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August 2011 - May 2016
September 2007 - August 2011
Publications
Publications (48)
Lower crustal recycling depletes the continental crust of Eu and Sr and returns Eu and Sr enriched materials into the man- tle (e.g., Tang et al., 2015, Geology). To test the hypothesis that the MORB source mantle balances the Eu and Sr deficits in the continental crust, we carried out high precision Eu/Eu* and Sr/Sr* measurement for 72 MORB glasse...
New crustal clues from old rocks
The ghost of continental crust long eroded away may exist in certain element ratios found in Archean rocks. Tang et al. used Ni/Co and Cr/Zn ratios as a proxy for the magnesium oxide that long ago weathered away in Earth's oldest rocks. This allowed a reconstruction of rock composition, which appears to be very diff...
Statistical analyses of Sm-Eu-Gd concentrations in more than 3000 samples from the upper, middle, and lower continental crust reveal that the enrichment of Eu in the lower continental crust cannot compensate for the Eu deficit in the upper and middle continental crust, leaving the bulk continental crust with a significant negative Eu anomaly. Becau...
Li isotopes in compositionally diverse Martinique lavas, as well as sea floor sediments cored at the southern (DSDP Site 144) and northern part (DSDP Site 543) of the subducting slab were analyzed in order to investigate the origin of the continental crust compositional signature seen in Lesser Antilles lavas and to investigate Li cycling in arcs....
Terrestrial planet Venus has a similar size, mass, and bulk composition to Earth. Previous studies proposed that local plume-induced subduction existed on both early Earth and Venus, and this prototype subduction might initiate plate tectonics on Earth but not on Venus. In this study, we simulate the buoyancy of submerged slabs in a hypothesized 2-...
The continental crust is strongly depleted in iron relative to mid-oceanic ridge basalt, broadly identical to the calc-alkaline magmas, suggesting that calc-alkaline differentiation is key to continent formation. However, it remains contentious as to what drives Fe depletion during magmatic differentiation in the crust. The two competing hypotheses...
The Grenville Province on the eastern margin of Laurentia is a remnant of a Mesoproterozoic orogenic plateau that comprised the core of the ancient supercontinent Rodinia. As a protracted Himalayan-style orogen, its orogenic history is vital to understanding Mesoproterozoic tectonics and paleoenvironmental evolution. In this study, we compared two...
Terrestrial planets Venus and Earth have similar sizes, masses, and bulk compositions, but only Earth developed planetary-scale plate tectonics. Plate tectonics generates weatherable fresh rocks and transfers surface carbon back to Earth’s interior, which provides a long-term climate feedback, serving as a thermostat to keep Earth a habitable plane...
In subduction zones, materials on Earth’s surface can be transported to the deep crust or mantle, but the exact mechanisms and the nature of the recycled materials are not fully understood. Here, we report a set of migmatites from western Yangtze Block, China. These migmatites have similar bulk compositions as forearc sediments. Zircon age distribu...
A boring billion for mountains
Earth's crust has changed over time as supercontinents formed and broke apart. Tied into this cycle are the building and erosion of high mountains, which are tied to collisions between tectonic plates. Tang et al. use europium anomalies in zircons to estimate the mean thickness of crust over Earth's history. This prox...
{{This dataset can be used to evaluate geochemical systematics of volcanic arcs on a global scale.}}
We extracted geochemical data from the GEOROC database (http://georoc.mpch-mainz.gwdg.de/georoc/) . Our compiled data cover nearly all active magmatic arcs on Earth, from island arcs to continental arcs. We filtered out plutonic, sedimentary, and m...
Much of the world's Li deposits occurs as basinal brines in magmatic orogens, particularly in continental volcanic arcs. However, the exact origin of Li enrichment in arc magmatic systems is not clear. Here, we show that, globally, primitive arc magmas have Li contents and Li/Y ratios similar to mid-ocean ridge basalts, indicating that the subducti...
A new data compilation shows that in intermediate to felsic rocks, zircon Eu/Eu* [chondrite normalized Eu/√(Sm×Gd)] correlates with whole rock La/Yb, which has been be used to infer crustal thickness. The resultant positive correlation between zircon Eu/Eu* and crustal thickness can be explained by two processes favored during high-pressure differe...
The field of high-temperature Li isotope geochemistry has been rattled by major paradigm changes. The idea that Li isotopes could be used to trace the sources of fluids, rocks, and magmas had to be largely abandoned, because Li diffusion causes its isotopes to fractionate at metamorphic and magmatic temperatures. However, diffusive fractionation of...
