan rifting. The composition and the sedimentary evolution of the Middle Triassic to Lowermost Jurassic continental redbeds of the San Marco d’Alunzio Unit (Peloritani Mountains, Southern Italy), based on mineralogical and chemical analyses, suggests that the studied mudrock sediments share common features with continental redbeds that constitute the Internal Domains of the Alpine Mediterranean Chains. Phyllosilicates are the main components in the mudrocks. The 10 A ° -minerals (illite and micas), the I–S mixed layers, and kaolinite are the most abundant phyllosilicates. The amount of illitic layers in I–S mixed layers coupled with the illite crystallinity values (IC) are typical of high degree of diagenesis, corresponding to a lithostatic/tectonic loading of about 4–5 km. The mineralogical assemblage coupled with the A-CN-K plot suggest post-depositional K-enrichments. Palaeoweathering proxies (PIA and CIW) record intense weathering at the source area. Further, the studied sediments are affected by reworking and recycling processes and, as consequence, it is likely these proxies monitor cumulative effect of weathering. The climate in the early Jurassic favoured recycling and weathering occurred under hot, episodically humid climate with a prolonged dry season. The source-area is the low-grade Paleozoic metasedimentary basement. Mafic supply is minor but not negligible as suggested by provenance proxies

Elemental mobility during the weathering of exposed lower crust: the kinzigitic paragneisses from the Serre, Calabria, southern Italy

Weathering and transportation studies of the chemical composition of sediments have determined how surface fractionation processes modify the elemental signature due to provenance and tectonic setting of siliciclastic rocks. Although the bulk of the exposed upper continental crust comprises granitoids, metamorphic rocks from the intermediate to lower crust may be, in some geological contexts, the provenance of siliciclastic sediments. A preferential enrichment of the LREE relative to the HREE is observed in weathered, garnet-rich, kinzigitic paragneisses from the Calabrian Arc, southern Italy. This fractionation is due mostly to the mineralogical control exerted by monazite, which is concentrated in the silt-size fraction of the soil. However, a significant part of HREE, released during garnet alteration, is trapped by secondary minerals in the clay-sized fraction of the soil, in a manner similar to Pb2+ and Cs+, cations of some concern in environmental geochemistry. In the weathered material monazite is also important in controlling the Eu-anomaly, the negative size of which increases with increasing Th addition. The Eu-anomaly in the clay-sized fraction of the soil is very similar to that of the fresh rock, suggesting that the Eu/Eu* index in pelitic sediments deriving from the intermediate to lower crust may be regarded as a reliable indicator of parental affinity. Other provenance indicators include La/Th, which share the same mineralogical control; indicators of contrasting mafic and felsic provenance, e.g. Sc/Th, should be used with care

Better Together: Connecting with Other Disciplines Builds Students\u27 Own Skills and Professional Identity

The Summer Research Community (SRC) at Boise State University brings STEM (science, technology, engineering, and mathematics) students together with faculty and other students from social sciences and humanities to form an interdisciplinary summer experience. The SRC was founded with impetus from a National Science Foundation grant to create efficiencies among NSF and other STEM education initiatives and to address critical junctures for undergraduate STEM students and faculty