Von Eynatten and Gaupp (1999) Provenance in the Eastern Alps

Integrated Provenance Study

Provenance of Cretaceous sandstones in the eastern Alps - framework grains, heavy minerals and mineral chemistry

von Eynatten and Gaupp (1999)

Detrital framework and heavy minerals in Cretacous sedimentary rocks of the Northern Calcareous Alps

reflects early Alpine evolution of the Austroalpine microplate
Two contrasting sources were identified on the basis of detrital grain analysis
Source 1: SE margin of Austroalpine - composed of Paleozoic sediments and metamorphic rocks, Mesozoic carbonates and ultramafic rocks from the suture zone of the Vardar/Meliata Ocean
Source 2: NW margin in a lower Austroalpine position - composed of Paleozoic low-grade metamorphic rocks (including high P rocks), late Paleozoic metasediments, Mesozoic carbonates, and ultramafic rocks.

Geologic setting

Cretaceous sedimentary rocks - part of the Northern Calcareous Alps (northernmost portion of the Austroalpine continental crust) on the Adriatic plate

Fig. 1. Simple geological–structural sketch of the Alpine arc showing location of the Northern Calcareous Alps (NCA) as the northernmost part of the Austroalpine unit.

In the middle Jurassic, the Adriatic and European plates were separated by the Penninic Ocean (linked to opening of the Atlantic).

The Vardar/Meliata suture represents closure of the western branch of the Tethys Ocean in the Late Jurassic - this also led to the development of nappes in the SW region

Change in plate tectonics style resulted in dextral transpressive motion of the Austroalpine microplate and ultimately closure of the Penninic Ocean in the Eocene

Fig. 2. Palaeogeographic sketch of the Alpine realm at the Jurassic/Cretaceous boundary (approx. 145 Ma). Arrows indicate transport directions of the later Cretaceous sediments into the depositional area of the Upper Austroalpine

4 Sedimentary successions of siliciclastics

Rossfeld Fm (RF) - eastern NCA in higher tectonic nappes - turbidite deposition in submarine slope/trench system in front of a prograding thrust front - derived from the SE
Lech Fm (LF) - in Lechtal nappe (intermediate in nappe sequence, lower than RF and higher than TLF) - deposition by sedimentary gravity flows - derived from the SE
Tannheim and Losenstein Fm (TLF) - structurally deepest nappe - deposition from prograding submarine fan - sourced from the NW
Branderfleck Fm (BF) - northernmost Allgau nappe - turbidites - sourced from the NW

Fig. 3. Schematic sketch of the biostratigraphic range of the analyzed sedimentary successions. Time scale after Harland et al. (1990).

All absolute ages in the paper refer to this time scale. RF = Rossfeld Formation, LF = Lech Formation, TLF = Tannheim (line pattern) and Losenstein Formations, BF = Branderfleck Formation.

Fig. 4. Simplified structural map of the Northern Calcareous Alps showing areal extent and structural position of the major nappes. Numbers indicate sample localities: 1 = Losenstein, 2 = Rossfeld, 3 = Lackbach, 4 = Wetzstein-Laine 5 = Branderfleck, 6 = Pfarrwiesbach, 7 = Hindelang (Krahenwand, Kleebach, Hausellochbach), 8 = Mohnenfluh area, 9 = Hochberg, 10 = Steristobel, 11 = Holzgau, 12 = Griesbachalm, 13 = Madau, 14 = Trittalm, 15 = Zurser See/Madlochspitze, 16 = Rote Wand, 17 = Loruns.

Methods

Modified Gazzi-Dickinson with minerals counted as fragments if attached and carbonates added to lithics
Heavy minerals disaggregated, cleaned and separated with tribromoethane
Electron microprobe analyses of separated heavy minerals

Framework grains

Fig. 5. Classification of the analyzed arenitic rocks based on light mineral data: (A) the first level classification scheme suggested by Zuffa (1980) and (B) the QFL diagram introduced by McBride (1963). All but one of the analyzed sandstones (n = 88) are litharenites

Fig. 6. Representation of the light mineral data set within the QmFLt provenance diagram of Dickinson (1985):

(A) lithoclasts including polycrystalline quartz grains but precluding carbonate clasts

(B) total lithoclasts including the carbonate extrabasinal clasts (CE). Both diagrams suggest a recycled orogen provenance of the litharenites.

Fig. 8. Representation of the light mineral data within the logratio diagram ln (Lu=M) vs. ln (D=Qm). The big grey circle with black cross inside indicates the average of nine TLF samples from Gaupp (1982).

Fig. 9. (A) Semi-quantitative weathering index based on semi-quantitative estimates for climate and relief. (B) The analyzed samples indicate a very low weathering index (wi = 0) based on the light mineral data: ln (Q/(L + CE)) vs. ln (Q/F).

Heavy minerals

Fig. 10. Average heavy mineral spectra for the analyzed sedimentary successions (for individual samples see Table 1; chr = chrome spinel, zrn = zircon, tur = tourmaline, rt = rutile, grt = garnet, cld = chloritoid, gln = blue sodic amphibole, epi = epidote group minerals, am/g = green calcic amphibole, ap = apatite, ZTR D zrn C tur C rt). BF samples are divided into three subgroups due to contrasting heavy and light mineral compositions.