Porphyry ore deposits, Earth’s most important resources of copper, molybdenum, and rhenium, are strongly associated with felsic magmas showing signs of high-pressure differentiation and are usually found in places with thickened crust (>45 kilometers). This pattern is well-known, but unexplained, and remains an outstanding problem in our understand...
The concentrations of Cu and Ag, both insoluble chalcophile elements, can be used to place tight constraints on the proportion of basalts in the upper continental crust (UCC) through time via analyses of fine-grained terrigenous sedimentary rocks. Copper and Ag concentrations in magmas are largely controlled by sulfide dissolution during melting an...
The lithospheric mantle beneath Archean cratons is conspicuously refractory and thick compared to younger continental lithosphere (Jordan, 1988, Boyd, 1989; Lee and Chin, 2014), but how such thick lithospheres formed is unclear. Using a large global geochemical database of Archean igneous crustal rocks overlying these thick cratonic roots, we show...
Resolving the geochemical discrepancies between the bulk continental crust and its building blocks, basaltic arc magmas, can provide insights into the processes by which the continental crust is formed. One of the discrepancies is that the bulk continental crust is depleted in Cu and has a lower Cu/Ag ratio (∼500) than basaltic arc magmas (∼3500)....
Much of the world's economic copper resources are hosted in porphyry copper deposits (PCDs), shallow level magmatic intrusions associated mostly with thick (>45km) magmatic arcs, such as mature island arcs and continental arcs. However, a well-known, but unresolved paradox, is that arc magmas traversing thick crust, particularly in continental arcs...
Identification of juvenile and mature crustal sources in granite formation relies on radiogenic isotopic systems such as Sm-Nd and Lu-Hf and assumes isotope systems reach equilibrium between the melt and residual phases prior to melt extraction. However, we hypothesise disequilibrium melting and residual zircon result in preferential retention of 1...
The Earth’s continental crust is thought to originate from melting of the mantle, but it is too felsic and depleted in Fe relative to a primary mantle melt. This depletion in Fe is also commonly found in continental arc magmas and is often attributed to magnetite crystallization. However, Fe depletion in arc magmas coincides with an enrichment in f...
The surfaces of rocky planets are mostly covered by basaltic crust, but Earth is unique in that it also has extensive regions of felsic crust, manifested in the form of continents. Exactly how felsic crust forms when basaltic magmas are the dominant products of melting the mantles of rocky planets is unclear. A fundamental part of the debate is cen...
Water influences the physics and chemistry of magmatic differentiation because it reduces the melting point, decreases melt viscosity, modifies phase equilibria, and controls how latent heat is released. Here, we explore how compositional trends of fractionating magmas can be used to evaluate the amount of water in the crystallizing system. Of inte...
The two most important magmatic differentiation series on Earth are the Fe-enriching tholeiitic series, which dominates the oceanic crust and island arcs, and the Fe-depleting calc-alkaline series, which dominates the continental crust and continental arcs. It is well known that calc-alkaline magmas are more oxidized when they erupt and are prefere...
The fine-grained matrix of glacial diamictites, deposited periodically by continental ice sheets over much of Earth history, provides insights into the average composition and chemical evolution of the upper continental crust (UCC) (Gaschnig et al., 2016, and references therein). The concentrations of platinum-group elements (PGEs, including Os, Ir...
Ion imaging of the condensate blanket around a laser ablation site provides a window to study elemental fractionation during condensation of a plasma plume. Here we used a Time-of-Flight Secondary Ion Mass Spectrometer (ToF-SIMS) to conduct depth profiling of the condensate blanket produced by excimer 193 nm laser ablation of NIST 610 glass. Compos...
Elemental fractionation during laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis has been historically documented between refractory and volatile elements. In this work, however, we observed fractionation between light rare earth elements (LREE) and heavy rare earth elements (HREE) when using ablation strategies invol...
We present a systematic geochronological and geochemical study on ca 800–760Ma volcanic rocks in the eastern part of the Jiangnan orogen. The Xucun composite dykes are dated at ca 805Ma; the mafic components have OIB-like trace-element patterns and positive anomalies in Zr and Hf. The least-contaminated sample has relatively depleted Nd isotopic fe...
A combined study including apatite geochemistry, zircon U–Pb, Lu–Hf isotopes and whole-rock geochemistry including Nd isotopes was carried out for the late Mesozoic volcanic rocks from the Luzong Basin, in the lower Yangtze River region, South China. Whole-rock geochemistry indicates the enrichments of large ion lithophile elements (LILE) and light...