EVIDENCE OF RARE EARTH ELEMENT ENRICHMENT IN SEDIMENTARY ROCKS FROM PENNSYLVANIA

The mid-Paleozoic volcanics of northern Sierra Nevada consist of the Sierra Buttes rhyolites, the Taylor basalts and andesites, and the Keddie Ridge basalt–latite–rhyolite suite. The Sierra Buttes calc-alkaline rhyolites display strong light rare-earth element enrichment and negative εNd values. The Taylor basalts and andesites in the northern Hough and Genesee blocks exhibit calc-alkaline affinities (REE rare-earth element patterns highly enriched in LREE), whereas in the southern Hough block they are tholeiitic (flat rare-earth element patterns). The abundance of silicic lavas, the low εNd values of both the Sierra Buttes and Taylor volcanics and the δ18O values of the Sierra Buttes rhyolite and Bowman Lake trondjhemite provide evidence that the northern Sierra Nevada island arc was continent based. The Keddie Ridge differentiated volcanics, characterized by high Zr, Y, Nb, K, and light rare-earth elements, are geochemically similar to a shoshonite suite. Their eruption at the end of the mid-Paleozoic volcanic episode suggests a reversal of subduction, uplift, and block faulting in the island arc.The mid-Paleozoic volcanics of the northern Sierra Nevada are thought to represent the remnant of a mature island arc because calc-alkaline rocks predominate over tholeiitic ones, the lavas display a K enrichment with time, and the volcanics are evolved in their isotopes, compared with rocks erupted in young or primitive island arcs.

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Rare earth element patterns and crustal evolution—I. Australian post-Archean sedimentary rocks

Geochimica et Cosmochimica Acta ◽

10.1016/0016-7037(76)90093-4 ◽

1976 ◽

Vol 40 (12) ◽

pp. 1539-1551 ◽

Cited By ~ 418

Author(s):

W.B Nance ◽

S.R Taylor

Keyword(s):

Rare Earth ◽

Rare Earth Element ◽

Earth Element ◽

Sedimentary Rocks ◽

Crustal Evolution

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Eu anomaly- reliability of the proxy in inferring source composition of clastic Sedimentary rocks: A case study from western Dharwar craton, Karnataka, India

10.5194/egusphere-egu2020-21526 ◽

2020 ◽

Author(s):

Anirban Mitra ◽

Sukanta Dey

Keyword(s):

Rare Earth ◽

Rare Earth Element ◽

Earth Element ◽

Sedimentary Rocks ◽

Dharwar Craton ◽

Source Rocks ◽

Granitic Rocks ◽

Negative Anomaly ◽

Eu Anomaly ◽

Ree Pattern

Use of trace and rare earth element concentration of terrigenous sedimentary rocks to deduce the composition of their source rocks in the hinterland is a very common and efficient practice. The results of geochemical analysis of the metaquartzarenites located at the basal part of Bababudan and Sigegudda belt, late Archean greenstone sequences of western Dharwar craton show that the sediments were most possibly supplied from Paleo to Mesoarchean granitoids of western Dharwar Craton. Rare earth element patterns of these basal quartzites display fractionated REE pattern in variable degree (LaN/YbN =1.47-10.63) with moderate to highly fractionated LREE (LaN/SmN=2.67-8.93) and nearly flat to slighly elevated HREE (GdN/ YbN=0.62-1.29) and a significant Eu negative anomaly (avg. Eu/Eu*=0.67). In general, presence of negative Eu anomaly in clastic rocks reflect the widespread occurrence of granitic rocks in the source area, which possess negative Eu anomaly. On the other hand, mechanical enrichment of zircon (having negative Eu anomaly, high HREE concentration and low LaN/YbN), if present, will hamper the whole REE pattern of the sediments and necessarily, do not actually mimic the source composition. Here, in our study, the Th/Sc vs Zr/Sc diagram show mineral Zircon has been concentrated by mechanical concentration in the sedimentary rocks. Few quartzite samples which have high Zr content typically exhibit low LaN/YbN values, reflecting pivotal role of mineral zircon in controlling the REE pattern of the sediments. Hence, in this case, we should be cautious in interpreting of the Eu negative anomaly of the basal quartzites for meticulously identifying their source rock composition. More geochemical and other analytical approaches are required in this regard.

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