Palaeoenvironmental and palaeoclimatic implications of the Late-Quaternary sediment record of Vico volcanic lake (central Italy)

Abstract Initial excess protactinium (231Pa) is a frequently suspected source of discordance in baddeleyite (ZrO2) geochronology, which limits accurate U/Pb dating, but such excesses have never been directly demonstrated. In this study, Pa incorporation in late Holocene baddeleyite from Somma-Vesuvius (Campanian Volcanic Province, central Italy) and Laacher See (East Eifel Volcanic Field, western Germany) was quantified by U-Th-Pa measurements using a large-geometry ion microprobe. Baddeleyite crystals isolated from subvolcanic syenites have average U concentrations of ~200 ppm and are largely stoichiometric with minor abundances of Nb, Hf, Ti, and Fe up to a few weight percent. Measured (231Pa)/(235U) activity ratios are significantly above the secular equilibrium value of unity and range from 3.4(8) to 14.9(2.6) in Vesuvius baddeleyite and from 3.6(9) to 8.9(1.4) in Laacher See baddeleyite (values within parentheses represent uncertainties in the last significant figures reported as 1σ throughout the text). Crystallization ages of 5.12(56) ka (Vesuvius; MSWD = 0.96, n = 12) and 15.6(2.0) ka (Laacher See; MSWD = 0.91, n = 10) were obtained from (230Th)/(238U) disequilibria for the same crystals, which are close to the respective eruption ages. Applying a corresponding age correction indicates average initial (231Pa)/(235U)0 of 8.8(1.0) (Vesuvius) and 7.9(5) (Laacher See). For reasonable melt activities, model baddeleyite-melt distribution coefficients of DPa/DU = 5.8(2) and 4.1(2) are obtained for Vesuvius and Laacher See, respectively. Speciation-dependent (Pa4+ vs. Pa5+) partitioning coefficients (D values) from crystal lattice strain models for tetra- and pentavalent proxy ions significantly exceed DPa/DU inferred from direct analysis of 231Pa for Pa5+. This is consistent with predominantly reduced Pa4+ in the melt, for which D values similar to U4+ are expected. Contrary to common assumptions, baddeleyite-crystallizing melts from Vesuvius and Laacher See appear to be dominated by Pa4+ rather than Pa5+. An initial disequilibrium correction for baddeleyite geochronology using DPa/DU = 5 ± 1 is recommended for oxidized phonolitic melt compositions.

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LATE-QUATERNARY TECTONICS ALONG THE PERI-ADRIATIC BELT OF CENTRAL ITALY: POSSIBLE EVIDENCE OF ACTIVE SHORTENING FROM TOPOGRAPHY, FLUVIAL NETWORK ANALYSIS, AND LANDSCAPE EVOLUTION

10.1130/abs/2019am-338495 ◽

2019 ◽

Author(s):

Federica Ferrarini ◽

◽

J Ramón Arrowsmith ◽

Francesco Brozzetti ◽

Daniele Cirillo ◽

...

Keyword(s):

Network Analysis ◽

Landscape Evolution ◽

Late Quaternary ◽

Central Italy ◽

Fluvial Network

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Time-integrated 3D approach of late Quaternary sediment-depocenter migration in the Tagus depositional system: From river valley to abyssal plain

Earth-Science Reviews ◽

10.1016/j.earscirev.2015.11.002 ◽

2016 ◽

Vol 153 ◽

pp. 192-211 ◽

Cited By ~ 11

Author(s):

Geert-Jan Vis ◽

Cornelis Kasse ◽

Dick Kroon ◽

Jef Vandenberghe ◽

Simon Jung ◽

...

Keyword(s):

Late Quaternary ◽

River Valley ◽

Abyssal Plain ◽

Quaternary Sediment ◽

Depositional System

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Seismogenesis in Central Apennines, Italy: an integrated analysis of minor earthquake sequences and structural data in the Amatrice-Campotosto area

Annals of Geophysics ◽

10.4401/ag-3371 ◽

2009 ◽

Vol 47 (6) ◽

Author(s):

P. Boncio ◽

G. Lavecchia ◽

G. Milana ◽

B. Rozzi

Keyword(s):

Late Quaternary ◽

Central Italy ◽

Normal Fault ◽

Structural Data ◽

Integrated Analysis ◽

Fault Plane Solutions ◽

Small Magnitude ◽

Fault Surface ◽

Displacement Profile ◽

Earthquake Sequences

We present a seismotectonic study of the Amatrice-Campotosto area (Central Italy) based on an integrated analysis of minor earthquake sequences, geological data and crustal rheology. The area has been affected by three small-magnitude seismic sequences: August 1992 (M=3.9), June 1994 (M=3.7) and October 1996 (M=4.0). The hypocentral locations and fault plane solutions of the 1996 sequence are based on original data; the seismological features of the 1992 and 1994 sequences are summarised from literature. The active WSWdipping Mt. Gorzano normal fault is interpreted as the common seismogenic structure for the three analysed sequences. The mean state of stress obtained by inversion of focal mechanisms (WSW-ENE-trending deviatoric tension) is comparable to that responsible for finite Quaternary displacement, showing that the stress field has not changed since the onset of extensional tectonics. Available morphotectonic data integrated with original structural data show that the Mt. Gorzano Fault extends for ~28 km along strike. The along-strike displacement profile is typical of an isolated fault, without significant internal segmentation. The strong evidence of late Quaternary activity in the southern part of the fault (with lower displacement gradient) is explained in this work in terms of displacement profile readjustment within a fault unable to grow further laterally. The depth distribution of seismicity and the crustal rheology yield a thickness of ~15 km for the brittle layer. An area of ~530 km2 is estimated for the entire Mt. Gorzano Fault surface. In historical times, the northern portion of the fault was probably activated during the 1639 Amatrice earthquake (I = X, M~ 6.3), but this is not the largest event we expect on the fault. We propose that a large earthquake might activate the entire 28 km long Mt. Gorzano Fault, with an expected Mmax up to 6.7.

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